Eavesdropping the pivotal defensive representatives of plant-thrips interaction

Abstract

The substantial economic impact of thrips on crop yield and productivity enthused us to review comprehensive research findings associated with plant-thrips interaction. An attempt has been made to summarize a broad spectrum of knowledge on thrips infestation in different crops regarding defensive traits including plant morphological features, biochemical alterations and transcriptional profiling of defensive genes along with effective thrips management strategies. Thrips feeding mechanism involves puncturing the outer (epidermal) layer of host tissue and evoking the plant defence mechanism. Plants respond to thrips attacks by activating the defensive genes, which lead to the production of physical barriers (trichomes, waxes, and papillae) and biochemical compounds (primary and secondary metabolites). It is imperative to appreciate the physiological responses, metabolic changes, and regulation at the transcriptional level of various phytoconstituents during thrips feeding. The literature survey revealed that leaf size, papillae and trichome density, total phenols, tannins and genes associated with phenylalanine metabolism and flavonoid biosynthesis contribute to plant resistance against thrips infestation. Thus, this comprehensive overview will serve as a roadmap for researchers, guiding future studies and the development of sustainable pest management practices to mitigate thrips-related damage and enhance crop resilience.

Introduction

Plants are continuously exposed to a variety of biotic and abiotic stresses due to their non-mobile nature. Among biotic stresses, pest infestations are regarded as the major constraints to crop productivity and yield (Kumar et al. 2021). Insects feed on plants either by chewing or sucking sap through piercing mouthparts. Thrips (also known as thunderflies) are becoming one of the prominent insect-pest of agricultural crops across the globe that are capable of causing significant economic losses either directly damaging or indirectly transmitting plant viruses (Ghosh et al. 2019; Reitz et al. 2020; Wu et al. 2021). Among the 6572 documented species of thrips (ThripsWiki. 2024), less than 1% have a significant economic impact, displaying detrimental effects on crop plants and ornamental species, thereby influencing the growth of agricultural and horticultural industries (He et al. 2020; Tang et al. 2023). Five species viz. Thrips tabaci (Lindeman), T. palmi (Karny), Frankliniella occidentalis (Pergande), F. schultzei, and Scirtothrips dorsalis (Hood) belonging to the family Thripidae are the chief species having highly polyphagous life cycle, global distribution, and strong viral transmission ability that cause severe plant damage (Tang et al. 2023). They can exhibit diverse degrees of host specificity, ranging from being strictly monophagous, such as Aptinothrips rufus, which exclusively inhabits grasses, to being polyphagous, as exemplified by Heliothrips haemorrhoidalis, commonly known as the greenhouse thrips, which can thrive on an extensive variety of host plant species (Kumar and Omkar 2021a, b).

Thrips infestation on plants cause damage to leaves, shoots, and fruits as well as have an evident effect on the visual appearance of plants. On the other hand, it can seldom harm or jeopardise the survival of trees and plants (He et al. 2020). Herbaceous ornamentals (Gladiolus hybridus L., Chrysanthemum, roses, and carnations) and some vegetable crops (beans, capsicum, tomato, and onion) are most vulnerable to thrips infestation and thrips-vectored viruses, particularly when the plants are at an early stage of development (Mouden and Leiss 2021). Plants respond to insect infestation at the cellular, physiological, and molecular levels. In general, plant exhibits changes in the composition and properties of cell walls, production of physical barriers (trichomes, waxes, and papillae) and biosynthesis of secondary metabolites that occurred by the activation of defensive genes (Divekar et al. 2022; Sun et al. 2024). In addition, thrips-infested rose plants can draw in the natural enemies of thrips through the release of specific volatile compounds such as β-Myrcene and limonene (Avellaneda et al. 2021). Mochizuki and Yano (2007) and Manjunatha et al. (1998) reported change in volatile compounds blend in thrips-infested eggplant and Chrysanthemum to attract the predatory bug Orius sauteri and mite Neoseiulus cucumeris, respectively.

While going through the literature available on thrips infestation, it was observed that although the status of thrips infestation damage at morphological, biochemical and transcriptome levels was available, there remains a significant gap in reporting these findings into a comprehensive, unified framework. To address this gap, it is crucial to identify the key biochemical processes and genes involved in resistance mechanisms, with the goal of leveraging biotechnological advancements to enhance pest management strategies. From a novelty perspective, this highlights the need for an integrated approach that combines insights across these various biological layers to provide a more holistic understanding of thrips resistance. Therefore, we sought to provide a comprehensive review of the key resistance determinants across various crops in response to thrips infestation along with effective thrips management strategies. This integrated analysis aims to consolidate findings from multiple biological levels, highlighting the potential for integrated approaches to mitigate the impact of thrips and improve crop protection. We reviewed the morphological traits, defensive proteins, metabolites, and associated gene expression profiles of various host plants in response to thrips feeding, and concluded the review by offering guidelines for effective thrips management.

Thrips biology and behavior

Thrips belong to the order Thysanoptera that come under the pest category of sap feeder (Munir-Zaki et al. 2024). During plant-thrips interaction, nymph or adult thrips inject the saliva that results in lysis of different components of plant cells. They nourish by piercing the host tissue's epidermal layer and sucking the sap from the lower and upper surfaces of leaves that results in stippling, formation of silvery or brown necrotic spots, wrinkles and curling on leaves and stunt plant growth (Gill et al. 2015). If the infestation is high at the vegetative stage, there will be late bud formation, premature dropping of squares during fruiting, delayed crop maturity and yield reduction (Cook et al. 2013). Thrips feeding is generally followed with specks of frass (excrement) that looks like black varnish. Certain thrips (F. schultzei, F. occidentalis, and T. tabaci) are useful predators that eat other insects including mites. Many thrips species (recognised in the subfamilies namely, Idolothripinae and Phlaeothripinae) are harmless having little to no detrimental effects of their own on their surroundings but feed on fungal spores and pollen (Varatharajan 2021). The adults of one thrips species from Panama exhibited parental care by feeding on the lichen fungal spores that habitat in the trunks of Gustavia superba trees (Kiester and Strates 1984). On the other hand, thrips that feed on African violets and orchids can leave unpleasant pollen deposits and reduce the lifespan of the blossoms (Suetsugu et al. 2019). Western flower thrips (WFT) is predominantly a pest of non-woody plants; but, widespread infestations can cause a floral loss on woody perennials such as roses (Wahyuni et al. 2021). Petals of a rose might get black streaks and blotches as a result of prior feeding damage, or the floral buds might shrivel and not open at all (Avellaneda et al. 2021). WFT also transmits impatiens necrotic spot virus and tomato spotted wilt virus, both of which can cause severe harm or even death of different vegetable crops and herbaceous ornamental plants (Reitz et al. 2020).

Thrips induce brown to silvery, scabby scars on the surface of citrus fruits and avocado however, have absolutely no impact on the fruit’s flavour or quality (Atakan 2024). When thrips lay their eggs on grapes, the fruit develops dark scarring flanked by lighter “halos.” Thrips may shrivel or damage growing fruit while they feed on apples, nectarines, or raspberries (Jambagi and Kambrekar 2023). Blueberry stem tips and leaves are significantly distorted by citrus thrips feeding, decreasing fruit production. Many thrips species might not be present by the moment their damage can be seen, for instance after buds open (Vono et al. 2022). Cotton thrips are small, hardly apparent, splinter-like insects that mostly harm cotton seedlings. With their pointing mouthparts, they rasp tender leaves and terminal buds and consume the juices. The margins of the leaves may become brown, take on a silvery hue, or they may wilt and curl upward. A significant infestation might kill or damage plant parts, including terminal buds (Chappell et al. 2020).

