Spotted wing drosophila (Drosophila suzukii) utilization and dispersal from the wild host Asian bush honeysuckle (Lonicera spp.)

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

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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.     

Influences of blackberry margins on population dynamics of Drosophila suzukii and grape infestation in adjacent vineyards

Understanding the dynamics of pest insect populations in relation to the presence of non‐crop habitats and infestation levels of adjacent crops is essential to develop sustainable pest management strategies. The invasive pest species Drosophila suzukii (Diptera: Drosophilidae) is able to utilize a broad range of host plants. In viticulture, scientific risk assessment for D. suzukii has only recently started and studies assessing the effects of field margins containing wild host plants on D. suzukii population dynamics and on infestation risks in adjacent vineyards are lacking. Thus, in a one‐year field study, the role of different field margins on fly abundance and crop infestation in adjacent vineyards of Vitis vinifera, variety “Pinot Noir,” were investigated. Different monitoring methods were conducted to assess fly distribution, sex ratio and grape infestation in 14 vineyards adjacent to field margins containing either blackberry (BB) Rubus spp. or non‐host (NH) plants. Our results show that blackberries strongly enhanced D. suzukii abundance within field margin vegetation all year long, whereas fly abundance in vineyards adjacent to BB margins was just enhanced in some seasonal periods. Moreover, the influence of BB margins was limited by distance. However, high fly numbers in BB field margins did result in zero egg infestation of “Pinot Noir” berries. These results may have important implications for winegrowers to make efficient management decisions: regardless of high abundance of adult D. suzukii, only grape berry monitoring can assess the actual infestation risk and the potential need to take management action.     

Spatiotemporal dynamics of active flying Diptera predators among different farmland habitats

1. Farmland habitats comprise an arrangement of cropped, uncropped and natural vegetation among the farms. Despite the differences in these habitats' features, generalist highly mobile predators are more likely to explore them in time and space.
2. We investigated the spatiotemporal dynamics of the species of Dolichopodidae (Diptera) in organic vegetable farms because they are one of the most abundant generalist highly mobile predators in Brazilian agroecosystems.
3. We simultaneously sampled the abundance of Condylostylus Bigot and Chrysotus Loew adults (both Dolichopodidae) in the crop, fallow areas, agroforests and forest fragments within five organic farms for 2 years.
4. Predators preferred open-field habitats to agroforests and forest fragments. Probably, open-field habitats present more opportunities to prey foraging, resulting in higher population densities.
5. To the extent that abiotic conditions become more restrictive during the dry season, agroforests and forests act as breeding sites and shelter, thereby maintaining the predators' populations in the overall farmland habitat.
6. Both predatory genera occupy habitats with distinct features across time, forming a dynamic and contiguous population unit within the farm. Therefore, conservation biological control strategies in organic crops should consider the role of agroforests and forest fragments in species conservation beyond the plot level.

     

Seasonal occurrence of spotted wing drosophila in various small fruits and berries in Pennsylvania and Maryland

Spotted wing drosophila (SWD) (Drosophila suzukii), a major invasive pest of small fruit crops, was first found in Pennsylvania and Maryland during the 2011 crop season, and since then, it has been established throughout the fruit growing regions of both states. A season‐long field study was conducted to find out the seasonal occurrence of SWD in several fruit crops (e.g. blueberry, tart and sweet cherry, floricane‐fruiting summer red raspberry, blackberry, primocane‐fruiting fall raspberries and table grapes) in Pennsylvania and Maryland in 2014. This is the first study determining seasonal occurrence of SWD using a standard commercial lure (Pherocon^® SWD Dual‐Lure^?)‐baited traps in this region. In both states, SWD adults were not captured prior to the month of July, and populations of SWD were found to build up in fruit crops only from mid‐July onwards. This indicates early season fruit crops or varieties are not at risk from SWD fruit injury in these two states. Such early fruit crops, for instance strawberry, sweet and tart cherry, are generally harvested before SWD populations build up in this region. In this context, implications of SWD population in various small fruit crops grown in this region and the utility of SWD Dual‐Lure ^? in season‐long monitoring of SWD population are discussed.     

