Trap designs for monitoring Drosophila suzukii (Diptera: Drosophilidae)

Methyl N,N-dimethylanthranilate and ethyl propionate: repellents effective against spotted wing drosophila, Drosophila suzukii

BACKGROUND

Spotted wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), is an economically important pest of soft and stone fruit crops. The aim of this study was to identify repellents, formulated in dispensers, which could protect crops from D. suzukii. Fourteen potential repellents were screened against summer- and winter-morph D. suzukii through electroantennography and behavioural bioassays. Repellents effective in the laboratory were tested in polytunnels to determine their efficacy in reducing catches in fruit-baited traps. Further trials of three potential repellents were conducted to determine the distances over which repellent dispensers could reduce D. suzukii emergence in a strawberry crop.

RESULTS

All 14 chemicals screened were detected by the antennae of both D. suzukii morphs. Hexyl acetate and geosmin both elicited a significantly greater corrected EAG response in summer morphs than winter morphs. Summer-morph D. suzukii were repelled by butyl acetate, ethyl propionate, methyl N,N-dimethyl anthranilate, geosmin, methyl salicylate, DEET and benzaldehyde at one or more doses test in laboratory bioassays. Winter morphs were repelled by ethyl propionate, methyl anthranilate, methyl N,N-dimethyl anthranilate, DEET, benzaldehyde and butyl anthranilate at one or more of the doses tested in the laboratory. Ethyl propionate, methyl N,N-dimethylanthranilate and benzaldehyde repelled both morphs from fruit-baited traps in polytunnel trapping trials. Ethyl propionate and methyl N,N-dimethylanthranilate reduced emergence of D. suzukii in a strawberry crop over 3-5 m.

CONCLUSIONS

Ethyl propionate and methyl N,N-dimethylanthranilate may protect strawberry crops against D. suzukii. Future work should test these repellents in combination with attractants in a 'push-pull' strategy. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Visual stimulus brightness influences the efficiency of attractant-baited traps for catching Drosophila suzukii Matsumura (Diptera: Drosophilidae)

Drosophila suzukii (Matsumura) is an exotic pest of economic importance that affects several soft-skinned fruits in Mexico. Previously, we found that yellow or yellow-green rectangular cards inside a transparent trap baited with attractants improved D. suzukii capture. In this study, we evaluated the influence of rectangular cards with different yellow shades inside a transparent multi-hole trap baited with apple cider vinegar (ACV) on D. suzukii capture in the field. Second, we tested whether ACV-baited traps with cards of other geometric shapes affected D. suzukii catches compared to traps with rectangular cards. Third, we evaluated the effects of commercial lures combined with a more efficient visual stimulus from previous experiments on trapping D. suzukii flies. We found that ACV-baited traps plus a yellow-shaded rectangle card with 67% reflectance at a 549.74 nm dominant wavelength captured more flies than ACV-baited traps with yellow rectangle cards with a higher reflectance. Overall, ACV-baited traps with rectangles and squares caught more flies than did ACV-baited traps without visual stimuli. The traps baited with SuzukiiLURE-Max, ACV and Z-Kinol plus yellow rectangles caught 57, 70 and 101% more flies, respectively, than the traps baited with the lure but without a visual stimulus.

Comparison of multimodal attract-and-kill formulations for managing Drosophila suzukii: Behavioral and lethal effects

Attract-and-kill (A&K) is a potential alternative control tactic for managing the invasive spotted-wing drosophila, Drosophila suzukii Matsumura. Here, we compared the efficacy of two novel A&K formulations based on proprietary blends-ACTTRA SWD OR1 (henceforth OR1) and ACTTRA SWD TD (henceforth TD)-in managing D. suzukii. Using two-choice bioassays, we compared OR1 and TD for their relative attractiveness to adult D. suzukii. Additionally, we tested how the addition of (1) a red dye (visual cue) and (2) the insecticide spinosad (Entrust™) to the OR1 and TD formulations influenced the attraction of adult D. suzukii in the presence of blueberry fruits. Finally, complementary laboratory efficacy (no-choice) bioassays were conducted to assess the mortality of adult D. suzukii exposed to OR1 and TD. A direct comparison between TD and OR1 formulations indicated the TD formulation was ~8 times more attractive than OR1. Adding a red dye to the TD or OR1 formulation did not significantly alter the attraction or mortality of adult D. suzukii compared to the formulation without a dye. Similarly, irrespective of dye status, adding spinosad to either the TD or OR1 formulation did not alter the adult D. suzukii behavioral response to these formulations but resulted in significantly higher D. suzukii mortality. Overall, the TD formulations resulted in significantly higher, or at least comparable, mortality to the OR1 formulations. In summary, our laboratory results demonstrated the higher efficacy of a TD-based A&K product in managing D. suzukii over its well-tested predecessor, the OR1 formulation, confirming its potential as a new behavioral tactic against this pest.

Establishment and Expansion Scenario of Drosophila suzukii (Diptera: Drosophilidae) in Central Brazil

Drosophila suzukii Matsumura (Diptera: Drosophilidae), also known as spotted wing drosophila (SWD), is an important pest that damages various wild and cultivated soft fruits worldwide, especially in the Northern Hemisphere. In Brazil, it occurs mainly in the subtropical climates of the southern and southeastern regions. However, SWD has also been sporadically found in the central region of the country in the natural vegetation of the tropical Brazilian Savanna. In this study, we investigated the occurrence of SWD at the northern limit of its range in South America - the central region of Brazil - by monitoring an established drosophilid community in an orchard located in the Brazilian Federal District. We also investigated the current geographical distribution of this pest in Brazil and its potential geographical distribution using species distribution models under two different future shared socioeconomic pathways scenarios (2040 and 2060, optimist and pessimist). Twenty drosophilid species were detected among the 6,396 captured specimens, most of which are exotic in the Neotropical region. The fly community greatly fluctuated throughout the year, and the highest abundance of SWD (3.5% relative abundance and 1.38 flies/trap/day) was recorded in April during the rainy season. Potential distribution models indicate that suitable areas for SWD spread will decrease in the south and southeast but increase in the central region of Brazil. We recommend continuous SWD monitoring and improving bioclimatic forecast models for mitigating damage to local fruit production.

