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

Exploring Matrine and Oxymatrine as Potential Bioinsecticide to Control Drosophila suzukii (Diptera: Drosophilidae)

A bottleneck in sustainable fruit production is the replacement of chemical products with natural compounds. Matrine and oxymatrine, derived from a Chinese medicinal herb, have exhibited potential for controlling agricultural pests. However, there is no information regarding their effectiveness in managing dipterans. Thus, we carried out experiments to evaluate the effect of the botanical compounds matrine and oxymatrine on Drosophila suzukii (Matsumura) adults under laboratory conditions. First, we tested four doses of the commercial product matrine, with distilled water as a control treatment. Each treatment was offered as a droplet, to five D. suzukii couples in screened cages. Adult mortality was evaluated at intervals of 12, 24, 36, 48, 60, and 72 h post-exposure. All doses tested of the commercial matrine-based product caused up to 58% of mortality in D. suzukii adults. Second, the consumption of pure extract of oxymatrine was evaluated using a CAFE assay. Three D. suzukii females were exposed to oxymatrine concentrations of 0.05, 1.0, 2.5, 5.0, and 7.0% in a 20% sugar solution for 24 h. Afterwards, the flies were deprived of food for 40 h, and mortality was evaluated. The pure extract of oxymatrine induced mortality in D. suzukii females only at doses of 2.5, 5.0, and 7.0%. These botanical compounds demonstrate the potential to be used to control D. suzukii adults and can be explored as one tool of the Integrated Management Program.

Evaluating global Vaccinium germplasm for resistance against invasive Drosophila suzukii (Diptera: Drosophilidae)

Control of spotted-wing Drosophila, Drosophila suzukii, in small fruits emphasizes biological, cultural, and chemical approaches, whereas studies of host plant resistance as a form of genetic control are just getting underway. The identification of resistance patterns among genotypes of host plants whose fruit, leaves, roots, stems, or seeds are specifically targeted by an invasive pest is the first step in the development of an effective genetic control. Therefore, a detached fruit bioassay was developed to screen for D. suzukii oviposition and larval infestation within berries from 25 representative species and hybrids of wild and cultivated Vaccinium. Ten Vaccinium species showed strong resistance; among them, two wild diploids originating from within the fly's native range: V. myrtoides and V. bracteatum. Other resistant species came from the sections Pyxothamnus and Conchophyllum. They included New World V. consanguineum and V. floribundum. Large-cluster blueberry, V. amoenum, and three Floridian genotypes of related rabbiteye blueberry, V. virgatum, were the only hexaploids expressing strong resistance against D. suzukii. Most screened blueberry genotypes from managed lowbush and cultivated highbush types were susceptible to the flies' attacks (i.e., oviposition). Tetraploid blueberries tended to host the most eggs, whereas diploids and hexaploids harbored 50%-60% fewer eggs, on average. D. suzukii cannot lay eggs or complete development in the smallest, sweetest, and firmest diploid fruits. Likewise, certain genotypes of large-fruited tetraploid and hexaploid blueberry strongly curbed D. suzukii egg-laying and larval growth, indicating the possibility of heritable resistance operating against this invasive fly species.

Comparing the effectiveness of different insecticide application orders for suppressing Drosophila suzukii Matsumura (Diptera: Drosophilidae) infestation: experimental and modeling approaches

Drosophila suzukii Matsumura (Diptera: Drosophilidae) is a key pest of soft-skinned fruit such as blackberry and blueberry. Differing seasonal spray regimes are expected to have variable effects on D. suzukii populations. Semi-field cage trials were performed at three locations in the United States (Georgia, Oregon, and North Carolina) on blueberry and blackberry crops to evaluate this hypothesis. Insecticides with different efficacy rates (ZC - zeta-cypermethrin, SPI - spinetoram, CYAN - cyantraniliprole) were applied during field experiments conducted within large cages. Treatment schedules consisted of two insecticide applications which performed over three weeks. Seasonal treatment schedules were applied in the following order: ZC-CYAN and CYAN-ZC in rabbiteye and highbush blueberry with the addition of a ZC-SPI treatment applied in blackberry. In addition, a population model was applied to simulate the relative efficacy of the insecticide schedules in Oregon on D. suzukii population model based on previously published efficacy, biological, and weather parameters. Overall, all schedules resulted in reduced D. suzukii infestation compared to untreated control (UTC) treatments, with statistical differences in all three locations. The numerically lower infestation was found in some cases in ZC-CYAN schedule. Population modeling conducted exclusively for blueberry, and the simulations indicated no discernible differences between the two respective schedules (ZC-CYAN vs CYAN-ZC). The present study demonstrates that seasonal infestation of D. suzukii could be suppressed irrespective of application order. Additional research is required to assess the optimal timing and sequence of insecticide applications for controlling seasonal populations of D. suzukii in fruit crops. Such information could be invaluable for growers who are seeking to strategize their insecticide applications.

