Evaluation of monitoring traps for Drosophila suzukii (Diptera: Drosophilidae) in North America

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.

Decoding attraction: Improving vine weevil monitoring by exploiting key sensory cues

BACKGROUND

Monitoring is an integral component of integrated pest management (IPM) programmes used to inform crop management decisions. Vine weevil, Otiorhynchus sulcatus F. (Coleoptera: Curculionidae), continues to cause economically significant losses in horticultural crops due to an inability to reliably detect the presence of this species before crop damage occurs. To improve vine weevil monitoring we investigated the behavioural responses of adult vine weevils to visual (monitoring tool shade/colour, height and diameter as well as the effect of monitoring tool and plant density) and olfactory (host plant and conspecifics) cues under glasshouse conditions.

RESULTS

Monitoring tool shade, height and diameter all influenced monitoring tool efficacy, with individuals exhibiting a preference for black, tall and wide monitoring tools. The total number of individuals recorded in monitoring tools increased with monitoring tool density. By contrast, plant density did not influence the number of individuals recorded in monitoring tools. Yew-baited monitoring tools retained a larger number of individuals compared to unbaited ones. Similarly, more vine weevils were recorded in monitoring tools baited with yew and conspecifics than in unbaited monitoring tools or those baited with only yew. Baiting monitoring tools with conspecifics alone did not enhance the number of vine weevils recorded in monitoring tools.

CONCLUSIONS

Our study confirms that visual and olfactory cues influence vine weevil behaviour. This provides information on key factors that influence vine weevil monitoring tool efficacy and can be used to inform the development of a new monitoring tool for this pest. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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.

Aromatic border plants in early season berries do not increase parasitism of spotted wing drosophila, Drosophila suzukii

BACKGROUND

The spotted wing drosophila, Drosophila suzukii Matsumura, is a South-East Asian vinegar fly that is a serious worldwide economic threat to the small fruit industry. Typical control consists of weekly pesticide applications, which can have nontarget effects, increase residual pesticides and lead to the development of resistance within pest populations. One potential alternate method of control is the planting of aromatic intercrops to attract the natural enemies of D. suzukii and/or repel the flies directly. We intercropped strawberry rows with flowering sweet alyssum or ryegrass-clover (control) to evaluate their efficacy at mitigating D. suzukii infestation through the attraction of two specialized larval parasitoids, Leptopilina japonica (Novkovic and Kimura) and Ganaspis brasiliensis (Ihering).

RESULTS

Our study did not demonstrate any significant effect of sweet alyssum intercropping on the infestation rate of D. suzukii in strawberries or parasitism level. However, we found that advanced sampling date and recorded numbers of D. suzukii larvae and parasitoids were positively correlated, indicating higher populations at the end of the strawberry-growing season.

CONCLUSIONS

Sweet alyssum intercrops did not reduce D. suzukii infestation rates or increase parasitism levels, likely due to low population numbers in early season berry varieties. Aromatic intercrops may be more effective for increasing pest control in later season crops. © 2022 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.

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.

Semi-Quantitative Detection of Drosophila suzukii (Diptera: Drosophilidae) From Bulk Trap Samples Using PCR Technology

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is a ubiquitous global pest of several fruit crops. Trapped adult numbers are used to monitor populations and make control decisions, but differentiating D. suzukii from other trapped Drosophila spp. is laborious. We developed a real-time PCR method for specific detection and semi-quantification of D. suzukii from trap samples. The PCR assay did not amplify DNA from 29 other Drosophilidae species tested. Drosophila suzukii was detected from ≥0.96 pg target DNA and from laboratory samples containing one D. suzukii in 2000 other Drosophila spp. flies. We tested DNA stability of one D. suzukii in 100 Drosophila spp. flies in water or ethanol at 20, 25, or 30°C for 1, 4, or 7 d. Only water at 30°C for 7 d fully impaired D. suzukii DNA detectability. Substituting mouthwash for water resulted in D. suzukii detection in all samples held for 7 d at 30°C or daily fluctuating temperatures of 33/23°C. Traps with mouthwash as a drowning liquid had D. suzukii captures equal to traps with water. A calibration curve was established using samples in mouthwash containing 1/1,000-100/1,000 D. suzukii/total Drosophila spp. flies and incubated at 25°C for 7 d. The curve had a coefficient of determination (R2) of 0.9279 between D. suzukii numbers from the PCR and the true D. suzukii numbers in samples prepared in 70% ethanol. Collecting samples in mouthwash is expected to improve detection accuracy, and the qPCR method can be a useful tool to support D. suzukii monitoring and management.