Optimizing a rapid LAMP assay for discrimination of Drosophila suzukii (Diptera: Drosophilidae) from common drosophilids captured in monitoring traps from the Midwest, United States

Spotted-wing Drosophila, Drosophila suzukii, is an economically important pest of small fruits worldwide. Currently, the timing of management strategies relies on detection of adult flies captured in baited monitoring traps; however, identifying D. suzukii in trap catch based on morphology can be challenging for growers. DNA-based diagnostic methods such as loop-mediated isothermal amplification (LAMP) have the potential to improve D. suzukii detection. This study evaluated a LAMP assay as a diagnostic tool to discriminate between D. suzukii and closely related drosophilid species found commonly in monitoring traps in the Midwestern United States. Targeting the mitochondrial cytochrome oxidase I (COI) gene, we found the LAMP assay accurately detected D. suzukii with as little as 0.1 ng/μl of DNA at 63 °C for 50 min. Under these optimal incubation conditions, D. suzukii could be discriminated from D. affinis and D. simulans consistently, when specimens collected from liquid monitoring traps were tested independently. Compared to other DNA-based diagnostic tools for D. suzukii, LAMP offers unique benefits: DNA extraction is not required, testing occurs at one temperature in less than 1 h, and positive results are visible as a colorimetric change from pink to yellow. The LAMP assay for D. suzukii can reduce reliance on morphological identification, enhance the adoption of monitoring tools, and improve accuracy of detection. Further optimization can be conducted to evaluate the accuracy and sensitivity of results when a mixture of DNA from both D. suzukii and congener flies are tested in a single LAMP reaction.

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.

A Coordinated Sampling and Identification Methodology for Larval Parasitoids of Spotted-Wing Drosophila

We provide recommendations for sampling and identification of introduced larval parasitoids of spotted-wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae). These parasitoids are either under consideration for importation (aka classical) biological control introductions, or their adventive (presumed to have been accidentally introduced) populations have recently been discovered in North America and Europe. Within the context of the ecology of D. suzukii and its parasitoids, we discuss advantages and disadvantages of estimating larval parasitism levels using different methods, including naturally collected fruit samples and sentinel baits. For most situations, we recommend repeated sampling of naturally occurring fruit rather than using sentinel baits to monitor seasonal dynamics of host plant-Drosophila-parasitoid associations. We describe how to separate Drosophilidae puparia from host fruit material in order to accurately estimate parasitism levels and establish host-parasitoid associations. We provide instructions for identification of emerging parasitoids and include a key to the common families of parasitoids of D. suzukii. We anticipate that the guidelines for methodology and interpretation of results that we provide here will form the basis for a large, multi-research team sampling effort in the coming years to characterize the biological control and nontarget impacts of accidentally and intentionally introduced larval parasitoids of D. suzukii in several regions of the world.

Efficacy and Species Specificity of Baits and Lures for Spotted-Wing Drosophila, Drosophila suzukii (Diptera: Drosophilidae)

Monitoring is an important element in management programs for Drosophila suzukii (Matsumura), helping users to avoid prophylactic treatments. Factors such as attractiveness, sensitivity, selectivity, longevity, and ease of use must be considered when developing a trap and lure system for monitoring and thresholds. We examined various baits and lures over a 5-yr period in sweet cherry orchards in the semiarid climate of eastern Washington. Using a jar trap, the attractants were evaluated for attractiveness (maximum capture), selectivity for D. suzukii (vs. other Drosophila species), and sex ratio of captured D. suzukii. We examined the relative performance of the attractants during periods of low (≈1 D. suzukii per trap per week) and high (232 D. suzukii per trap per week) density over the course of the growing season, which usually corresponded to mid-summer and autumn temperatures, respectively. The Scentry lure was consistently the most attractive lure, capturing the highest numbers of adult D. suzukii over the series of tests, but also had the highest levels of by-catch. Recipe-based baits (yeast, wine-vinegar, and apple cider vinegar) captured fewer D. suzukii overall, although the commercial baits Dros'Attract and Suzukii Trap were comparable to the Scentry lure in late season tests. The Trécé lures were consistently the most selective of the attractants, but had generally lower D. suzukii captures. Sex ratio varied widely among and within the tests, but with no consistent pattern among the various attractants. All attractants were successful in capturing flies, and the choice of attractant depends on the constraints and goals of the user.

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.

Mass Trapping Drosophila suzukii, What Would It Take? A Two-Year Field Study on Trap Interference

Simple Summary

Drosophila suzukii is an invasive fruit fly that have became a key pest of soft-skinned fruits during the past decade. Today, the control of this pest relies strongly on broad-spectrum insecticides. Deploying attractive traps to control the pest population (mass trapping) could be part of the management strategy of D. suzukii. The present study analyses whether mass trapping with different attractants could be viable for D. suzukii control and how far traps should be maximally spaced in a grid. Traps in a grid compete for the same insects when they are spaced close enough and their radii of attraction overlap. Since the traps on the corners of a grid have fewer competing traps around than fully surrounded centre traps, the ratio of the catches in the corner traps and the centre traps indicates whether the traps are spaced close enough. By quantifying that trap interference in 4 × 4 trapping grids, it was found in this two-year field study that workable trap densities can be expected to control D. suzukii. From June onwards, synthetic lures in dry traps show equal or better results than the same traps with a reference liquid bait (apple cider vinegar).

Abstract

The invasion of Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) worldwide has disrupted existing or developing integrated pest management (IPM) programs in soft-skinned fruits. Currently, with a reliance on only broad-spectrum insecticides, there is a critical call for alternative control measures. Behavioural control is one of the pillars of IPM, and, in the present study, it is investigated whether mass trapping could be viable for D. suzukii management. By quantifying trap interference in 4 × 4 replicate trapping grids, an estimate of the attraction radius for a certain attractant and context can be obtained. Traps designed for dry trapping (no drowning solution, but a killing agent inside) and synthetic controlled released experimental lures were tested in a two-year field study. Apple cider vinegar (ACV) was included as a reference bait and trials were performed with 5, 10 and 15 m inter-trap spacings at different seasonal timings. Clear trap interference and, hence, overlapping attraction radii were observed both in spring and summer for both the synthetic lures and ACV. In early spring, ACV shows the most potential for mass trapping, however from June onwards, the experimental dry lures show equal or better results than ACV. Based on our findings, workable trap densities are deemed possible, encouraging further development of mass trapping strategies for the control of D. suzukii.

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.

Optimization of a Larval Sampling Method for Monitoring Drosophila suzukii (Diptera: Drosophilidae) in Blueberries

Managing spotted-wing drosophila, Drosophila suzukii (Matsumura), in fruit crops is complicated by the unreliability of currently available traps for monitoring adult flies, combined with the difficulty of detecting larval infestation before fruit damage is apparent. A simple method to extract larvae from fruit in liquid, strain the solution, then count them in a coffee filter was developed recently for use in integrated pest management programs. Here, we present a series of experiments conducted to improve fruit sampling by making it faster, less expensive, and more accurate. The volume of blueberries sampled (59-473 ml) did not significantly affect the detection of second and third instars, but we found that 118-ml samples were best for detecting the smallest larvae. These small instars were more detectable when berries were lightly squeezed before immersion, whereas larger instars were similarly detectable without using this step. We also found that immersing fruit for 30 min was sufficient before counting larvae, and similar numbers of larvae were found in the filter using room temperature water rather than a salt solution. The process of filtering, detection, and counting larvae took only 2-4 min per sample to process, depending on larval density. Using a microscope to count the larvae was consistently the best approach for detecting D. suzukii larvae. Based on these results, we discuss how fruit sampling can be streamlined within IPM programs, so growers and their advisors can improve control and reduce the cost of monitoring this invasive pest.

