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. 2014 Jan 1;14:297. doi: 10.1093/jisesa/ieu159

Temperature- and CO 2 -Dependent Life Table Parameters of Spodoptera litura (Noctuidae: Lepidoptera) on Sunflower and Prediction of Pest Scenarios

D Manimanjari 1, M Srinivasa Rao 1,2, P Swathi 1, C A Rama Rao 3, M Vanaja 1, M Maheswari 1
PMCID: PMC5657882  PMID: 25528748

Abstract

Predicted increase in temperature and atmospheric CO 2 concentration will influence the growth of crop plants and phytophagous insects. The present study, conducted at the Central Research Institute for Dryland Agriculture, Hyderabad, India, aimed at 1) construction of life tables at six constant temperatures viz ., 20, 25, 27, 30, 33, and 35 ± 0.5°C for Spodoptera litura (Fabricius) (Noctuidae: Lepidoptera) reared on sunflower ( Helianthus annus L.) grown under ambient and elevated CO 2 ( e CO 2 ) (550 ppm) concentration in open top chambers and 2) prediction of the pest status in near future (NF) and distant future (DF) climate change scenarios at major sunflower growing locations of India. Significantly lower leaf nitrogen, higher carbon and higher relative proportion of carbon to nitrogen (C:N) were observed in sunflower foliage grown under e CO 2 over ambient. Feeding trials conducted on sunflower foliage obtained from two CO 2 conditions showed that the developmental time of S. litura (Egg to adult) declined with increase in temperature and was more evident at e CO 2 . Finite (λ) and intrinsic rates of increase ( rm ), net reproductive rate ( Ro ), mean generation time, (T) and doubling time (DT) of S. litura increased significantly with temperature up to 27–30°C and declined with further increase in temperature. Reduction of ‘ T ’ was observed from maximum value of 58 d at 20°C to minimum of 24.9 d at 35°C. The DT of population was higher (5.88 d) at 20°C and lower (3.05 d) at 30°C temperature of e CO 2 . The data on these life table parameters were plotted against temperature and two nonlinear models were developed separately for each of the CO 2 conditions for predicting the pest scenarios. The NF and DF scenarios temperature data of four sunflower growing locations in India is based on PRECIS A1B emission scenario. It was predicted that increased ‘ rm ’, ‘λ’, and ‘ Ro ’ and reduced ‘ T ’ would occur during NF and DF scenario over present period at all locations. The present results indicate that temperature and CO 2 are vital in influencing the population growth of S. litura and pest incidence may possibly be higher in the future.

Keywords: phytophagous insect, developmental time, insect pest, climate change, PRECIS

Global mean surface temperature has increased since the 19th century, each of the past three decades has been warmer than all previous decades, with the decade of the 2000’s being the warmest so far. The increase in temperature between the average of the 1850–1990 period and the 2003–2012 period is 0.78 (0.72–0.85) °C and the amount CO 2 in the atmosphere has grown by about 40% over preindustrial levels ( IPCC Climate Change 2013 ). The impacts of predicted increases in global average surface temperatures and atmospheric CO 2 concentrations on insect-plant interactions have been studied separately, only a few studies have considered them together ( Murray et al. 2013 ). Temperature influences the developmental rate of insects significantly and has direct effects, whereas the effect of elevated CO 2 ( e CO 2 ) is host-mediated and indirect ( Hunter 2001 ). It is well known that developmental rates increase with temperature up to certain levels beyond which they usually decrease ( Tshiala et al. 2012 ). The most predicted effects of climate change, i.e., increase in atmospheric temperature and CO 2 concentration, will have a significant effect on agriculture in general and on herbivore insect populations in particular. Quantification of the relationship between insect development and temperature is vital to predict population dynamics of the insect pests.