DNA Metabarcoding Enables High-Throughput Detection of Spotted Wing Drosophila (Drosophila suzukii) Within Unsorted Trap Catches

The spotted wing drosophila (Drosophila suzukii, Matsumara) is a rapidly spreading global pest of soft and stone fruit production. Due to the similarity of many of its life stages to other cosmopolitan drosophilids, surveillance for this pest is currently bottlenecked by the laborious sorting and morphological identification of large mixed trap catches. DNA metabarcoding presents an alternative high-throughput sequencing (HTS) approach for multi-species identification, which may lend itself ideally to rapid and scalable diagnostics of D. suzukii within unsorted trap samples. In this study, we compared the qualitative (identification accuracy) and quantitative (bias toward each species) performance of four metabarcoding primer pairs on D. suzukii and its close relatives. We then determined the sensitivity of a non-destructive metabarcoding assay (i.e., which retains intact specimens) by spiking whole specimens of target species into mock communities of increasing specimen number, as well as 29 field-sampled communities from a cherry and a stone fruit orchard. Metabarcoding successfully detected D. suzukii and its close relatives Drosophila subpulchrella and Drosophila biarmipes in the spiked communities with an accuracy of 96, 100, and 100% respectively, and identified a further 57 non-target arthropods collected as bycatch by D. suzukii surveillance methods in a field scenario. While the non-destructive DNA extraction retained intact voucher specimens, dropouts of single species and entire technical replicates suggests that these protocols behave more similarly to environmental DNA than homogenized tissue metabarcoding and may require increased technical replication to reliably detect low-abundance taxa. Adoption of high-throughput metabarcoding assays for screening bulk trap samples could enable a substantial increase in the geographic scale and intensity of D. suzukii surveillance, and thus likelihood of detecting a new introduction. Trap designs and surveillance protocols will, however, need to be optimized to adequately preserve specimen DNA for molecular identification.

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.

Optimising Vine Weevil, Otiorhynchus sulcatus F. (Coleoptera: Curculionidae), Monitoring Tool Design

Simple Summary

Vine weevil remains one of the most economically important insect pests of soft-fruit and ornamental crops globally. Growers currently lack effective monitoring systems to determine presence of vine weevil within crops, meaning that controls are often applied too late to prevent economic losses. Development of improved monitoring systems is currently hindered by a lack of knowledge of whether vine weevil adults select a monitoring tool based on its visual appearance. This study used paper cups as refuges to investigate the importance of colour, shape and position of entrances on monitoring tool efficacy. Results indicate that dark, tall refuges with entrances around their base were preferentially entered by adult vine weevil. This information provides the first steps towards developing improved designs for vine weevil monitoring tools.

Abstract

Vine weevil, Otiorhynchus sulcatus F. (Coleoptera: Curculionidae), is an economically important insect pest of horticultural crops. To identify an effective and reliable monitoring system for adult vine weevil, this study investigated the influence of colour, height and entrance position on the efficacy of a model monitoring tool using modified paper cups as refuges. Vine weevil preferences were determined by the number of individuals recorded within a refuge. When provided with a binary choice between black or white refuges, vine weevil adults showed a preference for black refuges. Vine weevils provided with a range of coloured refuges (blue, green, red and yellow) in addition to black and white refuges showed a preference for black and blue over the other colours and white refuges in group choice experiments. Refuge height and entrance position also influenced vine weevil behaviour with individuals exhibiting a preference for taller refuges and those with entrance openings around the refuge base. These results provide insights into refuge selection by adult vine weevils, which can be exploited to improve monitoring tool design. The importance of developing an effective monitoring tool for vine weevil adults as part of an integrated pest management programme is discussed.