Spatial synchrony in Drosophila suzukii population dynamics along elevational gradients

1. Spotted wing drosophila (SWD; Drosophila suzukii Matsumura, 1931) is a polyphagous invasive crop pest native of Southeast Asia able to attack a wide array of host plant species in both cultivated and natural habitats. SWD is now widespread in several mountain regions, but it is still unclear how the species moves to different elevations across the seasons, and how this depends on environmental conditions and food resources. 2. The temporal dynamics of several SWD populations were studied along elevational gradients in the Alps using a synchrony analysis. Twelve transects were selected, covering an overall elevational gradient of 2100 m. SWD abundance was monitored every 2 weeks during the growing season (from June to November 2015) when cultivated and wild hosts are potentially susceptible (i.e. fruits are ripe). 3. Spotted wing drosophila were widely distributed along all the tested elevations, revealing synchrony in population dynamics across ranges in elevation and geographic distance. Synchronised populations were observed at distances of up to 100 km at sites with similar temperatures. The high dispersal potential of the pest together with the seasonal variation in temperature are likely to be the dominant mechanisms causing the observed spatial synchrony. A factor that seemed to reduce synchrony is the large concentration of host plants (i.e. crop) in lowland agricultural landscapes. 4. The spatial synchrony in pest abundance at large spatial scale indicates that the risk of SWD outbreaks is highly dependent on drivers beyond the control of traditional field‐scale management. These findings could help in developing monitoring and predictive models of SWD population dynamics.     

Environmentally sustainable pest control options for Drosophila suzukii

The spotted‐wing drosophila or cherry vinegar fly (Drosophila suzukii) is native to Asia but has invaded other continents since 2008 and has spread throughout Europe. The females have a serrated ovipositor allowing them to penetrate the skins of intact ripening fruits to deposit their eggs, and the developing larvae rapidly destroy the fruits close to harvest. Drosophila suzukii has a rapid life cycle and the larvae develop well beneath the fruit surface. This means that the use of pesticides is problematic and often not effective, first due to their restricted use close to harvest to protect consumers, and second because the larvae are deep enough inside the fruit to avoid contact. There are currently no effective and environmentally sustainable pest control methods for this species, resulting in extensive damage to fruit crops. Here, we review the current status of D. suzukii as a fruit crop pest and discuss the feasibility of current pesticide‐free control methods. We also consider the potential of new technologies as a basis for the urgently needed specific and long‐term control of this species.     

Risk assessment for non-crop hosts of pea enation mosaic virus and the aphid vector Acyrthosiphon pisum

1. Viral insect-borne plant pathogens have devastating impacts in agroecosystems. Vector-borne pathogens are often transmitted by generalist insects that move between non-crop and crop hosts. Insect vectors can have wide diet breadths, but it is often unknown which hosts serve as pathogen reservoirs and which non-crop host harbours the highest density of vectors.
2. In the Pacific Northwest USA, the pea aphid (Acyrthosiphon pisum) is a key virus vector in pulse crops. Despite pea aphid having a large number of potential non-crop plant hosts occuring in the region, no reservoir has yet been identified for the economically-costly pathogen Pea Enation Mosaic Virus (PEMV).
3. We addressed these issues by linking field surveys of an aphid vector and plant virus with statistical models to develop risk assessments for common non-crop legumes; in 2018, we completed a 65-site survey where aphids were surveyed in weedy legumes within and outside dry pea fields.
4. We quantified the abundance of pea aphids on 17 hosts, and plant tissue was tested for PEMV. Relatively high densities of A. pisum were found in habitats dominated by hairy vetch (Vicia villosa), which was the only legume other than cultivated dry pea where PEMV was detected.
5. Our results indicate that V. villosa is a key alternative host for PEMV, and that pest management practices in this region should consider the distribution and abundance of this weedy host in viral disease mitigation efforts for pulses.

     

Ingestible insecticides for spotted wing Drosophila control: a polyol,Erythritol, and an insect growth regulator,Lufenuron