Sunflower ( Helianthus annuus L.), is one of the most important edible vegetable oil crops in the world. Sunflower oil is a frying oil, light in taste, appearance, and contains typical vegetable tri-glycerides with vit E ( http://en.wikipedia.org/wiki/sunflower ).The Russian federation, Ukraine, Argentina, China, and France are the major sunflower growing countries ( http://faostat.fao.org ). India stands in the 14th position in the world production with an average annual production of 5.17 million tons ( http://agricoop.nic.in ) from 7.32 m ha area with an average yield of 706 kg per ha. It is an introduced crop in India and the pest complex is different from temperate regions. The tobacco caterpillar, Spodoptera litura Fab. (Lepidoptera: Noctuidae) is a major pest of sunflower ( Basappa and Santhalakshmi 2005 ) and causes significant yield losses. Larvae cause severe defoliation during flower initiation stage leading to reduced supply of assimilates to the capitulum thereby affecting floret and seed production ( Sujatha and Lakshminarayana 2007 ). Temperature ( Ranga Rao et al. 1989 ) and CO 2 ( Srinivasa Rao et al. 2012 ) are known to alter the growth and development of S.litura.

Life tables are important tools for understanding the population dynamics of insect pests and explain the impact of various factors on the growth, survival, and reproduction of insect populations. Variation of life table parameters of lepidopterans (intrinsic rate of increase ‘ rm ’ and finite rate of increase ‘λ’) with temperature ( Hardev et al. 2013 ), larval host and diet ( Sheng 1994 ) and e CO 2 ( Dyer et al. 2013 ) have been reported. Life table parameters of S. litura were altered substantially in peanut ( Tuan et al. 2013 ) and in non- Bt cotton ( Prasad and Sreedhar 2011 ) with temperature. Studies analyzing variation of life table parameters with both temperae and CO 2 have not been attempted. The objectives of our study were 1) to measure the effect of constant temperatures and e CO 2 on life table parameters of S. litura on sunflower and 2) to predict the pest status during near future (NF) and distant future (DF) climate change scenarios.

Materials and Methods

Open Top Chambers

Two square open top chambers (OTC) of 4 × 4 × 4 m, were constructed at the Central Research Institute for Dryland Agriculture (CRIDA), Hyderabad (17.38° N; 78.47°E), one for maintaining e CO 2 at concentrations of 550 ± 25 ppm and another one for ambient CO 2 ( a CO 2 ) concentrations (380 ± 25 ppm CO 2 ). Chambers were replicated twice making a total of four OTCs for experimentation. Carbon dioxide gas was supplied to chambers and maintained at set levels using manifold gas regulators, pressure pipelines, solenoid valves, rotameters, a sampler, a pump, a CO 2 analyzer, a PC-linked Program Logic Control (PLC) and Supervisory Control and Data Acquisition (SCADA). The fully automated control and monitoring system includes a CO 2 analyzer PLC and SCADA programme with PC that enabled the maintenance of desired levels of CO 2 within the OTCs. The system monitored continuously the concentration of CO 2 , temperature, and relative humidity (RH) within the OTCs. The air was sampled from the centre point of the chamber through a coiled copper tube, which can be adjusted to different heights as the crop grows.

Sunflower (Var. KBSH-1) seeds were sown in the month of June in the four OTCs at two different CO 2 concentrations and crop plants were maintained during entire crop season till December.

Biochemical Constituents of Sunflower Foliage

Leaf tissue used in the feeding experiments was analyzed for carbon, nitrogen, and C: N ratio. To determine carbon and nitrogen concentrations, samples were dried at 80°C and subsequently ground to powder. Leaf carbon and nitrogen were measured using a CHN analyzer (Model NA 1500 N, Carlo Erba Strumentazione, Italy) using standard procedures ( Jackson 1973 ).

Insects

Egg masses of S. litura were collected from the field and maintained at the entomology laboratory of CRIDA. The cultures were maintained in a growth chamber (PERCIVAL I-36LL, Perry, Iowa, USA). Stock cultures were maintained on leaves of sunflower plants grown under open field condition. RH was maintained at 60% during the day and at 70% during the night. Temperatures were maintained at 27 ± 1°C and a photoperiod of 14:10 (L:D) h.