Thrips classification, life cycle and reproduction

Traditionally, nearly 6000 known species of thrips have been classified within a single order, Thysanoptera. Within this order, two suborders have been recognized: Tubulifera and Terebrantia (Mound et al. 1980). The suborder Tubulifera comprises a single family, Phlaeothripidae, with approximately 3500 described species, while Terebrantia includes around 2400 species spread across eight families (Mound and Minaei 2007) (Fig. 1). Mukherjee et al. (2023) studied global thrips distribution and found that 398,160 km² of cropland is currently affected. Their range would be largely confined to North-Western India, Eastern North America, and Northern Europe, while Indo-Malayan realm would experience the greatest loss, with thrips restricted to just 27 of 825 terrestrial ecoregions. The global distribution of five economically significant thrips species (T. palmi, T. tabaci, F. schultzei, F. occidentalis, and S. dorsalis) has been given in Table 1. These suborders are distinguished by unique morphological and behavioral traits, which play a significant role in their taxonomic classification. Tubulifera species are characterized by the presence of tubular ovipositors, specialized structures used for egg deposition (Kumar and Omkar 2021a, b). In contrast, Terebrantia species feature terebrate ovipositors-elongated, slender structures with a similar function. Additionally, Terebrantia includes species with piercing-sucking mouthparts, adapted primarily for feeding on plant tissues, whereas Tubulifera species tend to exhibit more specialized feeding behaviors and mechanisms. Despite this traditional classification, ongoing research continues to refine our understanding of thrips phylogeny, with new findings challenging and revising previous assumptions about their evolutionary relationships and diversity.

Fig. 1.

Classification of thrips with examples.

Source: Mound et al. (1980), Mound and Minaei (2007)

Table 1.

Global distribution of five economically significant thrips species

Species	Asia	Africa	North America	Central America and Caribbean	South America	Oceania	References
F. occidentalis	Cyprus, Israel, Japan, Turkey	Kenya, Reunion, South Africa, Zimbabwe	Canada (British Columbia, Ontario), Mexico, USA (widespread, except in the north; including Hawaii)	Costa Rica, Guatemala, Martinique	Argentina, Colombia	Australia (Western Australia), New Zealand	EPPO (2024a)
T. palmi	Bangladesh, Brunei Darussalam, China, India, Indonesia, Iraq, Japan, Korea Dem. People's Republic, Korea, Republic, Laos, Malaysia, Maldives, Myanmar, Pakistan, Philippines, Singapore, Sri Lanka, Taiwan, Thailand, Vietnam	Cote d'Ivoire, Mauritius, Nigeria, Reunion, Sudan	Mexico, United States of America (Florida, Hawaii)	Antigua and Barbuda, Bahamas, Barbados, Costa Rica, Cuba, Dominica, Dominican Republic, Grenada, Guadeloupe, Haiti, Jamaica, Martinique, Netherlands Antilles, Panama, Puerto Rico, Saint Lucia, St Kitts-Nevis, St Vincent and the Grenadines, Trinidad and Tobago, Virgin Islands (British)	Brazil, Colombia, Ecuador (Galapagos), French Guiana, Guyana, Peru, Suriname, Venezuela	American Samoa, Australia (Northern Territory, Queensland), French Polynesia, Guam, Micronesia, New Caledonia, Palau, Papua New Guinea, Samoa, Wallis and Futuna Islands	EPPO (2024b)
F. schltzi	Bangladesh, India, Indonesia, Java, Iran, Iraq, Israel, Malaysia, Pakistan, Philippines, Saudi Arabia, Sri Lanka, Thailand, Yemen	Angola, Botswana, Burkina Faso, Cameroon, Cape Verde, Chad, Congo, Egypt, Ethiopia, Gambia, Ghana, Kenya, Libya, Madagascar, Mauritius, Morocco, Namibia, Niger, Nigeria, Senegal, Somalia, South Africa, Sudan, Tanzania, Togo, Uganda, Zambia, Zimbabwe	USA, Florida, Hawaii	Barbados, British Virgin Islands, Cuba, Dominican Republic, Haiti, Jamaica, Puerto Rico	Argentina, Brazil, Minas Gerais, Parana, Rio Grande do Norte, Rio de Janeiro, Santa Catarina, Sao Paulo, Chile, Colombia, Guyana, Paraguay, Peru, Suriname, Uruguay, Venezuela,	Australia, New South Wales, Northern Territory, Queensland, South Australia, Victoria, Western Australia, French Polynesia, Guam, Kiribati, New Caledonia, Papua New Guinea	DMPP (1999)
T. tabaci	China, India, Iran, Iraq, Israel, Japan, Jordan, Korea, Lebanon, Myanmar, Pakistan Philippines, Qatar, Saudi Arab, Singapore, Taiwan, Thailand, Turkey, Uzbekistan and Vietnam	Algeria, Chad, Congo, Egypt, Ethiopia, Ghana, Kenya, Libya, Madagascar, Malawi, Mauritius, Morocco, Nigeria, Reunion, Senegal, Somalia, South Africa, Sudan, Tanzania, Tunisia, Uganda and Zimbabwe	Bermuda Canada, Mexico and USA	Antigua and Barbuda, Bahamas, Barbados, Costa Rica, Cuba, Dominican Republic, Grenada, Guadeloupe, Haiti, Honduras, Jamaica, Martinique, Montserrat, Nicaragua, Puerto Rico, Saint Kitts and Nevis, Saint Lucia, Trinidad and Tobago	Argentina, Brazil, Chile, Colombia, Ecuador, Guyana, Peru, Uruguay and Venezuela	Australia, Fiji, New Caledonia, New Zealand, Papua New Guinea and Solomon Island	Pal et al. (2019)
S. dorsalis	Bangladesh, Brunei Darussalam, China, India, Indonesia, Iran, Israel, Japan, Korea, Republic, Malaysia (West), Maldives, Myanmar, Pakistan, Philippines, Sri Lanka, Taiwan, Thailand, Vietnam	Cote d'Ivoire, Kenya, Uganda	Mexico, United States of America	Barbados, Cuba, Guadeloupe, Jamaica, Puerto Rico, Saint Lucia, St Vincent and the Grenadines, Trinidad and Tobago			EPPO (2024c)

Reproduction in thrips follows a haplodiploid system, where males are produced from unfertilized eggs and have half the chromosome count of females (Kumar and Omkar 2021a, b). However, some thrips species can also produce females from unfertilized eggs, a phenomenon known as thelytoky. The thrips life cycle consists of six stages: egg, two larval stages (first instar and second instar), two pupal stages (pre/pro-pupa and pupa), and the adult stage (Fig. 2). The larval stages, which are active feeders, last around 2–5 days. In Terebrantia, there are two pupal stages where antennal segmentation is reduced or absent, and the mouthparts are nonfunctional. Wing rudiments are present in the first pupal stage (pro-pupa) but are more developed in the second stage (pupa). Remarkably, Tubulifera species have three pupal stages (Cook et al. 2011). Female thrips deposit their characteristic bean-shaped eggs in the epidermal layer of various plant parts, such as leaves, stems, and flowers, using a saw-like ovipositor (Kumar and Omkar 2021a, b). The eggs hatch within 2–14 days, followed by the development of the first instar larvae in 2–3 days and the second instar larvae in 5–10 days, depending on environmental conditions. Afterward, the larvae enter a mobile, non-feeding pre-pupal stage. After 1–5 days, they drop to the soil and undergo pupation, with adults emerging after 1–10 days (Hinds 1903; Eddy and Clarke 1930; Bailey 1938; Lublinkhof and Foster 1977; Lowry et al. 1992). Thrips can produce up to eight generations per year, and in warm weather, the entire life cycle-from egg to adult-can be completed in as little as two weeks.

Fig. 2.

Life cycle and reproduction of thrips.

