Bisexual releases are as effective as male‐only releases to control Drosophila suzukii with the sterile insect technique

Alexandra Labbetoul; Simon Fellous

doi:10.1002/ps.70569

. 2026 Jan 23;82(5):4536–4543. doi: 10.1002/ps.70569

Bisexual releases are as effective as male‐only releases to control Drosophila suzukii with the sterile insect technique

Alexandra Labbetoul ¹, Simon Fellous ^1,^✉

PMCID: PMC13071196 PMID: 41574470

Abstract

BACKGROUND

The sterile insect technique (SIT) suppresses insect reproduction by repeatedly releasing sterile insects and allowing them to mate with insects of the same species in the wild. While the classical SIT relies on sterile males mating with wild females, there is a debate regarding the risks and benefits of releasing sterile females along with the sterile males (i.e. bisexual releases). In a replicated cage experiment, we compared the effect of unisexual and bisexual sterile releases of Drosophila suzukii on induced sterility. To ensure field‐realism, fertile females ‐ wild‐F0 freshly emerged from field‐collected sweet‐cherries ‐ were placed in cages with artificial vegetation and plastic berries.

RESULTS

The proportion of fertile females that produced offspring was not significantly different in unisexual and bisexual treatment (45% and 46%, respectively). Excluding females that had not mated (i.e. no sperm in the spermathecae) from the analysis had no influence.

CONCLUSION

These results suggest the release of sterile females does not always affect the efficacy of the SIT. Even though additional phenomena may arise when scaling up from cages to the field, we conclude that sorting females with genetic constructs or robotic systems is probably dispensable in D. suzukii SIT, at least when deployed in confined farming systems. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Keywords: fruit flies, spotted‐wing drosophila, crop protection, integrated pest management

Bisexual releases are as effective as male‐only releases to control Drosophila suzukii with the sterile insect technique. Releasing sterile Drosophila suzukii males or males and females in cages led to the same degree of induced sterility in wild females.

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1. INTRODUCTION

The sterile insect technique (SIT), an insect control method, involves the mass release of sterile insects to reduce reproduction in wild pest populations. ¹ , ² The core action of the classical SIT relies on the mating of sterile males with wild females. The sterile females produced and released along with sterile males do not participate directly in reducing the reproductive potential of the target populations. There has often been debate about whether bisexual (male and female) or unisexual (usually male) releases should be used for the SIT. ³ , ⁴ , ⁵ , ⁶ , ⁷ , ⁸ The use of bisexual or unisexual releases in a SIT program has economic and efficacy stakes. The use of bisexual releases involves additional costs for the production and transport of insects. ³ Furthermore, it may cause a problem of acceptability because of the potential negative effect of sterile females on crops or human health. These points are not dealt with in this paper, where we focus on the efficacy of sterile releases on induced sterility. In the literature, both positive and negative effects of bisexual releases have been reported, and these are discussed in the following two paragraphs.

The inclusion of sterile females in SIT releases can reduce the efficacy of the technique because of several phenomena, including assortative mating among insects of similar origin, different use of space or mismatched circadian rhythms of wild and sterile individuals, disease transmission and damage to crops by sterile females. Assortative mating is a significant concern because mass‐rearing can alter insect mating preferences, leading to a tendency for individuals to mate with conspecifics from the same origin. ⁹ Another issue is the different use of space by mass‐reared sterile and wild individuals. In Queensland fruit flies, Bactrocera tryoni, sterile individuals are found in lower parts of in the canopy than their wild counterparts. ¹⁰ Such differences can reduce the likelihood sterile males encounter wild females when sterile females are released for the simple reason that sterile males surrounded by sterile females may not make the effort of looking for wild females. Mismatched circadian rhythms between laboratory‐reared and wild insects also pose a challenge. Laboratory insects, conditioned by constant temperatures and alternating light and darkness, differ from wild insects, whose circadian rhythms are also influenced by temperature and daylight fluctuations. ¹¹ The courtship calling frequency of males and the time of mating during the day could also differ between mass‐reared sterile and wild flies, as demonstrated in melon fly Bactrocera cucurbitae. ¹² Additionally, sterile females can act as vectors for diseases during feeding, as observed in mosquitoes, raising concerns about disease transmission in SIT programs. ¹³ , ¹⁴ , ¹⁵ Lastly, sterile females of crop pest species may cause damage to fruits when they maintain their oviposition behavior, ¹⁶ , ¹⁷ although the literature suggests this is a minor problem.