Developmental Rate

Groups of newly laid eggs of S. litura (N ≥ 100) were placed in closed Petri dishes of 110 mm diameter and 10 mm height with a piece of wet filter paper to maintain humidity. Petri dishes were maintained at six constant temperatures (20, 25, 27, 30, 33, and 35 ± 0.5°C) at 75 ± 5% RH and a photoperiod of 14:10 (L:D) h in CO 2 growth chambers. The eggs were observed daily and the wet filter paper was replaced as required. The total number of eggs hatching at each temperature and the duration of egg development were recorded. After hatching of eggs, neonates were collected and feeding trials were initiated. At 10:00 am on the day of initiating the feeding trial, freshly hatched neonates were placed in petri dishes of 110 mm diameter and 10 mm height. Ten neonates were kept in each petri dish, forming one replication later larvae were transferred in each petri dish and tracked as a single replication till adult stage (egg laying). In total, 10 replications were used. Moistened filter papers were kept at the bottom of the petri dishes to maintain leaf turgidity. Neonate larvae were fed with tender sunflower leaves picked from plants grown under the two CO 2 concentrations in the OTCs. Fresh leaves were provided daily in the morning. Daily data were recorded corresponding temperature condition. Every day, larvae were provided with sunflower foliage obtained from e CO 2 and a CO 2 conditions separately and this was repeated throughout the experiment up to larval period. Mean larval period was recorded and after cessation of feeding, pre-pupae were collected and transferred to glass jars. Later pupae were collected from the respective treatments and pupal periods were noted according to the treatments. After the emergence of adults from pupae, moths were paired and each pair was kept in a separate plastic container and fed with 10% honey solution. Egg masses laid were collected separately and counted.

A visible exuvia was used as an evidence of molting when observed along with frass of developing larvae. Observations were recorded daily in order to measure survival and developmental time of each larval instar and pupa until adults emerged. After the emergence of adults, their sex ratio was also recorded. The number of eggs laid per female, longevity of adults, and total life span (TLS) at each temperature were recorded. All growing conditions (RH, photoperiod and fresh leaves as food source) were maintained as described above.

Life Table Parameters

Life table parameters were estimated by using TWOSEX–MS Chart software which groups the raw data and calculates a number of life-table parameters. The rm as a composite index of growth, development, and fecundity of the whole population was estimated by using the iterative bisection method from the Duler-Lotka formula ∑x=0∞e−r(x+1)lxmx=1  ( Chi 2005 ). The raw life history data of S. litura were analyzed based on the theory of age-stage, two-sex life table. The means and SEs of the life table parameters were estimated by using the Jackknife method. To facilitate life table analysis, a user-friendly computer program, TWOSEX-MS-Chart was adopted ( Chi 2005 ).

The life table parameters were estimated using sunflower foliage from e CO 2 and a CO 2 separately six temperatures and were plotted against temperature to compare the thermal sensitivities of parameters. Among different forms of distribution, a nonlinear (polynomial) relationship was observed against temperatures and was found to be the best fit equation. Two nonlinear models were developed separately for each of the CO 2 conditions and used for predicting the pest scenarios at four locations of the country.