Intercropping With Peppermint Increases Ground Dwelling Insect and Pollinator Abundance and Decreases Drosophila suzukii in Fruit

Intercropping can be used to reduce pest insects within agricultural systems, e.g., through deterring pests directly or by increasing habitat for their natural enemies. For example, plant produced volatile organic compounds (VOCs) can deter or confuse host-finding by insects through olfactory disruption. Drosophila suzukii is an invasive fruit fly of agricultural concern as it can lay its eggs in both ripening and fresh fruits and, uses olfactory cues to identify its wide range of host plants. Peppermint plants (Mentha × piperita) produce high levels of VOCs while growing and may, therefore, be suitable as an intercrop to reduce D. suzukii infestations in the field, as peppermint essential oil VOCs have previously been shown to deter D. suzukii in olfactory trials. We conducted a field intercropping experiment to evaluate the effectiveness of peppermint plants compared to traditional ryegrass/clover mixes in reducing D. suzukii oviposition in the field, and the effect of peppermint intercrops on other invertebrates. In the field, we monitored sentinel fruit baits weekly for D. suzukii infestation. Additionally, we monitored intercropping effects on the invertebrate community through weekly pitfall trap collection and through a pollinator point survey. We monitored for local, farm level presence of D. suzukii through apple cider vinegar traps within crop fields and along hedgerows and found high abundance of D. suzukii (>3,000 individuals trapped). Peppermint intercrops had fewer D. suzukii emerge from fruit baits and supported greater beneficial insect abundance (predators and pollinators) compared to ryegrass/clover. However, levels of D. suzukii were low across both intercrop types. Overall, we found that peppermint intercrops could be a potential aromatic intercrop used to reduce D. suzukii adult emergence from fruit compared to conventional ryegrass/clover mixes, however this trial should be replicated over multiple growing seasons, geographic locations, and host fruits. Furthermore, further study should determine the effects of the intercrop on the focal crop of interest.

Enterobacter sp. AA26 as a Protein Source in the Larval Diet of Drosophila suzukii

The Spotted-Wing Drosophila fly, Drosophila suzukii, is an invasive pest species infesting major agricultural soft fruits. Drosophila suzukii management is currently based on insecticide applications that bear major concerns regarding their efficiency, safety and environmental sustainability. The sterile insect technique (SIT) is an efficient and friendly to the environment pest control method that has been suggested for the D. suzukii population control. Successful SIT applications require mass-rearing of the strain to produce competitive and of high biological quality males that will be sterilized and consequently released in the wild. Recent studies have suggested that insect gut symbionts can be used as a protein source for Ceratitis capitata larval diet and replace the expensive brewer's yeast. In this study, we exploited Enterobacter sp. AA26 as partial and full replacement of inactive brewer's yeast in the D. suzukii larval diet and assessed several fitness parameters. Enterobacter sp. AA26 dry biomass proved to be an inadequate nutritional source in the absence of brewer's yeast and resulted in significant decrease in pupal weight, survival under food and water starvation, fecundity, and adult recovery.

Detection of Fruit Meals Within Laboratory-Raised and Field-Trapped Adult Drosophila suzukii (Diptera: Drosophilidae) Guts