The efficacy of the SIT could also be enhanced by including sterile females in releases. Sterile females could potentially increase SIT efficacy by depriving wild males of crucial resources such as time, sperm, and ejaculation opportunities. ¹⁸ As illustrated by a recent empirical study in two weevil species, ⁵ the release of sterile females only may contribute to population control. Nevertheless, in this study releasing sterile females only was less efficient than releasing both sexes or only sterile males. The study also showed that the efficacy of bisexual releases was at least equal to that of unisexual releases of males, and even superior in one of the two species. The variability among species and experimental conditions highlighted the dependency on the biological feature of the target species. A mathematical model ⁶ showed that bisexual releases could outperform unisexual releases, but that the effect depended on the mating systems of the targeted insect, the competitiveness of sterile males and courtship rates between wild and sterile insects. That study suggested bisexual releases could be particularly efficient when the sexual performance of sterile males is inferior to that of wild males. Although some mitigation techniques have been proposed on fruit flies, ¹⁹ , ²⁰ it is well established that sterilization diminishes the sexual performance of males, ²¹ , ²² suggesting that bisexual releases should be efficient.

The possible effects of sterile females on the efficacy of the SIT grant the need for empirical exploration whenever developing the technique on a new insect species. The spotted‐wing Drosophila, Drosophila suzukii (Matsumura, 1931), is a fly of Asian origin that has invaded the Americas, Europe, and some parts of Africa over the last 15 years. ²³ This fly is particularly difficult to manage because it has a rapid life cycle (egg‐adult = 12.8 ± 0.2 days at 22 °C), ²⁴ a high fecundity (up to 362 eggs during a female's lifetime), ²⁵ high dispersal capacities, ²⁶ , ²⁷ and the ability to exploit a wide range of cultivated and wild fruits. ²⁸ To date, limited solutions are available to control the damage it causes to red and stone‐fruit. ²⁹ Estimating precisely the breadth of economic losses due to a pest insect is always challenging, even more so when farmers are still adapting to its presence and while chemical solutions are gradually baned. A recent analysis in the Trento region (Italy) suggests a 9% revenue‐loss for soft‐fruit producers. ³⁰

Drosophila suzukii and the SIT applied to this species are currently the subject of intensive investigation. ³¹ After developing rearing methods ³² and studying the reproductive biology of the species, ³³ , ³⁴ , ³⁵ , ³⁶ research is being carried out on the choice of ionization dose for sterilizing males. ³⁴ , ³⁷ Some laboratories developed the incompatible insect technique, ³⁸ to be used in combination with classical SIT. ³⁹ Relevant to the present study, it should be noted that D. suzukii females mate several times and use the sperm of several males over their lifespan. ³⁶ To date, we have no information on sperm usage, a factor with important consequences for the SIT, ⁴⁰ , ⁴¹ even though a study by Krüger et al. ³⁷ has shown that sterile males induce the same refractory period as wild males. Recent SIT release studies have also been carried out in closed greenhouses ⁴² and open tunnels, ⁴³ and report promising effects of the SIT on D. suzukii reproduction. The non‐target effects of the SIT applied to D. suzukii are also being investigated. ⁴⁴ , ⁴⁵ Despite this wealth of knowledge, no high‐throughput sex‐sorting technology is available to date.

The aim of this study was to compare the efficacy of unisexual and bisexual releases in D. suzukii. To maximize the reliability of our cage experiment, we replicated conditions as realistically as possible: F0‐wild flies were sourced from infested cherries, a natural circadian rhythm was simulated using light ramps that emulate dawn and dusk, and a rich environment with artificial plants and berries was provided to encourage natural courtship behaviors.

2. MATERIAL AND METHODS

2.1. Biological material

We used two different populations for sterile and fertile flies. For sterile insects we used a laboratory strain, which had been selected for increased mating competitiveness (specific details of this procedure are omitted due to intellectual property rights) raising satisfactory efficacy, as described in Gard et al. ⁴² Starting with an initial pool of several thousand wild insects, collected near Montpellier (France) in 2018, the population was maintained for about 20 generations at a constant size of 600 individuals. The last selection event had been carried out 1 year before the experiment.