Bioassays tested insecticidal activity of Erythritol from the nutritive sweetener, Truvia, and an insect growth regulator, Lufenuron, against life stages (eggs, larvae, pupae, adults) of Drosophila melanogaster (Meigen) and Drosophila suzukii (Matsumura), the spotted wing Drosophila (SWD). These compounds were chosen for their demonstrated acute toxicity to adult and larval Drosophila and potential use on organic fruit farms. D. melanogaster fed on standard Drosophila diet media moistened with water containing known concentrations of Erythritol. Likewise, SWD consumed standard diet media as well as thawed host fruit (blackberries and blueberries) treated with solutions of Erythritol, Lufenuron or both. During the first bioassay, Erythritol at lower concentrations between 0 and 500 mm (~61 000 ppm) in water and mixed with instant diet media increased adult survival from ~80% to 97% for D. melanogaster and SWD. However, from aqueous concentrations ranging from 1750 (~414 000 ppm) to 2000 mm (~244 000 ppm), Erythritol killed 100% of adult Drosophila in culture vials. One hundred per cent mortality for SWD and D. melanogaster occurred at ≥0.5 m (~61 000 ppm) Erythritol added to diet media or topically applied to host fruit. In a second bioassay, 0.013–1.000 ppm of aqueous Lufenuron, a chitin synthase inhibitor, when added to dry diet media prevented 90–99% of SWD from reaching the pupal stage. In another assay, ~67% of SWD eggs or neonates (early first instars) died inside blackberries pre‐treated with (dipped in) a soapy solution of 10 ppm Lufenuron. Pre‐treating blackberry fruit with an Erythritol–Lufenuron mixture reduced SWD brood survival by 99%. Likewise, during our last fruit‐based bioassay, 98% of eggs and neonates died inside blueberries similarly pre‐treated. During the last experiment, Lufenuron in diet media also rendered adult females sterile. Sterility, however, dissipated over 7 days once females began feeding on a Lufenuron‐free diet media.     

Evaluation of organic insecticides for management of spotted‐wing drosophila (Drosophila suzukii) in berry crops

Spotted‐wing drosophila, Drosophila suzukii (Matsumura), is an invasive pest affecting fruit production in many regions of the world. Insecticides are the primary tactic for controlling D. suzukii in organic as well as conventional production systems. Organic growers have a greater challenge because fewer insecticides are approved for use in organic agriculture. The most effective organically approved product is spinosad, but alternatives are needed because of label restrictions limiting the number of applications per year, toxicity to beneficial arthropods and the risk of developing resistance. We evaluated several organically approved insecticides against D. suzukii in laboratory assays and field trials conducted on organic blueberry and raspberry farms. Spinosad was consistently the most effective insecticide, but a few other insecticides such as azadirachtin + pyrethrins, Chromobacterium subtsugae and sabadilla alkaloids showed moderate activity. None of the treatments had long residual activity. Mortality started to decline by 3 days after treatment, and by 5 days after application, the treatments were not different from the controls. These products may be useful in rotation programmes, necessary for reducing reliance on spinosad and mitigating resistance. Cultural and biological control approaches are needed in fruit production for D. suzukii management, but insecticides will likely continue to be the dominant management tactic while these other approaches are being optimized and adopted.     

Invasive host for invasive pest: when the Asiatic cherry fly (Drosophila suzukii) meets the American black cherry (Prunus serotina) in Europe

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Estimating temperature effects on Drosophila suzukii life cycle parameters

1. Drosophila suzukii is an invasive, polyphagous pest of soft-skinned fruits, having huge impact on fruit production in Asia, North and South America and Europe including Germany.
2. To investigate the effect of temperature on oviposition, egg-to-adult development success and duration, as well as immature heat survival and adult cold survival for a German D. suzukii population several experiments were conducted under different constant temperatures in the laboratory. The resulting life cycle data were described mathematically as functions of temperature and compared with experimental results of other researchers in a summary table.
3. Curve fittings used herein revealed that minimum, optimum and maximum temperatures are: 13.2, 26.7 and 33.6 °C for oviposition, 14.1, 22.6 and 30.0 °C for egg-to-adult development success, and 9.6, 27.3 and 35.7 °C for egg-to-adult development duration. Eggs and larvae of D. suzukii showed a reduced heat survival within the tested temperature range of 29 to 41 °C and exposure durations from 1 to 8 h. A cold survival rate of 50% was measured at e.g. −6 °C for 4 h in summer morph adults and at e.g. −6 °C for 45 h in winter morph adults confirming that the latter are more cold tolerant.
4. Results obtained in this study for a German population of D. suzukii are similar to those obtained for populations of other origins such as Canada, Japan, Spain and USA. Thus, presumably, present data based on a German D. suzukii population can be used for a new or fine-tune of already existing population dynamics models of D. suzukii in order to support an effective pest management strategy.

