Spotted wing drosophila (SWD) is native to South East Asia. It was first recorded as an invasive species in Hawaii in 1980, and in both California and parts of Europe in 2008. Since then it has spread rapidly throughout temperate North America and Europe, mainly due to global trade combined with an initial lack of regulatory controls. Its annual rate of range expansion has recently been estimated at approx. 1000 km (~620 miles) per year, and it is now established in parts of South America and the Middle East.
As a result of its global economic impact, spotted wing drosophila is the target of an intense global research effort encompassing various aspects of its biology and control. This article summarizes the results of some of this recent research that offers potential for the development of future pest management strategies. Please note that these reports do not constitute recommendations at this stage.
Summary of life-cycle
Spotted wing drosophila overwinters as a specialized (darker) adult morph that has greater cold tolerance than the summer form. Overwintered flies emerge in spring and feed on nectar from early flowering weeds and crops. Overwintering adults may live for more than 200 days, but the longevity of the summer form is considerably less. Reproductively mature female flies lay eggs in the ripening fruits of a wide range of host plants, including many wild, uncultivated species. Each female may produce 100–400 eggs, laying approximately 20 per day (depending on host availability and environmental conditions).
Recent research from Italy has shown that spotted wing drosophila can complete its lifecycle at temperatures as low as 53 °F; however, adult activity is highest at temperatures between 68 and 77 °F, and is reduced at temperatures above 86 °F. Adults are most active at dawn and dusk.
Larvae develop inside the fruit and complete their development in 3-13 days (depending on temperature). Pupation can occur in the fruit or in the soil, and the entire life-cycle can be completed in approx. 7–10 days (again, depending on temperature). Under optimal conditions, up to 13 generations per year are possible, although in the US and Canada 3–9 generations are more typical. Canadian research suggests that the lower lethal temperature for adult flies is in the region of 19 °F, although cold tolerance depends on the extent of prior exposure to fluctuating cool temperatures. There is evidence to suggest that females are more cold-tolerant than males.
Recent research results
i. Host plants
Fruits of susceptible host plants are liable to attack as soon as the fruit begins to soften and show color. Research with both raspberries and blueberries has shown that green, hard fruits are not at risk. The likelihood of egg-laying increases as the force needed to penetrate the fruit decreases: hence egg-laying is consistently high in raspberry and other thin-skinned fruits. In a recent US study, calcium treatments applied to blueberries in a field experiment produced firmer fruits that harbored fewer SWD eggs than fruits from untreated plots.
The wide host plant range of spotted wing drosophila can influence population levels at the landscape scale. In one US study, the abundance of wild hosts in nearby woods and hedgerows was implicated in the increased early-season risk of spotted wing drosophila in adjacent raspberries. However, it did not appear to influence the subsequent rate of population development in those crops.
As an indication of the wide host plant range of spotted wing drosophila, in recent field surveys in Europe, more than 24,000 adult flies successfully emerged from the fruits of 84 plant species from 19 different plant families, 38 of which were non-native species. The highest infestations were found in species of Cornus (dogwoods), Prunus (relatives of stone fruits such as cherries, plums, etc.), Rubus (raspberries, blackberries, and relatives), Sambucus (elderberry) and Vaccinium (blueberries and relatives). US research has shown a similarly wide range of hosts, including many of the above, as well as Morus (mulberry), edible blue honeysuckle (also known as haskap or honeyberry), and some common herbaceous weeds such as Solanum dulcamara (bittersweet nightshade). In Europe, spotted wing drosophila has also been found infesting mistletoe berries (Viscum album) – probably one of the earliest host fruits available for spring egg-laying.