Hinds (1903), Eddy and Clarke (1930), Bailey (1938), Lublinkhof and Foster (1977), Lowry et al. (1992)

Effect of environmental factors on thrips population dynamics

Thrips are daytime pests and prefer to infest during dry and warm environments, so, heat and warmness could be the potential players for thrips infestation. An individual plant can also suffer thrips damage over the entire ontogenetic developmental stages (the vegetative, flowering and fruiting stages) (Visschers et al. 2018). A study on the infestation period of citrus thrips in blueberry genotypes showed the maximum pest population during summer causing scarring, redness on branches, and twisting curling of new foliage (Vono et al. 2022). Southern high bush blueberry showed susceptibility for citrus thrips (S. citri) at increased temperatures in hoop-houses (Haviland et al. 2009). Resistance to a given pest is known to differ between young and old leaves and also among seasons. The avocado infestation by S. perseae evaluated during summer revealed more infestation on young leaves as compared to small fruit whereas during late spring due to hardening of leaves, depletion of leaf resources and increase in temperature provide susceptibility towards fruit (Yee et al. 2003). This could be due to leaves exhibiting a layer of surface waxes over the cuticles which serve as a protectant against insect feeding. Also, waxes prohibit the movement of an insect across a leaf surface and also possess chemicals that negatively affect insect growth. Rajashree et al. (2021) observed that thrips activity in groundnut genotypes peaked during the vegetative stages and declined thereafter. In onions, Shaikh et al. (2014) observed peak thrips populations during the 9th week, which decreased by the 16th week. Similarly, Choudhury et al. (2017) reported peak thrips populations at 71 days after planting in grape genotypes. A study by Barbosa et al. (2019) on F. schultzei in watermelon found that thrips density was higher during dry periods with stronger winds. These findings suggest that thrips development is closely influenced by environmental factors, such as temperature and humidity (Steenbergen et al. 2018).

Plant resistance mechanisms deployed against pest infestation

The interplay between plants and insect herbivores is indeed ancient, spanning hundreds of millions of years (Erb and Reymond 2019). Plants have evolved a variety of defense mechanisms to protect themselves from herbivores, ranging from physical barriers to chemical deterrents. These defenses can be categorized into two main types: direct and indirect. Direct defenses are mechanisms that directly impede herbivore performance or deter herbivores from feeding. Examples include tough leaves, spines, thorns, and the production of toxic chemicals or compounds that make the plant unpalatable or even poisonous to herbivores. On the other hand, indirect defenses rely on attracting or enhancing the effectiveness of natural enemies of herbivores, such as predators or parasitoids (de Bobadilla et al. 2022). Plants can release volatile organic compounds to attract predators or produce extrafloral nectar to lure in parasitoids, thus indirectly defending themselves against herbivores. Interestingly, both direct and indirect defenses can be constitutively expressed, meaning they are present in the plant even in the absence of herbivore attacks (Zust and Agrawal 2017). This suggests an ongoing investment by the plant in defense. However, these defenses are often upregulated or deployed more actively in response to herbivore attack, indicating a dynamic response to environmental cues. Plants usually deploy three defence mechanisms to alter insect feeding:

1. Antibiosis: adversely affects a pest’s physiological processes, thereby impairing arthropod survival, growth, development and behavior.

2. Antixenosis: operates by disrupting normal arthropod behavior. Antixenosis and antibiosis involve both plant and arthropod characteristics.

3. Tolerance: a plant’s response to injury that involves active biological responses (reallocating resources, producing protective compounds, modifying growth patterns, and altering metabolic pathways) enabling the plant to maintain fitness and reproductive success despite the challenge posed by pests, rather than merely enduring or coping with the damage.

Thrips face morphological barriers such as trichomes, or leaf pubescence, secondary metabolites such as phenolics or emission of volatile compounds as indirect defences or altering the cell signaling pathways. Thrips attack results in the activation of local plant immune response by producing jasmonic acid (JA) that is transported to other plant tissues that are not damaged.

Phenotypic and morphological factors influencing thrips resistance and population dynamics in various crops

Phenotypic screening is an empirical approach to evaluate and identify the available germplasm for resistance against insect-pest infestation (Kaur et al. 2018; Togola et al. 2019; Zhou et al. 2020). Phenotypic screening identifies traits like trichome density, leaf morphology, and chemical defenses (e.g., acylsugars, alkaloids) that contribute to pest resistance. Tailored to specific pests (e.g., aphids, thrips, caterpillars), it allows researchers to assess resistance based on pest damage (e.g., reduced feeding or oviposition). This approach can also uncover the genetic basis of resistance, linking phenotypic traits with genomic data to support marker-assisted breeding. Different software or commercial programs are available to quantify feeding damage caused by chewing insects. However, it is challenging to quantify thrips damage by different softwares as these insects only cause discolouration of leaves but do not remove parts of leaf lamina. The total leaf area damaged by thrips was used as one of the criteria to assess the resistance levels in cotton plants by Herbert (1998) (Table 2). We have also evaluated the pest damage on cotton genotypes (Gossypium hirsutum and G. arboreum) during the year 2021–2022 and observed that the resistant genotype (G. arboreum) had 9 thrips/3 leaves as compared to the susceptible genotype (G. hirsutum) with 20 thrips/3 leaves (unpublished data). Phenotypic assessment of large germplasm set of beans (~ 1138 genotypes) against the melon thrips showed that resistance levels in beans can be considered moderate, as none of the genotypes tested received damage scores of 3 on a 1–9 scale (Cardona et al. 2002).

Table 2.

Phenotypic assessment of cotton infested with thrips

Scale used	Characters	Rank	Appearance
0	No damage	Low	Presence of thrips with no symptoms
1	10% damaged leaves	Low	Silvery patches along the sides of leaf veins
2	25% leaves damaged but no bud damage	Medium	Shiny white oily patches extended on leaves above mid canopy
3	75% leaves and 0–25% buds damaged	Medium	Activity of thrips on the terminal leaves followed by upward cupping and light browning
4	90% leaves and greater than 25% buds damaged	High	Severe browning, stiffness, cracking of leaf lamina and erection of leaves
5	Dead plants	High	Plant perished

As thrips feed mainly on outer layers of plant tissues, morphological traits such as trichomes, papillae, and spines form the first line of defense (Jacob et al. 2020; Zhou et al. 2020; Mouden and Leiss 2021). Constitutive leaf-based resistance to thrips is a key trait for more sustainable and successful cultivation of various crops. Table 3 elucidates different morphological characters responsible for host fitness against thrips infestation. Trichomes are epidermal hairs found on the surface of leaves and stems. Trichomes enhance plant resistance through a combination of mechanical, chemical, and ecological strategies. They hinder pest movement and feeding by acting as physical barriers. Glandular trichomes secrete toxic or repellent compounds that deter feeding and reduce insect survival (Divekar et al. 2022). Vosman et al. (2018) highlighted the role of acylsugars released from glandular trichomes in tomato resistance to WFT. A specific combination of acylsugars with particular fatty acid profiles was found to reduce WFT oviposition on tomato plants (Ben-Mahmoud et al. 2019). High trichome density can also discourage oviposition of thrips in tomato cultivars (Escobar-Bravo et al. 2018). Additionally, trichomes modify the plant's microenvironment, reducing water loss and enhancing stress tolerance, which indirectly helps the plant to resist herbivore damage (Mouden and Leiss 2021). Zhang et al. (2022) found that the thrips-resistant alfalfa variety Caoyuan No. 4 exhibited thicker palisade and parenchyma tissues, wider collenchyma, phloem, cambium, and lignin layers, and smaller epidermal cells and stomatal apertures. It also had more non-glandular trichomes in both leaves and stems, fewer glandular trichomes, and increased wax in stems compared to the susceptible variety Caoyuan No. 2. Similarly, Kaur et al. (2018) reported that thrips-resistant cotton plants exhibit faster growth and higher trichome density, which limits thrips movement. Strawberry cultivars with high densities of non-glandular trichomes also showed lower F. occidentalis infestations (Abdelmaksoud et al. 2020). The specific role of trichomes can vary across plant species and herbivore types, and plants with dense trichomes are not necessarily more resistant to all the pests. For example, Chen et al. (2020) found that trichome density may not play a significant role in Chrysanthemum resistance to F. occidentalis infestation. A similar conclusion was drawn by Bac-Molenaar et al. (2019), who observed no significant impact of trichome density on foliar resistance to F. occidentalis in a tomato population derived from both resistant and non-resistant lines. On the other hand, papillae are protuberances formed by the thickening of the cell walls, which help to protect the cells from pest infestation (Wahyuni et al. 2021). Each epidermal cell produces one papilla and cultivars with smaller leaf cells tend to have a higher density of epicuticular papillae. For instance, the G. hybridus L. varieties having shorter mesophylls and epidermal cells, as well as a higher density of epicuticular papillae were less susceptible to WFT damage (Wahyuni et al. 2021). Soybean genotypes with low pubescence also showed reduced feeding damage by viruliferous thrips Neohydatothrips variabilis (Zhou et al. 2020).

