Biological Control of Alfalfa Blotch Leafminer (Diptera: Agromyzidae) in Delaware1

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Abstract
Biological control of alfalfa blotch leafminer, Agromyza frontella (Rondani), was attained in 1981 in Delaware by using the exotic parasite species Dacnusa dryas (Nixon) (Hymenoptera: Braconidae) and Chrysocharis punctifacies Delucchi (Hymenoptera: Eulophidae), which were released at two Newark fields in 1977 and became established in 1978. During the preestablishment period (1975 to 1977), parasitism in the first cutting was 18% by native parasites; yearly maximum number of mines per stem in first cutting was 10 to 25. In 1981, imported and native parasites produced 72% parasitism and reduced host populations to an average maximum of 0.05 mines per stem. During the preestablishment period, parasitism in the second cutting was 28% by native parasites; yearly maximum number of mines per stem in second cutting was 25 to 42. In 1981, imported and native parasites produced 71% parasitism and reduced host populations to an average maximum of two mines per stem. These populations are well below any of three tentative economic injury levels suggested for the pest.

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