Propensity for resistance development in the invasive berry pest, spotted-wing drosophila (Drosophila suzukii), under laboratory selection

BACKGROUND

Over the past 14 years, the invasive vinegar fly, spotted-wing drosophila (Drosophila suzukii), has become one of the most damaging fruit pests in the United States. With regional economic losses estimated as high as $500 million for moderate infestations, D. suzukii control represents an often-untenable cost to growers. Management relies heavily on chemical control, which may be applied up to nine times in one season. The widespread use of chemical controls has led to concerns about insecticide resistance, and resistant field populations have already been documented in California and Michigan.

RESULTS

We cultured sub-populations of three different Minnesota field populations of D. suzukii in the laboratory and exposed them to increasing concentrations of two commonly-used insecticides, zeta-cypermethrin (pyrethroid) and spinetoram (spinosyn). Over the exposure period, the sub-populations experienced an 8- to 45-fold increase in insecticide concentration. We saw significant increases in the median lethal concentration (LC50 ) values of one sub-population exposed to zeta-cypermethrin and one exposed to spinetoram. Across the spinetoram exposures, we also observed significant reductions in the top mortality values for three different sub-populations.

CONCLUSION

Our results suggest that field populations of D. suzukii can develop resistance to zeta-cypermethrin and spinetoram in short periods of time under laboratory selection but that resistance to spinosyns occurs more readily than to pyrethroids. These results support other studies that have documented spinosyn resistance in field populations and in laboratory selections. Resistance evolution to spinosyns is a particularly important issue, as they represent one of few organic insecticide options for D. suzukii. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Functional transcriptome analyses of Drosophila suzukii midgut reveal mating-dependent reproductive plasticity in females

BACKGROUND

Insect females undergo a huge transition in energy homeostasis after mating to compensate for nutrient investment during reproduction. To manage with this shift in metabolism, mated females experience extensive morphological, behavioral and physiological changes, including increased food intake and altered digestive processes. However, the mechanisms by which the digestive system responds to mating in females remain barely characterized. Here we performed transcriptomic analysis of the main digestive organ, the midgut, to investigate how gene expression varies with female mating status in Drosophila suzukii, a destructive and invasive soft fruit pest.

RESULTS

We sequenced 15,275 unique genes with an average length of 1,467 bp. In total, 652 differentially expressed genes (DEGs) were detected between virgin and mated D. suzukii female midgut libraries. The DEGs were functionally annotated utilizing the GO and KEGG pathway annotation methods. Our results showed that the major GO terms associated with the DEGs from the virgin versus mated female midgut were largely appointed to the metabolic process, response to stimulus and immune system process. We obtained a mass of protein and lipid metabolism genes which were up-regulated and carbohydrate metabolism and immune-related genes which were down-regulated at different time points after mating in female midgut by qRT-PCR. These changes in metabolism and immunity may help supply the female with the nutrients and energy required to sustain egg production.

CONCLUSION

Our study characterizes the transcriptional mechanisms driven by mating in the D. suzukii female midgut. Identification and characterization of the DEGs between virgin and mated females midgut will not only be crucial to better understand molecular research related to intestine plasticity during reproduction, but may also provide abundant target genes for the development of effective and ecofriendly pest control strategies against this economically important species.

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

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

Transcriptome analysis of sex-biased gene expression in the spotted-wing Drosophila, Drosophila suzukii (Matsumura)

Sexual dimorphism occurs widely throughout insects and has profound influences on evolutionary path. Sex-biased genes are considered to account for most of phenotypic differences between sexes. In order to explore the sex-biased genes potentially associated with sexual dimorphism and sexual development in Drosophila suzukii, a major devastating and invasive crop pest, we conducted whole-organism transcriptome profiling and sex-biased gene expression analysis on adults of both sexes. We identified transcripts of genes involved in several sex-specific physiological and functional processes, including transcripts involved in sex determination, reproduction, olfaction, and innate immune signals. A total of 11,360 differentially expressed genes were identified in the comparison, and 1,957 differentially expressed genes were female-biased and 4,231 differentially expressed genes were male-biased. The pathway predominantly enriched for differentially expressed genes was related to spliceosome, which might reflect the differences in the alternative splicing mechanism between males and females. Twenty-two sex determination and 16 sex-related reproduction genes were identified, and expression pattern analysis revealed that the majority of genes were differentially expressed between sexes. Additionally, the differences in sex-specific olfactory and immune processes were analyzed and the sex-biased expression of these genes may play important roles in pheromone and odor detection, and immune response. As a valuable dataset, our sex-specific transcriptomic data can significantly contribute to the fundamental elucidation of the molecular mechanisms of sexual dimorphism in fruit flies, and may provide candidate genes potentially useful for the development of genetic sexing strains, an important tool for sterile insect technique applications against this economically important species.

