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

Evaluation of a Push-Pull Strategy for Spotted-Wing Drosophila Management in Highbush Blueberry

We evaluated a novel push-pull control strategy for protecting highbush blueberry, Vaccinium corymbosum, against spotted-wing drosophila (SWD), Drosophila suzukii. Methyl benzoate (MB) was used as the pushing agent and a previously tested SWD attractive blend of lure-scents was used as the pulling agent. MB dispensers (push) were hung in the canopy and lure-scent dispensers (pull) were hung in yellow jacket traps filled with soapy water around the blueberry bushes. Blueberries were sampled weekly, and any infestation was inspected by examining the breathing tubes of SWD eggs which protrude through the skin of infested fruit. The frequency of infestation, i.e., the proportion of berries infested with at least one egg, and the extent of infestation, i.e., the mean number of eggs in infested berries, were significantly reduced in treatments receiving MB dispensers as a pushing agent when infestation rates were very high. However, the mass trapping devices as a pulling agent did not provide comparable protection on their own and did not produce additive protection when used in combination with the MB dispensers in push-pull trials. We conclude that MB has the potential to be implemented as a spatial repellent/oviposition deterrent to reduce SWD damage in blueberry under field conditions and does not require the SWD attractant as a pulling agent to achieve crop protection.

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.

Olfactory behavioral responses of two Drosophila species and their pupal parasitoid to volatiles from bananas

BACKGROUND

Behavior-based manipulation is an essential part of Drosophila integrated pest management (IPM). Effective compounds are useful for improving the efficiency of baits and the development of attract-and-kill or push-pull strategies to manage Drosophila populations. Here, we investigated the olfactory behavior of two Drosophila species, as well as their pupal parasitoid, to volatiles from bananas, for the identification of effective compounds to control fly populations.

RESULTS

The results showed that overripe bananas were most attractive to both flies, with a higher attraction index (AI) in Drosophila melanogaster than in Drosophila suzukii. The profiles of volatile organic compounds (VOCs) from bananas with three different ripening stages were compared, and six VOCs were selected for behavioral tests. D. suzukii showed significantly different responses to isoamyl alcohol with D. melanogaster. The effects of ethyl butyrate and ethyl isovalerate on the two flies were dose-dependent, with lower concentrations acting as repellent and higher concentrations acting as attractant. Isoamyl acetate, isoamyl butyrate and isoamyl isovalerate (0.005-0.05% v/v) were attractive to both flies. The parasitoid wasp Pachycrepoidus vindemmiae was repelled by isoamyl alcohol and ethyl butyrate, and attracted by ethyl isovalerate, but showed no significant response to isoamyl acetate, isoamyl butyrate and isoamyl isovalerate at the tested concentration.

CONCLUSION

This study indicated that the behavioral response of Drosophila to the odor of chemical compounds is dose-dependent. Isoamyl alcohol and isoamyl acetate at certain concentrations could be used as repellents, whereas ethyl isovalerate as an attractant in control strategy design for D. suzukii. © 2023 Society of Chemical Industry.

Using Red Panel Traps to Detect Spotted-Wing Drosophila and its Infestation in US Berry and Cherry Crops

Spotted-wing drosophila (SWD), Drosophila suzukii Matsumura (Diptera: Drosophilidae), is an invasive pest of thin-skinned fruits in the United States. Monitoring traps are an integral part of SWD integrated pest management, allowing early detection and timely management of this pest. An ideal monitoring trap should be easy to use, effective in capturing SWD, sensitive and selective to male SWD which are easy to identify due to their spotted wings, and able to predict fruit infestation from trap captures. Deli-cup-based liquid traps (grower standard), which make in-situ observations difficult, were compared with red-panel sticky traps, both baited with commercial lures (Scentry, Trécé Broad-Spectrum (BS), and Trécé High-Specificity (HS)), across several US states in blueberries (lowbush and highbush), blackberry, raspberry, and cherry crops during 2018 and 2021. Results showed that red-panel traps effectively captured SWD, were able to detect male SWD early in the season while also being selective to male SWD all season-long, and in some cases linearly related male SWD trap captures with fruit infestation. Scentry and Trécé BS lures captured similar numbers of SWD, though Trécé BS and Trécé HS were more selective for male SWD in red panel traps than liquid traps in some cases. In conclusion, due to its ease of use with less processing time, red-panel traps are promising tools for detecting and identifying male SWD in-situ and for predicting fruit infestation. However, further research is needed to refine the trap captures and fruit infestation relationship and elucidate the trap-lure interactions in berry and cherry crops.