For wild insects, we collected virgins (i.e. less than 14 h after emergence) that emerged from infested sweet cherries. These had been harvested in southern France: in the Mare valley (43.59627, 3.12980), the Jaur valley (43.52880, 2.83270), and Bellegarde (43.75682, 4.46063). Young adults of different locations were pulled and maintained separately by sex in pots (®DECA TP118‐480; H = 69 mm, ø = 118 mm) with 70 mL of artificial carrot medium ⁴⁶ from emergence until experimentation.

To produce the sterile individuals, we reared the laboratory population in 30‐cm cages (®Bugdorm, Taïwan) with artificial carrot medium and under controlled conditions [21 °C day, 19 °C night, 14 h light (L):10 h dark (D), 70 ± 10% relative humidity (RH)]. Pupae were manually collected and exposed to an X‐ray dose of 150 Gray within 24 h before emergence. This dose induces egg sterility rates of around between 95% and 100%. ⁴⁷ , ⁴⁸ , ⁴⁹ It is optimal, as it achieves a satisfactory sterilization rate while limiting somatic damage to the flies. ³⁵ , ³⁷ These conditions proved satisfactory in previous SIT experiments led by our group. ⁴² , ⁴⁵ Young sterile adults were maintained in groups of same sex, as were wild virgins, until the experimentation.

2.2. General experimental design

The experiment aimed to compare the proportion of wild females that produced offspring after being exposed to bisexual release, unisexual release or absence of sterile insects. The three treatments were conducted in 20‐cm experimental cages (®Bugdorm) under controlled conditions (21 °C day, 19 °C night, 14 h L:10 h D, 70 ± 10% RH). To simulate dawn and dusk, a 30‐min light ramp was included in the light cycle, corresponding to peaks of D. suzukii activity. ⁵⁰ Each cage contained a plastic plant and 20 red beads (simulating berries), sugar, yeast, and water (Fig. 1(A)). Plastic plants and red beads enabled normal behaviors of flies, such as territoriality and courtship, and made possible the use of different parts of the habitat by sterile and fertile flies. This protocol was tested in a preliminary experiment with laboratory flies in which results were similar to those reported below (Supporting Information, Figs S1.1 and S1.2).

Photograph of the inside of an experimental cage (A) and the synoptic scheme of the protocol (B).

Cages with the control treatment contained 10 virgin F0‐wild females and 10 virgin F0‐wild males (wild population). Cages with the unisexual treatment contained the same number of wild insects as in the controls and, in addition, 10 virgin sterile males. Cages with the bisexual treatment contained the same insects as in the unisexual treatment and, in addition, 10 virgin sterile females (Table 1), following the protocol of Gard et al. ⁴² A total of 19 replicates for controls, 20 for unisexual and 20 for bisexual treatments were carried out and separated in four blocs over 2 weeks. Fertile flies used for the experiments were 11 ± 3 and 12 ± 4 days‐old for females and males, respectively [mean ± standard deviation (SD)]. Sterile flies used were 14 ± 1 and 12 ± 3 days‐old for females and males, respectively (mean ± SD). The youngest flies used were 7 days old (i.e. post‐emergence from the pupa), which ensured their sexual maturity as all males and females are ready to reproduce from 4 days of age. ³³

Table 1.

Number of sterile and fertile adults of Drosophila suzukii per cage in the three experimental treatments

Experimental treatment of D. suzukii	Number of wild males	Number of wild females	Number of sterile males	Number of sterile females	Number of replicates
Control	10	10	0	0	19
Unisexual	10	10	10	0	20
Bisexual	10	10	10	10	20

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Wild and sterile females were marked with two fluorescent powder 24 h before the start of the experiment. Different powders were used to mark each type of insect for easy identification. The sterile females were kept in pots (H = 69 mm, ø = 118 mm) of carrot medium between marking and release, while the wild females were placed in the experimental cages 1 day before all other insects so that they could acclimatize to their environment.