Hormetic and transgenerational effects in spotted-wing Drosophila (Diptera: Drosophilidae) in response to three commonly-used insecticides

Although insecticide formulations and spray rates are optimized to achieve lethal exposure, there are many factors in agricultural settings that can reduce the effective exposure of insect pests. These include weather patterns, timing of application, chemical degradation/volatilization, plant structural complexity, and resistant populations. While sub-lethal exposure to insecticides can still have negative impacts on pest populations, they can also lead to stimulatory, or hormetic, responses that can increase the fitness of surviving insects. Sub-lethal concentrations may also produce increased tolerance in the offspring of surviving adults through transgenerational effects. Sub-lethal effects are pertinent for the invasive fruit pest, spotted-wing Drosophila, Drosophila suzukii (Matsumura), because its small size, diurnal movement patterns, and utilization of hosts with complex plant structures, such as caneberries and blueberries, make effective insecticide applications tenuous. In this study, we measured spotted-wing Drosophila survivorship, reproductive performance, and offspring tolerance in flies exposed to sub-lethal concentrations of three commonly-used insecticides (zeta-cypermethrin, spinetoram, and pyrethrin). We found some evidence for hormesis, with survival effects being sex- and concentration-dependent for all insecticides. Males were far more susceptible to insecticides than females, which in some cases exhibited higher eclosion success and reproductive rates when exposed to sub-lethal doses. We did not observe significant transgenerational effects at sub-lethal concentrations, despite trends of increased offspring viability for zeta-cypermethrin and spinetoram. More research, however, is needed to fully understand the role that sub-lethal effects may play in pest population dynamics, insecticide efficacy, and the development of genetic resistance.

Development and validation of a larval bioassay and selection protocol for insecticide resistance in Drosophila suzukii

The rapid invasion of Drosophila suzukii (Matsumura) throughout Europe and the Americas has led to an increased reliance on calendar-based broad-spectrum insecticide programs among berry and cherry growers. Relatively few active ingredients (AIs) are currently available for effective D. suzukii management, and studies from multiple growing regions indicate that susceptibility to at least some of these materials is declining. Greater effort is needed to understand the status of susceptibility across field populations and the potential for increased resistance to develop, as well as the possible fitness costs incurred by resistant individuals. However, current bioassay protocols used for resistance monitoring and selection studies (i.e. resistance risk assessments) are labor-intensive and costly, making large-scale studies difficult to conduct. Here, we first present a novel bioassay protocol using larvae that requires little effort or cost to implement beyond what is needed for basic D. suzukii laboratory colony maintenance. We then perform dose-response bioassays using this protocol to identify larval lethal concentrations for three commonly used insecticides (malathion, spinosad and zeta-cypermethrin) in a susceptible population. Finally, resistance risk assessments were conducted using a population of D. suzukii from commercial caneberry fields near Watsonville, CA. We find that five generations of larval selection with a discriminating dose is sufficient to significantly increase both larval (malathion and spinosad) and adult (spinosad) resistance to the target AIs. This approach provides a simple, cost-effective tool for assaying susceptibility of D. suzukii populations to insecticides and for selecting resistant insect lines for resistance management research.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

Field and greenhouse application of an attract-and-kill formulation based on the yeast Hanseniaspora uvarum and the insecticide spinosad to control Drosophila suzukii in grapes

BACKGROUND

The invasive insect Drosophila suzukii (Matsumura) is an important pest of several red grape varieties. The yeast Hanseniaspora uvarum (Niehaus), which is associated with D. suzukii, strongly attracts flies and stimulates them to feed on yeast-laden food. In the present study, a formulation based on H. uvarum culture with spinosad insecticide was applied to the foliage of vineyards and control of D. suzukii was compared to applying spinosad to the whole plant. After successful H. uvarum and insecticide application in the vineyard, we tested additional H. uvarum-based formulations with spinosad in a greenhouse to determine their capacity to control D. suzukii.

RESULTS

Application of the H. uvarum-spinosad formulation at 36.4 g of spinosad per hectare reduced the D. suzukii field infestation at the same rate as applying 120 g of spinosad per hectare and prevented spinosad residues on grapes. Leaves treated with H. uvarum and spinosad in the field and transferred to a laboratory assay caused high mortality to flies and reduced the number of eggs laid on fruits. Formulations with spinosad applied in the greenhouse showed that both H. uvarum culture and the yeast cell-free supernatant of a centrifuged culture increased fly mortality and reduced the number of eggs laid compared to the unsprayed control.

CONCLUSION

In comparison to typical spinosad spray applications, the use of H. uvarum in combination with spinosad as an attract-and-kill formulation against D. suzukii reduces pesticide residues on the fruits by targeting the treatment to the canopy and decreasing the amount of insecticide per hectare without compromising control efficacy.

