Susceptibility of cold hardy grapes to Drosophila suzukii (Diptera: Drosophilidae)

Drosophila suzukii (Diptera: Drosophilidae), known commonly as spotted wing drosophila, is a vinegar fly originating from South‐East Asia and a major pest to many soft‐skinned fruits. Due to the species recent arrival in North America in 2008, many fruit varieties are yet untested for susceptibility to infestation. While previous work has focused on Vitis vinifera, this study aimed to determine grape susceptibility of cold hardy varieties based on hybrids of V. labrusca, V. riparia and V. vinifera. Field sampling was conducted in Southern Wisconsin (USA) vineyards to establish adult and larval abundance and determine whether the number of adults caught in traps correlates with fruit infestation. Host susceptibility was further assessed through no‐choice bioassays of both intact and damaged fruits. The field study found D. suzukii adults present in all varieties, low larval abundance and no correlation between adult abundance and larval presence. Peak adult abundance occurred mid‐season between veraison and harvest, while larval infestation rates were highest near harvest. In laboratory no‐choice tests, significantly more eggs, larvae and adults occurred in damaged than undamaged grapes. In damaged grapes, larvae and adult abundance was comparable between varieties and to the highly susceptible control of undamaged raspberry; however, D. suzukii developed significantly faster in raspberry than grapes. Fruit characteristics (°Brix, titratable acidity, pH) in grapes were uncorrelated with D. suzukii performance. Together, these findings suggest that cold hardy grapes are overall resistant to D. suzukii if intact and highly susceptible if damaged.     

Screening of 25 different natural crop protection products against Drosophila suzukii

Drosophila suzukii is a major pest of soft‐skinned fruits, and insecticides are often used to prevent fruit damage caused by oviposition. As D. suzukii produces many generations per year, repeated insecticide applications are required. Furthermore, D. suzukii attacks ripening and ripe fruits shortly before harvest. Therefore, the use of synthetic insecticides is limited by long pre‐harvest intervals and maximum residue limits. To be able to offer producers immediate and sustainable solutions, we tested 25 natural crop protection products with three different application methods in a laboratory screening. We show that application method is an important factor for the efficacy of the tested products. Of six natural insecticides, only Spinosad was toxic for D. suzukii and reduced the oviposition on treated blueberries. The tested oil products had no control effect and products based on different entomopathogenic fungi and Bacillus thuringiensis rather enhanced oviposition. Mineral products (Kaolin, CaCO₃, Ca(OH)₂ and clinoptilolith) applied as spray solutions were not toxic, but significantly reduced oviposition on blueberries. We provide the first study in which different application methods have been used to compare numerous, commercially available, natural crop protection products with different modes of action against adult D. suzukii. Our findings provide consultants and producers with important insights for the development of sustainable pest control strategies against D. suzukii.     

Development of Asian parasitoids in larvae Of Drosophila Suzukii feeding on blueberry and artificial diet

In just a few years, the Asian fly Drosophila suzukii has invaded several continents and has become a very serious pest of many fruit crops worldwide. Current control methods rely on chemical insecticides or expensive and labour‐intensive cultural practices. Classical biological control through the introduction of Asian parasitoids that have co‐evolved with the pest may provide a sustainable solution on condition that they are sufficiently specific to avoid non‐target effects on local biodiversity. Here, we present the first study on the development of three larval parasitoids from China and Japan, the Braconidae Asobara japonica and the Figitidae Leptopilina japonica and Ganaspis sp., on D. suzukii. The Asian parasitoids were compared with Leptopilina heterotoma, a common parasitoid of several Drosophilidae worldwide. The three Asian species were successfully reared on D. suzukii larvae in both, blueberry and artificial diet, in contrast to L. heterotoma whose eggs and larvae were encapsulated by the host larvae. All parasitoids were able to oviposit one day after emergence. Asobara japonica laid as many eggs in larvae feeding in blueberry as in artificial diet, whereas L. heterotoma oviposited more in larvae on the artificial diet and the Asian Figitidae oviposited more in larvae feeding on blueberry. Ganaspis sp. laid very few eggs in larvae in the artificial diet, suggesting that it may be specialized in Drosophila species living in fresh fruits. These data will be used for the development of a host range testing to assess the suitability of Asian parasitoids as biological control agents in invaded regions.     