Wild males, sterile males and sterile females were introduced into the cages 3 h before dawn. The flies were then removed from the cages 18–23 h later, that is, 1–6 h after dusk. To avoid multiple mating, we limited the encounters between males and females to a single light cycle (S. Fellous, personal observation). To facilitate fly capture and sorting, the flies were put to sleep by keeping the cages at −20 °C for 1.5 min. Wild females, recognized by the color of their marking powder, were transferred to individual Drosophila vials (H = 95 mm, ø = 25 mm) containing an artificial raspberry medium ⁵¹ and maintained under controlled conditions (21 °C day, 19 °C night, 14 h L:10 h D, 70 ± 10% RH) for 2 weeks.

2.2.1. Proportion of wild females producing offspring

The proportion of wild females that produced offspring—and therefore induced sterility—was measured by observing whether the females had produced larvae within 14 days after being isolated (Fig. 1(B)). The 14‐day threshold was chosen based on the results of a preliminary experiment with laboratory flies (Supporting Information, Fig. S1.1). At the end of these 2 weeks, each vial was observed using a binocular microscope to determine the presence of eggs and larvae. We also recorded whether there were very few eggs in the tubes (≤3 eggs). Our goal was to not misclassify ‘females mated with fertile male but that produced very few unviable eggs’ (like all females do) as ‘mated with a sterile male’. In the end this only concerned 14 females over the 531 phenotyped. Vials were then frozen at −20 °C.

2.2.2. Proportion of mated wild females

The proportion of mated wild females was determined by observing if wild females that had not produced larvae nonetheless had sperm in at least one of their two spermathecae. To this end, females were dissected in Phosphate‐Buffered Saline (PBS ;1% unfiltered) following the protocol of Avanesyan et al. ⁵² The ovipositor was removed with forceps, which pulled out the spermathecae. Spermathecae were then isolated from the reproductive tract, ensuring they remained attached together to avoid damage. They were placed on a microscope slide with a drop of PBS buffer, covered with a coverslip, and gently pressed to break the spermathecae, allowing clear visualization of sperm mass during analysis. Samples were examined under a differential interference contrast microscope (Leica) at 400× magnification, and the presence of sperm mass was recorded. An illustration of mating status according to spermathecae dissection is available in Supporting Information, Fig. S2.

2.3. Statistical analysis

The proportion of wild females that produced offspring was calculated for each replicate cage by dividing the number of females producing larvae by the number of females that produced eggs or larvae. However, because even females mated to a fertile male occasionally lay non‐viable eggs, ²⁴ we removed the individuals that laid three or fewer eggs from the analysis. By excluding those females that laid few eggs, we avoided the misclassification of some females (mated with sterile or fertile male) and therefore improved the signal‐to‐noise ratio in our data.

The differences between treatments were analyzed using a linear mixed model (LMM) followed by contrasts, since the normality of the residuals was respected and the variance of the residuals was homogeneous between the groups. The model contained a random factor describing experimental blocs. To test whether differences among treatments could be due to differential mating rates, we carried out an additional analysis that took into account sperm presence data. The new variable was calculated by dividing the number of females producing larvae by the number of mated females (i.e. females that produced larvae + females without larvae but with sperm). As before, individuals who laid three or fewer eggs were excluded. As in previous analysis, the differences between treatments were analyzed using an LMM followed by contrasts, but with square transformation, to respect model conditions. The model also contained a random factor describing experimental blocs.

We also analyzed proportions of mated females. Females were considered mated when they produced larvae or contained sperm. In each replicate, their numbers were divided by the total number of retrieved females to obtain a mating rate. The total number of females per replicate varied among replicates due to mortality and averaged 9 ± 1 (mean ± SD). Since the normality of the residuals was respected and the variance of the residuals was homogeneous between the groups, the differences between treatments were analyzed using an LMM followed by contrasts. The model also contained a random factor describing experimental blocs.

All analyses and figures were made on the software RStudio version 4.3.3 with packages readxl, ⁵³ car (Fox & Weisberg, 2019), stats (R Core Team, 2023), tidyverse, ⁵⁴ lme4, ⁵⁵ emmeans, ⁵⁶ and ggplot2. ⁵⁷

The full dataset is available on the Zenodo platform (https://doi.org/10.5281/zenodo.15773154).