Pest Scenarios

Data of historical daily temperatures (maximum and minimum) for four study locations viz ., Akola (20° 42′ N, 77° 2′ E); Bangalore (12° 58′ N, 77° 35′ E); Hyderabad (17° 18′ N, 78° 60′ E); and Raichur (16° 12′ N, 77° 25′ E) were collected from a 1 × 1 degree grid database provided by the India Meteorological Department ( http://www.imd.gov.in/doc/nccraindata.pdf ) for the period 1991–2005 referred to as present (PR) period in this research. The future data was obtained using PRECIS model. A number of global circulation models with their corresponding versions of downscaled projections at a relatively smaller spatial resolution are available and the projections vary from the parent GCM ( Krishna Kumar et al. 2011 ). In this article, we chose to use the projections obtained at a resolution of 50 × 50 km grid using the PRECIS where the daily data on maximum temperature, minimum temperature, and rainfall are available. The output for the A1B emission scenario showing ‘reasonable skill in simulating the monsoon climate over India’ ( Krishna Kumar et al. 2011 ) was considered. A1B is ‘the most appropriate scenario as it represents high technological development, with the infusion of renewable energy technologies following a sustainable growth trajectory’ ( MoEF 2012 ).The future temperature data thus obtained were classified into two categories viz ., ‘NF consisting of 2,021–2,050 and DF consisting of 2,071–2,098. The daily data during the crop duration of 133 days commencing from 26 to 44 Standard Weeks was considered for predicting the life table parameters of S. litura in future as pest scenarios.

Statistical Analysis

The data on developmental rate of each stage of insect pest at six constant temperatures and two CO 2 conditions were analysed by using one-way analysis of variance (ANOVA). Results presented are mean value of each determination (treatment) ± standard deviation (SD). The differences between mean values of treatments were determined by Tukey’s test and the significance was defined at P  < 0.05. The mean values of life table parameters of S. litura across four locations for the three periods viz., present, near and future periods were compared using two-sample t -test assuming equal variances. The significance of mean values was defined at P  < 0.01. All statistical analyses were done using SPSS version 16.0.

Results

Biochemical Analysis of Sunflower Foliage

In this study, the nutritional quality of sunflower leaves differed significantly at e CO 2 and a CO 2 concentrations. Leaf nitrogen content was distinctly lower (2.67 %) in elevated compared with ambient (2.81%). However, with increased CO 2 concentrations, the carbon content of leaf tissue increased significantly (41.63 %) over a CO 2 which recorded 38.63 %. This resulted in a significant increase in C: N ratio under e CO 2 conditions (15.60) compared with ambient (13.76) ( Table 1 ).

Table 1.

Change in bio chemical constituents of sunflower foliage grown under e CO 2 and a CO 2

Biochemical CO 2 Concentrations
LSD
constituents e CO 2 a CO 2 F(P)
P  ≤ (0.05)
Nitrogen % 2.67 ± 0.10 2.81 ± 0.12 16.19 0.091
( P  ≤ 0.01)
Carbon % 41.63 ± 0.95 38.63 ± 0.83 46.71 1.129
( P  ≤ 0.01)
C:N ratio 15.60 ± 0.42 13.76 ± 0.59 61.17 0.606
( P ≤  0.01)
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Mean values ± SD.

Effect of Temperature and CO 2 on Developmental Rate

The variation in developmental time for egg, larva, pupa, and adult stages of S. litura on sunflower at six constant temperatures at two CO 2 conditions is presented in Table 2 . Reduction in average developmental time for the egg stage (F 5,495 =880.89; P  < 0.01), larva (F 5,295 =1,288.50; P  < 0.01), pupa (F 5,270 =93.72; P  < 0.01), adult (F 5,245 =9.79; P  < 0.01), and TLS (F 5,295 =26.04; P <  0.01) was observed with increase in temperature under both e CO 2 and a CO 2 . The duration of all stages was shorter under e CO 2 than a CO 2 ( Table 2 ). Decreased mean developmental time (days) of each stage, egg (from 7.61 to 3.32), larva (from 29.8 to 12.87), pupa (from 16.46 to 7.93), adult (from 5.33 to 3.67), and TLS (from 59.2 to 27.8) from 20 to 35°C temperature on e CO 2 foliage. Survivorship of four stages of S. litura was akin to developmental rate and significant variation was observed with temperature increase at e CO 2 . The highest (1.051) and lowest (1.013) survival rates from egg to adult were observed at 30 and 20°C temperature ( Table 2 ).

Table 2.