In another European study, the fruits of several plants stimulated egg-laying by SWD females, but did not support full larval development and successful adult emergence. If these lab reports are supported by future field studies, such plants might be a useful component of an integrated control strategy as trap plants or so-called ‘dead-end’ hosts. For such an approach to be successful, however, the fruits must either be significantly more attractive than the crop being protected, or be present either earlier or later than the fruits of the target crop.
ii. Interactions with yeast
Once mated, adult female spotted wing drosophila respond strongly to odors produced by wild yeast species associated with fruit. These yeast odors are used as feeding cues, and may form the basis for developing an “attract-and-kill” strategy: in recent research, exposing flies to a mixture of yeast and insecticide reduced egg-laying and increased the mortality of adult flies compared to insecticide treatments alone. However, related work has shown that the effect is dependent on both the insecticide used, and the species of yeast. In some cases, there was no additional benefit from adding yeast to an insecticide spray that was also supplemented with cane sugar.
A rather more advanced approach to exploiting the attraction of SWD to yeasts involves the use of a genetically modified yeast strain to disrupt the expression and regulation of some of the pest’s critical genes by interfering with the normal functioning of its ribonucleic acid (RNA). Such ‘RNA interference’ techniques (RNAi) are being developed for many important crop pests. Recent lab-based research in California involved feeding a genetically modified yeast strain to adult spotted wing drosophila and recording mortality, activity and post-treatment egg-production: while there was no increase in fly mortality as a result of the treatment, the flies were less active and laid fewer eggs, prompting speculation that further refinements of the technique might have a future role in pest management.
iii. Environmental factors
Previous research has shown that SWD trap catches decline when humidity is low. Several research groups are now investigating whether different pruning and irrigation practices can reduce within-crop temperature and humidity and hence slow the rate of SWD population increase. Other research groups are comparing the survival of SWD in blueberry plantings with or without black plastic weed mats: the higher temperatures associated with the mats may reduce the survival of pupae in infested fruit that falls to the ground.
iv. Biological control
Various research groups in both North America and Europe have addressed the possible impact on spotted wing drosophila of both native natural enemies and a range of commercially available predators, parasitic nematodes and fungal pathogens. However, many of the studies have been conducted only under laboratory conditions and the results have been rather variable.
Two species of parasitic wasps (parasitoids) (Trichopria drosophilae and Pachycrepoideus vindemiae) have been found attacking SWD pupae in both the USA and Europe, as well as in the pest’s native range (various parts of Asia, including Japan and Korea). Trichopria drosophilae has a narrower host range than P. vindemiae and may have potential for mass-rearing for use in augmentative release programs. Additional parasitoids collected from South Korea are currently undergoing evaluation under quarantine in California, but it will be some time before such tests are completed.
v. Chemical control
At present, commercial producers rely heavily on season-long applications of a rather limited range of insecticides for spotted wing drosophila. With a pest such as this, with rapid rates of development and multiple generations per year, the risk of selecting for insecticide resistance is high. This is particularly true for enclosed tunnel systems (because of limited fly movement) and in organic plantings, where there are few effective chemical control options. There is already some evidence of reduced susceptibility to spinosad (Entrust®) in some organically managed berries in the western US. On the other hand, a recent study in Canada showed no increase in resistance to malathion in a laboratory population of SWD exposed to sub-lethal concentrations for 30 generations. Baseline monitoring for resistance to the most widely used insecticides is currently being conducted in fruit-producing regions in various parts of the US. Such monitoring will provide a valuable early-warning system if and when resistance develops.
In the meantime, a recent report from Georgia on the efficacy of insecticides used for SWD in blueberries showed that the adjuvant Nu Film P had some effect on prolonging the activity of spinetoram and spinosad after a simulated rainfall equivalent to 0.5″, and of malathion after a rainfall of approx. 1″. Nu Film P is listed by the Organic Materials Review Institute (OMRI) as suitable for use in organic production.
In conclusion, the heavy investment in research on spotted wing drosophila is now starting to produce results that at the very least will provide some additional management tools, and which in future may form the basis of a multi-tactic, integrated approach to the management of this pest.
This article was contributed by Tess Grasswitz, Extension Associate, Lake Ontario Fruit Program, Cornell Cooperative Extension. Originally published in Fruit Notes, Vol 16, Issue 18, August 18, 2016.