Adaptation and correlated fitness responses over two time scales in Drosophila suzukii populations evolving in different environments

The process of local adaptation involves differential changes in fitness over time across different environments. Although experimental evolution studies have extensively tested for patterns of local adaptation at a single time point, there is relatively little research that examines fitness more than once during the time course of adaptation. We allowed replicate populations of the fruit pest Drosophila suzukii to evolve in one of eight different fruit media. After five generations, populations with the highest initial levels of maladaptation had mostly gone extinct, whereas experimental populations evolving on cherry, strawberry and cranberry media had survived. We measured the fitness of each surviving population in each of the three fruit media after five and after 26 generations of evolution. After five generations, adaptation to each medium was associated with increased fitness in the two other media. This was also true after 26 generations, except when populations that evolved on cranberry medium developed on cherry medium. These results suggest that, in the theoretical framework of a fitness landscape, the fitness optima of cherry and cranberry media are the furthest apart. Our results show that studying how fitness changes across several environments and across multiple generations provides insights into the dynamics of local adaptation that would not be evident if fitness were analysed at a single point in time. By allowing a qualitative mapping of an experimental fitness landscape, our approach will improve our understanding of the ecological factors that drive the evolution of local adaptation in D. suzukii.

Olfactory Cues From Host- and Non-host Plant Odor Influence the Behavioral Responses of Adult Drosophila suzukii (Diptera: Drosophilidae) to Visual Cues

While trapping methods for Drosophila suzukii Matsumura (Diptera: Drosophilidae) have typically relied on fermentation volatiles alone or in association with a visual stimulus, the relative contribution of visual and olfactory stimuli to the food- and host-seeking behavior of D. suzukii is poorly understood. This study quantified the type of response exhibited by male and female D. suzukii to color and the effects that volatiles (fermentation, fresh fruit, and leaf) exert on the outcome. Seven-, four- and two-choice assays were used to quantify interactions between visual and olfactory cues. When no volatiles were present in a seven-choice assay, D. suzukii preferred red, black, and green pigments. Black and red were preferred when yeast odors were present, and black alone was the most attractive color when blueberry odor was present. A strawberry leaf terpenoid, β-cyclocitral, seemed to have overridden the flies' response to color. In four-choice assays, blueberry odor was more likely to interact synergistically with color than yeast or β-cyclocitral. This study demonstrates that D. suzukii modulates the response to multimodal sensory modalities (vision and olfaction) depending, to some extent, on the type of olfactory stimuli. Our findings also provide insight into the relative importance of vision as a function of odor quality in this invasive species.

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.

The attractant, but not the trap design, affects the capture of Drosophila suzukii in berry crops

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is recognized as an invasive pest in Europe and North America. In Mexico, it is one of the main insect pests of soft-skinned fruits such as blueberries, strawberries, raspberries, blackberries, plums, and guava. Previous studies have shown that D. suzukii uses visual and chemical cues during host plant searching. This knowledge has been used to develop traps and attractants for monitoring D. suzukii. In this study, five trap designs were evaluated to monitor D. suzukii under field conditions. Traps were baited with SuzukiiTrap®, Z-Kinol, an attractant based on acetoin and methionol, or apple cider vinegar (ACV) enriched with 10% ethanol (EtOH) with the synergistic action of carbon dioxide (CO2). Our results suggested that the attractant was the determining factor in capturing D. suzukii, while trap design seemed to play a modest role. We found that traps baited with Z-Kinol captured the highest number of D. suzukii compared to that caught by traps baited with SuzukiiTrap®, or ACV + EtOH + CO2. The highest catch numbers occurred in blackberry, followed by strawberry, raspberry, and blueberry. Traps captured more females than males. The results obtained may be useful for monitoring D. suzukii populations in Mexico and elsewhere, particularly in states where soft fruit crops are a component of agricultural activities.

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.

The Presence and Accessibility of Competitive Resources Affect Trapping Efficiency of Spotted-Wing Drosophila (Diptera: Drosophilidae)

Spotted-wing drosophila (Drosophila suzukii, (Matsumura)) is an invasive vinegar fly that has become a serious threat to soft fruit crops. Monitoring for this pest is typically performed using drowning traps baited with live yeast cultures or fermentation volatile blends. Trapping programs using these compounds provide highly variable results across production systems, geographic regions, and growing seasons. Trap competition with fruit is one hypothesis for this inconsistency. This study evaluated the trapping efficiency of yeast and wine baits in the presence and absence of small quantities of host fruits in two binary-choice laboratory experiments. The first experiment evaluated trap capture in clear 946-ml traps with easily accessible water, apple pomace, blueberry, raspberry, strawberry, cherry, or grape as competitive influences. The second experiment evaluated the same competitors, but they were made less accessible. Recapture of flies in arenas containing competitive fruit was reduced by 64-88% when fruit was 'accessible' and from 0 to 51% when it was 'inaccessible' compared with arenas containing a water competitor. All fruit types provided statistically similar levels of trap interference. In the first experiment, yeast captured more flies compared with wine, whereas in the second experiment, wine captured more flies than yeast. Our results support the hypothesis that the presence of fruit or other reproductive resources will reduce trap captures and that this reduction is likely mediated by the relative accessibility of the fruit versus the trap. Thus, attempts to develop population estimates based on traps should incorporate fruit availability/accessibility.

Effect of Visual Cues and a Fermentation-Based Attractant Blend on Trap Catch of Two Invasive Drosophila Flies in Berry Crops in Mexico

Drosophila suzukii (Matsumura) and Zaprionus indianus (Gupta) (Diptera: Drosophilidae) are invasive pests of economic importance worldwide. This study was undertaken as a first step to investigate the interaction between visual and chemical cues on the captures of D. suzukii and Z. indianus under field conditions. Specifically, we evaluated the effect of color cardboards and their combinations on the capture of these drosophilids by attractant-baited multihole traps in blackberry and blueberry crops. Color had a significant effect on the captures of D. suzukii and Z. indianus by attractant-baited traps in both crops. Overall, attractant-baited traps with yellow and yellow + green cards captured the highest number of flies compared to attractant-baited traps using cards of other colors or without cards. Multihole traps without attractant and color cardboards caught very few flies of both species. In general, more females than male D. suzukii were captured, but no sexual differences were found in the captures of Z. indianus. The results obtained will be useful for the development of a monitoring or mass trapping system for the management of D. suzukii and Z. indianuspopulations in Mexico.