Table 3.

Morphological characters responsible for host fitness against thrips infestation

S. no	Thrips		Crops	Status	References
	Common name	Scientific name
1	WFT	F. occidentalis	Tomato	Release of acylsugars from glandular trichomes	Vosman et al. (2018)
2	WFT	F. occidentalis	Tomato	Release of acylsugars with particular fatty acid profiles from glandular trichomes	Ben-Mahmoud et al. (2019)
3	WFT	F. occidentalis	Tomato	High trichome density discourages oviposition	Escobar-Bravo et al. (2018)
4	Thrips	–	Alfalfa	The resistant variety exhibited thicker palisade and parenchyma tissues, wider collenchyma, phloem, cambium, and lignin layers, and smaller epidermal cells and stomatal apertures. It also had more non-glandular trichomes in both leaves and stems, fewer glandular trichomes, and increased wax in stems compared to the susceptible variety	Zhang et al. (2022)
5	Tobacco	F. fusca (Hinds)	Cotton	Thrips-resistant plants had faster growth and higher trichome density	Kaur et al. (2018)
	Thrips	F. occidentalis (Pergande)
	WFT
6	WFT	F. occidentalis	Strawberry	Cultivars with higher densities of non-glandular trichomes on the upper leaf surface hosted fewer F. occidentalis than those with lower densities	Abdelmaksoud et al. (2020)
7	WFT	F. occidentalis	Ornamental	Resistant plants had higher density of epicuticular papillae with shorter mesophylls and epidermal cells	Wahyuni et al. (2021)
			Gladiolus
8	Soybean	N. variabilis (Beach)	Soybean	Damage was lower in genotypes with low pubescence levels	Zhou et al. (2020)
	thrips
9	WFT	F. occidentalis	Chrysanthemum	Leaf trichome density did not play a relevant role in defenses against WFT	Chen et al. (2020)
10	WFT	F. occidentalis	Tomato	WFT resistance was independent of glandular trichome density or trichome-derived volatile profiles	Bac-Molenaar et al. (2019)
11	Flower	F. tritici	Cotton	Upper, middle and lower leaf position, terminals, squares, flowers and bolls were susceptible to Frankliniella tritici, Frankliniella fusca, and Frankliniella occidentalis whereas resistant to Neohydatothrips variabilis and Thrips tabaci	Reay-Jones et al. (2017)
	Thrips	F. fusca
	Tobacco	F. occidentalis
	Thrips	N. variabilis
	WFT	T. tabaci
	Soybean
	Thrips
	Onion thrips
12	Greenhouse	H. haemorrhoidalis	Strawberries	First report of infection of thrips on strawberries indicating leaves and sepals were more susceptible	de Souza et al. (2019)
	Thrips
13	Cuban	Gynaikothrips ficorum	Ficus microcarpa	Younger leaves were more susceptible as compared to mature leaves due to incomplete differentiation	de Souza et al. (2000)
	laurel thrips
14	Brazilian	Pseudophilothrips ichinis	Christmas berry	Younger terminals (stems and leaves) of plants were more susceptible than mature one	Cuda et al. (2009)
	Peppertree
	Thrips
15	WFT	F. occidentalis	Cucumber	Thrips reproduction was highest on apical leaves, intermediate on middle leaves and lowest on basal leaves whereas it did not get affected by plant age	de Kogel et al. (1997)
16	Onion	T. ttabaci F. occidentalis	Capsicum	Thrips reproduction was not affected by plant leaf position	Visschers et al. (2019)
	Thrips
	WFT
17	Banana	T. hawaiiensis	Banana	Damage rates were in the order: interior flowers > 3rd-layer flowers > 2nd-layer flowers > 1st-layer flowers > young fruits which were due to nutritional quality of bud	Yu et al. (2018)
	flower
	Thrips
18	Myoporum thrips	Klambothrips myopori	Myoporum	Resistant genotypes had smaller leaf size as compared to susceptible genotypes	Shogren and Paine (2019)
19	Melon	T. palmi	Beans	Thrips population did not get affected by plant maturity, growth habit, pubescence, and seed color or size	Cardona et al. (2002)
	Thrips

WFT, western flower thrips

Thrips population dynamics are influenced by several factors, including thrips species, their developmental stage, the species of host plant, specific plant parts, plant's growth stage, and prevailing environmental conditions. Various studies have examined these factors in detail. A study by Reay-Jones et al. (2017) examined the seasonal abundance and species distribution of thrips on various parts of cotton plants. The thrips species identified were T. tabaci (1.8%), N. variabilis (7.4%), F. occidentalis (17.1%), F. fusca (23.5%), F. tritici (46.8%), and other species (3.4%). F. tritici was most prevalent on flowers, terminals, and squares (75.1, 51.6, and 57.5%, respectively), while F. fusca dominated seedlings (86.7%). Across all leaf positions, F. fusca (28.8%) was the most abundant species, followed by F. tritici (19.2%), N. variabilis (18.8%), F. occidentalis (12.9%), and T. tabaci (5.2%), with other species accounting for 15%. While F. fusca was predominant on seedlings, F. tritici was the most common on squares, flowers, and terminals. The first evidence of damage to strawberry leaves and sepals caused by thrips (Heliothrips haemorrhoidalis) was reported by de Souza et al. (2019). Feeding by adult thrips, through the injection of saliva, alters the plant's hormonal balance, leading to distortions in growth or the formation of galls (or “domiciles”) (Gatjens-Boniche 2019). de Souza et al. (2000) found that Gynaikothrips ficorum, a member of the Phlaeothripidae, induced leaf galls on Ficus macrocarpa by causing structural changes. Younger leaves exhibited greater and more rapid laminal swelling than mature leaves, with cecidogenetic responses occurring more quickly in younger leaves due to their undifferentiated nature. A study by Cuda et al. (2009) on Pseudophilothrips ichinis infestation on S. terebinthifolius (Christmas berry) reported that both larval and adult stages formed large aggregations on young terminals (stems and leaves), which reduced the plant's vigor and growth.

de Kogel et al. (1997) observed that in cucumber accessions, F. occidentalis reproduction was highest on apical leaves, intermediate on middle leaves, and lowest on basal leaves, while plant age had no significant effect on thrips reproduction. Visschers et al. (2019) reported that thrips resistance in capsicum to F. occidentalis and T. tabaci was consistent across leaf positions and ontogenetic stages, likely due to the presence of adequate defense chemicals in all leaf positions. Yu et al. (2018) revealed that damage from T. hawaiiensis was highest in interior banana flowers, followed by flowers in the third, second, and first layers, and young fruits. Thrips likely migrate to lower bracts, young fruits, and flower buds as bracts open, possibly due to the nutritional quality of the buds. In their study, Shogren and Paine (2019) reported that host fitness of Myoporum species for Klambothrips myopori was influenced by leaf size, physiological response, nutritional content, and chemical traits. Susceptible Myoporum varieties had longer leaves (5–10 cm) compared to resistant ones (0.5–1.5 cm). Thrips infestation was highest on newly expanded apical leaves, which rolled into galls due to damage. On the other hand, a study on T. palmi infested beans showed that thrips population did not get affected by plant maturity, growth habit, pubescence, and seed color or size (Cardona et al. 2002).

Biochemical changes in various crops induced by thrips infestation

Host plant resistance is the heritable and key characteristic component of pest management. The deployment of biochemical host plant resistance traits as a plant defense mechanism is the most reliable control tactic in advanced agriculture that integrates technological advancements with traditional farming practices to boost food production, reduce environmental impact, and promote long-term sustainability (Horgan et al. 2020; El-Dessouki et al. 2022). Insect infestations induce significant changes in plant metabolites, affecting nutritional constituents (Yu et al. 2018; Suman et al. 2021). Plants respond through alterations in cell wall properties, production of reactive oxygen species (ROS), antioxidants, defensive enzymes, and secondary metabolites, which impact insect behavior, physiology, and metabolism (Kumar et al. 2017; Divekar et al. 2022; de Bobadilla et al. 2022). The biochemical effects of thrips on various crops have been summarized in Table 4.

Table 4.

