Suppression of Gypsy Moth (Lepidoptera: Lymantriidae) Populations on Oak Using Implants or Injections of Acephate and Methamidophos

The protection of individual oak trees from serious defoliation by gypsy moth, Lymantria dispar (L.), was achieved by implantation or injection of the systemic insecticides acephate or methamidophos. In 1984, significant differences (α = 0.05) were detected in population reduction and foliage protection compared with control trees when acephate or methamidophos was applied at budswell as liquids in Medicaps, when liquid acephate was applied at budswell using the Mauget Inject-A-Cide system, or when ACECAP implants (similar to Medicaps but containing acephate power) were applied at tight bud, budswell, or bud burst. All insecticide treatments were similarly effective. In 1983 and 1985, ACECAP implants applied 1 wk after bud burst (1983), or just before bud burst (1985), provided significant protection from defoliation over a wide range of gypsy moth population pressures. When leaves from trees treated in 1985 with acephate in ACECAP implants at budswell or bud burst were sampled for bioassay and residue analysis studies, residue levels for both acephate and its metabolite, methamidophos, peaked 12 dafter bud burst for both treatment timings, as did mortality in the parallel bioassay. Acephate levels were higher than methamidophos levels in the initial samples, but this pattern reversed over time.