Acceptability of Drosophila suzukii as prey for common predators occurring in cherries and berries

The invasive cherry vinegar fly, Drosophila suzukii, has been identified in Europe as a destructive fruit pest since its arrival in 2008. In the present laboratory study, three predatory insects (Orius majusculus, Chrysoperla carnea, and Forficula auricularia) naturally occurring on fruit crops in Europe were investigated for their ability to attack and feed on D. suzukii within and outside fruits. The predators were provided with various D. suzukii life stages (eggs, larvae, pupae or adults) exposed or within infested cherries. The anthocorid bug O. majusculus fed on eggs and larvae, but was not able to attack pupae. Larvae of the lacewing C. carnea preyed upon D. suzukii eggs, larvae and pupae and also captured adult flies. The European earwig F. auricularia was the most voracious predator of these three tested species. Although the earwigs were not able to catch adult flies, they readily preyed upon every other developmental stage. Adult O. majusculus or third instar larvae of C. carnea significantly reduced the offspring of D. suzukii from infested cherries, when these contained the egg stage of the pest. None of the predators were able to attack early larval stages inside the cherries. But pupae that protruded from the fruit epicarp or that had pupated outside the fruit were accessible to lacewing larvae and earwigs and significantly reduced by them. Orius bugs, lacewing larvae and earwigs were able, under laboratory conditions, to capture and prey upon various life stages of the invasive pest, if not completely concealed inside the fruit. Our findings suggest that these generalist predators may have some control capacity on infested fruit in cultivated fruit crops and also in non‐crop habitats.     

Olfactory responses of Drosophila suzukii females to host plant volatiles

Drosophila suzukii Matsumura, an endemic pest in southeast Asia, has invaded Europe and the U.S.A. Unlike most of its closely related sibling species, the serrated ovipositor of D. suzukii permits ovipositing in undamaged fresh fruits. In the present study, volatiles are identified from host plants that are potentially involved in D. suzukii host recognition and oviposition behaviour. It is shown that mated females are attracted to volatiles emitted from intact fruits. The antennally‐active suite of compounds released from the fresh fruits is identified by gas chromatography coupled with electroantennographic detection, as well as gas chromatography‐mass spectrometry. In olfactometer bioassays, mated females are significantly attracted to an electroantennographically active volatile, isoamyl acetate, when tested at 10 µg of synthetic compound in a rubber septa, which has a release rate comparable to that of fresh fruits. In addition, a genomic survey shows that D. suzukii not only possesses the full repertoire of genes encoding odorant receptors activated by isoamyl acetate in D. melanogaster, but also that one of the genes, OR67a, is represented by five duplicated copies. These results indicate that D. suzukii uses olfactory cues to select oviposition sites. The identification of volatiles emitted by host fruits that attract D. suzukii may aid in the development of a selective and efficient synthetic lure for monitoring this pest. As a close relative of Drosophila melanogaster, D. suzukii provides a unique opportunity for understanding the physiological mechanisms involved in the shift of this species from use of rotten to ripe fruits for oviposition.     