The feeding habits of adult Brachycera are understudied and may provide important context for understanding invasive pest biology, as with the polyphagous small fruit pest Drosophila suzukii. We developed molecular methods to study adult D. suzukii gut content in order to understand its feeding habits. We designed and verified two primer pairs specific for either blueberries or blackberries and used a qPCR melt curve analysis to determine whether we can detect the presence or absence of berry feeding by adult flies. In a laboratory assay, the blueberry fly meal DNA can be detected for longer periods than the blackberry meal DNA. Generally, female gut contents are less variable than male gut contents. We also tested recently emerged flies that were not fed as adults but developed as larvae in either blueberries or blackberries. Some adult flies from each fruit had detectable fruit DNA in their gut, which could be due to pupal meconium feeding after emergence. Next, we aimed to test the primers in the field to develop techniques to track fruit feeding by D. suzukii in its natural field environment. First, to identify the most appropriate collection method, we determined how long we could detect fruit DNA, using previously developed primers within D. suzukii gut preserved in four types of trap fluid in the laboratory. The likelihood of detecting blackberry DNA differed by day, trap fluid, and between sexes. For the blueberry primer, the possibility of detecting blueberry DNA differed by trap fluid only. Based on those results, we used RV antifreeze with a Scentry SWD lure in field trials at two research station locations, one containing blackberries and one with blueberries. We established transects away from each fruit planting and collected up to 120 total flies at each point along transects. There were no significant differences in the number of flies containing berry DNA among collection points along the transect in both locations. These results suggest that adult flies move between crop and non-crop habitats and may not be highly dependent on fruit food resources.

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.

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.

Identification of Blackberry (Rubus fruticosus) Volatiles as Drosophila suzukii Attractants

The spotted wing drosophila, Drosophila suzukii, is an invasive pest species from Southeast Asia that was recently introduced in Europe and North America. As this fruit fly lays its eggs in ripening soft-skinned fruit, it causes great damage to a variety of crops, including cherries, blueberries, blackberries, raspberries, grapes, plums and strawberries. Consequently, there is a great demand for an effective and species-specific lure, which requires the development of successful attractants. Until now, there is no lure available that is species-specific and can detect the presence of D. suzukii before infestation. As blackberry (Rubus fruticosus) is one of the preferred host crops of D. suzukii, the volatile compounds of R. fruticosus berries are here identified and quantified using multiple headspace SPME (solid phase micro extraction) GC-MS (gas chromatography-mass spectrometry). Subsequently, the attractivity of 33 of the identified compounds was tested with a two-choice laboratory bioassay. Acetaldehyde, hexyl acetate, linalool, myrtenol, L-limonene and camphene came out as significantly attractive to D. suzukii. The first four attractive compounds induced the strongest effect and therefore provided the best prospects to be implemented in a potential lure. These findings could contribute towards the development of more effective attractants for monitoring and mass trapping D. suzukii.

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.

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.

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.

Population Dynamics of Drosophila suzukii in Coastal and Mainland Sweet Cherry Orchards of Greece

Simple Summary

Drosophila suzukii or spotted-wing drosophila is a fruit fly of the same family as the vinegar fly. The majority of Drosophila fruit flies are not considered agricultural pests. However, D. suzukii is a pest of several high-value soft and thin skin fruits such as strawberries and sweet cherries. Drosophila suzukii is also considered worldwide as one of the most important invasive insect pests. We monitored the insect’s flight and we assessed the infestation levels of different sweet-cherry cultivars, in coastal and mainland cherry orchards of Greece, for two consecutive years (2018–2020). Adults were captured throughout the year in the coastal area with two peaks in spring and late-autumn. Captures were nearly zero during the hot summer months. Trap captures exhibited only one peak in autumn at the mainland area, and ceased during winter and spring. Higher sweet-cherry infestation levels were recorded in the coastal than in the mainland area and in unmanaged than in commercial orchards. Both early and late-ripening cultivars were highly susceptible to D. suzukii infestation in the coastal area. Infestation rates were higher in late-ripening cultivars than in early-ripening ones in the mainland area. We conclude that D. suzukii has adapted well to the Mediterranean climate of Greece, and is able to progressively exploit several crops and wild hosts of mainland and coastal areas.