Biochemical changes in various crops due to thrips infestation

S. no	Thrips	Crop	Status	References
1	T. tabaci	H. sampsonii	Leaves of infested plants exhibited significant decrease in chlorophyll a, b, and carotenoid, content with increased T. tabaci damage	Dai et al. (2009)
2	O. loti	Alfalfa	Thrips-resistant variety inhibited chlorophyll a, b, and total soluble proteins biosynthesis whereas markedly accumulated lignin content, SOD, CAT, and POX activity to resist thrips damage	Wu et al. (2021)
3	Thrips	Chili	Infested leaves showed reduced content of chlorophyll by 8% as compared to healthy leaves	Johari et al. (2016)
4	S. dorsalis	Onion	Thrips foraging resulted in the decrease of total soluble sugars, sucrose, and plant pigments in the leaves of all onion varieties (except for chlorophyll b)	Pobozniak et al. (2022)
5	S. dorsalis	Tomato	Infested plants showed reduction in chlorophyll, pH and protein content but higher proline content as compared to non-infested plants	Shahrin et al. (2021)
6	S. dorsalis	Chili	Thrips infestation had positive correlation with proline and negative correlation with chlorophyll and moisture contents	Nasrin et al. (2021)
7	T. tabaci	Cotton	Resistant genotypes showed higher content of ascorbate and β-carotene as compared to susceptible genotypes	Rani et al. (2018)
8	F. occidentalis	Gerbera jamesonii (Bolus)	Resistant Gerbera jamesonii (Bolus) plants showed higher activities of SOD, CAT, and POX in response to F. occidentalis infestation	Talla and Vardhini (2024)
9	F. occidentalis	Chrysanthemum	Induced PPO activity by JA against WFT	Chen et al. (2020)
10	Thrips	Alfalfa	Infested plants showed increase PPO activity	Liu (2009)
11	F. occidentalis and H. haemorrhoidalis	Peumus boldus	Higher sugar concentrations linked with higher thrips damage	Brown et al. (2002)
12	T. tabaci	Onion	Higher sugar concentrations linked with higher thrips damage	Akhtari et al. (2014)
13	T. tabaci	Leek	Higher sugar concentrations linked with higher thrips damage	Njau et al. (2017)
14	F. occidentalis	Capsicum	Higher sucrose concentrations linked with higher thrips damage whereas monomer and dimer acyclic diterpene glycosides are potential chemical defenses against thrips	Macel et al. (2019)
15	S. dorsalis, F. schultzei, T. palmi and Caliothrips indicus	Groundnut	Higher amount of tannins and phenols contributed for thrips resistance whereas higher levels of total soluble sugars, reducing sugars and amino acids showed positive relationship with number of thrips and their percent damage	Kandakoor et al. (2014)
16	T. tabaci	Cotton	Resistant parents had higher phenol and gossypol whereas susceptible parents exhibited maximum content of reducing sugar	Harijan et al. (2017)
17	T. hawaensis, T. palmi and S. dorsalis	Grape	Higher sugar and amino acid contents contributed for thrips susceptibility whereas higher tannins and phenols showed negative relationship with thrips incidence	Choudhury et al. (2017)
18	S. litura	Cotton	Higher protein levels were observed in infested plants in comparison to control	Rani and Pratyusha (2013)
19	T. tabaci	Cotton	Total soluble sugar, total nitrogen and crude protein showed positive correlation with thrips incidence	Aherkar et al. (2023)
20	F. occidentalis	Tomato	Leaf α-tomatine and an unidentified phenolic compound were isolated and had been linked to resistance against WFT	Bac-Molenaar et al. (2019)
21	F. occidentalis	Pepper	Higher amount of capsianosides and flavonoid contributed to resistance against WFT	Maharijaya et al. (2019)
22	S. dorsalis	Groundnut	Higher contents of total phenols and total tannin imparted resistance against thrips whereas higher amount of total sugars and amino acids contributed for thrips susceptibility	Rajashree et al. (2021)
23	S. cardamomi (Ramk.)	Small Cardamom	Infested capsules had lesser amount of proteins, total sugars, total phenols and acid phosphatase activity whereas higher activities of peptidase, trypsin like protease, peroxidase and essential oil constituent 1,8-cineole as compared to healthy capsules	Murugan et al. (2019)
24	T. tabaci	Cotton	Resistant variety had higher amount of total phenolics and flavonoids whereas susceptible genotype had higher soluble sugars and protein content	Rizwan et al. (2021)
25	O. loti	Alfalfa	Polyphenols, tannins and lignin increased faster in resistant lines than susceptible lines	Wang et al. (2014)
26	T. tabaci	Cotton	Resistant genotype exhibited higher levels of lignin, cellulose, and total phenols, while the susceptible genotype had higher concentrations of total soluble sugars, reducing sugars, and proteins	Unpublished data
27	T. tabaci	Cotton	Higher gossypol was observed in the roots, true leaves, stems, leaves of sympodium and flower buds in resistant cotton cultivar than susceptible cultivar	Ismail (2021)
28	T. tabaci	Onion	Higher levels of azulene and low levels of H-16 reduced thrips infestation	Basri and Ansari (2021)

SOD, superoxide dismutase; CAT, catalase: POX, peroxidase; PPO, polyphenol oxidase; JA, jasmonic acid; WFT, western flower thrips

Thrips feed on the foliage, petals, fruiting structures, and pollen of herbaceous plants, damaging leaf surfaces and removing mesophyll contents (Steenbergen et al. 2018). This disruption reduces the photosynthetic capacity, growth, and reproduction of plants by impairing chlorophyll pigments, which are crucial for capturing solar energy, ultimately lowering plant yield (Wu et al. 2021). Infestation by T. tabaci in H. sampsonii and Odontothrips loti in alfalfa leads to reduced chlorophyll a, b, and total chlorophyll content (Dai et al. 2009; Wu et al. 2021). Thrips attack on chili leaves decreased chlorophyll by 8% (Johari et al. 2016). Similarly, onion cultivars experienced reduced pigment content (except for chlorophyll b) due to S. dorsalis infestation (Pobozniak et al. 2022). Tomato varieties infested with thrips exhibited reduced leaf chlorophyll, pH, and protein content, while proline levels increased (Shahrin et al. 2021). A similar pattern was observed in chili varieties, where the severity of S. dorsalis infestation showed a positive correlation with proline content and a negative correlation with chlorophyll and moisture levels (Nasrin et al. 2021). This may be due to thrips feeding or stress conditions triggering the production of ROS, which can lower photosynthetic pigment production and stimulate proline biosynthesis. Rani et al. (2018) evaluated cotton genotypes for resistance to sucking pests by measuring ascorbate and β-carotene levels in the 2nd and 6th leaves at 50, 60, and 68 days after sowing. Resistant genotypes had higher pre-infection levels of ascorbate and β-carotene, and showed a greater increase in these concentrations after infection compared to susceptible genotypes.

Insect pest infestation triggers ROS production in plants, activating signaling pathways and an oxidative burst (Badenes-Perez 2022). This ROS accumulation activates antioxidant enzymes that mitigate oxidative damage and bolster plant defense against stresses (Praveen et al. 2023). SOD is a key antioxidant defense enzyme that converts superoxide into hydrogen peroxide and plays a crucial role in mitigating oxidative stress (Mishra and Sharma 2019). Thrips damage has been shown to significantly increase SOD activity in resistant alfalfa cultivars (Wu et al. 2021). CAT and POX detoxify H₂O₂, reducing oxidative damage from pest infestations by maintaining low ROS levels (Singh et al. 2022). Resistant Gerbera jamesonii (Bolus) plants showed higher activities of SOD, CAT, and POX in response to F. occidentalis infestation. Elevated POX activity was involved in lignin biosynthesis that played a protective role in the cell wall during infestation (Talla and Vardhini 2024). PPO generates quinones that alkylate dietary proteins, degrading essential amino acids in insect guts and preventing pest infestation (Zhang and Sun 2021). Chen et al. (2020) reported that Chrysanthemum resistance to WFT was linked to JA-induced PPO activity. Liu (2009) also observed a rapid increase in PPO activity in alfalfa following thrips infestation.