Seasonal monitoring of Drosophila suzukii and its non-crop hosts in Wuhu,Eastern China

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is a serious pest that prefers fresh fruits and is native to Southeast Asia. In our study, apple cider vinegar bait traps were used to capture and monitor the population dynamics of this native pest in Wuhu City, China, from May/June 2017 to May 2018. The research was conducted at 15 locations in two fruit orchards in Wuhu. Traps caught more adults in general in a Meiling blueberry orchard than in a Xicun mixed orchard, and the highest trap counts occurred near harvest time (October). Females had more mature eggs from September to November, and the number of mature eggs declined thereafter. We found several non-crop hosts, which can provide food and reproductive resources for D. suzukii and are common in forests and field margins. By comparing the number of captured adults in the Meiling and Xicun orchards, we found that blueberry was preferred by D. suzukii among the fruits in our search. Fruit ripening times differed among crops; therefore, fly populations moved between crop and non-crop habitats during the year or had varying population dynamics on different crops in different seasons. The D. suzukii population and the number of mature eggs decreased in summer and winter but increased in spring and autumn. Drosophila suzukii had higher survival rates with blueberry than those with other fruits, and D. suzukii could use four non-crop species growing around the orchards as host plants.     

Ecological, morphological and molecular studies on Ganaspis individuals (Hymenoptera: Figitidae) attacking Drosophila suzukii (Diptera: Drosophilidae)

Ganaspis individuals parasitizing Drosophila suzukii (Matsumura), a pest of fruit crops, were examined for host use and molecular and morphological differences from those attacking D. lutescens Okada and some other Drosophila species that breed on fermenting fruits. Wild cherry fruits were collected in the suburbs of Tokyo, and drosophilid pupae obtained from these fruits were examined for parasitism. Drosophila suzukii was the only drosophilid species infesting fresh wild cherry fruits, and Ganaspis individuals were the major parasitoids attacking D. suzukii in wild cherry fruits. In parasitism experiments, these Ganaspis individuals parasitized D. suzukii larvae in fresh cherry fruits, but did not parasitize those in Drosophila medium. In addition, they did not parasitize larvae of some other fruit-feeding Drosophila species even when these occurred in fresh cherry fruit. These Ganaspis individuals parasitizing D. suzukii were different from those parasitizing D. lutescens and some other drosophilids in nucleotide sequences of the COI gene, as well as in ITS1 and ITS2. They were also different in forewing and antenna morphology, although they showed some overlap in morphological traits. They are tentatively assigned as the suzukii- and lutescens-associated types of G. xanthopoda Ashmead. In the present field survey, Leptopilina japonica Novkovi? & Kimura and some Asobara species were also observed to attack D. suzukii larvae in wild cherry fruit.     

水果害虫斑翅果蝇体内微生物菌群研究进展

斑翅果蝇是一种在全球范围内造成危害的重要水果害虫,其主要分布于亚、美、欧三大洲。斑翅果蝇的产卵器可以刺破水果表皮,将卵产在未完全成熟的水果中,卵孵化为幼虫后,幼虫取食水果,直接降低产量,从而对水果产业造成损失。近年以来,越来越多的研究表明昆虫微生物对宿主昆虫影响很大。例如昆虫微生物可以调控寄主昆虫的生长发育、个体适应性及生殖等。昆虫与其共生微生物间的关系成为昆虫生物学研究的热点内容。本文综述了近些年关于斑翅果蝇微生物多样性的研究,探讨了微生物菌群及内共生菌Wolbachia对斑翅果蝇生长发育、行为、生殖、抗病毒等的影响,以便为寻找控制斑翅果蝇种群的策略提供参考依据。     

Effect of fruit host on wing morphology in Drosophila suzukii (Diptera: Drosophilidae): A first view using geometric morphometrics

The invasive alien fruit pest Drosophila suzukii, (Matsumura 1931) causes economic loss in soft‐skinned fruit production across Europe. After its first detection in 2008, the species has successfully expanded to a wide geographic area and invaded new host plants in a relatively short period of time. The aim of the present study was to analyze the connection between food preferences as host specialization and the morphology of D. suzukii. Population morphological variation in wings was investigated in two different host fruits (grape and strawberry) in which economic damage has been recorded. The geometric morphometric results revealed two noticeable wing shape morphotypes in D. suzukii (i.e. vein configuration) between the grape and strawberry fruits. Flies reared in grapes had wider wings, whereas flies grown in strawberries had more narrow wings. These differences in morphotype could be explained by the effects of wing aerodynamics, which affect the strength of the wings in flight. This, in turn, can lead to better dispersion within the associated fruit host. These results confirm that this extremely invasive species, found worldwide, is successful at spreading in part because of its potential to adapt rapidly under different rearing conditions. Therefore, adaptive variations in the wing shape of D. suzukii can be used to differentiate populations based on food preference (e.g. soft fruits) and can serve as an additional tool for detecting different bioecological types of D. suzukii.     