Abstract

Despite the recent invasion and wide spread of Drosophila suzukii Matsumura (Diptera: Drosophilidae) in Europe, little is known regarding its population trends in coastal areas of the southern Mediterranean countries. Using adult trapping and fruit sampling, we studied the population dynamics of D. suzukii in coastal and mainland (semi-highland) cherry orchards of Greece, from 2018 to 2020. Adults were captured in traps baited with apple cider vinegar, placed in conventional and unmanaged sweet-cherry orchards, and in neighbouring wild growing hosts. Sampling of sweet-cherry fruit to assess infestation levels was conducted from early and late-ripening cherry cultivars in both areas. Adults were captured throughout the year in the coastal area with two peaks registered in spring and late-autumn. Captures were nearly zero during the hot summer months. Flight activity exhibited only one peak in autumn at the mainland area, and ceased during winter and spring. Captures in wild hosts were lower during the sweet-cherry ripening period than later in the season. Higher sweet-cherry infestation levels were recorded in the coastal than in the mainland area and in unmanaged than in commercial orchards. Both early and late-ripening cultivars were highly susceptible to D. suzukii infestation in the coastal area. Infestation rates were higher in late-ripening cultivars than in early-ripening ones in the mainland area. We conclude that D. suzukii has well adapted to the Mediterranean climate of Greece, and is able to progressively exploit several crops and wild hosts of mainland and coastal areas.

Gumming Up The Works: Field Tests of a New Food-Grade Gum as Behavioral Disruptor for Drosophila suzukii (Diptera: Drosophilidae)

Drosophila suzukii Matsumura is an economically important pest of small and stone fruits. Its establishment in the Americas and Europe marked an important turning point in crop management programs. Ten years after its first detection, an effective integrated pest management program has yet to be developed and pesticides are mainly used to control this pest. Here we test a new behavioral control tool, with the aim to develop an alternative pest control strategy. A food-grade gum matrix, was evaluated under controlled and open field conditions for its ability to attract the pest and protect the ripening fruit. Here, we report that the gum effectively reduces fruit infestation when used under managed conditions. We show that a single point source can affect D. suzukii behavior over a 3.6 m radius and last for up to 21 d. Open field data reveal that the efficacy of the gum is significantly impacted by water content. We discuss these results in respect to the future implications for D. suzukii management, along with important considerations on gum mechanism of action, possible application strategies and economic suitability for growers.

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.

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.

Predicting Within- and Between-Year Variation in Activity of the Invasive Spotted Wing Drosophila (Diptera: Drosophilidae) in a Temperate Region

Invasive insect pests can be challenging to manage because their recent arrival provides limited information on which to build predictive population models. The magnitude and timing of activity by the invasive vinegar fly, Drosophila suzukii, in crop fields has been unpredictable due to its recent arrival in many new regions of the world and changes in methods for its detection. Using 7 yr of consistent trapping of adults at four blueberry farms in Michigan, United States, we modeled the temporal and environmental factors influencing D. suzukii activity. We found that this pest established high levels within 2 yr of being detected, with peak fly activity continuing to increase. Fly activity timing and abundance were predicted by the annual number of days below 0°C, the number of winter and spring days above 10°C, and by the fly activity in the preceding year, providing support for overwintering in our region. We monitored larval infestation for 4 yr at these same sites and found a moderate positive correlation between larvae in fruit and adults in traps. Finally, we developed a generalized additive model to predict D. suzukii fly capture throughout the season based on relevant environmental factors and examined the relative timing and magnitude of activity under varying winter and spring temperature conditions. Our results suggest that D. suzukii activity is predictable and that environmental conditions can be used in temperate regions to provide regional risk warnings as a component of strategies to manage this invasive insect pest.

Electrophysiological and Behavioral Responses of Drosophila suzukii (Diptera: Drosophilidae) Towards the Leaf Volatile β-cyclocitral and Selected Fruit-Ripening Volatiles

