Sexual Behavior of Drosophila suzukii

Sex Pheromone Mediates Resource Partitioning Between Drosophila melanogaster and D. suzukii

The spotted-wing drosophila, Drosophila suzukii and the cosmopolitan vinegar fly D. melanogaster feed on soft fruit and berries and widely overlap in geographic range. The presence of D. melanogaster reduces egg-laying in D. suzukii, possibly because D. melanogaster outcompetes D. suzukii larvae feeding in the same fruit substrate. Flies use pheromones to communicate for mating, but pheromones also serve a role in reproductive isolation between related species. We asked whether a D. melanogaster pheromone also modulates oviposition behaviour in D. suzukii. A dual-choice oviposition assay confirms that D. suzukii lays fewer eggs on blueberries exposed to D. melanogaster flies and further shows that female flies have a stronger effect than male flies. This was corroborated by treating berries with synthetic pheromones. Avoidance of D. suzukii oviposition is mediated by the female D. melanogaster pheromone (Z)-4-undecenal (Z4-11Al). Significantly fewer eggs were laid on berries treated with synthetic Z4-11Al. In comparison, the male pheromone (Z)-11-octadecenyl acetate (cVA) had no effect on D. suzukii oviposition. Z4-11Al is a highly volatile compound that is perceived via olfaction and it is accordingly behaviourally active at a distance from the source. D. suzukii is known to engage in mutual niche construction with the yeast Hanseniaspora uvarum, which strongly attracts flies. Adding Z4-11Al to fermenting H. uvarum significantly decreased D. suzukii flight attraction in a laboratory wind tunnel and a field trapping assay. That a D. melanogaster pheromone regulates oviposition in D. suzukii demonstrates that heterospecific pheromone communication contributes to reproductive isolation and resource partitioning in cognate species. Stimulo-deterrent diversion or push-pull methods, building on combined use of attractant and deterrent compounds, have shown promise for control of D. suzukii. A pheromone that specifically reduces D. suzukii attraction and oviposition adds to the toolbox for D. suzukii integrated management.

Oviposition experience affects oviposition preference in Drosophila melanogaster

Learning, memorizing, and recalling of potential ovipositing sites can influence oviposition preference. Classical conditioning experiments have shown that vinegar flies can learn the association of olfactory, gustatory, or visual stimuli with either positive or negative unconditioned stimuli. However, less is known about whether similar associations are formed in an ecologically more relevant context like during oviposition. Our experiments reveal that Drosophila melanogaster females increase their preference for substrates they have already experienced. However, this change of preference requires that the flies not only smelled or touched the substrates but also oviposited on them. We furthermore show that such an experience results in long-term memory lasting for at least 4 days, i.e., a duration that so far was shown only for aversive conditioning. Our study thus reveals a different form of associative learning in D. melanogaster that might be highly relevant for settling novel ecological niches.

Expansion of the genetic toolbox for manipulation of the global crop pest Drosophila suzukii: Isolation and assessment of eye colour mutant strains

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), commonly called spotted wing Drosophila, is an important agricultural pest recognised worldwide. D. suzukii is a pest of soft-skinned fruits as females can lay eggs in ripening fruit before harvest. While strains for genetic biocontrol of D. suzukii have been made, the development of transgenic D. suzukii strains and their further screening remain a challenge partly due to the lack of phenotypically trackable genetic-markers, such as those widely used with the model genetic organism D. melanogaster. Here, we have used CRISPR/Cas9 to introduce heritable mutations in the eye colour genes white, cinnabar and sepia, which are located on the X, second and third chromosomes, respectively. Strains were obtained, which were homozygous for a single mutation. Genotyping of the established strains showed insertion and/or deletions (indels) at the targeted sites. A strain homozygous for mutations in cinnabar and sepia showed a pale-yellow eye colour at eclosion but darkened to a sepia colour after a week. The fecundity and fertility of some of the cinnabar and sepia strains were comparable with the wild type. Although white mutant males were previously reported to be sterile, we found that sterility is not fully penetrant and we have been able to maintain white-eyed strains for over a year. The cinnabar, sepia and white mutant strains developed in this study should facilitate future genetic studies in D. suzukii and the development of strains for genetic control of this pest.

Blueberries infected with the fungal pathogen Colletotrichum fioriniae release odors that repel Drosophila suzukii

BACKGROUND

Spotted-wing drosophila, Drosophila suzukii, is a serious pest of thin-skinned fruits. Alternative methods to control this pest are needed to reduce insecticide use, including new repellents. Previous research demonstrated that D. suzukii adults use odor cues to avoid blueberries infected with the fungal pathogen Colletotrichum fioriniae, which causes the disease anthracnose. To identify novel D. suzukii repellents, we investigated the volatile emission from experimentally-infected fruit, which were inoculated with C. fioriniae isolates in the laboratory, and from field-collected fruit, which were naturally infected and harvested from a field. We then tested the pathogen-induced volatiles on D. suzukii adult behavior.

RESULTS

Volatile emission was similar between all five C. fioriniae strains, with good agreement between experimentally-infected and field-collected berries. In total, 14 volatiles were found to be more abundant in infected versus uninfected fruit headspace. In multiple-choice bioassays, nine of the 14 volatiles elicited repellency responses from adult D. suzukii. These nine volatiles were further evaluated in dual choice assays, where all nine reduced fly capture by 43-96% compared to the control. The most repellent compounds tested were the esters ethyl butanoate and ethyl (E)-but-2-enoate, which were more or equally repellent to the known D. suzukii repellents 1-octen-3-ol, geosmin, and 2-pentylfuran. Dose-response assays identified concentration-dependent effects on D. suzukii repellency and oviposition when applied individually and consistent aversion observed across doses of a 1:1 blend.

CONCLUSION

We report two repellents from C. fioriniae-infected blueberries that could be useful semiochemicals for the behavioral manipulation of D. suzukii in the field. © 2023 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

High promiscuity among females of the invasive pest species Drosophila suzukii

Drosophila suzukii (Matsumura, 1931), the spotted-wing drosophila, is a highly invasive fruit fly that spread from Southern Asia across most regions of Asia and, in the last 15 years, has invaded Europe and the Americas. It is an economically important pest of small fruits such as berries and stone fruits. Drosophila suzukii speciated by adapting to cooler, mountainous, and forest environments. In temperate regions, it evolved seasonal polyphenism traits which enhanced its survival during stressful winter population bottlenecks. Consequently, in these temperate regions, the populations undergo seasonal reproductive dynamics. Despite its economic importance, no data are available on the behavioural reproductive strategies of this fly. The presence of polyandry, for example, has not been determined despite the important role it might play in the reproductive dynamics of populations. We explored the presence of polyandry in an established population in Trentino, a region in northern Italy. In this area, D. suzukii overcomes the winter bottleneck and undergoes a seasonal reproductive fluctuation. We observed a high remating frequency in females during the late spring demographic explosion that led to the abundant summer population. The presence of a high degree of polyandry and shared paternity associated with the post-winter population increase raises the question of the possible evolutionary adaptive role of this reproductive behaviour in D. suzukii.