3. RESULTS

3.1. Proportion of wild females producing offspring

The experimental treatment significantly affected the proportion of wild females producing offspring (χ ² = 83.96, df = 2, P < 0.0001). Contrasts showed the proportion was greater in controls (84%) than in the unisexual (46%) (t = 7.89 L, P < 0.0001) and bisexual (45%) (t = 8.03, P < 0.0001) treatments, but there was no difference between the unisexual and bisexual treatments (t = 0.12, P = 0.9916) (Fig. 2A). The efficacy of SIT in unisexual releases was 45.2% and 46.4% in bisexual releases (proportion in unisexual or bisexual treatment divided by proportion in control treatment).

Effect of the treatments on (A) the total proportion of females producing offspring and (B) the proportion of mated females producing offspring. Each empty circle represents a replicate cage. Full dots represent the mean and error bars indicate the standard deviation. Means with different letters are significantly different (linear mixed model with contrasts, P < 0.05).

3.2. Proportion of mated wild females producing offspring

Among the females that did not produce larvae, it is possible some were not mated, so we repeated the analysis by removing unmated females. The experimental treatment significantly affected the proportion of mated wild females that produced offspring (χ ² = 56.13, df = 2, P < 0.0001). The control treatment exhibited a greater proportion of mated females producing offspring (94%) than unisexual (64%) (t = 5.64, P < 0.0001) and bisexual (56%) (t = 7.12, P < 0.0001) treatments. There was no significant difference between the unisexual and bisexual treatments (t = 1.48, P = 0.3066) (Fig. 2B).

3.3. Proportion of mated wild females

The experimental treatment significantly affected the proportion of mated females (χ ² = 8.94, df = 2, P = 0.0115) (Fig. 3). It was significantly higher in the control treatment (89%) than in the unisexual treatment (73%) (contrast: t = 2.95, P = 0.0129), but not different to the bisexual treatment (80%) (contrast: t = 1.89, P = 0.1526). Furthermore, there was no difference in the proportion of mated wild females between the unisexual and bisexual treatments (t = −1.08, P = 0.5291) (Fig. 3).

Effect of the treatments on the proportion of mated wild females. Each empty dot represents a replicate. Full dots represent the mean and error bars indicate the standard deviation. Means with different letters are significantly different (linear mixed model with contrasts, P < 0.05).

4. DISCUSSION

In this study, we focused on a central topic in SIT programs, namely the need for sorting out sterile females before releasing sterile males. We hence compared the effects of bisexual and unisexual releases on the efficacy of the SIT applied to D. suzukii. We observed no difference in the proportion of wild females producing offspring between the unisexual and bisexual treatments (Fig. 2(A)) even when non‐mated females were excluded from the analysis (Fig. 2(B)). The proportion of mated females in the bisexual treatment did not differ from that in the control and unisexual treatments (Fig. 3). Our experiment, for which statistical power gives confidence in the results (i.e. 20 replicate cages per treatment), therefore found no effect of releasing sterile females along with sterile males.

Recent statistical modeling predicted a positive effect of sterile females on induced sterility. ⁶ We did not find such efficacy gains (Fig. 2(A)), even though this has been reported in a number of empirical studies. It was, for example, the case in the moths Lobesia botrana and Cactoblastis cactorum, ⁴ , ⁸ where bisexual releases increased induced sterility compared to unisexual treatments. Earlier, Whitten & Taylor ¹⁸ showed in Lucilia cuprina that the sole release of sterile females, without sterile males, reduced the number of fertile females inseminated. This suggests that sterile females can interfere with the reproduction of wild females by preventing their mating with any type of female, possibly through sperm and energy depletion. In our study, the mating rate of fertile females was not reduced by the addition of sterile females (i.e. compare unisexual and bisexual in Fig. 3), and removing unmated females from the analysis of induced fertility did not change its conclusions (Fig. 2(B)). Another recent empirical study argues that the positive effects of releasing sterile females depend on subtle biological and environmental factors, such as species and population density. ⁵ When to expect such superior efficacy of bisexual releases over unisexual therefore remains an open question.