Molecular and behavioral studies reveal differences in olfaction between winter and summer morphs of Drosophila suzukii

Spotted-wing drosophila, Drosophila suzukii (Matsumura), is a major economic pest of several fruit crops in Europe, North and South America, and other parts of the world because it oviposits in ripening thin-skinned fruits. This vinegar fly exhibits two distinct morphotypes: a summer and a winter morph. Although adaptations associated with the winter morph enhance this invasive pest's capacity to survive in cold climates, winter is still a natural population bottleneck. Since monitoring early spring populations is important for accurate population forecasts, understanding the winter morph's response to olfactory cues may improve current D. suzukii management programs. In this study, a comparative transcriptome analysis was conducted to assess gene expression differences between the female heads of the two D. suzukii morphs, which showed significant differences in 738 genes (p ≤ 0.0001). Out of twelve genes related to olfaction determined to be differentially expressed in the transcriptome, i.e., those related to location of food sources, chemosensory abilities, and mating behavior, nine genes were upregulated in the winter morph while three were downregulated. Three candidate olfactory-related genes that were most upregulated or downregulated in the winter morph were further validated using RT-qPCR. In addition, behavioral assays were performed at a range of temperatures to confirm a differing behavioral response of the two morphs to food odors. Our behavioral assays showed that, although winter morphs were more active at lower temperatures, the summer morphs were generally more attracted to food odors. This study provides new insights into the molecular and behavioral differences in response to olfactory cues between the two D. suzukii morphs that will assist in formulating more effective monitoring and physiological-based control tools.

Factors Influencing the Efficacy of Novel Attract-and-Kill (ACTTRA SWD) Formulations Against Drosophila suzukii

In the continental United States, the invasive spotted-wing drosophila (SWD), Drosophila suzukii Matsumura, has become a primary pest of multiple stone and soft-skinned fruits. A new innovative adjuvant formulation, ACTTRA SWD, mixed with a suitable insecticide, constitutes a novel attract-and-kill tactic to manage D. suzukii in fruit crops. We hypothesized that background odors present in crop fields, particularly odors from host fruits, negatively affect the effectiveness of this attract-and-kill formulation, as odors from these sources can compete for insect attraction. Additionally, we evaluated the influence of adult D. suzukii sex and physiological status (age and mating status), and fruit ripeness on its response to the ACTTRA SWD formulation. For this, we used two-choice bioassays to test the response of adult D. suzukii to three ACTTRA SWD formulations (named OR1, TD, and HOOK SWD) in the presence and absence of host fruits (blueberries, raspberries, blackberries, and strawberries). Odors from raspberries were significantly more attractive than those from the TD formulation mixed with spinosad (Entrust). For the HOOK SWD formulation and OR1+Entrust formulation, odors from all the fruit types tested were significantly more attractive than the adjuvants. Compared with females, male D. suzukii were more attracted to the TD formulation over the blueberry fruits. Additionally, age and female mating status but not fruit ripeness influenced D. suzukii attraction to both OR1 and TD formulations. The results from this study indicate that D. suzukii physiological status and host fruit availability impact the efficacy of new attract-and-kill adjuvants such as ACTTRA SWD.