Assessing potential hybridization between a hypothetical gene drive-modified Drosophila suzukii and nontarget Drosophila species

Genetically engineered gene drives (geGD) are potentially powerful tools for suppressing or even eradicating populations of pest insects. Before living geGD insects can be released into the environment, they must pass an environmental risk assessment to ensure that their release will not cause unacceptable harm to non-targeted entities of the environment. A key research question concerns the likelihood that nontarget species will acquire the functional GD elements; such acquisition could lead to reduced abundance or loss of those species and to a disruption of the ecosystem services they provide. The main route for gene flow is through hybridization between the geGD insect strain and closely related species that co-occur in the area of release and its expected dispersal. Using the invasive spotted-wing drosophila, Drosophila suzukii, as a case study, we provide a generally applicable strategy on how a combination of interspecific hybridization experiments, behavioral observations, and molecular genetic analyses can be used to assess the potential for hybridization.

Applying Satyrization to Insect Pest Control: The Case of the Spotted Wing Drosophila, Drosophila suzukii Matsumura

Drosophila suzukii represents one of the major agricultural pests worldwide. The identification of safety and long-lasting tools to suppress its populations is therefore crucial to mitigate the environmental and economic damages due to its occurrence. Here, we explore the possibility of using satyrization as a tool to control the abundance of D. suzukii. By using males of D. melanogaster, we realized courtship tests, spermathecae analysis, and multiple-choice experiments to assess the occurrence and extent of pre- and post-zygotic isolation between the two species, as well as the occurrence of fitness costs in D. suzukii females due to satyrization. Our results showed that: (i) D. melanogaster males successfully courted D. suzukii females; (ii) D. melanogaster males significantly affected the total courtship time of D. suzukii males, which reduced from 22.6% to 6.4%; (iii) D. melanogaster males were able to inseminate D. suzukii and reduce their offspring, inducing a high fitness cost. Reproductive interference occurs at different steps between D. melanogaster and D. suzukii, both alone and in combination with other area-wide control approaches.

Seasonal changes in photoperiod and temperature lead to changes in cuticular hydrocarbon profiles and affect mating success in Drosophila suzukii

Seasonal plasticity in insects is often triggered by temperature and photoperiod changes. When climatic conditions become sub-optimal, insects might undergo reproductive diapause, a form of seasonal plasticity delaying the development of reproductive organs and activities. During the reproductive diapause, the cuticular hydrocarbon (CHC) profile, which covers the insect body surface, might also change to protect insects from desiccation and cold temperature. However, CHCs are often important cues and signals for mate recognition and changes in CHC composition might affect mate recognition. In the present study, we investigated the CHC profile composition and the mating success of Drosophila suzukii in 1- and 5-day-old males and females of summer and winter morphs. CHC compositions differed with age and morphs. However, no significant differences were found between the sexes of the same age and morph. The results of the behavioral assays show that summer morph pairs start to mate earlier in their life, have a shorter mating duration, and have more offspring compared to winter morph pairs. We hypothesize that CHC profiles of winter morphs are adapted to survive winter conditions, potentially at the cost of reduced mate recognition cues.

Responses in thermal tolerance and daily activity rhythm to urban stress in Drosophila suzukii

Cities experience changes in abiotic factors, such as warming, increases in noise and light. These changes can lead to phenotypic changes. Several studies have revealed that altered environments change phenotypes in plants and animals in cities. However, limited studies have isolated evolutionary from nongenetic changes. Here, we analyzed the evolution of thermal tolerance and diurnal activity patterns in the urban population of the fruit pest, Drosophila suzukii. Urban and rural isofemale lines were reared under constant conditions. We compared the lower and upper thermal limits (CTmin and CTmax, respectively), and effects of temperature exposure on the thermal limits of urban and rural populations. Common garden experiments showed that urban populations exhibit a lower CTmin than rural populations, suggesting genetic difference in CTmin among populations. On the other hand, the difference in CTmax between urban and rural populations was not significant. Exposure to cold temperature did not affect CTmin in both urban and rural populations. In contrast, exposure to hot temperature increased CTmax especially in urban population, suggesting that urban populations evolved in response to urban heat. We also investigated the daily activity patterns of urban and rural populations and the effect of lifelong artificial light at night on daily activity. We found that night-time light (dim light) reduced the total amount of activity compared to dark night condition. In addition, dim light at night altered the daily rhythm of activity and increased the activity rate at night. The effect of night light on total activity was less in urban than that in rural populations, suggesting that populations in cities evolved to mitigate decreased activity under night light. Our results showed that environmental temperature and artificial light at night evolutionarily and plastically influence ecologically important traits, such as temperature tolerance and diurnal activity.

Behavioral manipulation of Drosophila suzukii for pest control: high attraction to yeast enhances insecticide efficacy when applied on leaves

BACKGROUND

The invasive pest, Drosophila suzukii attacks fresh soft-skinned fruit. Broad-spectrum insecticides are implemented for control but there is a need to reduce environmental risks and insecticide residues on fruits. Hanseniaspora uvarum is a yeast frequently found on ripe fruits and associated with D. suzukii. We aim to exploit the ecological association and attraction of D. suzukii to H. uvarum by developing an attract-and-kill strategy, with spray-application on canopy but not fruit. We therefore investigated D. suzukii attraction, egg-laying and mortality when exposed to insecticidal yeast-based formulations.

RESULTS

Hanseniaspora uvarum strongly attracted D. suzukii when applied on leaves of grapevine, Vitis vinifera. Notably, this attractiveness was competitive to ripe grape berries that were susceptible to D. suzukii infestation. Moreover, adding H. uvarum enhanced the efficacy of insecticidal formulations against D. suzukii. Flies exposed to leaves treated with yeast-insecticide formulations showed higher mortality and laid a lower number of eggs compared to flies exposed to insecticide alone. In a wind tunnel, all treatments containing H. uvarum alone or in combination with insecticides, caused similar upwind flight and landing at the odor source, which provides evidence that the addition of insecticide did not reduce D. suzukii attraction to yeast.

CONCLUSION

Hanseniaspora uvarum can be used to manipulate the behavior of D. suzukii by attracting flies to insecticide formulations. Yeast attraction is competitive to grape berries and improves insecticide effectiveness, suggesting that sprays covering canopy only, could reduce residues on fruit without compromising management efficacy.

Genetically engineered insects with sex-selection and genetic incompatibility enable population suppression

Engineered Genetic Incompatibility (EGI) is a method to create species-like barriers to sexual reproduction. It has applications in pest control that mimic Sterile Insect Technique when only EGI males are released. This can be facilitated by introducing conditional female-lethality to EGI strains to generate a sex-sorting incompatible male system (SSIMS). Here, we demonstrate a proof of concept by combining tetracycline-controlled female lethality constructs with a pyramus-targeting EGI line in the model insect Drosophila melanogaster. We show that both functions (incompatibility and sex-sorting) are robustly maintained in the SSIMS line and that this approach is effective for population suppression in cage experiments. Further we show that SSIMS males remain competitive with wild-type males for reproduction with wild-type females, including at the level of sperm competition.