Ein Winzling lehrt das Fürchten

The invasive Spotted Wing Drosophila – a significant pest The Spotted Wing Drosophila (Drosophila suzukii), native in South-East Asia, is an invasive pest belonging to the small fruit fly family of Drosophilidae, also named vinegar flies. Apparently displaced by global trade to the USA and Europe, this pest was able to disperse enormously over the continents since 2008. Ideal preconditions for this spread were suitable climatic conditions, the availability of a wide variety of host plants and the use of an ecological niche, namely healthy ripening and ripe fruits. In addition, D. suzukii is highly reproductive and owns excellent overwintering strategies. The Spotted Wing Drosophila is difficult to control and causes enormous damage.     

Potential host fruits for Drosophila suzukii: olfactory and oviposition preferences and suitability for development

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), the spotted wing drosophila, is a pest endemic to Southeast Asia that invaded the Americas and Europe in 2008. In contrast to most of its congeners, D. suzukii possesses a serrated ovipositor that allows it to lay eggs in unwounded commercial fruits, resulting in severe revenue losses for the industry. The purpose of this study was to determine the susceptibility of known host fruits, including cherry, strawberry, blueberry, and grape, and potential host fruits, such as banana and apple, to attack by D. suzukii. Based on the responses to volatile cues offered in a six‐choice olfactometer, the preference of female D. suzukii was ranked in the following order: strawberry = cherry > banana = apple = blueberry = grape, but in no‐choice and choice oviposition tests, the preferences were ranked as follows: cherry > strawberry = blueberry > grape = banana > apple. Furthermore, we reconfirmed that D. suzukii mainly targets rotten fruit for feeding and ripe fruit for oviposition, and females preferred fruits with intensive mechanical damage. Based on developmental parameters, apple was the least suitable host. This study has implications for the control of D. suzukii, especially in mixed fruit orchards, by providing a promising avenue for exploiting behaviour‐based control tools and emphasizing the importance of phenology in host fruit susceptibility.     

Spillover of Drosophila suzukii between noncrop and crop areas: implications for pest management

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Capacity of Japanese Asobara species (Hymenoptera; Braconidae) to parasitize a fruit pest Drosophila suzukii (Diptera; Drosophilidae)

Drosophila suzukii is a pest of soft fruit such as cherry, strawberry or blueberry and recently colonized North America and Europe from Asia. In this study, we assessed the utility of Japanese Asobara species as agents for the biological control of this pest species by examining their host use in nature and their capacity to parasitize this pest species. From Japan, eight Asobara species including putative three undescribed species were found; Asobara japonica was recorded from all over Japan, Asobara tabida from high altitude areas in central and northern Japan, Asobara rossica and Asobara rufescens from central to northern Japan, three undescribed species from central to western or southern Japan and Asobara pleuralis from a subtropical island of Japan. Among them, an undescribed species Asobara sp. TK1 may be useful as an agent for the biological control because it was recorded only from D. suzukii. All of the remaining seven species were generalists mainly using drosophilid species associated with fermenting fruits, and four of them had no or very low abilities to parasitize D. suzukii, indicating that these seven species are not or less appropriate as agents for biological control.     