Developmental time (days) of different stages of Spodoptera litura on sunflower at six constant temperatures and two CO 2 conditions

Temperature °C Developmental time at e CO 2
Egg Larva Pupa Adult Fecundity Total life span
20 7.61 ± 0.51a 29.80 ± 2.21a 16.47 ± 1.73a 5.34 ± 1.00a 1,769 ± 549b 59.20 ± 2.69a
25 6.19 ± 0.68b 15.07 ± 2.12b 10 ± 0.88b 3.70 ± 5.3b 2,880.8 ± 569a 35.13 ± 2.91b
27 4.15 ± 4.00c 14.07 ± 0.78c 9.92 ± 1.14b 5.36 ± 1.72a 2,172.37 ± 1,039b 33.27 ± 6.51bc
30 3.48 ± 0.60d 12.27 ± 0.59d 6.71 ± 1.07c 5.00 ± 2.64a 2,092.7 ± 324b 28.00 ± 6.96d
33 4.21 ± 0.56c 12.87 ± 1.19d 10.43 ± 2.22b 2.94 ± 0.97b 585.8 ± 97c 30.33 ± 3.28cd
35 3.32 ± 0.49d 12.87 ± 1.3d 7.96 ± 0.98c 3.56 ± 1.57b 518 ± 48c 27.80 ± 2.90d
Temperature °C Developmental time at a CO 2
Egg Larva Pupa Adult Fecundity Total life span
20 7.53 ± 0.74a 27.60 ± 1.55a 16.80 ± 4.04a 7.0 ± 1.93a 1,952 ± 355b 58.93 ± 2.84a
25 7.26 ± 0.96b 15.20 ± 1.82c 12.40 ± 1.14b 4.13 ± 1.16b 1,896.8 ± 447b 39.00 ± 2.68b
27 4.08 ± 0.56cd 17.73 ± 2.64b 9.73 ± 2.13c 3.60 ± 2.13bc 2,834 ± 1939a 35.13 ± 8.43c
30 3.98 ± 0.56cd 14.53 ± 1.74c 9.53 ± 1.05c 3.80 ± 0.7bc 477.8 ± 256c 30.86 ± 4.41d
33 4.14 ± 0.52c 13.20 ± 1.08d 7.86 ± 0.45d 3.87 ± 0.67bc 779.40 ± 569c 29.06 ± 1.85d
35 3.68 ± 0.49 e 13.13 ± 1.77 d 6.66 ± 0.79 d 2.60 ± 0.40 d 273.4 ± 64 c 26.06 ± 1.78 e
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Means in the same column followed by different letter (a,b,c and d) are significantly different at P  < 0.05 (ANOVA) by Tukey’s test.

Life Table Parameters

The data on life table parameters viz ., ‘ rm ’, net reproductive rate (‘ Ro ’), ‘ T ’, and ‘λ’ at six constant temperatures with two CO 2 levels are shown in Table 3 . The ‘ rm ’ increased with increase in temperature from 20 to 30°C and declined with further increase in temperature. The ‘ Ro ’ of S. litura was higher at 27°C temperature according to records obtained from observation of 1,056 offspring. Comparison of values of ‘ rm ’ and ‘ Ro ’ with temperature indicated a gradual increase to a maximum values. The reduction of ‘ T ’ was observed from a maximum value of 58 days at 20°C to minimum of 24.9 days at 35°C and followed polynomial trend under e CO 2 . The ‘λ’ which is the indicator of reproductive value of new eggs was found to be highest at 30°C and followed a decreasing trend with increase in temperature. The doubling time (DT) of population was highest (5.88 days) at 20°C and lowest (3.05 days) at 30°C temperature under e CO 2 ( Table 3 ). The results on two nonlinear models developed for e CO 2 and a CO 2 conditions separately are depicted in Figure 1 a and b. The relationship between ‘ rm ’ and temperature followed the polynomial/quadratic form and was found to be the best fit with R2 in the range of ( R2 =0.899). A polynomial pattern was observed when the ‘ Ro ’ values were plotted against temperature ( R2  = 0.896) and the highest value was recorded at 21.48°C under e CO 2. The highest values of ‘ rm ’ were observed at 28.0°C for e CO 2 (0.227) and 23.5°C for a CO 2 (0.220).The reduction of ‘ T ’ and increase in ‘λ’ were observed at 33.28 and at 33.50°C, temperature respectively.