Large-scale characterization of sex pheromone communication systems in Drosophila

Insects use sex pheromones as a reproductive isolating mechanism to attract conspecifics and repel heterospecifics. Despite the profound knowledge of sex pheromones, little is known about the coevolutionary mechanisms and constraints on their production and detection. Using whole-genome sequences to infer the kinship among 99 drosophilids, we investigate how phylogenetic and chemical traits have interacted at a wide evolutionary timescale. Through a series of chemical syntheses and electrophysiological recordings, we identify 52 sex-specific compounds, many of which are detected via olfaction. Behavioral analyses reveal that many of the 43 male-specific compounds are transferred to the female during copulation and mediate female receptivity and/or male courtship inhibition. Measurement of phylogenetic signals demonstrates that sex pheromones and their cognate olfactory channels evolve rapidly and independently over evolutionary time to guarantee efficient intra- and inter-specific communication systems. Our results show how sexual isolation barriers between species can be reinforced by species-specific olfactory signals.

Despite the profound knowledge of sex pheromones, little is known about the coevolutionary mechanisms and constraints on their production and detection. Whole-genome sequences from 99 drosophilids, with chemical and behavioural data, show that sex pheromones and their cognate olfactory channels evolve rapidly and independently.

Insecticide-mediated effects on mating success and reproductive output of Drosophila suzukii

Exposure to sublethal concentrations can have adverse effects on certain individuals, but, can also favor survival and reproduction of others. This study aimed to evaluate the effects of exposing Drosophila suzukii (Matsumura, 1931) (Diptera: Drosophilidae) adults to LC₅₀ of spinetoram and lambda-cyhalothrin and field rate of thiamethoxam on their mating, reproductive output and longevity. The LC₅₀ for lambda-cyhalothrin and for spinetoram were 7.83 and 32.91 ng a.i./cm², respectively. Thiamethoxam, in the concentrations tested, was not toxic to D. suzukii, therefore, we use the recommended concentration for strawberry, 231.25 ng a.i./cm², in the sublethal tests. Insects exposed to LC₅₀ of lambda-cyhalothrin were more likely to mate, but presented shorter copula. Sublethal exposure to thiamethoxam lead to an increase in total fecundity. Among the insecticides tested, spinetoram presented the least expressive effects. Longevity was not affected by any of the tested insecticides. Results presented in this study are relevant to D. suzukii management since the stimulatory effects shown on this pest species can collaborate to outbreaks and insecticide resistance.

How varying parameters impact insecticide resistance bioassay: An example on the worldwide invasive pest Drosophila suzukii

Monitoring pesticide resistance is essential for effective and sustainable agricultural practices. Bioassays are the basis for pesticide-resistance testing, but devising a reliable and reproducible method can be challenging because these tests are carried out on living organisms. Here, we investigated five critical parameters and how they affected the evaluation of resistance to the organophosphate phosmet or the pyrethroid lambda-cyhalothrin using a tarsal-contact protocol on Drosophila suzukii, a worldwide invasive pest. Three of the parameters were related to insect biology: (i) sex, (ii) age of the imago (adult stage) and (iii) genetic diversity of the tested population. The two remaining parameters were linked to the experimental setup: (iv) the number of individuals tested per dose and (v) the duration of exposure to the active ingredient. Results showed that response to insecticide differed depending on sex, males being twice as susceptible to phosmet as females. Age principally affected young females' susceptibility to phosmet, because 0-24 hour-old flies were twice as susceptible as 24-48 hour-old and 72-96 hour-old females. Genetic diversity had no observable effect on resistance levels. The precision and accuracy of the median lethal dose (LD50) were greatly affected by the number of individuals tested per dose with a threshold effect. Finally, optimal duration of exposure to the active ingredient was 24 h, as we found an underestimation of mortality when assessed between 1 and 5 h after exposure to lambda-cyhalothrin. None of the main known point mutations on the para sodium channel gene associated with a knockdown effect were observed. Our study demonstrates the importance of calibrating the various parameters of a bioassay to develop a reliable method. It also provides a valuable and transferable protocol for monitoring D. suzukii resistance worldwide.

Social signals mediate oviposition site selection in Drosophila suzukii

The information that female insects perceive and use during oviposition site selection is complex and varies by species and ecological niche. Even in relatively unexploited niches, females interact directly and indirectly with conspecifics at oviposition sites. These interactions can take the form of host marking and re-assessment of prior oviposition sites during the decision-making process. Considerable research has focused on the niche breadth and host preference of the polyphagous invasive pest Drosophila suzukii Matsumura (Diptera: Drosophilidae), but little information exists on how conspecific signals modulate oviposition behavior. We investigated three layers of social information that female D. suzukii may use in oviposition site selection-(1) pre-existing egg density, (2) pre-existing larval occupation, and (3) host marking by adults. We found that the presence of larvae and host marking, but not egg density, influenced oviposition behavior and that the two factors interacted over time. Adult marking appeared to deter oviposition only in the presence of an unmarked substrate. These results are the first behavioral evidence for a host marking pheromone in a species of Drosophila. These findings may also help elucidate D. suzukii infestation and preference patterns within crop fields and natural areas.

Plasticity and modulation of olfactory circuits in insects

Olfactory circuits change structurally and physiologically during development and adult life. This allows insects to respond to olfactory cues in an appropriate and adaptive way according to their physiological and behavioral state, and to adapt to their specific abiotic and biotic natural environment. We highlight here findings on olfactory plasticity and modulation in various model and non-model insects with an emphasis on moths and social Hymenoptera. Different categories of plasticity occur in the olfactory systems of insects. One type relates to the reproductive or feeding state, as well as to adult age. Another type of plasticity is context-dependent and includes influences of the immediate sensory and abiotic environment, but also environmental conditions during postembryonic development, periods of adult behavioral maturation, and short- and long-term sensory experience. Finally, plasticity in olfactory circuits is linked to associative learning and memory formation. The vast majority of the available literature summarized here deals with plasticity in primary and secondary olfactory brain centers, but also peripheral modulation is treated. The described molecular, physiological, and structural neuronal changes occur under the influence of neuromodulators such as biogenic amines, neuropeptides, and hormones, but the mechanisms through which they act are only beginning to be analyzed.

Modelling Drosophila suzukii Adult Male Populations: A Physiologically Based Approach with Validation

The Spotted Wing Drosophila (SWD), Drosophila suzukii (Matsumura), is a harmful insect pest for soft fruit cultivations. Even though its main hosts belong to the genera Prunus and Rubus, its high polyphagy and adaptability to new environments makes it a serious problem for farmers worldwide, who have reported several economic losses because of this pest. A wide series of proposals to control SWD are available and operate in line with the mechanisms of integrated pest management, demonstrating their high efficiency when applied at the opportune moment. This work aims to apply and validate a physiologically based model which summarises all the available information about D. suzukii biology, such as the relationship between environmental temperature and its development, fertility and mortality rates. The model provided, as a result, a description of a population of SWD females taking into consideration the multiple generations that occurred during the year. Simulations were then compared with field data collected in a three-year survey in two experimental fields located in the Sabina Romana area (Lazio, Italy). More specifically, D. suzukii males were monitored with traps in fields cultivated with mixed varieties of cherries and they were selected because of their clearer identification in comparison to females. Results showed a high level of reliability of simulations in representing the field data, highlighting at the same time that there is no discrepancy in simulating D. suzukii females in order to represent male populations.