Efficacy of biopesticides on spotted wing drosophila,Drosophila suzukii Matsumura in fall red raspberries

Drosophila suzukii Matsumura is a significant pest of soft‐skinned fruit. Larvae of D. suzukii develop within the fruit making it unmarketable as fresh berries and increasing the risk of rejection by processors. We evaluated selected biopesticides for control of D. suzukii in fall red raspberries, Rubus idaeus L. The trial results highlight a small number of biopesticides with the potential to reduce infestation of Drosophila larvae in raspberries. In addition to the standard biopesticide spinosad, we found that sabadilla alkaloids and Chromobacterium subtsugae both reduced the number of Drosophila larvae in raspberry fruit. Treatments that included corn syrup as a feeding stimulant showed no significant difference in their infestation levels compared to treatments without the syrup. In the final week of the 5‐week trial, treatments with rotations of either spinosad/C. subtsugae or spinosad/sabadilla alkaloids had a 67% and 57% reduction in infestation when compared to untreated raspberries. Treatments of spinosad alone on a 7 day rotation and C. subtsugae alone on a 3–5 day rotation both had a 62% and 61% reduction in larval infestation when compared to untreated raspberries. Third instar larvae, the largest and most damaging, were significantly reduced in plots treated with spinosad only, a rotation of spinosad/sabadilla alkaloids and the rotation of spinosad/C. subtsugae with corn syrup added when compared to untreated plots. This suggests that either of these biopesticides could be used as effective rotation partners along with spinosad for control of D. suzukii. Our results highlight that biopesticides can provide significant reduction in this devastating pest when used alone or in combination, providing options to support resistance management.     

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

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

Evaluation of adjuvants to improve control of spotted‐wing drosophila in organic fruit production

Spotted‐wing drosophila, Drosophila suzukii (Matsumura), is a key pest of berry crops in the United States. It is managed intensively using insecticides, but organic fruit growers have few effective chemical control options. Spinosad is the most effective organically approved product for control of D. suzukii, while other organic options have not shown high levels of control. Adjuvants are products added to pesticides to improve effectiveness, and these may function as stickers, spreaders or surfactants improving the spray coverage of insecticides on surfaces and thereby increasing the likelihood that pests will contact residues. We conducted experiments evaluating organically approved biopesticides in combination with three adjuvants including poly‐1‐p‐menthene, alcohol ethoxylate and polyether‐polymethylsiloxane‐copolymer polyether to determine whether addition of adjuvants improved efficacy and residual activity of these products. Alcohol ethoxylate and poly‐1‐p‐menthene showed some inherent insecticidal activity against D. suzukii in laboratory assays. Adjuvants increased mortality of some insecticides but not to a level that would provide adequate fruit protection. Poly‐1‐p‐menthene had a negative effect when combined with hydrogen peroxide + PAA and sabadilla alkaloids. Mortality in semi‐field bioassays was quite low except for spinosad. Polyether‐polymethylsiloxane‐copolymer polyether had a negative effect on the efficacy of spinosad. The adjuvants did not extend residual activity of the insecticides. Adjuvants did not provide the expected benefits of increased performance against D. suzukii when combined with organic biopesticides. Other methods for enhancing these insecticides will need to be explored to provide organic growers with more effective chemical control options for this invasive pest.     

Effects of sweet alyssum flowers and their volatile compounds on Drosophila suzukii (Matsumura) in the laboratory

Drosophila suzukii (Matsumura) is a major global pest of soft fruit crops. Based on field observations, we tested in the laboratory whether sweet alyssum (Lobularia maritima (L.)) flower volatiles and their major constituent compounds, acetophenone and benzaldehyde, repelled D. suzukii flies. Volatiles from cut flowers and acetophenone reduced numbers of D. suzukii attracted to raspberries, and acetophenone reduced numbers of larvae in the raspberries. Testing of sweet alyssum plantings or dispensing acetophenone to repel D. suzukii in fields and lower fruit infestation should be conducted.     