     

A review on temperature and humidity effects on Drosophila suzukii population dynamics

1. Drosophila suzukii is an invasive polyphagous pest of wild and cultivated soft‐skinned fruits, which can cause widespread economic damage in orchards and vineyards.
2. The simulation and prediction of D. suzukii's population dynamics would be helpful for guiding pest management. Therefore, we reviewed and summarized the current knowledge on effects of air temperature and relative humidity on different life cycle parameters of D. suzukii.
3. The literature summary presented shows that high oviposition rates can occur between 18 and 30 °C. Temperatures between 16 and 25 °C resulted in fast and high egg‐to‐adult development success of more than 80%. Oviposition and adult life span were positively affected by high relative humidity; however, the factor humidity is so far rarely investigated.
4. We assume that this is one reason why relative humidity usually is not considered in modelling approaches, which are summarized herein. The high number of recently published research articles on D. suzukii's life cycle suggests that there is already a lot of knowledge available on its biology. However, there are still considerable research gaps mentioned in the literature, which are also summarized herein.
5. Nevertheless, we conclude that sufficient temperature data in the literature are suitable to understand and predict population dynamics of D. suzukii, in order to assist pest management in the field.

     

Bacillus thuringiensis serovar. israelensis has no effect on Drosophila suzukii Matsumura

The spotted wing drosophila (SWD), Drosophila suzukii, is an invasive species to the USA, and Europe and biological control methods are urgently sought for. In this study, the potential of commercial microbial control products based on the Dipteran‐specific B. thuringiensis serovar. israelensis (B.t.i.) were evaluated in laboratory experiments. These products were tested on SWD larvae and adults but neither one showed more than 10% mortality. A repellent effect of the products to SWD adults was also ruled out. We conclude that B.t.i. products are not suitable for SWD control.     

Interactive effects of local and landscape factors on farmland carabids

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Landscape-scale forest cover increases the abundance of Drosophila suzukii and parasitoid wasps

Agricultural landscapes rich in natural and semi-natural habitats promote biodiversity and important ecosystem services for crops such as pest control. However, semi-natural habitats may fail to deliver these services if agricultural pests are disconnected from the available pool of natural enemies, as may be the case with invasive species. This study aimed to provide insights into the relationship between landscape complexity and the abundance of the recently established invasive pest species Drosophila suzukii and a group of natural enemies (parasitoid wasps), which contain species that parasitize D. suzukii in native and invaded ecosystems. The importance of landscape complexity was examined at two spatial scales. At the field scale, the response to introduction of wildflower strips was analysed, while the relationship with forest cover was assessed at the landscape scale. Half of the surveys were done next to blueberry crops (Vaccinium corymbosum), the other half was done in landscapes without fruit crops to examine effects of D. suzukii host presence. As expected, the number of observed parasitoid wasps increased with amount of forest surrounding the blueberry fields, but the number of D. suzukii individuals likewise increased with forest cover. Establishment of wildflower strips did not significantly affect the abundance of D. suzukii or parasitoid wasps and insect phenology was similar in landscapes with and without blueberry crops. This suggests that D. suzukii is enhanced by landscape complexity and is largely unlinked from the species group that, in its native range, hosts key natural enemies. Although management practices that rely on enhancing natural enemies through habitat manipulations can contribute to the long-term stability of agroecosystems and to control agricultural pests, other control measures may still be necessary in the short term to counteract the benefits obtained by D. suzukii from natural habitats.     

Efficacy of commercially available predators,nematodes and fungal entomopathogens for augmentative control of Drosophila suzukii

The recent arrival of Drosophila suzukii, an invasive pest of soft‐skinned fruit with a wide host range, has resulted in increased production costs for growers and the need for additional insecticide applications each growing season. There are few effective organic insecticides for D. suzukii, and insecticide use in conventional farms may be disruptive to natural enemies, suggesting a need for effective biological control to combat D. suzukii. Commercially available natural enemies were evaluated for their potential use in augmentative releases, including: the predators Orius insidiosus and Dalotia coriaria; the entomopathogenic fungi Metarhizium anisopliae, Beauveria bassiana and Paecilomyces fumosoroseus; and the entomopathogenic nematodes Heterorhabditis bacteriophora, Steinernema feltiae and S. carpocapsae. This suite of natural enemies was chosen to target D. suzukii adults as well as larvae in hanging or dropped fruit. Of the cultured fungal strains tested, only M. anisopliae significantly decreased D. suzukii survival, but it had low residual activity and no effect on D. suzukii fecundity. O. insidiosus decreased D. suzukii survival in simple laboratory arenas but not on potted blueberries or bagged blueberry branches outdoors. D. coriaria did not decrease D. suzukii survival in infested blueberries in simple laboratory arenas. The nematodes tested showed low infection rates and were not able to affect D. suzukii survival. Although this suite of natural enemies showed limited ability to suppress D. suzukii under the tested conditions, these and related natural enemies are present as part of the endemic natural enemy community in agricultural fields, where they may contribute to D. suzukii suppression.     

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.     

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.