Tunnel entries and a killing agent uncover the importance of fly retention in Drosophila suzukii traps

BACKGROUND

Spotted wing drosophila (SWD), Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), is a pest of stone and small fruits causing considerable economic losses. Current management strategies rely primarily on calendar-based spraying, owing to the poor relationship between monitoring data and damage levels, and the lack of success of mass-trapping tools. The aim of this study was to evaluate different trap models for SWD, with an emphasis on their fly-retention capacity. To this end, we examined and quantified the added value of two fly-retaining trap features; tunnel entries to impede escape and an insecticide-coated inner surface as a killing agent.

RESULTS

An insecticide-coated inner surface resulted in significantly higher trap retention after 24 h in the laboratory (4.9- to 7.4-fold greater, depending on trap type) compared to a noncoated trap. Trapping efficacy was significantly improved in field trials by such a killing agent in the trap (1.2- to 4.5-fold greater). Tunnel entries significantly improved trap retention in the laboratory and field (by 1.5-fold).

CONCLUSION

The outcomes of this study clearly reveal the substantial impact of the fly-retention capacity of SWD traps on their overall capture performances. It was demonstrated for the first time that an insecticide-coated inner surface as a killing agent significantly improves trap efficacy for SWD. This finding can readily be implemented in any trap model to improve monitoring and mass trapping of SWD. Also tunnel entries were shown to have a significant influence on the fly retention and, hence, substantially enhance trapping efficacy.

Agricultural-Grade Apple Cider Vinegar Is Remarkably Attractive to Drosophila suzukii (Diptera: Drosophiliadae) in Mexico

Due to its availability and low cost, apple cider vinegar (ACV) is a frequently used as an attractant for monitoring the invasive spotted wing drosophila, Drosophila suzukii. In laboratory cage experiments, the attraction of ACV alone was compared with ACV in mixtures with different concentrations of acetic acid, propionic acid, different hydrolyzed proteins, synthetic fruit flavors (strawberry, blackberry and apple) and the addition of fruit nectars (grape, pineapple and apple). The addition of 5% apple nectar to ACV significantly increased fly captures, whereas other combinations were similar to or less attractive than ACV alone. Apple flavored vinegar was not attractive to flies. Captures did not vary significantly among the brands of ACV commonly sold in Mexico, except for one poorly-performing brand, but cup traps baited with an agricultural-grade ACV unfit for human consumption captured approximately two-fold more flies than the commercial attractants Suzukii Trap, Suzukii Trap Max Captures or ACV alone in cage experiments. Field trials performed in polytunnels planted with raspberry crops in Mexico resulted in two-fold to ten-fold higher numbers of D. suzukii captured by the agricultural-grade ACV compared to Droskidrink (a mixture of ACV, red wine and sugar), Suzukii Trap, Suzukii Trap Max Captures or edible grade ACV alone. The species selectivity of the agricultural grade ACV was similar to that of other attractants tested. Agricultural-grade ACV also captured higher numbers of female than male flies in field trials. We conclude that the remarkably high attractiveness and low cost of agricultural-grade ACV makes it a useful tool for monitoring D. suzukii populations in berry crops.

Morphometric criteria to differentiate Drosophila suzukii (Diptera: Drosophilidae) seasonal morphs

Temperate insect species often enter diapause in preparation for overwintering. One such species is the invasive vinegar fly, Drosophila suzukii (Matsumura), which has seasonal polymorphisms, considered winter and summer morphs. To date, the morphs have been differentiated by color and size with winter morphs typically being darker and larger compared to summer morphs. ‘Dark’ and ‘large’ are subjective, however, and standardizing an identification process can ensure that the morph of interest is being accurately characterized. The goal of our research was to investigate a quantitative method to distinguish between D. suzukii morphs based on body and wing size. We reared winter and summer morph D. suzukii in the laboratory using standard procedures, and measured wing length, wing width, and hind tibia length. Additionally, we collected field D. suzukii to document the seasonal phenology of the morphs in Minnesota based on our model’s cutoff criteria. A classification and regression tree analysis were used to determine which metrics would be best for predicting field-caught D. suzukii morphs. Using laboratory-reared flies as our known morphs for the training data in the classification model we developed classification trees based on wing length and the ratio of wing length to hind tibia length. The frequency of winter and summer morphs present in the field varied based on which classification tree was used. Nevertheless, we suggest ratio of wing length to hind tibia length as the most robust criteria for differentiating D. suzukii morphs because the ratio accounts for the size variability between laboratory-reared and field-caught flies and the error rate of misclassification is reduced to 0.01 for males. The results from this work can aid in future D. suzukii research by allowing scientists to objectively differentiate the morphs, and thereby improve our understanding of the biology and phenology of seasonal morph dynamics.

Mass-Rearing of Drosophila suzukii for Sterile Insect Technique Application: Evaluation of Two Oviposition Systems

Drosophila suzukii (Diptera: Drosophilidae) is an invasive pest of a wide range of commercial soft-skinned fruits. To date, most management tactics are based on spraying of conventional and/or organic insecticides, baited traps, and netting exclusion. Interest has been expressed in using the sterile insect technique (SIT) as part of area-wide integrated pest management (AW-IPM) programs to control D. suzukii infestations. Mass-rearing protocols are one of the prerequisites for successful implementation of the SIT. To establish mass-rearing methods for this species, two different egg-collection systems were developed and compared with respect to the number of eggs produced, egg viability, pupa and adult recovery, adult emergence rate, and flight ability. Female flies kept in cages equipped with a wax panel produced significantly more eggs with higher viability and adult emergence rate, as compared to the netted oviposition system. The wax panel system was also more practical and less laborious regarding the collection of eggs. Furthermore, the wax panel oviposition system can be adapted to any size or design of an adult cage. In conclusion, this system bears great promise as an effective system for the mass production of D. suzukii for SIT.

Color preference of the spotted wing Drosophila, Drosophila suzukii

Drosophila suzukii Matsumura (Diptera: Drosophilidae) is a significant invasive pest in soft-skin fruits and berries in Asia, Europe, and North and South America. Many herbivorous insects use multiple cues for host selection, particularly olfactory and visual stimuli. The visual system of closely-related Drosophila melanogaster is well-documented, expressing strong sensitivity to short-wavelength colors (ultraviolet to green) and only limited sensitivity to long-wavelength colors (red to infrared). Our results suggest that D. suzukii have limited ability to distinguish red consistent with visual sensitivity range within the melanogaster subgroup. We propose that color contrast rather than color appearance may be of greater importance in orientation and attraction. We propose that differences in reflectance between light wavelengths important for color opponency are key to color discrimination to provide color contrast between foreground and background, as occurs between fruit and foliage, during host-finding.