Sugars are essential for plant growth, development, and stress responses, and can enhance pathogen-triggered immunity (Morkunas and Ratajczak 2014). Genetic variability in sugar accumulation may influence insect feeding (Zhao et al. 2008). Elevated sugar levels have been linked to increased susceptibility to thrips damage. For example, F. occidentalis and H. haemorrhoidalis feeding on Peumus boldus was associated with higher sugar concentrations (Brown et al. 2002), and similar correlations were observed in onion and leek against T. tabaci infestation (Akhtari et al. 2014; Njau et al. 2017). Increased sucrose levels in capsicum leaves were also linked to greater vulnerability to F. occidentalis (Macel et al. 2019). Studies on groundnut (Kandakoor et al. 2014), cotton (Harijan et al. 2017), and grapes (Choudhury et al. 2017) showed that higher sugar content was associated with increased susceptibility to thrips. However, onion varieties exhibited decrease in total soluble sugars and sucrose content in response to S. dorsalis infestation (Pobozniak et al. 2022). Proteins are highly complex and diverse molecules that are essential for maintaining the structure and function of living organisms (Praveen et al. 2023). They act both directly and indirectly to inhibit pest feeding, enhance resistance, and activate broader defense mechanisms, contributing to overall pest management. Increased protein content is a key mechanism of host resistance to pests, as higher protein levels in S. litura-infested cotton plants, compared to controls, resulted from the synthesis of defense proteins following pest infestation (Rani and Pratyusha 2013). Also, previous studies have shown a positive correlation between crude protein, total sugars, and thrips incidence in cotton (Aherkar et al. 2023). In contrast, Shahrin et al. (2021) and Wu et al. (2021) found reduced protein content in S. dorsalis-infested tomato and O. loti-infested alfalfa plants, respectively.

Plants use phenolics to defend against herbivores due to their toxic and deterrent properties (Badenes-Perez 2022). These compounds have antioxidant, anti-mutagenic, and anti-carcinogenic effects and can modify gene expression. Their polyphenolic structure enables them to scavenge harmful and interfere with biomolecule oxidation by chelating metal ions or scavenging oxygen (Praveen et al. 2023). A study by Bac-Molenaar et al. (2019) showed that leaf α-tomatine and an unidentified phenolic compound, which were isolated through metabolomic profiling, have been linked to resistance against WFT in tomato plants. Similarly, Maharijaya et al. (2019) reported genetic variations in phytochemical profiles in capsicum leaves that contribute to resistance against WFT infestations. Lignin is one of the most important secondary metabolites that plays a multifaceted role in plant defense by acting as both a physical barrier and a chemical deterrent to pests. Its presence in plant cell walls makes tissues harder for pests to penetrate, while its breakdown products, such as phenolic compounds, can have toxic effects on herbivores, reducing feeding and growth (Praveen et al. 2023). Lignin production is upregulated in response to pest damage, enhancing resistance over time.

Rajashree et al. (2021) screened groundnut cultivars for biochemical traits related to thrips resistance and found that thrips population and damage were positively correlated with total sugars and amino acids. Similarly, Kandakoor et al. (2014) reported a positive correlation between reducing sugars and thrips population. Additionally, both studies reported that higher levels of phenols and tannins contributed to thrips resistance in groundnuts. Similar studies on table grape genotypes (Choudhury et al. 2017) and alfalfa cultivars (Wu et al. 2021) showed that thrips intensity was positively correlated with total soluble sugars and proteins, but negatively correlated with phenols, tannins, and lignin content. Macel et al. (2019) identified monomer and dimer acyclic diterpene glycosides as potential chemical defenses against thrips in capsicum species through metabolomic studies. Murugan et al. (2019) evaluated enzyme activities and phytochemical changes in small cardamom capsules in response to thrips infestation. Infested capsules showed reduced levels of protein, total sugars, total phenols, and acid phosphatase activity, while exhibiting higher activity of peptidase, trypsin-like protease, peroxidase, and the essential oil component 1,8-cineole. Rizwan et al. (2021) observed that cotton genotypes resistant to sucking insects exhibited higher levels of total phenolics and flavonoids, while susceptible genotypes contained more soluble sugars and proteins. Aherkar et al. (2023) reported a positive correlation between thrips incidence and total soluble sugars, nitrogen, and crude protein in cotton. Additionally, Wang et al. (2014) observed that resistant alfalfa lines showed increased levels of polyphenols, tannins, and lignin as compared to susceptible lines during O. loti infestation. Also, our study on thrips-infested cotton genotypes found that the resistant genotype exhibited higher levels of lignin, cellulose, and total phenols, while the susceptible genotype had higher concentrations of total soluble sugars, reducing sugars, and proteins (unpublished data). This might be attributed to the fact that thrips cause greater damage to plants with high sugars and amino acids as they take up these nutrients for their growth and development. The phytoconstituents such as total phenolics, tannins and total flavonoids displayed antioxidant activity, helping to reduce thrips infestation and prevent herbivory.

Gossypol, a phytoalexin, acts as a natural insecticide in plant defense, reducing pest growth, feeding, and reproduction, making it a key component of the plant's defense arsenal (Samtiya et al. 2020). A study on recombinant inbred lines of cotton revealed that resistant lines have higher phenol and gossypol levels and lower reducing sugars compared to susceptible lines. Gossypol plays a key role in cotton's defense, acting as an antibiosis agent against pests (Harijan et al. 2017). A field study conducted to evaluate the gossypol levels in various parts of cotton at different growth against T. tabaci revealed that resistant cultivars possessed higher gossypol content in all the tissues as compared to susceptible cultivars (Ismail 2021). This may be due to the fact that gossypol induces cell cycle arrest at the G₀/G₁ phase, inhibiting DNA replication and triggering apoptosis, thereby acting as a natural insecticide and enhancing resistance to thrips. Plant waxes act as a physical barrier against pests, hindering feeding and movement, while also containing deterrent that repel herbivores and protect against pest infestation. In onion plants, accumulated epicuticular wax was a key factor in their natural resistance to T. tabaci (Basri and Ansari 2021). Gas chromatography/mass spectrometry profiling of epicuticular wax components, including hentriacontanone-16 (H-16), azulene (1,4-dimethyl-7-(1-methylethyl)), and 2-methyl octacosane, revealed that higher levels of azulene and lower levels of H-16 reduced thrips infestation.

Nutrition involves the essential chemicals required by organisms for growth, tissue maintenance, and reproduction. Insect nutrition studies the interaction of nutrients and substances in food related to maintenance, growth, reproduction, health, and disease, including processes such as intake, absorption, assimilation, biosynthesis, catabolism, and excretion. Nitrogen enhances insect performance by increasing the biosynthesis of proteins, free amino acids, and sugars that attract insects. Potassium strengthens plant resistance by promoting secondary compound metabolism, reducing carbohydrates, and limiting pest damage. Phosphorus decreases host suitability to pests, while calcium, zinc, and sulfur help reduce pest populations. Silicon strengthens plant defenses through physical and biochemical mechanisms, acting as a feeding deterrent without pesticide residues. A study by Malik et al. (2009) found that high nitrogen levels led to a 73.9% increase in thrip abundance on onions. Pathak et al. (2018) showed that the lowest thrips populations occurred in the absence of nitrogen. Zheng et al. (2024) found that low nitrate levels in eggplants enhanced defense against the western flower thrips, F. occidentalis, by activating the JA pathway and increasing defense marker gene expression. Additionally, JA application reduced western flower thrips damage in Chrysanthemum (Chen et al. 2019).