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.

Laboratory Selection and Assessment of Resistance Risk in Drosophila suzukii (Diptera: Drosophilidae) to Spinosad and Malathion

Drosophila suzukii (Matsumura) is one of the most economically important pests of soft-skinned fruits worldwide. Repeated insecticide applications commonly used to prevent fruit infestations increase the risk of resistance development in D. suzukii. Assessment of resistance risk in D. suzukii using artificial selection can be valuable in developing proactive resistance management strategies to retain susceptibility in the field populations. Here, we artificially selected a colony of field-collected D. suzukii for resistance against spinosad and malathion. A quantitative genetic approach was then used to estimate realized heritability (h²) of resistance and predict the rates of resistance development. After 10 and 11 generations of selection, resistance to spinosad and malathion in D. suzukii females significantly increased by 7.55- and 2.23-fold, respectively. Based on the predicted rates of resistance development, assuming h² = 0.14 (mean h² of spinosad resistance in this study) and 90% of population was killed at each generation, 10-fold increase in LC₅₀ of D. suzukii females would be expected in nine generations for spinosad. However, 10-fold increase in LC₅₀ of D. suzukii females for malathion would be expected in 37 generations, assuming h² = 0.08 (mean h² of malathion resistance) and 90% of population was killed at each generation. These results indicate that the risk of resistance in D. suzukii populations exists against both spinosad and malathion. However, resistance would develop faster against spinosad as compared to malathion. Thus, resistance management strategies should be implemented proactively to maintain the effectiveness of these insecticides to control D. suzukii.

Genome editing efficiency of four Drosophila suzukii endogenous U6 promoters

The invasive spotted-wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) has caused serious economic losses to the fruit industry. The conventional control methods have many limitations and genetic engineering technologies such as CRISPR/Cas9-mediated gene drive are promising approaches. In the CRISPR/Cas9 system, the transcriptional regulatory elements play an important role in the activities of gRNA. Thus, in order to improve the genome editing efficiency of the CRISPR/Cas9 system in D. suzukii, we cloned and tested four endogenous U6 promoters to drive mutagenesis of the white gene. Our results showed that all the four promoters could be used with variable efficiency. The promoter DsU6-3 had the highest genome editing efficiency among the four DsU6 promoters. Compared with the DsU6-3 promoter, the DmU6:3 promoter showed lower efficiency to drive mutagenesis in D. suzukii. These findings expand the range of promoters available to express gRNAs in D. suzukii, facilitating the basic and applied research on this important pest.

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

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

Identification of natural pathogens from wild Drosophila suzukii

BACKGROUND

Drosophila suzukii (Matsumura, 1931) (spotted wing drosophila), an invasive species, has recently become a significant global pest of soft-skinned fruits such as berries. Unlike other Drosophila species, female D. suzukii have evolved a specialized sharp, serrated ovipositor that pierces and penetrates ripe and ripening fruits, causing them to lose commercial value and preventing their sale. A first step for the development of biological control agents for pest management may be achieved through the identification of microbes infectious for D. suzukii in the wild.

RESULTS

We first determined that D. suzukii is susceptible to chemicals commonly used to rear Drosophilids in the laboratory and established a diet able to sustain healthy D. suzukii growth. Using this diet, we demonstrated that of 25 species of culturable bacteria and fungi isolated from field-collected D. suzukii, eight microbes decreased host survival when injected. Three of the eight bacteria (Alcaligenes faecalis, Achromobacter spanius and Serratia marcescens) were acutely pathogenic to both D. suzukii and Drosophila melanogaster adults by injection. Feeding of these bacteria resulted in susceptibility only in larvae.

CONCLUSION

We successfully identified multiple microbes from field-collected D. suzukii that are pathogenic to both larvae and adults through different routes of infection, some of which could be candidates for biocontrol of this species. © 2020 Society of Chemical Industry.

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

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

Determining the Effect of Postharvest Cold Storage Treatment on the Survival of Immature Drosophila suzukii (Diptera: Drosophilidae) in Small Fruits

We evaluated the effect of postharvest cold storage temperature (0.0-2.2°C) and duration (3-5 d) on pupal emergence of single life stage populations of laboratory-generated Drosophila suzukii (Matsumura) and mixed-age populations collected in the field from blackberries, blueberries, strawberries, and raspberries. For field-infested fruit, cold storage at any temperature and duration resulted in less pupal emergence compared with the control held at 20°C, but D. suzukii subjected to higher temperatures and shorter storage durations in caneberries had higher survival. When a single life stage of D. suzukii was exposed to cold storage, pupal emergence was significantly reduced across all fruit types held at 0°C and for most life stages and fruit types held at 1.5 and 2.2°C, dependent on the substrate. Freshly laid eggs exposed to cold storage produced the lowest pupal emergence. Our results suggest using cold storage treatment is an effective postharvest management strategy for small-fruit growers to use on-farm as part of an integrated program to manage D. suzukii infestation. An economic assessment was made to examine the profit implications of an investment in cold storage units to counter pest pressure. Results suggest that investment in a cold storage unit would breakeven in about 4 yr. On farms that already have cold storage installed, we estimated a $0.11/kg decrease in blueberry market price for holding fruit for 3 d. Together, this cost assessment will provide growers with the knowledge to make decisions based on infestation risk and the seasonal sale price of blueberries.