Hanseniaspora uvarum Attracts Drosophila suzukii (Diptera: Drosophilidae) With High Specificity

Since the early phase of the intercontinental dispersal of Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), fermentation baits have been used for monitoring. Self-made lures and commercial products are often based on wine and vinegar. From an ecological perspective, the formulation of these baits is expected to target especially vinegar flies associated with overripe fruit, such as Drosophila melanogaster (Meigen) (Diptera: Drosophilidae). Hanseniaspora uvarum (Niehaus) (Ascomycota: Saccharomyceta) is a yeast closely associated with D. suzukii and fruit, and furthermore attractive to the flies. Based on this relation, H. uvarum might represent a suitable substrate for the development of lures that are more specific than vinegar and wine. In the field, we therefore, compared H. uvarum to a commercial bait that was based on vinegar and wine with respect to the number of trapped D. suzukii relative to other drosophilids and arthropods. Trap captures were higher with the commercial bait but specificity for D. suzukii was greater with H. uvarum. Moreover, H. uvarum headspace extracts, as well as a synthetic blend of H. uvarum volatiles, were assayed for attraction of D suzukii in a wind tunnel and in the field. Headspace extracts and the synthetic blend induced strong upwind flight in the wind tunnel and confirmed attraction to H. uvarum volatiles. Furthermore, baited with H. uvarum headspace extract and a drowning solution of aqueous acetic acid and ethanol, 74% of field captured arthropods were D. suzukii. Our findings suggest that synthetic yeast headspace formulations might advance the development of more selective monitoring traps with reduced by-catch.

Sodium Chloride Added to Diluted Concord Grape Juice Prior to Fermentation Results in a Highly Attractive Bait for Drosophila suzukii (Diptera: Drosophilidae)

At the interface of behavioral chemical ecology and pest management lays the evaluation of kairomones that can be used for either, monitoring or attract-and-kill of insect pests. Diluted Concord grape juice (DGJ) was previously reported to be highly attractive to male and female D. suzukii. Here, we conducted cage and field studies aimed at (1) comparing the attractiveness of fresh DGJ against that of commercial lures over a 3-year period in multiple locations, (2) quantifying the effects of DGJ aging for 1 and 2 weeks on D. suzukii attraction, and (3) ascertaining the effects of adding sodium chloride to DGJ prior to fermentation on the outcome. For all field studies, captures of non-target insects were recorded. Combined findings from the cage and field studies comparing DGJ and commercial lures indicate that fresh DGJ is as attractive or more attractive than the commercial lures that were evaluated. The results of the aging studies revealed that 7- and 14- day old DGJ baits are at least twice as attractive to female D. suzukii when compared to fresh DGJ. The response of other Drosophilids to the aged olfactory treatments mirrored that of D. suzukii. Remarkably, the addition of 2% sodium chloride to DGJ prior to aging resulted in a fourfold increase in attractiveness to male and female D. suzukii while reducing the number of non-target insects captured in traps. In conclusion, DGJ is an effective bait that can be deployed in traps and, when 2% sodium chloride is added, the resulting material outcompetes the performance of commercial lures and greatly reduces captures of non-target insects, thereby increasing bait selectivity. Overall, our findings increase our understanding of D. suzukii olfactory-driven behavior in response to fruit-based odor and demonstrate the potential use of a low-cost attractant for farmers who are not able to monitor for D. suzukii when commercially produced lures are expensive or less accessible.

Drosophila suzukii (Diptera: Drosophilidae): A Decade of Research Towards a Sustainable Integrated Pest Management Program

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) also known as spotted-wing drosophila (SWD), is a pest native to Southeast Asia. In the last few decades, the pest has expanded its range to affect all major European and American fruit production regions. SWD is a highly adaptive insect that is able to disperse, survive, and flourish under a range of environmental conditions. Infestation by SWD generates both direct and indirect economic impacts through yield losses, shorter shelf life of infested fruit, and increased production costs. Fresh markets, frozen berries, and fruit export programs have been impacted by the pest due to zero tolerance for fruit infestation. As SWD control programs rely heavily on insecticides, exceedance of maximum residue levels (MRLs) has also resulted in crop rejections. The economic impact of SWD has been particularly severe for organic operations, mainly due to the limited availability of effective insecticides. Integrated pest management (IPM) of SWD could significantly reduce chemical inputs but would require substantial changes to horticultural management practices. This review evaluates the most promising methods studied as part of an IPM strategy against SWD across the world. For each of the considered techniques, the effectiveness, impact, sustainability, and stage of development are discussed.

