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Fruit Notes |
Fate of Apple Maggot Flies Alighting on Pesticide-treated Spheres in a Commercial Apple Orchard |
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Fruit Notes |
Xingping Hu, Eric Gemborys, Max
Prokopy, and Ronald Prokopy |
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Fruit Notes |
As mentioned in the preceding article, unusually large numbers of apple maggot flies (AMF) invaded certain commercial apple orchards in Massachusetts in 1998. In most cases, invasion was attributable to a combination of large numbers of AMF emerging from overwintered pupae beneath unmanaged apple trees nearby commercial orchards and to near or total absence of any fruit on such unmanaged trees, leading to AMF abandonment of unmanaged trees and movement to fruiting trees in commercial orchards. We took advantage of this situation in a cooperating orchard and studied the fate of AMF that were observed to alight on pesticide-treated red spheres. Methods & Materials Eight wooden spheres, 3 inches in diameter, were coated with a mixture containing 2% active ingredient of imidacloprid (Merit 75 WP), 20% sucrose, and 78% Glidden Red Latex Gloss Enamel paint. Four similar spheres, serving as non-toxicant checks, received only the sucrose and paint. All of the spheres were exposed outdoors for 3 weeks before testing (but no rain fell during this period). On three sunny days (July 21, 27, and 29), each of three observers hung two pesticide-treated and one check sphere about 2 feet apart in an apple tree and watched each sphere continuously for alighting AMF for a period of about 6 hours per day. An attempt was made to capture each AMF after it departed or fell from a sphere. Captured AMF were placed singly in small clean cups, supplied with food and water, and observed 1, 24, and 72 hours later for mortality. Results In all, 36 AMF were observed alighting on pesticide-treated spheres and 19 AMF on untreated check spheres. Of the 36 alighting on pesticide-treated spheres, the median duration of stay was about 3 minutes and 25 died while still on a sphere or within 1 hour after having fallen from a sphere. All remaining 11 AMF flew from a pesticide-treated sphere to nearby foliage. Of these, six were captured. All six died within 24 hours. The other five AMF evaded capture. Of the 19 AMF alighting on untreated check spheres, the median duration of stay was about 4 minutes and none died while on a sphere. Unfortunately, none could be captured after departing an untreated sphere, as flight was too fast and far to permit capture. Conclusions Results of this study of responses of wild-population AMF in a commercial orchard to wooden spheres treated with imidacloprid, sucrose and latex paint confirm results of a study reported in the preceding article conducted using laboratory-maintained AMF. Among all wild-population AMF observed here to alight on pesticide-treated spheres, 86% (31 of 36) died within 24 hours and most died within 1 hour. The fate of the 14% that were not captured after alighting is unknown. Some of these also may have died. In the preceding article, data showed that pesticide-treated spheres comparable both in type (2% a.i. imidacloprid) and field-exposure before testing (3 weeks) to those used here yielded 75% mortality of tested AMF. It is thus reassuring to know from this study of wild-population AMF that we can use response patterns of laboratory-maintained AMF placed directly on pesticide-treated spheres as an accurate guide to the performance of pesticide-treated spheres in commercial orchards. It is also reassuring to know that pesticide-treated spheres treated with 2% a.i. imidacloprid and sucrose are highly effective against AMF. Acknowledgments This work was supported by a grant from the Washington Tree Fruit Research Commission and a USDA SEA CSRESS grant (#97-34365-5043). |
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