CRISPR/Cas9 mediated disruption of the white gene leads to pigmentation deficiency and copulation failure in Drosophila suzukii

The Spotted-wing Drosophila (Drosophila suzukii) is a devastating invasive pest of fruit crops. In D. melanogaster, the white (w) gene was associated with pigmentation and mating behavior, which are also important aspects to understand the invasion biology as well as to develop control strategies for D. suzukii. Here, we show that the generation of D. suzukii white-eyed mutants by CRISPR/Cas9 mutagenesis of the w gene resulted in the complete failure of copulation when w^- males were individually paired with w^- females in small circular arenas (diameter 0.7 cm) for 24 h. Further analysis showed that the mating defect was associated with w^- males and could not be rectified by two years of inbreeding by crossing sibling w^- females with w⁺ males, dim red illumination, male-female sexual training, changing to large arenas (diameter 3.5 cm), or different sex ratios. Profound pigmentation deficiency was detected in the compound eyes, ocelli, Malpighian tubules and testis sheaths in the w^- flies. Specifically, testis imaging showed that w^- males failed to deposit any pigments into pigment cells of the testis sheath, and produced smaller sperms and less seminal fluid compared to those from wildtype males. Together these observations suggest that the w gene plays an essential role in the regulation of sexual behavior and reproduction in D. suzukii. The similarities and differences in w gene function between D. suzukii and D. melanogaster in the context of pigmentation and mating behavior are discussed.

Repellent, oviposition-deterrent, and insecticidal activity of the fungal pathogen Colletotrichum fioriniae on Drosophila suzukii (Diptera: Drosophilidae) in highbush blueberries

Spotted-wing drosophila, Drosophila suzukii, and the anthracnose pathogen Colletotrichum fioriniae are an important insect pest and fungal disease of highbush blueberries, respectively, in the United States. However, whether C. fioriniae infection affects D. suzukii preference and performance remains unknown. Here, we conducted choice and no-choice studies to determine the repellent, oviposition-deterrent, and insecticidal effects of C. fioriniae on D. suzukii. In choice tests, blueberry fruit treated with anthracnose solutions containing spores from either field-collected infected fruit (‘fruit’) or a laboratory C. fioriniae culture (‘colony’) were less attractive to sexually mature D. suzukii females, but not males, than untreated fruit. The plant tissue (fruit or leaves) did not influence C. fioriniae repellency effects on D. suzukii. In no-choice tests, 55% fewer numbers of eggs were laid on, and 65% fewer adults emerged from, blueberry fruit treated with either the ‘fruit’ or ‘colony’ anthracnose solution than untreated fruit. Egg-to-adult D. suzukii survival was also 12% lower on C. fioriniae-infected fruit. No repellency or negative effects on survival were observed when C. fioriniae spores were filtered out of the solution. These findings will help efforts towards the discovery of microbial-derived repellent/oviposition-deterrent compounds that could be used in behavior-based management strategies for D. suzukii.

Association between olfactory sensitivity and behavioral responses of Drosophila suzukii to naturally occurring volatile compounds

Drosophila suzukii Matsumura (Diptera: Drosophilidae) is an invasive, destructive crop pest that originated in South East Asia. D. suzukii recently invaded Western countries and is threatening both European and American fruit industries. It is extremely attracted to otherwise undamaged, ripening fruits, unlike most other Drosophila species that attack only decaying or rotten fruits. Recent studies on different insect species showed that several naturally occurring compounds of easy market availability showing deterrent action may be used to supplement mass catches with food traps. Based on these considerations, the aim of the present work was to test the effects of some natural compounds (alone or in the mixture) on the olfactory system of the D. suzukii and the behavioral responses evoked. We measured by electroantennogram (EAG) recordings, the olfactory sensitivity of antennae to increasing concentrations of eugenol, vanillin, menthol, cis-jasmone; eugenol + vanillin, +menthol, +cis-jasmone; vanillin + menthol, +cis-jasmone. In addition, the behavioral responses to the same compounds and mixtures were evaluated. Our electrophysiological results show a dose-response relationship between the EAG amplitudes and the increasing concentrations of the olfactory compound. The behavioral results show that the number of laid eggs is significantly different between the standard diet and the standard diet + natural compound. These results underline a specificity in the olfactory sensitivity and in the ovipositing behavior of D. suzukii females; also, they could be valuable for the identification of key chemicals aimed at the future development of strategies in the management and control of this harmful insect for crops.

Aggressive Behaviour of Drosophila suzukii in Relation to Environmental and Social Factors

Aggression plays a crucial role in survival all across the animal kingdom. In this study, we investigate the aggressive behaviour of Drosophila suzukii, a known agricultural pest. Bioassays were performed between same sex pairs and the effect of environmental (food deprivation, sex, age and photophase) and social factors (non-social and social). Initially the inter-male and inter-female aggression was determined ethologically consisting of several behaviour patterns. Two hours starvation period increase locomotor activity of flies, promoting increased aggressive behaviour. Most of the behavioural patterns were common between males and females with a few sex-selective. Number of male encounters was higher in flies held in isolation than in those that had been reared with siblings whereas in case of females, only those that were isolated exhibited increased aggression. Females and males D. suzukii that were 4-day-old were more aggressive. In addition it is found that on the 3^rd hour after the beginning of photophase, regardless of age, both males and females rise to high intensity aggression patterns.

Diurnal and Seasonal Activity Patterns of Drosophilid Species (Diptera: Drosophilidae) Present in Blackberry Agroecosystems With a Focus on Spotted-Wing Drosophila

Drosophilid species with different life histories have been shown to exhibit similar behavioral patterns related to locating and utilizing resources such as hosts, mates, and food sources. Drosophila suzukii (Matsumura) is an invasive species that differs from other frugivorous drosophilids in that females lay eggs in ripe and ripening fruits instead of overripe or rotten fruits. We hypothesized that there may be diurnal and/or seasonal patterns associated with the movement of drosophilid species into and out of crop fields and their attraction to fermentation-odor-based monitoring traps, and that D. suzukii would conform to similar patterns. To test these hypotheses, we deployed passive, 2-headed Malaise traps between crop fields and wooded edges to simultaneously catch flies moving into and out of crop fields. We also deployed monitoring traps with a fermentation-based bait between crop fields and wooded edges and within crop rows. Traps were deployed weekly in June-August in 2014 and 2015 at two commercial blackberry farm in Cleveland County, NC, and were checked hourly for 24 h, except during darkness. Both D. suzukii and other drosophilid species moved between crop fields and wooded edges and were attracted to monitoring traps primarily during the morning and evening hours. Whereas other drosophilids were captured in traps throughout the season, few D. suzukii were caught in traps until early to mid-July in both years and increased as the season progressed. Understanding D. suzukii movement and activity patterns is essential for the development of effective management strategies.