Curative Activity of Insecticides Used to Control Spotted-Wing Drosophila (Diptera: Drosophilidae) in Tart Cherry Productions

Spotted-wing drosophila (Drosophila suzukii Matsumura) is a major pest of soft-skinned fruit and due to the low infestation tolerance for marketable fruit, growers take preventive actions to hinder spotted-wing drosophila damages. Insecticides application is one of the measures taken by growers. Although intensive spraying programs have been used to manage spotted-wing drosophila, its early infestation, rapid reproduction, and vast range of host have caused damage to still occur in fruit, including tart cherries, Prunus ceraus (Linnaeus). Therefore, there is a merit for information on insecticide's curative activity to understand whether sprays manage spotted-wing drosophila individuals within infested fruit. Tart cherry fruit were exposed to spotted-wing drosophila adults for 3 d. After this infestation period, insecticides were applied 1 and 3 d later. Small larvae, large larvae, and pupae were counted 9 d after initial infestation. A parallel set of insecticide-treated tart cherries were subjected to residue analysis. Phosmet and spinetoram were able to reduced live spotted-wing drosophila counts compared with the control at all life stages and insecticide application times, whereas zeta-cypermethrin, acetamiprid, and cyantraniliprole were less consistent in reducing spotted-wing drosophila numbers. Chromobacterium subtsugae demonstrated no curative action. Residue analysis demonstrated that zeta-cypermethrin residues mostly remained on fruit surface. Small portions of phosmet, spinetoram, and cyantraniliprole were able to penetrate fruit surfaces and move into subsurface tissues. Acetamiprid was the only compound which >47% penetrated into the fruit subsurface consistently across both years. Curative activity demonstrated in this study can provide additional tactics for spotted-wing drosophila management in tart cherry Integrated Pest Management (IPM) programs.

The use of light spectrum blocking films to reduce populations of Drosophila suzukii Matsumura in fruit crops

Spotted wing drosophila, Drosophila suzukii, is a serious invasive pest impacting the production of multiple fruit crops, including soft and stone fruits such as strawberries, raspberries and cherries. Effective control is challenging and reliant on integrated pest management which includes the use of an ever decreasing number of approved insecticides. New means to reduce the impact of this pest that can be integrated into control strategies are urgently required. In many production regions, including the UK, soft fruit are typically grown inside tunnels clad with polyethylene based materials. These can be modified to filter specific wavebands of light. We investigated whether targeted spectral modifications to cladding materials that disrupt insect vision could reduce the incidence of D. suzukii. We present a novel approach that starts from a neuroscientific investigation of insect sensory systems and ends with infield testing of new cladding materials inspired by the biological data. We show D. suzukii are predominantly sensitive to wavelengths below 405 nm (ultraviolet) and above 565 nm (orange & red) and that targeted blocking of lower wavebands (up to 430 nm) using light restricting materials reduces pest populations up to 73% in field trials.

The Gram-Positive Bacterium Leuconostoc pseudomesenteroides Shows Insecticidal Activity against Drosophilid and Aphid Pests

Insect pests reduce global crop yields by up to 20%, but the most effective control measures are currently based on environmentally hazardous chemical pesticides. An alternative, ecologically beneficial pest-management strategy involves the use of microbial pathogens (or active compounds and extracts derived from them) that naturally target selected insect pests. A novel strain of the bacterium Leuconostoc pseudomesenteroides showed promising activity in our preliminary tests. Here, we investigated its effects in more detail, focusing on drosophilid and aphid pests by testing the survival of two species representing the family Drosophilidae (Drosophila suzukii and D. melanogaster) and one representing the family Aphididae (Acyrthosiphon pisum). We used oral and septic infection models to administer living bacteria or cell-free extracts to adult flies and aphid nymphs. We found that infection with living bacteria significantly reduced the survival of our insect models, whereas the administration of cell-free extracts had a significant effect only in aphids. These results confirm that L. pseudomesenteroides has potential as a new biocontrol agent for sustainable pest management.