The spotted-wing drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), is attracted to numerous volatile organic compounds (VOCs) emitted from several ripening, small fruit crops. However, the strawberry leaf terpenoid, β-cyclocitral, is reportedly very attractive to D. suzukii (but not to all Drosophila spp.). This suggests that leaf and fruit VOCs may be critical sources needed to further develop a more species-specific D. suzukii monitoring lure, or semiochemically based attract-and-kill systems. This study investigated the electrophysiological responses of male and female D. suzukii towards selected host fruit-ripening VOCs and β-cyclocitral, along with behavioral responses toward combined fruit VOCs with β-cyclocitral. Electroantennogram (EAG) results revealed a positive dose-response, for both sexes, as concentrations increased for all VOCs tested. For β-cyclocitral, hexyl acetate and methyl butyrate, the mean male EAG responses were significantly greater than the female responses at lower doses. In caged behavioral bioassays, only in the β-cyclocitral treatments were the mean number of flies captured (sexes combined) significantly greater than that captured in solvent (mineral oil) controls. Our study has demonstrated that while single fruit-based VOCs alone are not enough to cause a strong behavioral attraction by both male and female D. suzukii, the addition of β-cyclocitral did produce a significant attraction response from both sexes. In both bioassays, males had higher responses to β-cyclocitral than females, which suggest a greater sensitivity to this compound. Further studies are needed to ascertain the role β-cyclocitral may play in the development of a more species-specific D. suzukii monitoring lure.

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.

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.

Raspberry as a Source for the Development of Drosophila suzukii Attractants: Laboratory and Commercial Polytunnel Trials

Several commercial products and home-made attractants have been developed for monitoring and mass-trapping of the spotted wing drosophila, Drosophila suzukii. Growers in Mexico have adopted an attractant based on a fermenting mixture of raspberry pulp and sucrose, with anecdotally promising results. We compared the capture rates of traps baited with raspberry pulp + sucrose with captures from a range of alternative attractants. Raspberry pulp alone or with sucrose was more attractive than apple cider vinegar (ACV) or SuzukiiTrap and similar to baker's yeast + sucrose in laboratory cage studies. Synthetic raspberry aroma (0.1-10% concentration), in water or mixed with ACV, did not improve capture rates in the laboratory. Traps baited with raspberry + sucrose or ACV had similar captures of D. suzukii in raspberry or blackberry polytunnels in Michoacán, Mexico. Raspberry + sucrose baited traps captured significantly higher numbers of other drosophilid species, leading to higher total numbers of captured flies (all species), which may explain why Mexican growers favor the raspberry-based attractant. The commercial products SuzukiiTrap and Z-Kinol had lower captures than ACV in polytunnels, although SuzukiiTrap had the highest selectivity in captures of D. suzukii (81% of flies captured). A two-component trap (2C trap) baited with ACV + ethanol as the drowning solution and raspberry pulp + sucrose or baker's yeast + sucrose in a ventilated tube device was markedly more effective than the trap currently used by growers. We conclude that raspberry pulp + sucrose is as effective for the attraction of D. suzukii as ACV under commercial polytunnel conditions. The 2C trap performed better than the transparent cup trap currently used by berry producers in Mexico.

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.

Multistate Comparison of Attractants and the Impact of Fruit Development Stage on Trapping Drosophila suzukii (Diptera: Drosophilidae) in Raspberry and Blueberry

Spotted-wing drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), is an invasive pest of soft-skinned fruits across the globe. Effective monitoring is necessary to manage this pest, but suitable attractants are still being identified. In this study, we combined lures with fermenting liquid baits to improve D. suzukii trapping specificity and attractiveness. We also measured the efficiency and specificity of baits/lures during different times of the season; the reproductive status of females among baits/lures; and the effects of locations and crop type on these response variables. We developed a metric that combined mating status and fat content to determine differences in types of females attracted. Lures utilizing yeast and sugar-based volatiles trapped the most D. suzukii. The addition of a commercial lure to yeast and sugar-based lures increased catches in most locations, but was also the least specific to D. suzukii. Apple juice-based chemical lures tended to be most specific to D. suzukii, while lures comprised of a singular attractant tended to trap more D. suzukii with a higher reproductive potential than combinations of attractants. Trap catch and lure specificity was lower during fruit development than fruit ripening. While catch amounts varied by geographic location and crop type, attractants performed similarly relative to each other in each location and crop. Based on the metrics in this study, the yeast and sugar-based attractants were the most effective lures. However, further work is needed to improve early season monitoring, elucidate the effects of physiological status on bait attraction, and understand how abiotic factors influence bait attraction.