Evolution of wing pigmentation in Drosophila: Diversity, physiological regulation, and cis-regulatory evolution

Fruit flies (Drosophila and its close relatives, or “drosophilids”) are a group that includes an important model organism, Drosophila melanogaster, and also very diverse species distributed worldwide. Many of these species have black or brown pigmentation patterns on their wings, and have been used as material for evo‐devo research. Pigmentation patterns are thought to have evolved rapidly compared with body plans or body shapes; hence they are advantageous model systems for studying evolutionary gains of traits and parallel evolution. Various groups of drosophilids, including genus Idiomyia (Hawaiian Drosophila), have a variety of pigmentations, ranging from simple black pigmentations around crossveins to a single antero‐distal spot and a more complex mottled pattern. Pigmentation patterns are sometimes obviously used for sexual displays; however, in some cases they may have other functions. The process of wing formation in Drosophila, the general mechanism of pigmentation formation, and the transport of substances necessary for pigmentation, including melanin precursors, through wing veins are summarized here. Lastly, the evolution of the expression of genes regulating pigmentation patterns, the role of cis‐regulatory regions, and the conditions required for the evolutionary emergence of pigmentation patterns are discussed. Future prospects for research on the evolution of wing pigmentation pattern formation in drosophilids are presented, particularly from the point of view of how they compare with other studies of the evolution of new traits.

Drosophila suzukii wing spot size is robust to developmental temperature

Phenotypic plasticity is an important mechanism allowing adaptation to new environments and as such it has been suggested to facilitate biological invasions. Under this assumption, invasive populations are predicted to exhibit stronger plastic responses than native populations. Drosophila suzukii is an invasive species whose males harbor a spot on the wing tip. In this study, by manipulating developmental temperature, we compare the phenotypic plasticity of wing spot size of two invasive populations with that of a native population. We then compare the results with data obtained from wild-caught flies from different natural populations. While both wing size and spot size are plastic to temperature, no difference in plasticity was detected between native and invasive populations, rejecting the hypothesis of a role of the wing-spot plasticity in the invasion success. In contrast, we observed a remarkable stability in the spot-to-wing ratio across temperatures, as well as among geographic populations. This stability suggests either that the spot relative size is under stabilizing selection, or that its variation might be constrained by a tight developmental correlation between spot size and wing size. Our data show that this correlation was lost at high temperature, leading to an increased variation in the relative spot size, particularly marked in the two invasive populations. This suggests: (a) that D. suzukii's development is impaired by hot temperatures, in agreement with the cold-adapted status of this species; (b) that the spot size can be decoupled from wing size, rejecting the hypothesis of an absolute constraint and suggesting that the wing color pattern might be under stabilizing (sexual) selection; and (c) that such sexual selection might be relaxed in the invasive populations. Finally, a subtle but consistent directional asymmetry in spot size was detected in favor of the right side in all populations and temperatures, possibly indicative of a lateralized sexual behavior.

Aged virgin adults respond to extreme heat events with phenotypic plasticity in an invasive species, Drosophila suzukii

Climate warming has increased the frequency of extreme heat events. Alien species usually invade new areas with a low-density population and often have limited mating opportunities due to the unsynchronized emergence of adults. Early-emerging virgin adults often have to wait to mate with later-emerging partners at the cost of aging, which reduces thermal tolerance. To understand the adaptive strategies of virgin males/females versus those of mated males/females in response to heat stress during aging, we conducted a fully factorial experiment to test the basal and plastic heat tolerance (CTmax, critical thermal maximum) of males and females with different mating statuses (virgin and mated) at different ages (5, 10, and 15 days after eclosion) after different acclimation regimes (null, rapid and developmental heat acclimation) in a well-known invasive species, Drosophila suzukii. We found that mating could change the heat tolerance of adults during aging. Mated females had higher basal heat tolerance than virgin females, while mated males had lower tolerance than virgin males. Mating could generally decrease the acclimation capacity (i.e., plasticity of heat tolerance) during aging. Aged virgin adults had a much higher acclimation capacity than aged mated adults. Our findings suggest that phenotypic plasticity of heat tolerance may be a main strategy used by virgin adults to cope with heat events. The phenotypic plasticity of thermal tolerance could increase the invasion success of alien species in new areas by allowing them to rapid respond to local temperature changes.

Context-Dependence and the Development of Push-Pull Approaches for Integrated Management of Drosophila suzukii

Sustainable pest control requires a systems approach, based on a thorough ecological understanding of an agro-ecosystem. Such fundamental understanding provides a basis for developing strategies to manipulate the pest’s behaviour, distribution, and population dynamics, to be employed for crop protection. This review focuses on the fundamental knowledge required for the development of an effective push-pull approach. Push-pull is a strategy to repel a pest from a crop, while attracting it toward an external location. It often relies on infochemicals (e.g., pheromones or allelochemicals) that are relevant in the ecology of the pest insect and can be exploited as lure or repellent. Importantly, responsiveness of insects to infochemicals is dependent on both the insect’s internal physiological state and external environmental conditions. This context-dependency reflects the integration of cues from different sensory modalities, the effect of mating and/or feeding status, as well as diurnal or seasonal rhythms. Furthermore, when the costs of responding to an infochemical outweigh the benefits, resistance can rapidly evolve. Here, we argue that profound knowledge on context-dependence is important for the development and implementation of push-pull approaches. We illustrate this by discussing the relevant fundamental knowledge on the invasive pest species Drosophila suzukii as an example.

Laboratory and Field Evaluation of Host-Related Foraging Odor-Cue Combinations to Attract Drosophila suzukii (Diptera: Drosophilidae)

The invasive spotted-wing drosophila, Drosophila suzukii (Matsumura), is a major pest of soft-skinned fruits. Since its introduction into North America and Europe, significant progress has been made in understanding the volatile cues used by this fly during food, oviposition site, and mate finding. Despite this progress, commercially available lures are non-selective. Here, we tested two Hanseniaspora uvarum (Niehaus) yeast compounds (isoamyl acetate and isobutyl acetate) and a leaf compound β-cyclocitral alone and in combination with a blend of four fermentation compounds ('Fermentation lure': acetic acid, ethanol, methionol, and acetoin) to improve D. suzukii attraction and selectivity. In laboratory assays, males and females were attracted to all seven individual compounds, although in electrophysiological assays, their antennae exhibited a dose-dependent response to only four of these compounds. In two-choice cage studies, the Fermentation lure was more attractive to D. suzukii than water controls, whereas β-cyclocitral and the mixture of isoamyl acetate and isobutyl acetate were not attractive in this larger-cage study. Moreover, adding the two-component H. uvarum compound blend to the Fermentation lure reduced D. suzukii attraction to the Fermentation blend. When these experiments were repeated in blueberry, raspberry, blackberry, and cherry orchards across several states in the United States over 2 yr, similar outcomes were observed: β-cyclocitral or the mixture of the H. uvarum blend did not improve the attractiveness of the Fermentation lure or its selectivity. This study demonstrates that cues from different sources may interfere with each other and reduce D. suzukii attraction to otherwise attractive odor combinations.

