Jul 9, 2009
This a brief summary of the information presented at yesterday’s meeting in Stockton about the cherry vinegar fly, now known as the spotted wing drosophila (SWD), Drosophila suzukii. The purpose of the meeting was to update researchers, growers and industry personnel on the status of this pest.
Spotted wing drosophila has now been found in cherries, raspberries, blackberries, blueberries, and strawberries in California. It has been found in many (I think the number was 21) counties across California, as well as several other states. However, in the case of detections from other states, it has not yet been determined whether the detections come from fruit grown in those states or simply were fruit from infested areas of California incidentally brought back into California.
Of the 3000 species of Drosophila commonly known as vinegar flies only two have been found to be harmful to crops, of which the spotted wing drosophila is one. The female has a serrated ovipositor, meaning she can penetrate the skin of most thin skinned fruit. In the lab it takes from 2-3 minutes to oviposit, and this oviposition is not necessarily successful each time. Nevertheless, in an experiment done by Artyom Kopp from UC Davis, three females put in a test tube with a Thompson seedless grape had several dozen eggs laid overnight. A female will lay 2-3 eggs per fruit, and will lay around 350 eggs in her lifetime. The life cycle in the laboratory, from egg to egg laying female, is 12 to 15 days at 65o F. The egg and larvae develop inside of the fruit, and while experts at the meeting said that pupation takes place inside of the fruit also, I have taken many samples of strawberry and raspberry and they are always exiting to pupate.
It is thought that SWD will have ten generations per year, and probably 3 generations in one crop of cherries. Thus, the population growth potential of this pest is tremendous. They are most active at 68o F and activity becomes reduced at temperatures above 86o F. Above 86o F, males become sterile. Eggs, larvae and adults (probably pupae are not far behind) die at temperatures below freezing, but this does not necessarily mean a whole population will be eradicated at lower temperatures, since D. suzukii is firmly established on the island of Hokkaido in Japan, where winters are quite cold. Additionally, vinegar flies in general are very sensitive to dessication, and will die within 24 hours in the absence of water.
On the regulatory side, we were informed that neither the CDFA nor the USDA are recommending any regulatory action (such as a quarantine) at this time. On a conference call regarding SWD with USDA and the National Plant Board, no other states made any commitment to conduct a survey for this fly. While the state of Oregon may have some concerns with this pest, they have to prove an absence of it before any action can be taken.
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