Impact of phagostimulants on effectiveness of OMRI‐listed insecticides used for control of spotted‐wing drosophila (Drosophila suzukii Matsumura)

Spotted‐wing drosophila, Drosophila suzukii Matsumura, is an invasive pest in the United States that causes considerable damage to fruit crops. It is responsible for many millions of dollars of revenue loss. The female D. suzukii has a heavily sclerotized ovipositor and can lay eggs in ripening or ripe fruit. The arrival of this invasive species has disrupted existing integrated pest management programmes, and growers rely on repeated insecticide applications to protect fruit. Organic growers have few chemical control options, and their reliance on spinosad increases the risk of developing insecticide resistance. We hypothesized that combining phagostimulants with insecticides would increase insecticide efficacy by prompting flies to spend more time in contact with residues. Therefore, the objective of this study was to evaluate the effectiveness of sucrose and the yeast Saccharomyces cerevisiae as phagostimulants in combination with organic biopesticides against D. suzukii in blueberries. Adding sucrose with or without yeast did not improve insecticide efficacy in terms of adult fly mortality or fruit infestation. Spinosad was very effective in all experiments, and for this product, there is little room for improvement. The phagostimulants had no effect on residual activity of any insecticide. The addition of sucrose with or without yeast did not improve the effectiveness of organic insecticides for D. suzukii. Concentrations of these phagostimulants in our experiments (0.36%) may have been too low to elicit a response. Further research is recommended to test different types and concentrations of phagostimulants.     

A chitinase from Euphorbia characias latex is a novel and powerful plant‐based pesticide against Drosophila suzukii

Drosophila suzukii attacks on developing soft fruits have recently caused important economic losses in Europe. This study explores the effectiveness of a new control strategy against this insect pest that is based on a plant chitinase extracted from the latex of the Mediterranean spurge, Euphorbia characias. The ability of the purified Euphorbia latex chitinase (ELC) to degrade the chitin exoskeleton of D. suzukii was assessed using confocal laser scanning microscopy. ELC treatment caused reduced larval growth, higher mortality and notable degradation of external insect structures. Therefore, the chitinase may induce a double effect on the D. suzukii larvae, a direct injury on the larval bodies and an action as antifeedant. The effects of the ELC treatment were also tested on leaves of the insect's host plants, Fragaria × ananassa and Rubus idaeus, using physiological parameters (chlorophyll concentration, chlorophyll fluorescence, leaf gas exchange and water potential) and defence gene expression (FaPGIP, FaChi2_1 and FaChi2_2) as stress indicators. ELC at concentrations effective against D. suzukii did not damage the host plants. Only plant defence gene expression was somewhat enhanced during the early hours after ELC application. In conclusion, ELC, a natural product, proved to be an effective tool for use in the development of an environmentally friendly integrated management strategy against D. suzukii, a pest whose control by conventional chemical insecticides is problematic.     

Not berry hungry? Discovering the hidden food sources of a small fruit specialist,Drosophila suzukii

1. Although polyphagy is widespread among Drosophila, some specialist species have evolved in response to resource competition and other selection factors favouring niche separation. The small fruit specialist Drosophila suzukii Matsumura has evolved a unique serrated ovipositor that allows it to access ripening fruit, a niche unavailable to most Drosophila. However, it is unclear whether ancestral traits (the use of non‐fruit resources) are maintained in this specialist species. 2. In this study, maternal preferences and offspring fitness in response to novel apple, mushroom, and bird manure‐based diets were investigated by comparing oviposition and offspring survival and development on various diets. The effect of those diets on survival at cool temperatures and the effect of natal environment/previous exposure on adult preferences were evaluated. 3. Female D. suzukii accepted non‐fruit diets such as mushroom and bird manure, and offspring completed their larval development on all diets tested. However, D. suzukii did not perform well on diets that included bird manure. By contrast, combinational apple/mushroom diets were associated with greater oviposition, lower mortality, faster development, and larger offspring than other diets. These diets were also associated with increased resistance to cold stress, and preference for these diets was positively affected by previous feeding experience. 4. These data suggest that D. suzukii may use non‐fruit resources when preferred resources are scarce. Given that this pest is adapted to temperate climates, alternative resources might provide seasonal nutritional support when fruit resources are not temporally available, although field data are needed to support this hypothesis.