Control of Daily Locomotor Activity Patterns in Drosophila suzukii by the Circadian Clock, Light, Temperature and Social Interactions

Understanding behavioral rhythms in a pest species can contribute to improving the efficacy of control methods targeting that pest. However, in some species, the behavioral patterns recorded in artificial conditions contrast greatly with observed wild-type behavioral rhythms. In this study, we identify the determinants of daily activity rhythms of the soft and stone fruit pest Drosophila suzukii. The impact of gender, space, social housing, temperature, light, fly morph, and the circadian clock on D. suzukii locomotor rhythms was investigated. Assays were performed under artificial laboratory conditions or more natural semifield conditions to identify how these factors affected daily locomotor behavior. Daily locomotor activity patterns collected under semifield conditions varied very little between the various sex and social condition combinations. However, in lab-based assays, individual and group-housed males often exhibited divergent activity patterns, with more prominent hyperactivity at light/dark transitions. In contrast, hyperactivity responses were suppressed under lab protocols mimicking summer conditions for groups of females and mixed-sex groups. Moreover, when environmental cues were removed, flies held in groups displayed stronger rhythmicity than individual flies. Thus, social interactions can reinforce circadian behavior and resist hyperactivity responses in D. suzukii. Fly morph appeared to have little impact on behavioral pattern, with winter and summer morph flies displaying similar activity profiles under April semifield and laboratory mimic environmental conditions. In conclusion, separate and combined effects of light, temperature, circadian clock function, and social interactions were apparent in the daily activity profiles of D. suzukii. When groups of female or mixed-sex flies were used, implementation of matching photoperiods and realistic daily temperature gradients in the lab was sufficient to re-create behavioral patterns observed in summer semifield settings. The ability to leverage lab assays to predict D. suzukii field behavior promises to be a valuable asset in improving control measures for this pest.

Spotted-Wing Drosophila (Diptera: Drosophilidae) Adult Movement, Activity, and Oviposition Behavior in Maine Wild Blueberry (Vaccinium angustifolium; Ericales: Ericaceae)

Over a period of 5 yr (2012-2016), we conducted laboratory and field studies on activity, movement, and response to trap placement of adult Drosophila suzukii (Matsumura) in wild blueberry, Vaccinium angustifolium Aiton, fields in Maine. When measuring temporal patterns in fruit infestation, we found that D. suzukii females are most active in the morning and that they are 10 times more likely to lay eggs in blueberries at the top of the plant canopy compared with berries located in the lower part of the bush. Flies were found to be more abundant in fruit-bearing (crop) fields compared with pruned (vegetative) fields based on trap capture of adults. They are also most abundant along edges of fields compared with interiors. Trap efficiency is significantly better in traps 1.2 m above the ground and above the crop canopy of this low-growing crop plant than within the crop canopy. Three experiments involving the marking of laboratory-reared flies with fluorescent marker, their release, and capture with traps along a grid in fields suggest that: 1) fluorescent markers do not affect the distance moved of marked flies, 2) dispersal rates are not different between sexes, 3) there is little difference in the dispersal pattern through pruned fields and fruit-bearing fields, and 4) flies disperse at a low rate of 0.1-30 m per day, with an average of 5 m per day, but that long-distance dispersal over 1-2 km is feasible based on statistical model extrapolation.

Olfactory Preference of Drosophila suzukii Shifts between Fruit and Fermentation Cues over the Season: Effects of Physiological Status

Worldwide monitoring programs of the invasive fruit pest Drosophila suzukii Matsumura (Diptera: Drosophilidae), using fermentation baits like apple cider vinegar (ACV), revealed a counterintuitive period of low trap catches during summer, followed by an autumn peak. In this study, we demonstrate that ACV baited traps indeed provide a distorted image of the D. suzukii population dynamics as it is possible to capture higher numbers during this "low capture period" with synthetic lures. It was hypothesised that the preference of D. suzukii populations for fermentation cues like ACV is most pronounced during autumn, winter and spring, while the flies prefer fresh fruit cues during summer and that this seasonal preference is related to the changing physiology of the flies over the season. To test this hypothesis, the preference between fermentation cues (ACV) and host fruits (strawberries) and the effect of physiology (sex, seasonal morphology and feeding, mating and reproductive status) was investigated both in olfactometer laboratory experiments and a year-round field preference experiment. In olfactometer experiments we demonstrated that protein deprived females, virgin females with a full complement of unfertilised eggs and males show a strong preference for fermentation cues while fully fed reproductive summer morph females generally prefer fruit cues. These findings indicate that D. suzukii is attracted to fermentation volatiles in search of (protein-rich) food and to fruit volatiles in search of oviposition substrates. Winter morph and starved females displayed indiscriminating olfactory behaviour. In the field preference experiment, the hypothesised seasonal shift between fermentation and fruit cues was confirmed. This shift appeared to be highly temperature-related and was similarly observed for summer and winter morphs.

Intraspecific Competition Affects the Pupation Behavior of Spotted-Wing Drosophila (Drosophila suzukii)

In Drosophila, intraspecific competition (IC) may cause stress, cannibalism, and affect survival and reproduction. By migrating to less crowded environments, individuals can escape IC. Larvae of spotted-wing drosophila (SWD, Drosophila suzukii) are often exposed to IC. They are known to pupate either attached to or detached from their hosts. Here, we hypothesized that SWD pupates detached from the larval host as a means to escape IC and increase their survival and fitness. Under laboratory conditions, IC resulted in increased pupation detached from the larval host in both cornmeal medium and blueberry fruit. Males were more prone to detached pupation than females. In blueberry, IC-exposed larvae pupated farther away from the fruit relative to singly-developed individuals. Detached pupation was associated to survival and fitness gains. For example, larvae that displayed detached pupation showed shorter egg-pupa development times, higher pupa-adult survival, and larger adult size relative to fruit-attached individuals. These findings demonstrate that SWD larvae select pupation sites based on IC, and that such a strategy is associated with improved survival and fitness. This information contributes to a better understanding of SWD basic biology and behavior, offering insights to the development of improved practices to manage this pest in the field.

Brown Rice Vinegar as an Olfactory Field Attractant for Drosophila suzukii (Matsumura) and Zaprionus indianus Gupta (Diptera: Drosophilidae) in Cherimoya in Maui, Hawaii, with Implications for Attractant Specificity between Species and Estimation of Relative Abundance

Drosophila suzukii (Matsumura) is an agricultural pest that has been observed co-infesting soft-skinned fruits with Zaprionus indianus Gupta. The characterization of olfactory preferences by species is a necessary step towards the development of species-specific attractants. Five olfactory attractants were used to survey the populations of two invasive drosophilids in cherimoya in Maui, Hawaii. The attractants used were apple cider vinegar (ACV), brown rice vinegar (BRV), red wine (RW), apple cider vinegar and red wine (ACV+RW; 60/40), and brown rice vinegar and red wine (BRV+RW; 60/40). For D. suzukii, BRV+RW resulted in more captures than BRV, ACV, and RW, while ACV+RW resulted in more captures than ACV. No differences were observed between BRV+RW and ACV+RW. BRV had greater specificity in attracting D. suzukii compared to ACV, ACV+RW, and RW. For Z. indianus, no significant differences were observed in either the mean captures or specificity for any attractant used. Collectively, these findings demonstrate that (1) BRV and BRV+RW are effective field attractants and (2) D. suzukii has unique olfactory preferences compared to non-target drosophilids, while (3) Z. indianus’ preferences do not appear to vary from non-target drosophilids, and (4) the accuracy of relative abundance is impacted by the specificity of the attractants.

