- Author: Kathy Keatley Garvey
But agriculturists and scientists have.
The spotted-wing drosophila (SWD), Drosophila suzukii, is an agricultural pest that is super tiny.
It's approximately 2 to 4 millimeters in length with a wingspan of 5 to 6.5 millimeters. One millimeter is approximately 0.039 inches. There are 25.4 millimeters in 1 inch. So, the adult is about the size of a grain of sand, which can measure 0.5 to 2 mm in diameter.
SWD, native to southeast Asia and first discovered in California in 2008, lays its eggs in such soft-skinned, ripening fruits as strawberries, raspberries, cherries, blueberries, peaches, nectarines, apricot and grape.
In 2008, the first year of its discovery in California, the economic loss attributed to this pest amounted to $500 million. Latest statistics from 2015 indicate a $700 million national economic loss.
Lead author of the paper, “Transcriptome Analysis of Drosophila suzukii Reveals Molecular Mechanisms Conferring Pyrethroid and Spinosad Resistance,” is Christine Tabuloc, then a doctoral candidate and now a postdoctoral researcher working under the mentorship of Professors Chiu and Zalom.
"In this work, we leveraged high throughput sequencing to identify biomarkers of insecticide resistance in D. suzukii,” Tabuloc explained. “We found that different genes are responsible for resistance to different chemicals. Specifically, we found that genes involved in metabolism are highly expressed in flies resistant to pyrethroid insecticides. We also observed evidence of two different mechanisms of resistance in 2 lines generated from a single spinosad-resistant population. We found an increased expression of metabolic genes in one line and increased expression of cuticular genes in the other.”
Tabuloc added that “our work has enabled for the detection of resistance in California populations, and we are currently doing a nationwide screening to determine whether resistance is now present in other states. Currently, we are working with the Zalom lab to use the results of our assays to try and combat resistance. There are experiments in progress trying to increase the efficacy of insecticides by blocking some of the genes involved in resistance, such that the enzymes encoded by those genes have decreased function."
A giant in the entomological world, Zalom directed the UC Statewide Integrated Pest Management Program for 16 years. He is an Honorary Member of the Entomological Society of America (ESA), the highest ESA honor, and he served as its president in 2014.
“This work not only represents good science; it has very practical implications," Zalom said. He and Tabuloc presented results of the work at a special berry grower seminar on insecticide resistance organized by UC Agriculture and Natural Resources (UC ANR) Farm Advisor Mark Bolda, strawberry and caneberry farm advisor in Santa Cruz, Monterey and San Benito counties, Mark Bolda in Watsonville.
"The presentations were extremely well-received," Zalom noted. "The original program was targeted for about 1.5 hours, but the meeting extended to over three hours due to the extent of questions and great discussion that followed. Growers and their consultants are hungry for new information that they find interesting and potentially useful, and this work was clearly of interest to them.”
Said Bolda: “The research was top shelf and the need, of course, is very great. Some of the information that Frank and Christine presented has been put into immediate use in the industry.”
What most people don't know is that Bolda was the first to discover the pest in North America. That was in 2008.
"He asked me to come down to look at it and the problem...we weren't able to get an actual species identification until 2009!" Zalom said.
As the pest continues to spread throughout much of the country, anxious growers are worried about its increased resistance to pesticides. The UC Davis research team is alleviating that worry.
- Author: Surendra K. Dara
Male spotted wing drosophila adult. Photo by Gevork Arakelian, Los Angeles County Ag Commissioner's Office
Spotted wing drosophila (SWD), Drosophila suzukii is a pest of several small fruit in California and other states. SWD belongs to the group of flies that are generally known as vinegar flies or lesser fruit flies. It was initially known as cherry fruit fly in 1930s and is now referred to as spotted wing drosophila. SWD can be distinguished from other Drosophila spp. based on the following traits:
- Females have a hard and dark (sclerotized) ovipositor with prominent serrations or saw-teeth that enable the fly to lay eggs in intact ripening fruit.