The effect of warming on pesticide toxicity is reversed between developmental stages in the mosquito Culex pipiens

A better understanding of interactions between pesticides and warming is important to improve ecological risk assessment in a warming world. Current insights are almost exclusively based on studies that exposed animals simultaneously to both warming and a pesticide and focused on effects during the pesticide exposure period and within a single developmental stage. We studied two ignored aspects of the interplay between warming and pesticide exposure: (i) the role of delayed effects after the pesticide exposure period, and (ii) the dependence on the developmental stage. We carried out a longitudinal experiment from the egg stage to the adult stage in the mosquito Culex pipiens where we crossed a warming treatment (20 °C vs 24 °C) with 48 h exposures to the pesticide chlorpyrifos in three developmental stages (early L1 larvae, late L4 larvae and adults). Chlorpyrifos induced mild to moderate mortality in all developmental stages (10-30%). A key finding was that warming shaped the chlorpyrifos-induced mortality but in opposite directions between stages. Chlorpyrifos was 7% less toxic under warming in L1 larvae, yet more toxic under warming in L4 larvae (22%) and in adult males (33%), while toxicity did not change under warming in adult females. We hypothesize that the general, stage-specific differences in the effects of warming on body size (increased size in early larvae, decreased size in later stages) caused the reversal of the effects of warming on toxicity between stages. Previous larval exposure to chlorpyrifos caused delayed effects that strongly reduced survival to the adult stage (̰25% at 24 °C). Notably, warming also modulated these delayed mortality effects in opposite ways between developmental stages, matching the patterns of mortality during the pesticide exposure periods. Integrating the general stage-specific patterns of how warming shapes body size is important to advance our mechanistic understanding of the interactions between pesticides and warming.

Canopy spray deposition and related mortality impacts of commonly used insecticides on Drosophila suzukii Matsumura (Diptera: Drosophilidae) populations in blueberry

BACKGROUND

Insecticide applications in blueberry production systems play a crucial role in the control of Drosophila suzukii populations. Here, quantitative spray deposition patterns were obtained under replicated field experiments in blueberry during two field seasons with three sprayers, i.e. cannon, electrostatic, and air-blast. Seven insecticides were tested (at 6 hours using a Potter spray tower) to determine the mortality data for adult D. suzukii. Spray deposition and mortality data for adult D. suzukii were used to create model simulations for insect populations. Model simulations included field deposition rates of sprayers and insecticide mortality as factors. Simulations were applied in different combinations with five applications over a 6-week period.

RESULTS

Relative deposition rates for the cannon sprayer were elevated in the upper zones of the canopy, whereas for the air-blast sprayer, deposition was greater in the bottom zones. Electrostatic spray deposition was relatively uniform within the six canopy zones. Clear trends in D. suzukii laboratory mortality were found with lowest to highest mortality recorded for phosmet, spinetoram, spinosad, malathion, cyantraniliprole, zeta-cypermethrin, and methomyl respectively. Maximum D. suzukii population impacts, as shown by model outputs, were observed with air-blast sprayers together with zeta-cypermethrin.

CONCLUSION

The electrostatic sprayer had the least variable canopy deposition among the three types of spray equipment, and the air-blast sprayer had the highest overall deposition rates. This study provides new hypotheses that can be used for field verification with these spray technologies and insecticides as key factors. © 2019 Society of Chemical Industry.

Potential of the European earwig (Forficula auricularia) as a biocontrol agent of the soft and stone fruit pest Drosophila suzukii

BACKGROUND

The unintentional introduction of Drosophila suzukii (Matsumura) from Asia has caused global economic losses in the soft and stone fruit industries. Pesticide use can have unintended negative impacts on natural enemies, disrupting attempts to incorporate integrated pest management programmes. Generalist predators could potentially act as biocontrol agents of D. suzukii. In this context, the predatory capabilities of the European earwig (Forficula auricularia) were investigated.

RESULTS

In semi-field conditions, F. auricularia were effective at reducing the reproductive rate of D. suzukii in more densely populated enclosures. In controlled laboratory conditions, significant negative effects of earwigs were observed for both low (three breeding pairs) and high (six breeding pairs) D. suzukii densities. Both semi-field and laboratory experiments revealed that F. auricularia predation on adult D. suzukii could not account for the subsequent reductions in population density.

CONCLUSIONS

Reductions in both larval and adult offspring in the presence of earwigs indicate an impact on D. suzukii via predation prior to metamorphosis or disruption of oviposition. Although F. auricularia may predate D. suzukii populations, its capacity to act as a biocontrol agent may be limited. However, results suggest that F. auricularia may be a more effective biocontrol agent earlier in the growing season. © 2019 Society of Chemical Industry.