Evaluation of Monitoring Traps and Lures for Drosophila suzukii (Diptera: Drosophilidae) in Berry Plantings in Florida

Drosophila suzukii (Diptera: Drosophilidae) is an invasive insect pest that was detected in Florida in August 2009 in Hillsborough County. Very limited information is available for berry growers to properly detect and monitor this serious pest in southern highbush blueberry (hybrids of Vaccinium corymbosum L. × V. darrowi Camp), rabbiteye blueberry (Vaccinium virgatum L.), and blackberry (Rubus fruticosus L.) production systems. We compared several D. suzukii traps and lures/baits at two sites in Florida. The traps evaluated included Trécé, Scentry, and a standard homemade cup trap. These traps were compared with various baits and lures, including Trécé lure, Scentry lure, yeast bait, and Suzukii trap, under Florida production systems. Early detection is important to develop an effective monitoring system so management action can be taken before economic damage occurs. Data were recorded as overall trends, as well as in 4–5 trapping periods from early to late season. Overall, the Scentry trap baited with Scentry lure, the Trécé trap baited with Trécé lure + yeast, and the Trécé trap baited with Scentry lure were the best performing traps. Yeast-based traps were also attractive to D. suzukii early in the season, but they did not provide consistent captures as the season progressed. The Scentry trap with yeast bait, the Scentry trap with Scentry lure, the Trécé trap with Trécé lure + yeast bait, and a cup trap with yeast bait caught most of the flies during the first trapping period in 2015 and 2016 in the rabbiteye blueberry. In the southern highbush blueberry, the population of D. suzukii was much lower than in the rabbiteye blueberry planting, and the Scentry trap with Scentry lure captured the highest number of flies during the first trapping period in 2016. In the blackberry, the Scentry trap with Scentry lure numerically had the highest captures during the first trapping period, but this was not significantly different from the cup trap with yeast bait, the Trécé trap baited with Suzukii trap, and the Trécé trap with Trécé lure. Overall, the Scentry trap with Scentry lure was the most consistent trap that captured D. suzukii flies throughout the season in the three production systems—rabbiteye blueberry, southern highbush blueberry, and blackberry. Growers in low pressure systems that are similar to Florida can use the Scentry trap with Scentry lure to monitor D. suzukii populations.

Oviposition Preference and Larval Performance of Drosophila suzukii (Diptera: Drosophilidae), Spotted-Wing Drosophila: Effects of Fruit Identity and Composition

A better understanding of the factors affecting host plant use by spotted-wing drosophila (Drosophila suzukii) could aid in the development of efficient management tools and practices to control this pest. Here, proxies of both preference (maternal oviposition behavior) and performance (adult emergence) were evaluated for 12 different fruits in the form of purees. The effect of the chemical composition of the fruits on preference and performance traits was then estimated. We synthesized the literature to interpret our findings in the light of previous studies that measured oviposition preference and larval performance of D. suzukii. We show that fruit identity influences different parts of the life cycle, including oviposition preference under both choice and no-choice conditions, emergence rate, development time, and number of emerging adults. Blackcurrant was always among the most preferred fruit we used, while grape and tomato were the least preferred fruits. Larvae performed better in cranberry, raspberry, strawberry, and cherry than in the other fruits tested. We found that fruit chemical compounds can explain part of the effect of fruit on D. suzukii traits. In particular, oviposition preference under choice conditions was strongly influenced by fruit phosphorus content. In general, the consensus across studies is that raspberry, blackberry, and strawberry are among the best hosts while blackcurrant, grape and rose hips are poor hosts. Our results generally confirm this view but also suggest that oviposition preferences do not necessarily match larval performances. We discuss opportunities to use our results to develop new approaches for pest management.

Varietal and Developmental Susceptibility of Tart Cherry (Rosales: Rosaceae) to Drosophila suzukii (Diptera: Drosophilidae)

Drosophila suzukii (Matsumura) is an invasive species of vinegar fly that infests soft-skinned and stone fruits. Since its first detection in the United States, D. suzukii has become a prominent economic threat in fruit crop industries, particularly affecting caneberry and sweet cherry growers. This study examined the susceptibility of tart cherries (Prunus cerasus) to D. suzukii and sampled for larvae and adult D. suzukii during the tart cherry growing season. Four tart cherry cultivars (Montmorency, Balaton, Carmine Jewel, and Kántorjánosi) were tested at three different ripeness stages (unripe, ripening, and ripe), in no-choice laboratory bio-assays. Field monitoring and sampling revealed that first adult D. suzukii detection occurred on 16 June, and first field larval D. suzukii detection occurred on 28 July. Adult D. suzukii populations increased through late August, and high numbers of adults overlapped with the tart cherry harvest. Lab assays indicated that tart cherry cultivars generally became more susceptible to D. suzukii as they ripened. As the fruit developed, °Brix (sugar content) increased and firmness generally decreased. Tart cherry °Brix and firmness were not correlated with the number of D. suzukii eggs per gram of fruit, but showed a significant interaction effect with the number of larvae and adults per gram of fruit. This study shows that tart cherries are largely not susceptible to D. suzukii when unripe and become susceptible as soon as the fruits change color, suggesting that fruits should be protected as soon as they begin to ripen and D. suzukii populations begin to rise.

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.

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.

A Novel Passive Sampling Technique for Collecting Adult Necrophilous Insects Arriving at Neonate Pig Carcasses

Neonate pigs have been used as decomposition models in experimental forensic entomology studies. Their small size, however, poses challenges to traditional sampling methods of necrophilous insects, like the sweep net, the most commonly used sampling method in forensic entomology research and practice. Previous research experimentally demonstrated the potential for sticky traps as an effective sampling method for collecting necrophilous insects from neonate pigs. While sticky traps effectively sampled fly diversity from the pigs, they shared with the sweep net low sample diversity and abundance, particularly of necrophilous beetles. Motivated by chemosensory host-finding of necrophilous insects and the architecture of carrion-mimicking thermogenic flowers, we developed a 'vented-chamber' method and optimized its design experimentally. In this approach, a neonate pig was transiently enclosed in a chamber. The decomposition process thermally convected the natural decomposition odors in the headspace above the pig toward a pair of sticky traps. The vented-chamber method collected significantly more necrophilous flies, representing a greater diversity, than the sweep net. Nevertheless, this approach caught few beetles, and hand collections must be used as well to most effectively sample beetle diversity.