- Antennae with branched bristle-like part called arista.
- Males have a distinctive dark spot at the tip of each wing.
- Males also have two dark bands (combs) of 3-6 teeth on each front leg.
Sclerotized ovipositor of SWD (right) compared to the normal ovipositor of a vinegar fly (left).
Distinctive combs on the front legs of male spotted wing drosophila. Photo by Gevork Arakelian.
Origin and distribution: It is traditionally known to be a pest in Asia, but it is now reported in Neotropics, North America, and Europe. In the US, it has been reported in Hawaii, Washington, Oregon, California, Utah, Minnesota, Michigan, Missouri, Louisiana, West Virginia, Pennsylvania, North Carolina, South Carolina, and Florida.
Host range: They generally infest thin-skinned fruit and prefer temperate climate. Host range includes apple, blackberry, blueberry, cherry, dogwood, grape, mulberry, peach, persimmons, plum, raspberry, and strawberry. Non-crop hosts that support SWD populations include barberry, brambles (wild raspberry and blackberry), buckthorn, cotoneaster, currant, dogwood, elderberry, fig, honeysuckle, laurel, mulberry, nightshade, oleaster, orange jasmine, pin cherry, pokeweed, purple flowering raspberry, spicebush, sweet box, and yew.
Biology: SWD prefer 68-86 oF and overwinter as adults. Various sources suggested 5-10 generations per year. Eggs are translucent to milky-white. Females lay an average of 384 eggs at 7-16 per day and there can be 1-3 eggs per oviposition site. Multiple females may deposit eggs in the same fruit. Eggs hatch in 2-72 hours and larval stage lasts for 3-13 days. Larvae milky-white with a legless body tapering towards the anterior end (towards the head). Mouthparts are dark and sclerotized. Pupation takes place inside the fruit or in the soil and lasts for 3-15 days. Pupae are reddish brown and have two spiracles (breathing tubes) at the anterior end. Adults are small (2-3 mm) flies. Life cycle takes anywhere from 21-25 days at 59 oF to 7 days at 82 oF. Females can start laying eggs within 1 day after their emergence and can lay more than 400 eggs in their lifetime. Based on the degree day (DD) calculations, egg, larval, and pupal stages require 20.3, 118.1, and 200 DD.
Damage: Other fruit flies usually infest overripe and fallen fruit, but SWD infests fresh fruit because of its powerful ovipositor. Adults feed on fallen fruit but lay their eggs under the skin of intact fruit. Softening and collapse of the tissue results from larval feeding inside the fruit. Oviposition holes can be seen on the fruit with close observation. In addition to the direct damage, SWD makes the infested fruit vulnerable to other pests and diseases. Monitoring SWD is very important to avoid harvesting and marketing infested berries.
Monitoring: Use traps made with apple cider vinegar or yeast-sugar solutions for early detection of SWD. There are numerous studies using a variety of containers and attractants. Pherocon traps and lures are commercially available for SWD monitoring.
Management: A variety of organic and conventional management options are available.
Cultural – Discard fallen and unmarketable fruit in the field to prevent infestation. Remove wild hosts in the vicinity that might harbor SWD populations.
Botanical – Pyrethrins and azadirachtin products are used in multiple studies.
Chemical – Research indicates that organophosphates, pyrethroids, and spinosyns are among the chemicals that can be used against SWD. Remember to rotate chemicals among different mode of action groups to reduce the risk of resistance development.
Microbial – Entomopathogenic fungi (Beauveria bassiana or Isaria fumosorosea) and bacteria-based products such as Grandevo (Chromobacterium subtsugae) and Venerate (Burkholderia rinojensis) against adults, and entomopathogenic nematodes (Heterorhabditis spp. and Steinernema spp.) against pupae that form outside the fruit can be used.