Temperature variation magnifies chlorpyrifos toxicity differently between larval and adult mosquitoes

To improve risk assessment there is increasing attention for the effect of climate change on the sensitivity to contaminants and vice versa. Two important and connected topics have been largely ignored in this context: (i) the increase of daily temperature variation (DTV) as a key component of climate change, and (ii) differences in sensitivity to climate change and contaminants between developmental stages. We therefore investigated whether DTV magnified the negative effects of the organophosphate insecticide chlorpyrifos on mortality and heat tolerance and whether this effect was stronger in aquatic larvae than in terrestrial adults of the mosquito Culex pipiens. Exposure to chlorpyrifos at a constant temperature imposed mortality and reduced the heat tolerance in both larvae and adult males, but not in adult females. This provides the first evidence that the TICS ("toxicant-induced climate change sensitivity") concept can be sex-specific. DTV had no direct negative effects. Yet, consistent with the CITS ("climate-induced toxicant sensitivity") concept, DTV magnified the toxicity of the pesticide in terms of larval mortality. This was not the case in the adult stage indicating the CITS concept to be dependent on the developmental stage. Notably, chlorpyrifos reduced the heat tolerance of adult females only in the presence of DTV, thereby providing support for the reciprocal effects between DTV and contaminants, hence the coupling of the TICS and CITS concepts. Taken together, our results highlight the importance of integrating DTV and the developmental stage to improve risk assessment of contaminants under climate change.

Development of a rapid assessment method for detecting insecticide resistance in spotted wing Drosophila (Drosophila suzukii Matsumura)

BACKGROUND

Spotted wing Drosophila is an invasive pest of fruit crops in most production regions globally, and insecticides are commonly used for its control. The biology of this pest combined with repeated pesticide exposure increases the risk of resistance to insecticides. We tested malathion, methomyl, spinetoram, spinosad, and zeta-cypermethrin against multiple colonies from each state using a contact bioassay method to determine diagnostic doses for assessment of insecticide susceptibility in this species. These were used to test populations collected in Michigan and Georgia, USA.

RESULTS

Concentrations required to reach 50% (LC₅₀ ) and 90% mortality (LC₉₀ ) were calculated for the tested populations, and male mortality consistently occurred at lower concentrations than female mortality. Fly mortality did not vary significantly among populations collected from unmanaged, organic, and conventional fields. Similar results were found using the diagnostic concentrations applied to glass jars.

CONCLUSIONS

Using this method, samples of D. suzukii that are freshly caught or reared from fruit can be tested within 1 day for their mortality in response to discriminating doses of five key insecticides. This method can be used to inform proactive resistance management strategies within integrated pest management programs. © 2019 Society of Chemical Industry.

Identification and risk assessment of spinosad resistance in a California population of Drosophila suzukii

BACKGROUND

The bioinsecticide spinosad is among the most widely used insecticides for managing spotted-wing drosophila, Drosophila suzukii (Matsumura), and is critical for preventing fruit infestation in organic berry production. Recent reports, however, have raised concerns that the efficacy of this material is declining in fields near Watsonville, CA, a major hub of commercial berry production in the USA and the first location where D. suzukii was reported in North America.

RESULTS

In this study, we performed dose-response analyses on D. suzukii from commercial raspberry plantings near Watsonville as well as a second untreated site in California using a widely implemented bioassay protocol. We found that Watsonville flies exhibited spinosad LC₅₀ values 4.3-7.7 times higher than those from the untreated location and 11.6-22.4 times higher than previously reported susceptible baselines. Additionally, tolerance to spinosad continued to increase after additional selection for five generations, though this result was only statistically significant after prolonged exposure to residues.

CONCLUSIONS

These findings confirm that spinosad resistance is emerging in the Watsonville area and document the first known occurrence in the USA, presenting an urgent need for the development of alternative management strategies to control this pest. Additional work is needed to resolve the underlying molecular mechanism(s) that confers spinosad resistance in D. suzukii and assess the potential for this trait to spread into new populations. © 2018 Society of Chemical Industry.

A Phylogeographic Approach to the Drosophila suzukii (Diptera: Drosophilidae) Invasion in Brazil

Biological invasions have reached large parts of the globe, due to human actions across the planet. Drosophila suzukii (Matsumura, 1931) is a globally invasive species, always associated with enormous and costly damage to agricultural crops. Native to Southeast Asia, D. suzukii recently (i.e., 2013) invaded and is dispersing through South America. Here, we used a phylogeographic approach based on the cytochrome c oxidase subunit I gene fragment to explore the invasion dynamics of D. suzukii populations in Brazil. We identified five haplotypes and moderate genetic diversity in Brazilian populations, which are undergoing demographic and spatial expansion. The analyses of molecular variance indicated a high genetic structure among the populations, which is partially explained by their morphoclimatic origin and invasion history. Drosophila suzukii expanded from southern to southeastern Brazil, aided by human-mediated transport of fruits from region to region. The sharing of haplotypes among Brazilian and other invaded regions of the world suggests a single invasion event of D. suzukii in Brazil, originating from previously invaded areas (e.g., North America and Europe). The rapid geographic dispersal and wide variety of fruits attacked by of D. suzukii require immediate implementation of control strategies (legal and phytosanitary) to manage this pest in Brazil.

