Effect of low-rate pyrethroid applications on the spotted tentiform leafminer (Lepidoptera: Gracillariidae) and its parasitoids in an apple orchard
1992
Li, S.Y. | Clements, D.R. | Harmsen, R.
The effect of applications of low rates of the pyrethroid lambdacyhalothrin on populations of the spotted tentiform leafminer, Phyllonorycter blancardella (F.), its endoparasite Pholetesor (= Apanteles) ornigis Weed, and ectoparasitic chalcids were studied in the field from 1988 through 1990. Results indicate that lambdacyhalothrin reduces leafminer infestation of apple trees. All counts of eggs, larvae, and pupae were higher in untreated trees than in those treated with the pyrethroid. At 2.5 g (AI)/ha (20% of the recommended rate of 12.5 g [Al]/ha), the pyrethroid suppressed the second-generation leafminer populations to < 2 mines per leaf; in untreated trees an average of 5.74 active mines per leaf were present in 1989. Reduced rates of lambdacyhalothrin (10-50% of the recommended rate) allowed parasitoids to survive in the orchard. Although absolute numbers of parasitoids were reduced by pyrethroid applications, percentage parasitism did not differ significantly among treatments. Because of these results, and problems associated with the existing strategy of a single prebloom pyrethroid spray for first-generation leafminer populations, we suggest that targeting the second generation with lower rates should be explored on an experimental basis.
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