Evaluation of Protein Bait Manufactured From Brewery Yeast Waste for Controlling Drosophila suzukii (Diptera: Drosophilidae)

We evaluated a protein bait based on an enzymatically hydrolyzed beer yeast and two widely used baits including a sugar + vinegar + wine mixture and apple cider vinegar for their ability to trap Drosophila suzukii (Matsumura) in the laboratory and outdoors. The protein bait was a more attractive lure than the other tested baits, with the protein bait capturing significantly more female and male adults at different developmental stages than the other baits. Furthermore, the protein bait with 20% vinegar attracted significantly more adult flies than the other baits, and the protein bait without dilution attracted the most adults. Except for the addition of 0.05% spinosad, increased insecticide content in protein bait reduced its attractiveness to adult flies. Moreover, we found that D. suzukii has a bimodal activity pattern in visiting protein bait, where maximum activity occurs during 8:00-10:00 a.m. and 14:00-16:00 p.m. The antennae and maxillary palpi played an important role in detecting the chemicals emitted from the protein bait, as the number of intact flies that responded to new protein bait was significantly higher than the number of flies without antennae that responded, but almost 15% of defective flies still responded to the protein bait. Our results suggested that the protein bait based on spent brewery yeast could be a promising alternative for D. suzukii population monitoring and for managing this pest when combined with bioinsecticides, providing guidance for using this protein bait as a component of integrated pest management.

Differential Susceptibility of Wild and Cultivated Blueberries to an Invasive Frugivorous Pest

Highbush blueberry is a crop native to the northeast USA that has been domesticated for about 100 years. This study compared the susceptibility of wild and domesticated/cultivated highbush blueberries to an invasive frugivorous pest, the spotted wing drosophila (Drosophila suzukii). We hypothesized that: 1) cultivated fruits are preferred by D. suzukii for oviposition and better hosts for its offspring than wild fruits; and, 2) wild and cultivated fruits differ in physico-chemical traits. Fruits from wild and cultivated blueberries were collected from June through August of 2015 and 2016 from 10 to 12 sites in New Jersey (USA); with each site having wild and cultivated blueberries growing in close proximity. The preference and performance of D. suzukii on wild and cultivated blueberries were studied in choice and no-choice bioassays. In addition, we compared size, firmness, acidity (pH), total soluble solids (°Brix), and nutrient, phenolic, and anthocyanin content between wild and cultivated berries. In choice and no-choice bioassays, more eggs were oviposited in, and more flies emerged from, cultivated than wild blueberries. Cultivated fruits were 2x bigger, 47% firmer, 14% less acidic, and had lower °Brix, phenolic, and anthocyanin amounts per mass than wild fruits. Levels of potassium and boron were higher in cultivated fruits, while calcium, magnesium, and copper were higher in wild fruits. These results show that domestication and/or agronomic practices have made blueberries more susceptible to D. suzukii, which was associated with several physico-chemical changes in fruits. Our study documents the positive effects of crop domestication/cultivation on an invasive insect pest.

Assessing the use of wing ornamentation and visual display in female choice sexual selection

Conspicuous sexual dimorphism is often ascribed to sexual selection. When the differences between the sexes are ornamental, this is thought to indicate a role for female choice. In spotted winged Drosophila species courtship, a male positioned in front of a female waves his wings, which have a patch of melanization on the exterior margin. In this study, we examine both female preference for wing spots and the role of vision in mating success in three species of the suzukii group: Drosophila biarmipes, D. suzukii, and D. subpulchrella. To assess female preference for wing spot, we removed the spot with a novel, non-invasive method, and competed spotless males with males with two spots. Phenotype did not affect mating success in any species. To eliminate the potential effect of competitive behavior on male mating success, we also ran a no-choice analysis. Mating frequency and timing was not different between phenotypes within these species. The effect of vision on mating success was assessed by comparing mating success of spotted males between light and dark conditions, both for frequency of mating, as well as timing of multiple courtship parameters. Species varied in the extent that lack of vision negatively affected mating success. Though vision is important for mating success, the spot itself may not be providing the signal that females use to make mating decisions.

Recording and reproducing the diurnal oviposition rhythms of wild populations of the soft- and stone- fruit pest Drosophila suzukii

Drosophila suzukii is a horticultural pest on a global scale which causes both yield and economic losses on a range of soft- and stone-fruit. Tackling this pest is problematic but exploiting behavioral rhythms could increase the impact of control. To do this, a better understanding of behavioral patterns is needed. Within this study we aimed to investigate rhythms in reproductive behavior of wild D. suzukii under natural conditions in the field. Environmental parameters were also recorded to decipher how they influence these rhythms. Assays were then performed on laboratory cultures, housed under artificial conditions mimicking the temperature and light cycles, to see if these patterns were reproducible and rhythmic. We were able to promote field like oviposition patterns within the laboratory using realistic temperature and light cycles regardless of variations in other factors including substrate, humidity, and lighting type. Locomotion activity was also recorded under these mimicked conditions to identify how this behavior interacts with oviposition rhythms. Both our field and laboratory assays show that oviposition behavior is likely under the control of the circadian clock and primarily occurs during the day. However, consistent with prior reports we observed that these patterns become crepuscular when day-time temperature peaks exceeded 30°C. This was also found within locomotion rhythms. With an increased understanding of how these behaviors are influenced by environmental conditions, we highlight the importance of using realistic temperature and light cycles when investigating behavioral patterns. From an increased understanding of D. suzukii behavior we increase our ability to target the pest in the field.

The role of cuticular hydrocarbons in mate recognition in Drosophila suzukii

Cuticular hydrocarbons (CHCs) play a central role in the chemical communication of many insects. In Drosophila suzukii, an economically important pest insect, very little is known about chemical communication and the possible role of CHCs. In this study, we identified 60 CHCs of Drosophila suzukii and studied their changes in function of age (maturation), sex and interactions with the opposite sex. We demonstrate that age (maturation) is the key factor driving changes in the CHC profiles. We then test the effect on courtship behaviour and mating of six CHCs, five of which were positively associated with maturation and one negatively. The results of these experiments demonstrate that four of the major CHC peaks with a chain length of 23 carbons, namely 9-tricosene (9-C23:1), 7-tricosene (7-C23:1), 5-tricosene (5-C23:1) and tricosane (n-C23), negatively regulated courtship and mating, even though all these compounds were characteristic for sexually mature flies. We then go on to show that this effect on courtship and mating is likely due to the disruption of the natural ratios in which these hydrocarbons occur in Drosophila suzukii. Overall, these results provide key insights into the cuticular hydrocarbon signals that play a role in D. suzukii mate recognition.

Nutritional geometry and fitness consequences in Drosophila suzukii, the Spotted-Wing Drosophila

Since its arrival to North America less than a decade ago, the invasive Spotted-Wing Drosophila (Drosophila suzukii) has inflicted substantial economic losses on soft fruit agriculture due to its ability to oviposit into ripening fruits. More effective management approaches for this species are needed, but little is known about the factors that influence behavioral choices made by D. suzukii when selecting hosts, or the consequences that their offspring experience when developing in different environments. Using a nutritional geometry methodology, we found that the ratio of proteins-to-carbohydrates (P:C) present in media greatly influenced adult D. suzukii behavior and subsequent offspring development. Whereas adult flies showed a strong bias in their oviposition and association behaviors toward carbohydrate-rich foods, larval survival and eclosion rate were strongly dependent on protein availability. Here, we explore the preference-performance hypothesis (PPH), in which females are predicted to oviposit on medias that provide the greatest offspring benefits, in regard to its relevance in D. suzukii behavior and consequences for management. Our results provide valuable insight into the ecology and evolution of this species that may hopefully lead to more effective management strategies.