Previous research on fruit flies has concluded that sterile females must be removed before insect release. ⁵⁸ In open fields, these authors compared plots treated with unisexual and bisexual releases of C. capitata and found dramatic differences: even with 1000:1 sterile:fertile ratios, bisexual releases failed to control the insect. In contrast, McInnis et al. ⁷ carried out cage experiments and found no efficacy difference between bisexual and unisexual releases of C. capitata. The discrepancy between these two studies likely stems from the questionable genetic background of the flies assayed in the cage study. The authors used the same 30‐year laboratory strain for both sterile and fertile flies, masking possible assortative mating and behavioral differences among sterile and fertile populations. However, one must be also cautious with the conclusions of Rendón et al. ⁵⁸ because in this open‐field study unisexual and bisexual releases were carried out using two genetically distinct populations, the Petapa bisexual strain and the Vienna‐4/Tol‐94 male‐only strain. Competitive differences among strains could partially explain the striking differences reported by the authors. As often with the SIT, insect genetics and rearing conditions appear paramount factors affecting efficacy.

In our study, we found no difference in terms of SIT efficacy between the unisexual and bisexual treatments (46% efficacy for bisexual treatment vs 45% for unisexual), as in the study of McInnis et al. ⁷ How likely is it that here again our cage results do not transpose in the field? Our design allowed possible assortative mating in the bisexual treatment: we used F0‐wild D. suzukii flies for the fertile population and a laboratory strain for sterile flies. On the basis of the results of Inskeep et al., ¹⁰ we also considered the possibility that wild and laboratory insects may use different parts of the habitat, in particular plants and berries. Our cages hence contained artificial plants and berries (Fig. 1(A)). In addition, we also took into account that the circadian rhythms of laboratory and wild insects may diverge. ⁵⁹ , ⁶⁰ In D. suzukii, circadian activity responds to abiotic factors such as temperature and light, and biotic factors such as crowding. ⁶¹ Our conditions were, however, close to those that elicit behaviors similar to those observed in semi‐field conditions. ⁶¹ None of the elements of assortative mating, differential use of plant parts, circadian rhythms, or male courtship calling frequency appeared to reduce the likelihood of wild females mating with sterile males, even in the presence of sterile females.

However, our design did not reproduce other important factors taken into account in the studies of McInnis et al. ⁷ and Rendón et al. ⁵⁸ First, the size of our cages (c. 20 cm cubic) enabled the study to be replicated enough to gain strong statistical power, but did not scale to the environment of wild D. suzukii. It is therefore possible that laboratory and wild insects would have used different compartments of the environments too distant to be included here. For example, it is known that D. suzukii lays fewer eggs in fruit located at the upper edges of the canopy than in the inner canopy. ⁶² The insect is also more frequently found close to field margins than deep inside fields. ⁶³ , ⁶⁴ , ⁶⁵ Additionally, we used plastic plants and berries, which limited environmental complexity and reduce natural stimuli. Finally, we used a 1:1 sterile:fertile ratio to maximize the resolution of our estimate of the proportion of fertile females that mated with either sterile or fertile males. This ratio 1:1 is not representative of typical SIT programs, where wild populations are often flooded with sterile insects. ⁶⁶ A recent article by Himuro and Ikegawa, ⁵ on a weevil species, found that differences between unisexual and bisexual treatments can depend on this ratio, but other studies in lepidoptera ⁴ , ⁸ showed that the sterile:fertile ratio does not necessarily affect the efficacy differences between unisexual and bisexual releases.

Another line of evidence that the release of sterile females may not be a burden comes from the study of Gard et al. ⁴² These authors carried out bisexual releases in medium‐sized cages (150 × 70 × 70 cm) that contained production‐grade strawberry plants with delicious berries (A. Labbetoul, personal observation). This set‐up efficiently reproduced farming conditions in confined crops, such as strawberry greenhouses, where sterile insects would be released. They found that bisexual releases with a 5:1 sterile:fertile ratio reduced by a factor of three the number of offspring produced by fertile females. In these conditions, the release of sterile females therefore had no dramatic effect on SIT efficacy. We should, however, keep in mind that ecological and behavioral features specific to open‐field contexts could nonetheless hamper the efficacy of bisexual releases in area‐wide management programs.

Eventually, damage to crops due to sterile females is a concern that must be taken into account when deciding to carry out bisexual releases. Very few studies have investigated whether sterile females, or even fertile females mated with sterile males, cause actual damage to crops. A study by Reynolds et al. ¹⁷ on Bactrocera tryoni showed that fruit from orchards protected by the bisexual SIT is not more damaged than fruit from an orchard protected with conventional chemicals. Recently, we reported in D. suzukii that sterilized females do not lay eggs. ⁴⁵ Damage could still occur if sterile females bite fruit. We and other colleagues with extensive experience with the D. suzukii SIT (Ghaïs Zriki, CTIFL France and Robin Guilhot, IPCL‐AIEA Austria, personal communications) have never observed any egg‐laying behavior by sterile females (i.e piercing of fruit skin). However, this has never been formally tested. It follows that releasing sterile females, together with sterile males, seems both safe and efficient.