The Distance Between Forests and Crops Affects the Abundance of Drosophila suzukii During Fruit Ripening, But Not During Harvest

Drosophila suzukii (Matsumura; Diptera: Drosophilidae) is an invasive pest with the ability to reproduce not only in various soft fruit crops, but also in numerous wild hosts. Forests and forest edges harbor many wild hosts, provide suitable microclimatic conditions and are therefore thought to enhance the abundance of D. suzukii. Although the comprehension of pest activity based on specific landscape elements is important to implement efficient management strategies, knowledge of how forests affect the abundance of D. suzukii in nearby crops is very limited. We conducted a monitoring study with liquid baited traps across different crops at different distance from the forests. During fruit ripening, more flies were captured in crops closer to forests (22.21 % decrease per 500 m distance), whereas there was no significant relationship during harvest. Since color can affect the efficiency of D. suzukii traps, we have used traps either with a red or black lid. Acquired data suggest that traps with black lids capture significantly more flies than traps with red lids. We provide a quantitative estimation of how and when distance from adjacent forests affects the abundance of D. suzukii in crop fields. Our results can help consultants and farmers to estimate the pest pressure of D. suzukii in crop fields near forested, noncrop areas and to implement appropriate control strategies when D. suzukii populations increase and fruit becomes susceptible to infestation.

Effect of Color and Contrast of Highbush Blueberries to Host-Finding Behavior by Drosophila suzukii (Diptera: Drosophilidae)

Drosophila suzukii Matsumara (Diptera: Drosophilidae) has become a serious pest in soft-skin fruits and berries, infesting both ripe and ripening fruits. Crop damage in highbush blueberry has been particularly severe. During blueberry fruit development, fruits of various degrees of ripeness are present simultaneously. In addition, foliage color changes as the season progresses. We investigated the influence of blueberry fruit and leaf color on host-finding behavior in D. suzukii. Opposing shifts between reflectance spectra of ripening fruits and senescing leaves increased contrast between ripe fruit and senesced foliage. Developmental changes in contrast between fruit color and leaf color may act as a visual contextual cue in finding suitable host fruits. Opposing shifts in reflectance spectra of ripening fruits and senescing leaves increased the contrast between ripe fruit and senesced foliage. These opposing changes in color may contribute to the attractiveness of blueberry fruit as a late season host for D. suzukii.

Spotted Wing Drosophila in Sweet Cherry Orchards in Relation to Forest Characteristics, Bycatch, and Resource Availability

Forest vegetation is essential for the population development of the spotted wing drosophila (SWD). Yet, little is known of how the structure of surrounding forest areas influence the abundance of SWD within orchards. In this work, we use data from a field trial at five sites in Switzerland to analyse the relationship between the extent of forest area, its edge density, and its distance from the orchard with the occurrence of SWD in sweet cherry orchards in a Bayesian hierarchical model. Availability of cherries and bycatch were also included in the model to account for effects of resource availability and trap attractiveness, respectively. For all main effects and their interactions, we accounted for potential temporal changes by adding interactions with time. We found that the closer an orchard was to a forest, the more SWD were trapped within the orchard. However, the interaction of forest proximity with forest area caused a disproportionate decrease of SWD catches. Also, the within orchard variables, trap catches of other drosophilid flies and resource availability affected SWD trap catches, but their relation changed in the course of the experiment. The findings imply that reducing SWD occurrence in orchards and other crop fields requires not only the consideration of processes outside and within the host crop field, but also of temporally changing relationships between SWD and other factors.

Development of a Novel Dry, Sticky Trap Design Incorporating Visual Cues for Drosophila suzukii (Diptera: Drosophilidae)

Drosophila suzukii Matsumura (Diptera: Drosophilidae) is currently one of the most serious invasive pests for berry crops and cherries worldwide. The development of an effective monitoring trap that is reliable at detecting small populations to guide management decisions is greatly needed. To develop a novel dry trapping system, D. suzukii were trapped under field conditions in cherry orchards and raspberry high tunnels using various baited dry trap designs that were compared with the currently available deli-cup style traps that utilize a liquid bait or drowning solution. In a test in cherry orchards, red panel and combination yellow panel plus red sphere traps captured significantly more flies than yellow panel traps when all were baited with a Scentry lure. In a separate test in cherry, red sphere traps with the Scentry lure captured significantly more flies than the deli-cup traps with the Scentry lure or with the yeast sugar bait, and red panel traps with the Scentry lure captured significantly more flies than deli-cup traps with the Scentry lure. In raspberry high tunnels, red sphere traps with the Scentry lure captured significantly more flies than deli-cup traps with the Scentry lure. Red traps baited with the same lure as clear deli-cup traps consistently captured more D. suzukii, demonstrating that traps integrating a visual cue in combination with an olfactory cue are superior tools for monitoring D. suzukii. A dry trap requires less labor and maintenance than cup traps containing a liquid, improving the ease of use of D. suzukii monitoring traps.

Advances in the Chemical Ecology of the Spotted Wing Drosophila (Drosophila suzukii) and its Applications

Significant progress has been made in understanding the cues involved in the host and mate seeking behaviors of spotted wing drosophila, Drosophila suzukii (Matsumura). This insect pest has been discovered in many fruit growing regions around the world since 2008. Unlike closely related Drosophila species, D. suzukii attacks fresh fruit and has become a severe pest of soft fruits including strawberry, cherry, blackberry, blueberry, raspberry, and may pose a threat to grapes. Prior to 2008, little was known about the courtship and host-seeking behaviors or chemical ecology of this pest. Since then, researchers have gained a better understanding of D. suzukii attraction to specific odors from fermentation, yeast, fruit, and leaf sources, and the visual cues that elicit long-range attraction. Several compounds have also been identified that elicit aversive behaviors in adult D. suzukii flies. Progress has been made in identifying the constituent compounds from these odor sources that elicit D. suzukii antennal responses in electrophysiological assays. Commercial lures based on food volatiles have been developed to attract D. suzukii using these components and efforts have been made to improve trap designs for monitoring this pest under field conditions. However, current food-based lures and trap technologies are not expected to be specific to D. suzukii and thus capture large numbers of non-target drosophilids. Attractive and aversive compounds are being evaluated for monitoring, mass trapping, and for the development of attract-and-kill and push-pull techniques to manage D. suzukii populations. This review outlines presently available research on the chemical ecology of D. suzukii and discusses areas for future research.