Infection of Drosophila suzukii with the obligate insect-pathogenic fungus Entomophthora muscae

Physiological constraints restrict specialist pathogens from infecting new hosts. From an applied perspective, a narrow host range makes specialist pathogens interesting for targeting specific pest insects since they have minimal direct effects on non-target species. Entomopathogenic fungi of the genus Entomophthora are dipteran-specific but have not been investigated for their ability to infect the spotted wing drosophila (SWD; Drosophila suzukii) a fruit-damaging pest invasive to Europe and America. Our main goal was to study whether SWD is in the physiological host range of the entomophthoralean species E. muscae. We investigated pathogenicity and virulence of E. muscae towards its main natural host, the housefly Musca domestica, and towards SWD. We found that E. muscae readily infected and significantly reduced survival of SWD by 27.3% with the majority of flies dying 4-8 days post-exposure. In comparison with SWD, infection of the natural host M. domestica resulted in an even higher mortality of 62.9% and larger conidial spores of E. muscae, reflecting the physiological constraints of the pathogen in the atypical host. We demonstrated that pathogens of the E. muscae species complex that typically have a narrow natural host range of one or few dipteran species are able to infect SWD, and we described a new method for in vivo transmission and infection of an entomophthoralean fungus to SWD.

Diurnal Activity of Drosophila suzukii (Diptera: Drosophilidae) in Highbush Blueberry and Behavioral Response to Irrigation and Application of Insecticides

Spotted wing Drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), is an invasive vinegar fly that has become a primary direct pest of berry crops worldwide. We conducted 2 yr of behavioral studies in blueberry plantings to determine how fly activity varied throughout the day. Observations of diurnal activity of adult D. suzukii found the greatest activity in the morning hours between 0600 and 0800 hours, when the majority of flies were on the berries. Flies were also active in the evening mainly between 1800 and 2000 hours; however, this trend was more prominent in 2015, which had cooler and more humid evenings. Experiments examining the effect of irrigation on D. suzukii behavior showed that flies remained active during and after irrigation. The effect of insecticide treatments alone and in combination with irrigation revealed that treatment with spinosad had limited effects on the number of flies per bush, whereas spinetoram reduced the number flying and on the bushes in some cases. Zeta-cypermethrin caused longer and more consistent reduction in D. suzukii flying and on bushes. In all treatments, we observed surviving flies flying near and on treated bushes, indicating that these insecticides do not completely deter fly activity. Irrigation did not influence the effects of zeta-cypermethrin on fly behavior during daily observations up to 3 d after application. Our results highlight that the diurnal patterns of activity of D. suzukii on host plants are flexible and are relatively unaffected by irrigation or insecticide applications.

Reproductive Status of Drosophila suzukii (Diptera: Drosophilidae) Females Influences Attraction to Fermentation-Based Baits and Ripe Fruits

Drosophila suzukii (Matsumura) is an invasive species that is a devastating pest of soft-skinned fruit crops. Although much effort has been directed toward developing traps and attractants to monitor for D. suzukii, current monitoring tools do not reliably predict fruit infestation. The objective of this study was to determine if D. suzukii females at different developmental stages are differentially attracted to monitoring traps with fermentation-based baits and ripe fruits. Females were collected on the surface of traps, within traps, and on ripe fruits during three experiments at field locations in North Carolina, USA, and were dissected to determine their reproductive status. In general, females collected on ripe fruits were more likely to have mature eggs present in their ovaries and had higher numbers of mature eggs than females collected on the surface of or within monitoring traps. The results of this study have implications for D. suzukii monitoring and the development of effective baits for use in integrated pest management programs.

Isolating Spermathecae and Determining Mating Status of Drosophila suzukii: A Protocol for Tissue Dissection and Its Applications

The spotted wing drosophila, Drosophila suzukii (Diptera: Drosophilidae), is an emerging invasive pest, which attacks a wide variety of fruits and berries. Although previous studies have focused on different aspects of D. suzukii reproductive biology, there are no protocols available for determining the mating status of D. suzukii females and drosophilids in general. In this study, a step-by-step protocol for tissue dissection, isolating spermathecae, and determining the mating status of females was developed specifically for D. suzukii. This protocol is an effective and relatively quick method for determining female mating status. It has important applications from exploring reproductive output of D. suzukii females to understanding the biology of D. suzukii winter morph, which presumably plays the main role in the overwintering of this invasive species. We demonstrated applicability of this protocol for both field collected flies and flies reared in the lab, including fly specimens stored on a long-term basis.

Quantitative analysis of visually induced courtship elements in Drosophila subobscura

We developed a new paradigm for quantitative analysis of courtship behavior in flies, Fly Motion-detector with an Actuator-Coupled Stimulator (FlyMacs), in which the stimulation of a fly with a moving visual target and recording of induced behaviors are automated under computer control. We employ FlyMacs for the identification of motion features that trigger specific courtship elements in Drosophila subobscura, whose mating is suggested to be strongly vision dependent. A female abdomen attached to the actuator, when moved in an appropriate pattern, evokes in the test male tapping-like foreleg motions, midleg swing and proboscis extension, which are considered to be elementary actions in male courtship behavior. Tapping is primarily induced when the target is moving, whereas midleg swing and proboscis extension are most frequently observed after the target stops moving. In contrast to midleg swing, which tends to occur immediately after target cessation (∼3000 ms), the incidence of proboscis extension gradually increases with time after target cessation, reaching a plateau at 3000 ms. The results suggest that tapping, midleg swing and proboscis extension are each induced by different movement features of the visual target. These findings do not support the view that a single key stimulus induces the entire courtship ritual. Rather, courtship behaviors in D. subobscura are correlated with movement and position of the target, which suggests that D. subobscura uses sensory information to pattern its courtship.

Physiological and behavioral responses in Drosophila melanogaster to odorants present at different plant maturation stages

The fruit fly Drosophila melanogaster feeds and oviposits on fermented fruit, hence its physiological and behavioral responses are expected to be tuned to odorants abundant during later stages of fruit maturation. We used a population of about two-hundred isogenic lines of D. melanogaster to assay physiological responses (electroantennograms (EAG)) and behavioral correlates (preferences and choice ratio) to odorants found at different stages of fruit maturation. We quantified electrophysiological and behavioral responses of D. melanogaster for the leaf compound β-cyclocitral, as well as responses to odorants mainly associated with later fruit maturation stages. Electrophysiological and behavioral responses were modulated by the odorant dose. For the leaf compound we observed a steep dose-response curve in both EAG and behavioral data and shallower curves for odorants associated with later stages of maturation. Our data show the connection between sensory and behavioral responses and are consistent with the specialization of D. melanogaster on fermented fruit and avoidance of high doses of compounds associated with earlier stages of maturation. Odor preferences were modulated in a non-additive way when flies were presented with two alternative odorants, and combinations of odorants elicited higher responses than single compounds.