5. CONCLUSION

To conclude, this experiment compared for the first time the efficacy of bisexual versus unisexual releases in the context of the SIT applied to D. suzukii. Even though additional phenomena may arise when scaling‐up from cages to the field, we conclude that sorting females with genetic constructs or robotic systems is probably dispensable in the D. suzukii SIT, at least when deployed in confined farming systems.

CONFLICT OF INTEREST

The authors have no conflict of interest to declare.

Supporting information

Figure S1.1. Proportion of vials with larvae at 6, 11 and 14 days after female isolation in individual vial.

Figure S1.2. Effect of treatments on the proportion of laboratory females of Drosophila suzukii producing offspring. Each empty circle represents a replicate. Full dots represent the mean and error bars indicate standard deviation. Means with different letters are significantly different (Wilcoxon test, P < 0.05).

Figure S2. Spermathecae of unmated (A) and mated (B) Drosophila suzukii female under a differential interference contrast microscope (Leica at 400× magnification).

PS-82-4536-s001.docx^{(6.2MB, docx)}

ACKNOWLEDGEMENTS

We would like to thank Nicolas Leménager for help in the laboratory during our vacations and the CBGP acarology team for letting us use their microscope. We thank Mickaël Combes (Sica du Caroux) and Ghais Zriki (CTIFL) for supplying us with cherries infested with Drosophila suzukii. This study received support from the Agence Nationale de la Recherche (ANR‐21‐ECOM‐0002) and Office Français de la Biodiversité. Open access publication funding provided by COUPERIN CY26.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are openly available in Zenodo at https://doi.org/10.5281/zenodo.15773154.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Figure S1.1. Proportion of vials with larvae at 6, 11 and 14 days after female isolation in individual vial.

Figure S2. Spermathecae of unmated (A) and mated (B) Drosophila suzukii female under a differential interference contrast microscope (Leica at 400× magnification).

PS-82-4536-s001.docx^{(6.2MB, docx)}

Data Availability Statement

The data that support the findings of this study are openly available in Zenodo at https://doi.org/10.5281/zenodo.15773154.

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[ps70569-bib-0037] 37. Krüger AP, Schlesener DCH, Martins LN, Wollmann J, Deprá M and Garcia FRM, Radiation effects on Drosophila suzukii (Diptera: Drosophilidae) reproductive behaviour. J Appl Entomol 143:88–94 (2018). [Google Scholar]

[ps70569-bib-0038] 38. Cattel J, Nikolouli K, Andrieux T, Martinez J, Jiggins F, Charlat S et al., Back and forth Wolbachia transfers reveal efficient strains to control spotted wing drosophila populations. J Appl Ecol 55:2408–2418 (2018). [Google Scholar]

[ps70569-bib-0039] 39. Nikolouli K, Sassù F, Mouton L, Stauffer C and Bourtzis K, Combining sterile and incompatible insect techniques for the population suppression of Drosophila suzukii . J Pest Sci 93:647–661 (2020). [DOI] [PMC free article] [PubMed] [Google Scholar]

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[ps70569-bib-0043] 43. Homem R, Mateos‐Fierro Z, Jones R, Gilbert D, Mckemey A, Slade G et al., Field suppression of spotted wing drosophila (SWD) (Drosophila suzukii Matsumura) using the sterile insect technique (SIT). Insects 13:328 (2022). [DOI] [PMC free article] [PubMed] [Google Scholar]

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[ps70569-bib-0048] 48. Schnell P, Développement de la Technique de l'Insecte Stérile sur Drosophila suzukii : Évaluation de la qualité des mâles stériles Drosophila suzukii en laboratoire et en conditions semi‐naturelles [Mémoire de Master 2] (2019).

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PERMALINK

Bisexual releases are as effective as male‐only releases to control Drosophila suzukii with the sterile insect technique

Alexandra Labbetoul

Simon Fellous