Synthetically engineered Medea gene drive system in the worldwide crop pest Drosophila suzukii

Synthetic gene drive systems possess enormous potential to replace, alter, or suppress wild populations of significant disease vectors and crop pests; however, their utility in diverse populations remains to be demonstrated. Here, we report the creation of a synthetic Medea gene drive system in a major worldwide crop pest, Drosophila suzukii We demonstrate that this drive system, based on an engineered maternal "toxin" coupled with a linked embryonic "antidote," is capable of biasing Mendelian inheritance rates with up to 100% efficiency. However, we find that drive resistance, resulting from naturally occurring genetic variation and associated fitness costs, can be selected for and hinder the spread of such a drive. Despite this, our results suggest that this gene drive could maintain itself at high frequencies in a wild population and spread to fixation if either its fitness costs or toxin resistance were reduced, providing a clear path forward for developing future such systems in this pest.

Synthetically engineered Medea gene drive system in the worldwide crop pest Drosophila suzukii

Here we describe a fully functional gene drive system constructed in a major worldwide crop pest, Drosophila suzukii. This system is composed of a synthetic Medea drive with a maternal miRNA “toxin” and a zygotic “antidote,” and we demonstrate that it can bias inheritance with 100% efficiency and can persist in a population given high release frequencies. We discuss how such a system may be used to suppress D. suzukii populations or render them harmless to target crops.

Synthetic gene drive systems possess enormous potential to replace, alter, or suppress wild populations of significant disease vectors and crop pests; however, their utility in diverse populations remains to be demonstrated. Here, we report the creation of a synthetic Medea gene drive system in a major worldwide crop pest, Drosophila suzukii. We demonstrate that this drive system, based on an engineered maternal “toxin” coupled with a linked embryonic “antidote,” is capable of biasing Mendelian inheritance rates with up to 100% efficiency. However, we find that drive resistance, resulting from naturally occurring genetic variation and associated fitness costs, can be selected for and hinder the spread of such a drive. Despite this, our results suggest that this gene drive could maintain itself at high frequencies in a wild population and spread to fixation if either its fitness costs or toxin resistance were reduced, providing a clear path forward for developing future such systems in this pest.

Baseline susceptibility of spotted wing Drosophila (Drosophila suzukii) to four key insecticide classes

BACKGROUND

The invasive drosophilid pest, Drosophila suzukii Matsumura, is affecting berry production in most fruit-producing regions of the world. Chemical control is the dominant management approach, creating concern for insecticide resistance in this pest. We compared the insecticide susceptibility of D. suzukii populations collected from conventional, organic or insecticide-free blueberry sites.

RESULTS

The sensitivity of D. suzukii to malathion and spinetoram declined slightly across the 3 years of monitoring, whereas it was more consistent for methomyl and zeta-cypermethrin. The sensitivity of D. suzukii to all four insecticides (LC₅₀ and LC₉₀ values) did not differ significantly among the blueberry fields using different management practices.

CONCLUSIONS

The baseline sensitivity of D. suzukii has been characterized, allowing future comparisons if field failures of chemical control are reported. The concentration achieving high control indicates that effective levels of control can still be achieved with field rates of these four insecticides. However, declining susceptibility of some populations of D. suzukii to some key insecticides highlights the need for resistance monitoring. © 2017 Society of Chemical Industry.

The sterile insect technique for the management of the spotted wing drosophila, Drosophila suzukii: Establishing the optimum irradiation dose

The spotted wing drosophila Drosophila suzukii Matsumura (Diptera: Drosophilidae), a pest of berries stone fruits, invaded North America and Europe in 2008. Current control methods rely mainly on insecticides. The sterile insect technique (SIT) has potential as an additional control tactic for the integrated management of D. suzukii. As a step towards the development of the SIT, this study aimed at finding the optimum irradiation dose to sterilize D. suzukii under controlled laboratory conditions. Four-day-old D. suzukii pupae were irradiated 12 to 24 hours prior to adult emergence in a ⁶⁰Co Gamma Cell 220 and in a ¹³⁷Cs Gamma Cell 3000 with doses of 30, 50, 70, 80, 90, 100 or 120 Gy. Emergence rate (88.1%), percent of deformed flies (4.0%) and survival curves were not affected by the tested irradiation doses. However, some reproductive parameters of the flies were affected by irradiation. Females irradiated with a dose of 50 Gy or more had almost no fecundity. When non-irradiated females were mated with irradiated males, egg hatch decreased exponentially with irradiation dose from 82.6% for the untreated control males to 4.0% for males irradiated with 120 Gy. Mortality of F1 individuals from the irradiated treatment also occurred during larval and pupal stages, with an egg to adult survival of 0.2%. However, descendants produced by the irradiated generation were fertile. These results are an encouraging first experimental step towards the development of the SIT for the management of D. suzukii populations.

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.