Comparison of Commercial Lures and Food Baits for Early Detection of Fruit Infestation Risk by Drosophila suzukii (Diptera: Drosophilidae)

Drosophila suzukii (Matsumura; Diptera: Drosophilidae) is one of the most serious invasive pests of berries and cherries worldwide. Several adult monitoring systems are available to time foliar application of insecticides with the expectation of detecting the presence of D. suzukii before they infest susceptible crops. We tested this by comparing four different trapping systems based on two homemade baits, apple cider vinegar (ACV) or fermenting dough, and two fermentation volatile-based commercial lures, Scentry and Trécé. Traps baited with dough or Scentry captured more D. suzukii than traps baited with ACV or Trécé in blueberries and traps baited with Trécé in raspberries. In blueberries, traps baited with Scentry, Trécé and dough provided 11-21 d of warning prior to first detection of fruit infestation. However, these traps were not as effective in summer floricane raspberries. The Scentry lure baited traps detected D. suzukii on the same week as the first detection of fruit infestation and other trapping systems detected the fly 4 to 11 d after the first detection, suggesting the need for an improved D. suzukii detection system in raspberries. Both synthetic lures (Scentry and Trécé) were significantly more selective for D. suzukii than dough bait, although the selectivity of all four tested lures/baits were relatively low at <20%. Our results suggest that in locations where D. suzukii adults are not trapped in late winter and spring, adult monitoring of D. suzukii using a sensitive trapping system may provide early warning of pending infestation risk thereby potentially reducing unnecessary insecticide applications.

Trapping system comparisons for and factors affecting populations of Drosophila suzukii and Zaprionus indianus in winter-grown strawberry

BACKGROUND

Drosophila suzukii (Matsumura) is a major fruit pest in temperate regions worldwide, but in subtropical Florida, winter-grown strawberries have not been severely affected. Zaprionus indianus Gupta is another invasive drosophilid species and a pest of some tropical fruits. To improve monitoring, trapping systems for D. suzukii and Z. indianus were tested. Morphology, ovarian status and the suitability and availability of non-crop hosts as possible D. suzukii population-limiting factors were assessed.

RESULTS

Traps with commercial attractants captured more D. suzukii but fewer Z. indianus than those with a homemade mixture. In central and northern Florida, < 10% and 30-80% of D. suzukii, respectively, exhibited darker, winter morph coloration, and 55-75% of females from central Florida were carrying mature and/or immature eggs. Adult D. suzukii were reared from fruits of two of 28 potential hosts: elderberry (Sambucus nigra) and nightshade (Solanum americanum). Nightshade, but not elderberry, was common on field perimeters (21 and six of 36 fields, respectively). Traps placed in wooded or partially wooded field edges yielded the most D. suzukii.

CONCLUSION

Florida strawberry is at risk of D. suzukii infestation, as flies were captured throughout the growing season. However, fly captures remained relatively low, peaking at 1.5 flies per trap per day. In central Florida, the low availability and suitability of non-crop hosts likely limit population growth. The finding of few flies in northern Florida may additionally be attributable to a greater proportion of flies displaying winter morph coloration than in central Florida. © 2018 Society of Chemical Industry.

Improved capture of Drosophila suzukii by a trap baited with two attractants in the same device

The improvement of trap-lure combinations is an important part of integrated pest management programs that involve monitoring pests for timely insecticide applications, or for their use in control strategies such as mass trapping or bait stations. In this study improvements in the capture of Drosophila suzukii were not observed following the inclusion of different color stimuli with respect to a red-black stripe cup trap. This red-black stripe trap with a hemispherical dome-shaped lid had a significantly improved physical retention of flies compared to traps fitted with a flat lid. Retention was further improved when an additional tube device, which could be baited with a supplemental attractant, was introduced through the dome-shaped lid. Under laboratory conditions, this trap, in which apple cider vinegar + 10% ethanol was present as the drowning solution and the additional tube device was baited with a fermenting mixture of sugar and yeast, was significantly more effective in catching D. suzukii flies than other conventional attractants or a commercial lure. The capture rate of this trap-lure combination remained higher than that of a commercial lure, even after 20 days of use under laboratory conditions. In a guava orchard this trap was 15-fold more effective in catching D. suzukii flies than similar traps baited with apple cider vinegar alone, 4 to 7 fold more effective than similar traps baited with a commercial lure, and 1.7-fold more effective than a fermenting mixture of yeasts and wheat flour. In commercial blackberry orchards, this trap was 6-fold more effective in trapping D. suzukii flies than the clear trap baited with apple cider vinegar used by growers. The efficacy of this trap presents a promising line of future research for monitoring and control of D. suzukii and likely other drosophilid pests.

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.

Evaluation of Food-Based Attractants for Drosophila suzukii (Diptera: Drosophilidae)

The Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is a highly invasive species attacking a wide range of ripening soft-skinned fruits. A series of laboratory choice tests were conducted to determine whether different levels of rice vinegar affected attraction of Merlot wine to D. suzukii, as well as to compare attractiveness of two common fermentation food baits: wine-vinegar and yeast-sugar water mixtures. The relative attraction of various combinations was used to develop a bait whose effectiveness was tested in the field. In laboratory choice experiments, wine-vinegar (80:20, v:v, hereafter referred to as wine) was more preferred over a yeast-sugar water mixture (hereafter referred to as yeast) by D. suzukii. Combination baits, either a mixture of wine and yeast or a mixture of wine and a supernatant from the yeast (comboS), were significantly more attractive than each product alone. The two combination baits were equally attractive to D. suzukii, so were the yeast and its supernatant, suggesting that yeast supernatant could be used as a replacement for the yeast-sugar mixture currently used for trapping D. suzukii. The additive effect between wine and yeast supernatant in the field was not as profound as observed in the laboratory. In the field trial, numerically more male and female D. suzukii were captured in traps baited with comboS than those baited with the wine or yeast alone; however, significant differences were only found between the comboS and wine or between the comboS and yeast in some weeks over the period of the experiment.

Evaluation of Attractants for Monitoring Drosophila suzukii (Diptera: Drosophilidae)

Drosophila suzukii Matsumura is an economically important pest of soft and small fruit crops. Unlike other drosophilid flies, D. suzukii is capable of infesting ripe and partially ripe fruit, which poses a significant pest management challenge, as there is no tolerance for infested or damaged fruit in the marketplace. As a result, producers in many regions rely on calendar-scheduled insecticide applications for D. suzukii management. In order to develop an integrated pest management approach, better tools for monitoring adult fly populations are needed. Over two growing seasons in southern Ontario, we evaluated three commercial (Pherocon SWD dual-lure, Suzukii Trap, and Scentry Lure) and two homemade baits (apple cider vinegar and yeast + sugar water) for their ability to capture D. suzukii in raspberry and highbush blueberry fields. In general, commercial attractants captured D. suzukii earlier in the growing season and in greater numbers, with fewer nontarget captures, compared with homemade baits. Scentry Lure tended to perform better than other attractants, capturing D. suzukii earlier and in larger numbers during peak harvest. Pherocon SWD dual-lure was highly specific to D. suzukii. The combination of Scentry Lure with Suzukii Trap had possible synergistic effects, as numbers of D. suzukii captured to the combined treatment were more than additive. Using commercial attractants improves D. suzukii monitoring and will allow growers to improve the timing of insecticide applications with D. suzukii activity in the field.