Table 3.

Variation of table parameters of Spodoptera litura on sunflower at six constant temperatures and two CO 2 conditions

Temperature °C r m
Net reproductive rate ( Ro )
T
Finite rate of increase (λ)
DT
e CO 2 a CO 2 e CO 2 a CO 2 e CO 2 a CO 2 e CO 2 a CO 2 e CO 2 a CO 2
20 0.1179 0.125 933 625.33 58 52.65 1.125 1.133 5.88 5.55
25 0.189 0.1721 933.73 601.4 36.19 37.18 1.208 1.187 3.67 4.03
27 0.207 0.202 1,056.1 612.75 33.63 31.73 1.23 1.224 3.35 3.43
30 0.227 0.22 539.55 275.55 27.64 29.92 1.255 1.206 3.05 3.15
33 0.1868 0.193 188.73 181.13 28.06 26.89 1.205 1.213 3.71 3.59
35 0.205 0.194 165.86 123.2 24.9 24.77 1.227 1.214 3.38 3.57
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Fig. 1.

Fig. 1.

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(a) Relationship between temperature and life-table parameters (‘ rm ’ and ‘ Ro ’) of Spodoptera litura on sunflower at e CO 2 and a CO 2 . (b) Relationship between temperature and life-table parameters (‘ T ’ and ‘λ’) of Spodoptera litura on sunflower at e CO 2 and a CO 2 .

Prediction of Pest Scenarios Using Life Table Parameters Under Climate Change Scenario

Predicted life table parameters of S. litura at four sunflower growing locations during climate change scenarios are presented in Table 4 . The ‘ rm ’ (0.15) values increased significantly during the NF climate change scenario compared with current climatic conditions (0.02–0.07) making it possible to produce greater numbers of females per female per day. At Bangalore location the negative value of ‘ rm ’ increased to 0.14 in NF scenario. It was predicted that similar increases of ‘ rm ’ would occur during DF scenario. The ‘λ’ recorded an increasing trend in NF (2.66–2.90) and DF (2.94–3.13) scenario in comparison within present period (0.96 - 0.99) at four locations. Results showed that ‘ Ro ’ would be higher (602–911offspring) during future climate change scenarios than during present period (486–525). The ‘ T ’ of insect pest was found to decrease significantly during NF (1–2 d at three locations) and DF (5–6 d at all locations) climate scenarios.

Table 4.

Prediction of pest scenarios using life table parameters during NF and DF CCS at four sunflower growing locations

Locations Present NF DF
r m
Akola 0.02 ± 0.02 0.15 ± 0.00 ** 0.15 ± 0.00 **
Bangalore (−0.05) ± 0.01 0.14 ± 0.00 ** 0.15 ± 0.00 **
Hayathnagar 0.07 ± 0.01 0.15 ± 0.00 ** 0.14 ± 0.00 **
Raichur 0.03 ± 0.01 0.15 ± 0.00 ** 0.14 ± 0.01 **
R o
Akola 525.44 ± 13.73 871.41 ± 31.14 ** 704.51 ± 89.01 **
Bangalore 571.71 ± 8.25 911.38 ± 36.95 ** 775.44 ± 56.68 **
Hayathnagar 486.11 ± 11.56 849.25 ± 47.15 ** 653.78 ± 88.48 **
Raichur 519.63 ± 10.45 799.01 ± 58.39 ** 602.20 ± 105.78 **
T
Akola 33.29 ± 0.79 32.82 ± 1.28 ** 28.57 ± 1.46 **
Bangalore 36.46 ± 0.69 35.01 ± 2.31 ** 29.86 ± 1.24 **
Hayathnagar 31.34 ± 0.49 32.06 ± 1.61 ** 27.75 ± 1.11 **
Raichur 32.95 ± 0.56 30.53 ± 1.66 ** 27.18 ± 0.98 **
λ
Akola 0.97 ± 0.00 2.76 ± 0.07 ** 3.05 ± 0.13 **
Bangalore 0.99 ± 0.00 2.66 ± 0.10 ** 2.94 ± 0.09 **
Hayathnagar 0.96 ± 0.00 2.81 ± 0.09 ** 3.13 ± 0.12 **
Raichur 0.97 ± 0.00 2.90 ± 0.11 ** 3.20 ± 0.14 **
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**The difference relative to the present period is significant at P  < 0.01.