Two male SWD were caught in Steuben County on August 13, 2016 in a trap set within a small planting of raspberry and blueberry; no SWD were caught in the trap outside the planting. The following week, sustained catch occurred with 5 male SWD caught within the planting and 2 male SWD caught in the trap outside the planting. These traps are being monitored by Stephanie Mehlenbacher, association community educator, Steuben County Cornell Cooperative Extension.
This report completes SWD early season monitoring. All New York monitoring sites have caught SWD. Maintain an effective SWD management strategy on late season berry crops.
Got drought issues on your farm? Help us collect regional information on the 2016 drought so we can help you be better prepared in the future. Fill out the 2016 Drought Survey.
This summer we have experienced a period of lower than average rainfall combined with higher than average temperatures that has led to a drought of moderate to unprecedented severity in New York and much of the Northeast. Learn more about monthly precipitation and this year’s drought on the Northeast Regional Climate Center, on You’re NEWA, and on Cornell Climate Change. “There is no unique climate change signature to this drought. It is largely an unlucky sequence of events…”
A 2016 drought survey is being conducted and we need your input. The survey is online, has 15 questions and should take only 5-15 minutes to complete. If your crops and irrigation water have been affected by this year’s drought, please help us help you by filling out the survey. Please go to the following link: https://cornell.qualtrics.com/jfe/form/SV_9FDNwygyIV07kXP to access and complete the survey.
At this critical time, the survey seeks information on regional impacts and how you are coping with this situation. Our goal is for growers and those institutions and industries that support growers to be better prepared for drought in the future. If your farm is affected by the current drought, but you are outside of New York State, please include the state in your answer to question 1. Where is your farm located (nearest town, and county(ies))?
This research is being conducted by NatureNet Science Postdoctoral Fellow Shannan Sweet and Professor David Wolfe as part of their larger project on New York State water resources and agriculture.
Thanks for your help!
For more details on the 2016 drought see: http://climatechange.cornell.edu/drought-takes-its-toll/
This post was contributed by Shannan Sweet, Postdoctoral Fellow, Horticulture Section of the School of Integrative Plant Science, Cornell University, email@example.com.
Four male SWD were caught in traps set in a summer raspberry planting in Clinton County in the week ending July 11, 2016, indicating sustained catch. The following week, high numbers of SWD were caught and enumerated on July 19, 2016—10 male and 15 female SWD in the raspberries.
Traps set in the blueberries at this same location only had 2 female SWD in traps checked on July 19. A similar scenario was seen on another farm in New York where raspberry and blueberry are both grown. This would suggest that raspberry is more attractive to SWD and that traps set in raspberry may provide earlier warning of SWD arrival. This also suggests that raspberry is at higher risk of SWD infestation than blueberry.
Traps at this Clinton County location are being monitored by Lauren Fessler, summer intern, who is working with Amy Ivy, Extension Educator, Eastern NY Commercial Horticulture Program and Clinton County Cornell Cooperative Extension.
First trap catch in Essex County occurred on July 18, 2016 with a very large number of SWD caught in a summer raspberry planting. A total of 49 SWD, 33 male and 16 female, were enumerated in the four traps by Lauren Fessler, summer intern, who is working with Amy Ivy, Extension Educator, Eastern NY Commercial Horticulture Program and Clinton County Cornell Cooperative Extension. It is likely that sustained trap catch has occurred at this location by now.
A large number of SWD were caught during the week preceding August 3, 2016—53 females and 18 males—in traps set in a blueberry planting in Onondaga County. Luckily blueberry harvest at this location is winding down, because SWD populations are building up! These traps are being monitored by Nicole Mattoon, Field Technician, and Juliet Carroll, Fruit IPM Coordinator, NYS IPM Program.
On July 20, 2016 first catch of 7 female SWD was found in a blueberry planting in Seneca County. The following week SWD had been caught again in the traps, indicating sustained catch. Traps at this location are being monitored by Gabrielle Brind’Amour, technician with Greg Loeb’s small fruit entomology program, NYSAES, Cornell University, Geneva, NY.