Laboratory studies of insecticide efficacy and resistance in Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) populations from British Columbia, Canada

BACKGROUND

Spotted wing drosophila (SWD), Drosophila suzukii (Matsumura), control can be improved with better knowledge of insecticide efficacy, timing of sprays and rotations with registered products during the crop year. An efficacy bioassay was applied to study the dose response of adult laboratory-reared SWD collected from a cherry orchard in British Columbia (BC), Canada, to 11 insecticides.

RESULTS

Age- and sex-specific toxicities with the most effective insecticide, malathion, determined that older male SWD were significantly more susceptible than females. The selection for polygenic resistance to malathion using repeated exposure to sublethal concentrations with both the original and an additional blueberry-collected population of laboratory-reared SWD determined no significant difference in susceptibility after 30 generations.

CONCLUSION

Possible reasons reported in D. melanogaster studies where resistance did not occur after insecticide selection included avoidance and associated microbial complexes. The low level of malathion resistance observed in the selected SWD populations and a field-collected population is useful information in the development of insecticide resistance management programmes. © 2016 Her Majesty the Queen in Right of Canada Pest Management Science © 2016 Society of Chemical Industry.

Behavioral Responses of Drosophila suzukii (Diptera: Drosophilidae) to Visual Stimuli Under Laboratory, Semifield, and Field Conditions

Drosophila suzukii Matsumura (Diptera: Drosophilidae) is an invasive pest in North America and Europe that attacks soft-skinned ripening fruit such as raspberries, blackberries, and blueberries. Little is known regarding the specific cues D. suzukii utilizes to locate and select host fruit, and inconsistencies in trap performance indicate the need for the development of improved monitoring and management techniques for this insect. Our studies focused on identifying attractive visual cues for adult D. suzukii and incorporating these cues into a potential attract-and-kill tactic for D. suzukii management. We evaluated D. suzukii response to color, shape, and size-specific stimuli. For color, we evaluated 10.2-cm-diameter spheres painted black, red, purple, orange, green, yellow, blue, or white. Shape stimuli (254 cm³ surface area) included sphere, cube, pyramid, inverted pyramid, vertical or horizontal cylinder and were painted red. Size stimuli included red 2.5-, 10.2-, 15.2-, and 25.4-cm-diameter spheres. Trials were conducted under laboratory, semifield, and field conditions. For color, adults preferred black and red spheres to all other colors evaluated. Among shapes, there was no significant preference. For size, larger spheres captured significantly more D. suzukii compared with a small 2.5-cm-diameter sphere. Determining D. suzukii visual preference will aid in trapping and behaviorally based management programs.

Behavioral and Antennal Responses of Drosophila suzukii (Diptera: Drosophilidae) to Volatiles From Fruit Extracts

Native to Southeast Asia, the spotted wing drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), has become a serious pest of soft-skinned fruit crops since its introduction into North America and Europe in 2008. Current monitoring strategies use baits based on fermentation products; however, to date, no fruit-based volatile blends attractive to this fly have been identified. This is particularly important because females are able to cut into the epicarp of ripening fruit for oviposition. Thus, we conducted studies to: 1) investigate the behavioral responses of adult D. suzukii to volatiles from blueberry, cherry, raspberry, and strawberry fruit extracts; 2) identify the antennally active compounds from the most attractive among the tested extracts (raspberry) using gas chromatography (GC)-mass spectrometry and coupled gas chromatography -electroantennographic detection (GC-EAD); and 3) test a synthetic blend containing the EAD-active compounds identified from raspberry extract on adult attraction. In olfactometer studies, both female and male D. suzukii were attracted to all four fruit extracts. The attractiveness of the fruit extracts ranks as: raspberry ≥ strawberry > blueberry ≥ cherry. GC analyses showed that the fruit extracts emit distinct volatile compounds. In GC-EAD experiments, 11 raspberry extract volatiles consistently elicited antennal responses in D. suzukii. In choice test bioassays, a synthetic EAD-active blend attracted more D. suzukii than a blank control, but was not as attractive as the raspberry extract. To our knowledge, this is the first report of a behaviorally and antennally active blend of host fruit volatiles attractive to D. suzukii, offering promising opportunities for the development of improved monitoring and behaviourally based management tools.

Effective trapping of fruit flies with cultures of metabolically modified acetic acid bacteria

Acetoin in vinegar is an attractant to fruit flies when combined with acetic acid. To make vinegar more effective in attracting fruit flies with increased acetoin production, Komagataeibacter europaeus KGMA0119 was modified by specific gene disruption of the acetohydroxyacid isomeroreductase gene (ilvC). A previously constructed mutant lacking the putative ligand-sensing region in the leucine-responsive regulatory protein (KeLrp, encoded by Kelrp) was also used. The ilvC and Kelrp disruptants (KGMA5511 and KGMA7203, respectively) produced greater amounts of acetoin (KGMA5511, 0.11%; KGMA7203, 0.13%) than the wild-type strain KGMA0119 (0.069%). KGMA7203 produced a trace amount of isobutyric acid (0.007%), but the other strains did not. These strains produced approximately equal amounts of acetic acid (0.7%). The efficiency of fruit fly attraction was investigated with cultured Drosophila melanogaster. D. melanogaster flies (approximately 1,500) were released inside a cage (2.5 m by 2.5 m by 1.5 m) and were trapped with a device containing vinegar and a sticky sheet. The flies trapped on the sticky sheet were counted. The cell-free supernatant from KGMA7203 culture captured significantly more flies (19.36 to 36.96% of released flies) than did KGMA0119 (3.25 to 11.40%) and KGMA5511 (6.87 to 21.50%) cultures. Contrastingly, a 0.7% acetic acid solution containing acetoin (0.13%) and isobutyric acid (0.007%), which mimicked the KGMA7203 supernatant, captured significantly fewer flies (0.88 to 4.57%). Furthermore, the KGMA0119 supernatant with additional acetoin (0.13%) and isobutyric acid (0.007%) captured slightly more flies than the original KGMA0119 supernatant but fewer than the KGMA7203 supernatant, suggesting that the synergistic effects of acetic acid, acetoin, isobutyric acid, and unidentified metabolites achieved the efficient fly trapping of the KGMA7203 supernatant.