The results of per cent change in predicted life table parameters during NF and DF scenarios over present climate period were calculated and are depicted in Figure 2 . The per cent change in ‘ rm ’ was higher at three locations under both NF and DF scenarios excepting Bangalore where negative ‘ rm ’ values were predicted to occur indicating that the number of females per female would be reduced. The increase in ‘ Ro ’ was found to be higher in NF (50–70%) than DF (15–35%) at all four locations. The reduction of ‘ T ’ is expected to be higher in DF (11–18%) at four locations than NF scenario (1–7%). A minimal increase (2 %) of ‘ T ’ would occur at Hyderabad during NF scenario. At all four locations λ was found to increase in both NF and DF by 69–230%.

Fig. 2.

Fig. 2.

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Per cent change in pest scenarios during NF and DF Climate change over persent period.

Discussion

Plant growth and biochemical constitution varied with CO 2 concentration causing a reduction in foliar nitrogen, which is the single most important limiting resource for phytophagous insects ( Hunter 2001 , Srinivasa Rao et al. 2012 ). Our results on biochemical analysis of sunflower foliage revealed a significant reduction (5%) of leaf nitrogen under e CO 2 compared with a CO 2 condition. In addition to this, most herbivorous insects appear to be negatively affected by e CO 2 because of the reduction in foliar N and increase in C: N ratio. In our study, an 8% increase of ‘C’ and 13% increase in C: N ratio was observed under e CO 2 . Similar increase of C: N ratio was reported by De La Mata et al. (2013) for sunflower. The reduction in protein content and increase of C/N ratio in leaves under e CO 2 ( Bezemer and Jones 1998 , Hunter 2001 ) imply changes in food quality which can influence insect growth and development.

Temperature is the most significant factor influencing growth and development of insects ( Bale et al. 2002 ). The effects of temperature on insects are species specific. Generally lower temperatures result in a decrease in the rate of development and an increase in the duration of the time of each developmental stage. It is well known that the relationship between temperature and development in insects is linear over most of the normal operating, middle range of temperature, but becomes sigmoid over the whole temperature range that permits development ( Arbab et al. 2006 ). Earlier studies have revealed that the growth and development of S. litura are significantly influenced by temperature ( Ranga Rao et al. 1989 ) and CO 2 ( Srinivasa Rao et al. 2012 ) on various hosts. The results of the present study showed that the developmental time of four stages of S. litura (Egg-adult) declined with increase in temperature on sunflower and was more evident at e CO 2 . The rate of development was lower at both lower (20°C) and higher temperatures (35°C) studied, signifying that the two extreme temperatures had adverse effects on growth of S. litura .

It is well known that insects do not live in stable environments with constant temperature; however the results of the present study under constant temperature are relevant in comprehending the dynamics of insect pests ( Tshiala et al. 2012 ). Life table parameters showed that the ‘ rm ’ values of S. litura on e CO 2 foliage are higher than those previously reported in the literature highlighting the significant influence of e CO 2 in altering biochemical constituents, though Yin et al. (2010) observed a non-significant effect of e CO 2 on ‘ rm ’ for cotton boll worms. In case of aphids, e CO 2 influenced performance by producing an increase of ‘ rm ’, ‘λ’, ‘ T ’ and ‘DT’ ( Amirijami et al. 2012 ). Significant variation of ‘ rm ’ of S. litura with host plants and temperature was reported by Zhu et al. (2000) and Gedia et al. (2008) .