A Multiple-Choice Bioassay Approach for Rapid Screening of Key Attractant Volatiles

Fermentation volatiles attract a wide variety of insects and are used for integrated pest management. However, identification of the key behavior modifying chemicals has often been challenging due to the time consuming nature of thorough behavioral tests and unexpected discrepancies between laboratory and field results. Thus we report on a multiple-choice bioassay approach that may expedite the process of identifying field-worthy attractants in the laboratory. We revisited the four-component key chemical blend (acetic acid, ethanol, acetoin, and methionol) identified from 12 antennally active wine and vinegar chemicals for Drosophila suzukii (Matsumura) (Diptera: Drosophilidae). The identification of this blend took 2 yr of continuous laboratory two-choice assays and then similarly designed field trials. This delay was mainly due to a discrepancy between laboratory and field results that laboratory two-choice assay failed to identify methionol as an attractant component. Using a multiple-choice approach, we compared the co-attractiveness of the 12 potential attractants to an acetic acid plus ethanol mixture, known as the basal attractant for D. suzukii, and found similar results as the previous field trials. Only two compounds, acetoin and, importantly, methionol, increased attraction to a mixture of acetic acid and ethanol, suggesting the identification of the four-component blend could have been expedited. Interestingly, the co-attractiveness of some of the 12 individual compounds, including a key attractant, methionol, appears to change when they were tested under different background odor environments, suggesting that background odor can influence detection of potential attractants. Our findings provide a potentially useful approach to efficiently identify behaviorally bioactive fermentation chemicals.

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.

Identification of attractive blend for spotted wing drosophila, Drosophila suzukii, from apple juice

Drosophila suzukii, commonly known as the spotted wing drosophila (SWD), is an exotic fruit fly from Southeast Asia that was introduced to the temperate regions of North America and Europe in 2008. It attacks a wide variety of fruits and has become a devastating pest of soft-skinned fruit crops. Due to the rapid spread of SWD across the newly invaded continents, fresh fruit markets have a zero-tolerance policy regarding D. suzukii infestation. Specific and efficient D. suzukii detection tools are urgently needed so that farmers can deliver timely management interventions to meet market demands. Since SWD is known to be attracted to damaged and rotting fruits, headspace volatiles from fresh and fermented apple juices were collected and analyzed by gas chromatography-mass spectrometry. Special attention was given to the compounds produced and/or enriched during the fermentation process. After performing a series of laboataory and field tests, we identified a quinary blend, which is more efficient and selective for D. suzukii than the currently standard apple cider vinegar and commercially available SWD lure under field conditions. Identification of SWD attractant will help growers accurately detect D. suzukii adult infestations in orchards, thereby allowing for timely pest management interventions while reducing conventional insecticidal usage to protect our crops, environment, and ecosystem.

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.

Economic Impact of the Introduction and Establishment of Drosophila suzukii on Sweet Cherry Production in Switzerland

First detected in Switzerland in 2011, the invasive Drosophila suzukii, spotted wing drosophila, has caused recurring costs for growers of berries and fruit. Recommended management approaches rely on a set of methods, tailored to suit crop requirements under the prevailing local conditions. Control of D. suzukii represents a substantial economic burden for growers, in terms of material, equipment, new infrastructure and extra labour. However, those growers who invest wisely to deliver unblemished produce are rewarded with high payoffs. We present insights from a growers’ survey conducted in 2015 and 2016 to gauge the impact of the introduction and establishment of D. suzukii on Swiss sweet cherry production. The surveyed growers (111 in 2015 and 298 in 2016) observed the recommended surveillance, sanitation and control measures. The use of insecticides (78% and 79% of respondents in 2015 and 2016, respectively) and the harvest of all fruits (93% and 59% of respondents in 2015 and 2016, respectively) were the most widespread methods used to reduce damage. Nearly one-third of the respondents set up enclosure nets. Our economic evaluation of different scenarios provides a quantitative indication of the potentially incurred costs. We argue for enhanced stakeholder involvement to raise the acceptance of integrated pest management practices, and to inform research and outreach by providing insights into the motivations and barriers to adoption.

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.