On July 6, 2016 first catch of 1 female and 3 male SWD was found in a raspberry planting in Orange County. The following week, 2 female and 4 male SWD had been caught in the traps, indicating sustained catch. Traps at this location are being monitored by Tim Lamposona, technician with Peter Jentsch’s entomology program, Hudson Valley Research Lab, Cornell University, Highland, NY.
Eight female and one male SWD were caught on July 23, 2016 in traps set on the edge of a red raspberry planting in St. Lawrence County by Paul Hetzler, who works with Cornell Cooperative Extension of St. Lawrence County.
Climate, Weather, Data: Protecting Our Crops and Landscapes will be held August 15, 2016 at the Albany County Cornell Cooperative Extension Office, 24 Martin Rd., Voorheesville, NY 12186. Because space is limited, pre-register on the Registration page. Pre-registration closes on August 10. The Climate, Weather, Data portal has maps, an agenda and registration details. If you have questions, call Amanda Grace at firstname.lastname@example.org or 315-787-2208. The program will run from 9:00-4:15 and costs $45 – which includes lunch, breaks and materials. Yes, get NYS DEC credits, too!
With all the talk about climate change you might be wondering how it will affect food production, pests, and even landscapes—and what you can do about it. This is definitely a year when weather changes have affected our crops in the Northeast – from the Valentine’s Day massacre winter freeze to plant life gasping for water. Come and learn how gathering information on weather and climate can help growers, gardeners and landscapers plan for changes. Find details on The Climate and Weather Conference webpage.
We are honored that Richard Ball, the Commissioner of the New York State (NYS) Department of Agriculture and Markets, will kick off the conference with opening remarks. A wide variety of speakers from NYS and the Northeast will provide background information on the current state of knowledge on climate change and changes in our weather patterns, and how collecting climate and weather data can help us predict and manage pests. Open discussion sessions are included so you can ask your own questions. Join us to learn and discuss!
The morning session features information on Collecting weather data and predicting pests culminating with a discussion session with the speakers. The afternoon session covers Climate change and its impact on pests, also punctuated with an open floor when you can discuss your questions with the afternoon’s speakers.
Changing climates will affect our farms, from the crops we grow and the yields we can expect to the pests, weeds, plant and human pathogens, and other biological stressors we face. Nor are our landscapes, forests and wildlife, our homes and gardens, or our cities and roads exempt. What we can do about it? We have choices. Speakers from New York and across the Northeast offer their expertise. You’ll learn
- how “mesonets,” “Ag-Radar”, and “NEWA” help predict pest or disease outbreaks — in turn preventing infestations while reducing or eliminating sprays, whether on the farm or in our communities
- how growers in environmentally sensitive areas use data to their advantage
- how growers can lessen greenhouse gas emissions while improving their resiliency to drought or storms — and their productivity too
- what changing climate patterns could mean for where crop pests will show up next and what new tools can address the needs
- farmer-friendly tools that help people make climate-savvy decisions
- diseases and us: how changing climates could change where we find vectors — the critters new and old that carry diseases to our communities
- how a real-world simulation of crop growth in 2050 teaches us about which crops are at risk and which others might fill that niche
And especially — what you can do.
Experts from New York and the Northeast include: Richard Ball, commissioner of NYS Ag and Markets; Jerry Brotzge: NYS Mesonet; Becky Wiseman and Laurie McBride: Suffolk County Extension; Julie Carroll, NEWA and NYSIPM; Katie Campbell-Nelson, UMass Extension; Glen Koehler, UMaine Extension; Mike Hoffman and Allison Chatrchyan, Cornell Institute for Climate Change and Agriculture; Steve Young, NE IPM Center; David Hollinger, USDA NE Regional Climate Hub; Bryon Backenson, NY Bureau of Communicable Disease Control; Elizabeth Lamb, NYSIPM.
Portions of this post contributed by Mary Woodsen, Science Writer, NYS IPM Programkeep looking »