Decrease of developmental time and increase in ‘ rm ’ of Sunn pest, Eurygaster integriceps ( Iranipour et al. 2010 ) and sugar cane pest Elasmopalpus linosellus ( Hardev et al. 2013 ) with increase in temperature has been reported.

Our studies recorded higher ‘ rm ’, ‘λ’, with lower ‘ T ’ and ‘DT’ at 30°C temperature and higher ‘ Ro ’ at 27°C under e CO 2 . These findings are in agreement with Tuan et al. (2013) who reported ‘ rm ’ values for S. litura in the range of 0.13 - 0.18 on peanut. The present results revealed that the association between temperature and life table parameters was a non-linear polynomial relationship. Many empirical models incorporating ‘ rm ’ as a key parameter have been used for prediction of insect pest population dynamics. Temperature-driven phenology models developed using laboratory information and projections of future populations can be made ( Vincent et al. 1997 ). The approach of using laboratory measurements of temperature was adopted by Tshiala et al. (2012) to model the empirical relationship between LT parameters and temperature and assess the impact of climate change on leaf miner population dynamics. The quantified relationship between life table parameters and temperature for e CO 2 foliage was used for predicting pest incidence in NF and DF climate change scenarios at four major sunflower growing locations of India. The ‘ rm ’ (0.15 ± 0.004) and ‘λ’ (2.94 ± 0.10) values for S. litura increased significantly during NF and DF over present period. At one location, the negative value (−0.05) of ‘ rm ’ during the present period predicted a reduction of population. It was predicted that the ‘ Ro ’ would be higher during future climate change scenarios than during the present period. The decrease in ‘ T ’ of insect pest during NF and DF scenarios would lead to more generations of insect pests. The reduction of ‘ T ’ and the possibility of occurrence of more generations under climate change scenario was reported earlier in Phthorimaea operculella ( Abolmaaty et al. 2011 ), and Cydia pomonella ( Hirschi et al. 2012 ).

For the majority of insect pest populations the rm gradually increases with temperature up to a certain level and later it decreases sharply. The increasing phase is often related to decrease in development time and increase in reproductive rate. The present results indicated that the mean generation time needs to increase to Ro -fold of its size was reduced, defined as the time length that a population as the stable age distribution and the stable increase rate are reached. The reduction of development time can lead to more number of generations in a year. Current investigations showed that increased ‘ rm ’, ‘ R ’ o , and ‘λ’ with a reduction in ‘ T ’ due to increase in temperature and e CO 2 condition which will be more evident in future climate change scenarios.

In conclusion, the growth and development of S.litura were significantly influenced by temperature and CO 2 . Results from this study showed that both low and high temperatures limited the survival and development of this insect pest and the ideal condition for the growth was at 27°C temperature, while the developmental rate increases with temperature up to 30°C However the life table parameters are sensitive to temperature and CO 2 which are the major factors of climate change. Our prediction of pest scenarios based on PRECIS A1B emission scenario data at four sunflower growing locations of India during NF and DF future climate change scenarios shows increase of ‘ rm ’ and ‘λ’ with higher ‘ Ro ’ and reduced ‘ T ’ meaning that pest incidence would be higher in the future. These findings indicate that S. litura has potential to become even more damaging insect pest on sunflower as a result of climate change. Further investigations are required to quantify the role of biotic and other abiotic factors on possible predicted pest scenarios.

Acknowledgments

Authors are thankful to Prof. Dr. Hsin Chi Laboratory of Theoretical and Applied Ecology, Department of Entomology, National Chung Hsing University, Taichung, Taiwan, Republic of China, for providing a computer programme on ‘Age-Stage, Two—Sex life table analysis’. This work was financially supported by grants from the Indian Council of Agricultural Research (ICAR), New Delhi in the form of National Initiative on Climate Resilient Agriculture (NICRA) Project.

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