Additional resources:
http://ipm.ucanr.edu/PMG/PESTNOTES/pn74158.html
http://www.omafra.gov.on.ca/english/crops/facts/swd-wildhosts.htm
http://www.ipm.msu.edu/uploads/files/SWD/em9113.pdf
http://entnemdept.ufl.edu/creatures/fruit/flies/drosophila_suzukii.htm
http://pest.ceris.purdue.edu/map.php?code=IOAPAUA
http://www.ipm.msu.edu/invasive_species/spotted_wing_drosophila/factsheets
- Author: Mary Louise Flint
[From March 2013 issue of the Retail Nursery and Garden Center IPM News.]
Spotted winged drosophila (SWD), Drosophila suzukii, is a fruit fly that first arrived in
Unlike other fruit flies that attack fruit only after it has ripened and is starting to deteriorate, SWD attacks healthy fruit on the tree just before the fruit ripens. On trees with mid- to late-season ripening varieties, almost every cherry can be affected. Unfortunately, gardeners don't often notice the infestation until harvest. By then it is too late to do anything to manage the problem.
Adults lay eggs inside fruit just as it begins to ripen, creating tiny pinprick holes (Figure 2). Eggs hatch into small maggots that feed internally in the fruit. Infested fruit may often have a number of maggots (Figure 3). Fruit turns mushy and brown and is sometimes invaded by secondary bacteria or fungi.
Home gardeners who had SWD infestations last year will probably want to take some steps to reduce the problem this year. If cherries weren't infested last year, gardeners with cherries should regularly check ripening fruit for damage before unnecessarily treating with a pesticide. They may also wish to hang a fruit fly trap baited with pure apple cider vinegar to help with detection.
Timing Sprays. Sprays should begin as soon as fruit begins to turn from yellow to pink (usually about two to three weeks before harvest). If you didn't have damage from SWD last year, look for stings on fruit to confirm an infestation. You can also hang a fruit fly trap baited with apple cider vinegar and check regularly for fruit flies with spotted wings. If infestations were significant last year, it is probably advisable to treat. In any case, spray when stings are first seen. A second spray should be applied 7 to 10 days later, but be sure to observe the preharvest interval on the label. The only organically approved less toxic insecticide known to be effective on SWD is spinosad. Other products such as malathion can be used, but these are very toxic to natural enemies and bees and can lead to outbreaks of secondary pests.
Gardeners should be urged to clean up and destroy any cherries that drop on the ground or remain infested on trees.
For more information, see Pest Notes: Spotted Wing Drosophila.
This article was originally published in the March 2013 issue of the Retail Nursery and Garden Center IPM News. See this and other articles at http://www.ipm.ucdavis.edu/RETAIL/retail-newsletter.html.
/span>- Author: Surendra Dara
Spotted wing drosophila (SWD), Drosophila suzukii has become a potential concern for strawberries following its damage to cherries, blackberries, raspberries, and blueberries in coastal California. Other species of Drosophila are morphologically not equipped to attack ripening strawberries. Their ovipositors or egg laying parts are not strong enough to penetrate unripe or ripening berries. They may damage overripe strawberries left on the crop, but since such berries are not marketed, they have not been an issue for growers. However, SWD has a heavily sclerotized, serrated ovipositor that enables it to lay eggs in fruits that are not fully ripe.
In response to the concern that SWD could be a potential pest to strawberries, I monitored some fields in Santa Maria last year. Five fields – four conventional and one organic – in various parts of Santa Maria were monitored for five months from March to July, 2011. Two kinds of traps, one with apple cider vinegar and the other with yeast-sugar extract were used in each location and were observed every week. During this monitoring there were no signs of SWD in any of these traps. However, I recently received some specimens from a Santa Maria grower in which I found what seemed to be the females of SWD among other Drosophila sp. There were no males with their obvious characteristic of spotted wings, but the following and other characters of the females suggest these were SWD:
- Hard and dark (sclerotized) ovipositor with prominent serrations or saw-teeth that enable the fly to lay eggs in intact ripening fruit.