Transcriptional profiling of thrips responsive genes

Although there is existing literature on thrips resistance, including structural defenses, anti-nutritional compounds, and secondary metabolites, the molecular and genetic basis of resistance remains poorly understood. Thrips' rapid mobility and short reproductive cycles make them difficult to control, with insecticides being the most common management strategy. However, overuse of chemicals leads to resistance, increased production costs, and harm to beneficial insects. To address this, molecular techniques, particularly RNA sequencing, and comparative transcriptomics are increasingly used to study pest-plant interactions and transcriptional changes, aiding in the development of integrated crop management systems. RNA sequencing provides insights into gene expression and defense signaling pathways activated by insect feeding, helping to enhance plant resistance (Gill et al. 2022). The documented studies related to transcriptional profiling of thrips responsive genes in various crops have been given in Table 5. Thrips attack results in the activation of local plant immune responses by producing different biosignaling molecules. The role of JA, ethylene (ET) and salicylic acid (SA) in Arabidopsis thaliana responses to F. occidentalis feeding was studied by Abe et al. (2008). The response analysis of A. thaliana hormone-related mutants (i.e., JA-insensitive coi1-1 mutant, ET-sensitive ein2-1 and ein3-1 mutants, and SA defective mutant eds16-1) and transcriptome-based comparative analysis showed JA as the core of the plant's response to the feeding effect of thrips. The induction of JA and defensive compounds synthesis in soybean in response to thrips feeding has been reported by Dillon et al. (2018). Sarde et al. (2019) observed the involvement of CaLOX2 and CAPIN II in JA dependent induced defense against WFT in sweet pepper. Eggplant infested with WFT showed increased transcript levels of key genes in the JA pathway, along with the accumulation of JA-amido conjugates (such as jasmonoyl-phenylalanine, jasmonoyl-valine, and jasmonoylisoleucine), the JA precursor 12-oxophytodienoic acid, and methyl jasmonate. Additionally, higher expression levels of defense marker genes (MPK3, MPK7, and WRKY53) were observed, along with enhanced activities of polyphenol oxidase and peroxidase (Zheng et al. 2024). Liu et al. (2022) conducted a comparative analysis of the metabolomic profiles of WFT-resistant and thrips-susceptible eggplant using a GC–MS-based approach. Their findings indicated a higher concentration of quinic acid in the thrips-resistant eggplant compared to the susceptible plant. RNA sequencing analysis further identified DEGs by comparing the genome-wide gene expression profiles of both cultivars of eggplant. Consistent with the metabolomic results, KEGG pathway enrichment analysis of these DEGs highlighted the starch and sucrose metabolism pathway, which includes quinic acid as a metabolic by-product, as being significantly enriched.

Table 5.

Transcriptional profiling of thrips responsive genes in various crops against thrips infestation

S. no	Crop	Pest	Transcriptome analysis					Differential Expressed Genes (DEGs)	Reference
			RNA extraction	RNA analysis	cDNA library preparation	RNA sequencing	Transcriptional analysis
1	Arabidopsis thaliana	WFT						Expression of marker genes VSP2 and LOX2—JA pathway chiB and PDF1.2—JA/ET pathway PR1 and BGL2—SA pathway	Abe et al. (2008)
2	Alfalfa	Thrips	RNA plant mini kit with column DNase digestion	RNA Nano 6000 Assay Kit of the Bioanalyzer 2100 system	NEB Next Ultra™ RNA Library Prep Kit for Illumina	Illumina Hiseq 2500 platform	COG KEGG	33 DEGs mapped to 11 pathways for resistant (GN-1) and 80 mapped to 14 pathways for susceptible (WL323) alfalfa cultivar	Tu et al. (2018)
3	Sweet pepper	WFT	Bioline kit		iScript cDNA synthesis kit (BioRad)			JA-related CaLOX2 and CaPIN II was induced	Sarde et al. (2019)
4	Alfalfa	Thrips	Trizol method	Nanodrop 2000 and gel electrophoresis	TruseqTM RNA sample prep kit (Illumina)	Illumina Hiseq4000 (Version 2 × 150 bp) at Majorbio Bio-pharm Biotechnology Co., Ltd. (Shanghai, China)	COG KEGG RSEM	Genes related to host-pest interaction: CDPK, CaMCML, Pit6, RPM1, CERK1, SGT, HSP90, EDS1, WRKY, NHO1 and PR – up-regulated in susceptible accession (Caoyuan No.2) CDPK, CNGCS, FLS2, RPM1 and EDS1—downregulated in resistant accession (Caoyuan No.4)	Zhang et al. (2020)
5	Alfalfa	Thrips	Trizol method	Nanodrop 2000 and gel electrophoresis	TruseqTM RNA sample prep kit (Illumina)	Illumina Hiseq4000 (Version 2 × 150 bp) at Majorbio Bio-pharm Biotechnology Co., Ltd. (Shanghai, China)	COG KEGG RSEM	Genes related to isoflavonoid biosynthesis: CYP93C, HI40MT, HIDH, I2’H, IF7MAT, 7-IOMT, VR, CYP81E9 and PTR—unregulated in Caoyuan No.2	Zhang et al. (2021)
6	Hemerocallis citrina (daylily)	T. palmi	Trizol method	1% agarose gel electrophoresis		Illumina Hiseq platform	GO KEGG	DEGs involved in pathways such as secondary metabolite synthesis, defense hormone signaling, defense enzyme production, the MAPK signaling pathway, cell wall strengthening, carbohydrate metabolism, and photosynthesis: MYB, WRKY, bHLH, and AP2/ERF were upregulated	Sun et al. (2024)

WFT, western flower thrips; KEGG, Kyoto encyclopedia of genes and genomes; RSEM, RNA-Seq by expectation–maximization; COG, clusters of orthologous genes; GO, gene ontology; JA, jasmonic acid; ET, ethylene; SA, salicylic acid; MAPK, mitogen-activated protein kinase

Tu et al. (2018) compared the transcriptome responses of susceptible (WL323) and resistant (GN-1) cultivars of Medicago sativa L. against thrips infestation. The results showed that genes such as lipoxygenase, tryptophan synthase beta chain, and mitochondrial ATP synthase g subunit were up-regulated after thrips infestation. In contrast, enzymes involved in plant growth and stress responses, including isoflavone-7-O-methyltransferase, pathogenesis-related protein PR10, and thaumatin-like protein 1a, were down-regulated. Both thrips-resistant and susceptible plants exhibited up-regulation of genes related to epidermal resistance, such as sieve element occluding proteins, and stress tolerance genes, including viral methyltransferase and alfalfa mosaic virus RNA2. Genes involved in the flavonoid biosynthesis and phenylalanine metabolism pathways were up-regulated in both cultivars, while fatty acid metabolism genes were down-regulated. Notably, the resistant cultivar showed increased synthesis of linoleic and alpha-linolenic acids, enhancing its immune response to thrips feeding, while the susceptible cultivar did not exhibit this response.

Zhang et al. (2020) compared the transcriptomes of thrips-resistant (Caoyuan No. 4) and thrips-susceptible (Caoyuan No. 2) alfalfa accession and concluded that Caoyuan No. 4’s defense contained both constitutive and potentially triggered defensive genes. Furthermore, these two types of protective genes can be triggered at the same time. Under control conditions, up-regulation of 851 and down-regulation of 434 constitutive genes were found in resistant accession as compared to Caoyuan No. 2. On the other hand, upon thrips infestation, only 13 DEGs were detected in Caoyuan No. 4 whereas 3326 contigs DEGs related to flavonoid & isoflavonoid biosynthesis, amino & nucleotide sugar metabolism, proteasome, and host-pest interaction was detected in susceptible accession. Zhang et al. (2021) further carried out the combined study of transcriptome and metabolome against thrips infestation in susceptible (Caoyuan No. 2) accession of M. sativa L. The flavonoid and isoflavonoid biosynthesis pathways were the most substantially enhanced pathways in response to infestation by thrips.

Sun et al. (2024) investigated the response of Hemerocallis citrina (daylily) to T. palmi feeding by analyzing the expression of defense-related genes. The DEGs in daylilies exposed to T. palmi infestation were primarily involved in pathways such as secondary metabolite synthesis, defense hormone signaling, defense enzyme production, the MAPK signaling pathway, cell wall strengthening, carbohydrate metabolism, and photosynthesis, all contributing to insect resistance. The transcription factors linked to these DEGs were identified in the MYB, bHLH, AP2/ERF, WRKY, bZIP, and NAC families. Notably, MYB, WRKY, bHLH, and AP2/ERF transcription factors were significantly upregulated after T. palmi feeding, indicating their crucial role in mediating the daylily’s induced resistance to thrips. Our transcriptomic analysis of thrips-infested cotton cultivars revealed upregulation of key defense pathways, particularly phenylpropanoid and flavonoid biosynthesis, which enhance the plant's physical and biochemical defenses (unpublished data). Overall, the comprehensive information given here could improve fundamental knowledge of molecular responses to herbivore-inducible plant defense and contribute to the design of strategies against thrips.