Assessment of Attractant Lures and Monitoring Traps for Drosophila suzukii (Diptera: Drosophidae) Using Electrophysiology, Laboratory Choice Assays, and Field Trials

Monitoring is critical to control efforts for Drosophila suzukii Matsumura, an invasive polyphagous fly that has the potential to cause significant losses in commercial soft fruit and berry production worldwide. We used an iterative process to identify trap colors, trap designs, and volatile mixtures to improve monitoring efforts in commercial blueberry, raspberry, and blackberry crops. Our results suggest that the selection of trap color and design and attractant lures should be customized to the crop in which they are deployed. In raspberries grown in high tunnel systems, DrosaLure paired with Drosal traps painted green and purple were highly specific to D. suzukii although actual capture counts were low. However, in field grown raspberries, BioLure and Multilure traps were most effective, but with significant nontarget bycatch. In blueberries, we had greatest success with a 5 µg:50 ng mixture of ethyl acetate-acetoin in a green/purple-colored jar-style trap with large (5 cm) mesh covered openings.

Field Evaluation of Different Attractants for Detecting and Monitoring Drosophila suzukii

Drosophila suzukii, more commonly known as the spotted-wing drosophila (SWD), is an invasive pest of soft, thin-skinned fruit responsible for significant economic losses for growers worldwide. To detect and monitor this pest, several host attractants have been developed for use in trapping SWD; however, they lack selectivity. Therefore, there is a significant need for more selective monitoring devices to enable growers to make timely pest management decisions to properly protect vulnerable crops. Previous studies identified a quinary blend (QB), based on fermenting apple juice odors, which offers significantly higher selectivity by reducing non-target captures compared with the standard apple cider vinegar bait commonly used by growers in the orchards. In this study, the selectivity and efficacy of a home-made QB dispenser was compared to an industry formulated version of the QB components (ChemTica) and two commercially available (Scentry and Trécé) SWD dispensers across blueberry and raspberry fields in Maryland, West Virginia, and New Jersey in different seasons. Controlled-release dispensers of the QB (home-made and ChemTica) consistently had higher selectivity within the blueberry and raspberry field sites compared with the two commercial dispensers; although efficacy was compromised such that total SWD captures per trap tended to be lower. The selectivity ratio range of SWD to non-targets (all non-SWD) for a QB-based (ChemTica) dispenser averaged from 15 to 57% compared with other commercial dispensers that ranged from 1 to 30% based on location and year. Due to high selectivity of the controlled-release dispenser of the QB, the potential for this dispenser to be utilized by growers as a SWD detection and monitoring tool is high.

Detection and monitoring of Drosophila suzukii in raspberry and cherry orchards with volatile organic compounds in the USA and Europe

Spotted wing drosophila (SWD) causes significant economic loss in fruit crops to growers worldwide. There is immediate need for efficacious and selective monitoring tools that can detect infestations early. Previously, volatile organic compounds derived from apple were studied and a quinary chemical component blend (QB) was identified as the key SWD attractant in a blueberry orchard in the United States. This study’s aim was to determine whether previously observed QB efficacy, selectivity, and early detection levels could be attained within raspberry and cherry fields in the USA and Europe. Results demonstrated that sticky trap baited QB dispenser provided earlier SWD detection potential than the usually adopted apple cider vinegar (ACV) trap. The number of SWD captured/trap by QB baited trapping systems was significantly lower than that of the ACV trap. However, percent SWD/trap of QB baited traps was same within cherry. Lower non-target capture will save farmer/grower’s labor and time allocated to traps installation and drosophila species identification. Within the USA, SWD selectivity of QB baited liquid traps was consistently greater than sticky trap in raspberry field, suggesting that the QB dispenser can be an alternative to the standard ACV lure and that trap design could improve selectivity further.