- Antennae with branched bristle-like part called arista.
According to Dr. Brian Cabrera, Santa Barbara County Ag Commissioner Entomologist, there haven't been any SWD infestations that were brought to his attention. So, it appears to be the first report of SWD in Santa Maria strawberries. Sanitation, trapping, and chemical control are among the available options to manage SWD. Close monitoring is necessary in vulnerable areas. More details about identifying and managing SWD can be found in the listed references. Here is a brief note about this pest.
SWD belongs to the group of flies that are generally known as vinegar flies or lesser fruit flies. It was initially known as cherry fruit fly in 1930s and is now referred to as spotted wing drosophila.
Origin and distribution: It is traditionally known to be a pest in Asia, but it is now reported in Neo Tropics, North America, and Europe. In the US, it has been found in Hawaii, Washington, Oregon, California, and Florida.
Host range: They generally infest thin-skinned fruit and prefer temperate climate. Host range includes apple, blackberry, blueberry, cherry, dogwood, grape, mulberry, peach, persimmons, plum, raspberry, and strawberry.
Biology: SWD prefer 68-86 oF and overwinter as adults. Various sources suggested 5-10 generations per year. According to Kanzawa (1939) egg laying starts in spring and can last for 10-59 days. Females lay an average of 384 eggs at 7-16 per day. Eggs hatch in 2-72 hours and larval stage lasts for 3-13 days. Pupation takes place inside the fruit or in the soil and lasts for 3-15 days. Life cycle takes anywhere from 21-25 days at 59 oF to 7 days at 82 oF.
Damage: Other fruit flies usually infest overripe and fallen fruit, but SWD infests fresh fruit because of its powerful ovipositor. Adults feed on fallen fruit but lay their eggs under the skin of intact fruit. Softening and collapse of the tissue results from larval feeding inside the fruit. Oviposition holes can be seen on the fruit with close observation. In addition to the direct damage, SWD makes the infested fruit vulnerable to other pests and diseases. Monitoring SWD is very important to avoid harvesting and marketing infested berries.
Maggots (of unknown species) in infested fruits showing up in processed strawberry container. Photo by Surendra Dara
http://ucanr.edu/articlefeedback
References
Calabria G., J. Máca, G. Bächli, L. Serra and M. Pascual. 2012. First records of the potential pest species Drosophila suzukii (Diptera: Drosophilidae) in Europe. J. Appl. Entomol. 136:139-147.
Kanzawa, T. 1939. Studies on Drosophila suzukii Mats. 49 pp. (http://www.cabdirect.org/abstracts/19410501073.html;jsessionid=81E9221496390100F7C13052E18F8079)
http://www.agf.gov.bc.ca/cropprot/swd_identification.pdf
http://www.al.gov.bc.ca/cropprot/swd.htm
http://entnemdept.ufl.edu/creatures/fruit/flies/drosophila_suzukii.htm
http://www.freshfromflorida.com/pi/pest-alerts/drosophila-suzukii.html
http://www.ipm.ucdavis.edu/EXOTIC/drosophila.html
- Author: Chris M. Webb
UC Integrated Pest Management (IPM) Program has recently published Pests in Gardens and Landscapes: Spotted Wing Drosophila.
The spotted wing drosophila (SWD), Drosopila suzukii was first found in California in 2008. Unlike the common vinegar fly, which it closely resembles, SWD attacks undamaged fruit in commercial fields and home gardens. SWD can have up to 10 generations per year. Because it has such a quick development rate, large populations can develop rapidly and cause severe crop damage.
The new pest note includes the following topics:
- Identification and life cycle
- Damage
- Management
For more information about SWD, including local research on this pest, please see our previous blog posts.
Commercial growers can find SWD resources by crop at the UC IPM Pest Management Guidelines webpage.