Management of thrips

As mentioned earlier, thrips pose a significant challenge in agriculture due to their mobility, feeding behavior, and protected life stages. Sustainable control requires an integrated approach that combines cultural practices, natural enemies, and selective or low-toxicity insecticides (Jangra et al. 2021). Figure 3 illustrates various traditional and advanced management strategies to combat thrips infestation.

Fig. 3.

Different management strategies to combat thrips infestation

1. Traditional management strategies.

Many farmers rely on cultural or physical methods for thrips management, with sanitation practices-such as removing weeds and plant debris-serving as a primary defense (Nyasani et al. 2013). Positive-pressure ventilation systems with insect-proof screens can help prevent thrips infestations (Sugiyama et al. 2014), while UV-reflective mulch can disrupt their host-searching behavior (Kigathi and Poehling 2012). Though irrigation can reduce thrips populations, high humidity often favors their development (Steiner et al. 2011). Fertilizer use, particularly nitrogen and phosphorus, increases aromatic amino acid levels, promoting F. occidentalis abundance (Chen et al. 2014). Trap cropping with Chrysanthemum and intercropping of French beans with crops like sunflowers or potatoes can reduce thrips damage (Nyasani et al. 2012). Mesh screens on greenhouse windows can reduce F. occidentalis infestations up to 20% (Tinoco et al. 2014).

An alternative pest control strategy involves using semiochemicals, such as pheromones and allelochemicals, to manipulate insect behavior (Kundu et al. 2024). For instance, F. occidentalis is attracted to the sexual aggregation pheromone neryl (S)−2-methylbutanoate (Hamilton et al. 2005), while alarm pheromone analogs like decyl and dodecyl acetate reduce oviposition and landing (MacDonald et al. 2002). Allelochemicals, such as benzenoids and terpenes, attract female thrips in a dose-dependent manner (Koschier et al. 2000). These semiochemicals could be effective in mass trapping and "lure and kill" strategies for thrips management (Broughton et al. 2015). Biological control of thrips includes augmentative release of natural enemies and conservation strategies. These enemies are categorized into microbials (entomopathogenic fungi and nematodes) and macrobials (predators and parasitoids) (Mouden et al. 2017). Predators such as parasitic wasps, lacewings, mites, and minute pirate bugs help to control thrips populations, while nematodes from order Heterorhabditis and Steinernema target soil-dwelling thrips (Ebssa et al. 2006). Thripinema nematodes induce sterility in F. occidentalis females (Arthurs and Heinz 2006). Entomopathogenic fungi infect thrips by penetrating their conidia in the cuticle of thrips and using their bodies as a nutrient source for growth and reproduction. Investigating secondary metabolites and defensive proteins in crops could lead to new protection methods, such as using biostimulants or boosting specific defensive compounds (Jangra et al. 2021). Insecticides like organophosphates, carbamates, pyrethroids, and more recently, avermectins and spinosyns, are widely used for thrips control (Wakil et al. 2023). Contact insecticides are effective with minimal residue, while systemic insecticides, absorbed by plant roots, offer rapid control (Skendzic et al. 2021). Plant hormones like JA can trigger natural defenses, reducing thrips density and damage (Praveen et al. 2023).

• (b)Advanced management strategies.

Current thrips management strategies face challenges due to resistance and environmental concerns, highlighting the need for more sustainable, integrated pest management approaches. Research on host plant resistance is advancing through high-throughput phenotypic screening and 'omics' technologies, offering new opportunities for crop protection (Jangra et al. 2021; Gill et al. 2022; Kundu et al. 2024). Thrips genome data enables the development of molecular control methods focused on thrips, host plant, and virus interactions (Mouden et al. 2017). Genomic studies of thrips species, such as F. occidentalis and T. palmi, have identified gene families related to detoxification, particularly in cytochrome P450 enzymes (Rotenberg et al 2020; Guo et al 2020). Studies show that modulating genes like vacuolar ATP synthase subunit B can reduce F. occidentalis fecundity (Whitten et al. 2016). Further, transgenic plants and protease inhibitors, such as cystatin and equistatin, can improve thrips resistance (Thomas et al. 1994; Outchkourov et al. 2004). The discovery of a Bacillus thuringiensis (Bt) toxin effective against thrips offers a promising new pest control method, particularly for cotton. Akbar et al. (2019) reported that Cry51Aa2.834_16, a modified Bt protein, provides strong protection against thrips when expressed in genetically engineered cotton (MON 88702). Huseth et al. (2020) found that this toxin reduces thrips' egg-laying through behavioral avoidance, particularly affecting F. fusca. Additionally, D’Ambrosio et al. (2020) showed the toxin acts as an antifeedant, reducing feeding attempts. While promising, further research is needed to evaluate its effectiveness in other crops.

RNA interference (RNAi) is an emerging approach for pest control, with potential for managing thrips species like T. tabaci, T. palmi, and F. occidentalis (Han et al. 2019; Priti and Ghosh 2022). Transgenic tomato plants expressing dsRNA targeting thrips genes showed improved resistance (Venkatesh et al. 2023). However, better delivery systems, such as plant-based dsRNA expression and sprays, are needed for RNAi to be effective (Taning et al. 2020). Chloroplast-mediated RNAi offers stronger protection than traditional methods (Wu et al. 2022). While nanoparticles and other delivery methods (cationic liposomes and BioClay) show promise, challenges like environmental degradation, uptake, and RNAi resistance remain (Kim and Kim 2023). Despite these hurdles, RNAi holds promise as a species-specific pest control strategy. Han et al. (2024) demonstrated the first successful use of CRISPR-Cas9 genome editing in a Thysanopteran species, F. occidentalis, providing a simple method for creating heritable mutations in its germline. This technique targets genes involved in ommochrome pigment biosynthesis, offering a clear phenotypic effect. CRISPR-Cas9 holds potential for investigating gene function in thrips and developing genetic strategies to control their populations, including suppression or replacement approaches, which could help reduce virus transmission by thrips as vectors.

Combining genetic approaches with metabolomics could identify metabolic markers for resistance and enable ‘metabolite breeding’ for multi-resistance programs. Understanding the molecular mechanisms of thrips feeding behavior and plant defense responses will lead to more targeted management strategies (Kundu et al. 2024). Climate change may impact plant defenses and pest dynamics, making it essential to study how environmental factors like soil, temperature, and humidity influence plant resistance at the genetic and biochemical levels (Skendzic et al. 2021). Focusing on these areas will improve crop resistance, enhance yields, and support sustainable agricultural practices (Singh et al. 2020; Kundu et al. 2024).

Conclusion

This review offers a novel perspective by integrating a comprehensive analysis of the morphological traits, defensive proteins, metabolites, and gene expression profiles of host plants specifically in response to thrips feeding, alongside effective thrips management strategies. The data and insights provided in this review showed that defensive traits of plants, such as smaller leaf size, increased papillae and trichome density, higher levels of total phenols and tannins, as well as the upregulation of the shikimic acid pathway and flavonoid biosynthesis genes, have been linked to enhance resistance against thrips infestation (Fig. 4). Despite current progress, there is still considerable potential to improve plant resistance to thrips. Future research should focus on identifying novel resistance genes and regulatory networks through “omics technologies,” which could be utilized in genetic engineering or selective breeding for thrips-resistant crops. Additionally, integrating plant resistance with biocontrol agents, such as predators and parasitoids, offers a more sustainable alternative to chemical pesticides. A multidisciplinary approach combining plant biology, pest ecology, and advanced pest management technologies is essential for developing effective, sustainable solutions to thrips management.

Fig. 4.

Schematic illustration of diverse resistance determinants in various agricultural crops against thrips infestation

Author contributions

Sunidhi: Writing-original draft, review and editing. Prabhjot Singla: Writing-original draft, review and editing. Rimaljeet Kaur: Conceptualization, Supervision and Writing-review. Sucheta Sharma: Supervision and Writing-review.

Declarations

Conflict of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.