Search for Alternative Control Strategies of Drosophila suzukii (Diptera: Drosophilidae): Laboratory Assays Using Volatile Natural Plant Compounds

Simple Summary

Adult flies of the invasive fruit pest, Drosophila suzukii, commonly known as spotted wing drosophila, showed susceptibility towards several natural plant products tested in bioassays under laboratory conditions. Depending on the compound tested, contact toxicity, modified food uptake, or reduction in numbers of eggs deposited and hatched was found. The natural plant substances thereby identified will be further assessed under field conditions and can be used to develop innovative pest control strategies.

Abstract

Drosophila suzukii (Diptera: Drosophilidae), is native to southeastern Asia and invaded Europe during the past decade. It causes serious economic damage in cherries and soft fruits. Control strategies rely on few insecticides with varying success. Due to environmental concern, the use of synthetic chemicals is restricted. Therefore, research effort is put into the quest for alternative substances applicable in chemical pest control. In laboratory assays, we tested 17 volatile plant compounds from different chemical classes for their contact toxicity, feeding modification, and oviposition repellency. Toxicity through contact with treated surfaces was evaluated after 1 h, 4 h, and 24 h; effects on food uptake were observed with capillary feeding (CAFE)—tests and oviposition trials compared egg numbers laid in raspberry medium with or without treated filter paper. Cinnamon oil and its components had the highest contact toxicity with an LC₉₀ = 2–3%, whereas lemongrass oil, its main components, and farnesol were less toxic (LC₉₀ = 7–9%), and geraniol was the least toxic. In CAFE tests, feeding stimulation was observed through 0.1% and 1% solutions of citronellol, lemongrass oil and farnesol. Cinnamon oil, cinnamaldhyde, and ethyl cinnamate were not consumed at a concentration of 1%. In the presence of citral, eugenol, and lemongrass oil, oviposition was reduced, and in the presence of limonene, no eggs were deposited. The natural products found most efficient in either bioassay will be further tested under field conditions.

Interpreting Temporal and Spatial Variation in Spotted-Wing Drosophila (Diptera: Drosophilidae) Trap Captures in Highbush Blueberries

Integrated pest management (IPM) programs for the spotted-wing drosophila Drosophila suzukii (Diptera: Drosophilidae) rely on insecticide applications to reduce adult populations and prevent fruit infestation. Although monitoring traps are used for early D. suzukii adult detection to time the start of insecticide applications, it remains unclear whether trap counts can be used to determine the efficacy of these programs and predict the risk of fruit infestation. To address this, a 2-yr study (2016-2017) was conducted in highbush blueberries in New Jersey (USA) to interpret D. suzukii trap count variation in relation to the frequency of insecticide applications and proximity to forest habitats. We also correlated trap counts with fruit infestation and used traps to determine the maximum dispersive distance traveled by D. suzukii adults within blueberry fields by using mark-release-capture studies. Using a trapping network across nine farms, we demonstrated that insecticide applications reduce D. suzukii trap counts, but this varied according to seasonality, and that traps placed closer to forest habitats within farms had higher fly counts than those placed in farm interiors. Moreover, blueberry fields that had zero fruit infestation also had predictably lower trap counts than fields with infested fruit, and the maximum dispersive distance for D. suzukii within blueberry fields was 90 m. In summary, while D. suzukii trap counts in blueberry farms could predict the frequency of insecticide applications and fruit infestation, the predictive power of our trap data was too variable across the blueberry harvest period to make it a reliable tool.

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.

Plasticity Is Key to Success of Drosophila suzukii (Diptera: Drosophilidae) Invasion

After its initial discovery in California in 2008, Drosophila suzukii Matsumura has become one of the most important invasive agricultural pest insects across climate zones in much of Asia, Europe, North America, and South America. Populations of D. suzukii have demonstrated notable behavioral and physiological plasticity, adapting to diverse environmental and climatic conditions, interspecific competition, novel food sources, and potential predators. This adaptability and plasticity have enabled rapid range expansion and diversified niche use by D. suzukii, making it a species particularly suited to changing habitats and conditions. This article reviews factors and evidence that influence plasticity in D. suzukii and promotes this species' invasiveness.