EVALUATION OF ENTOMOPATHOGENIC NEMATODE SPECIES FOR THE CONTROL OF MELONWORM (LEPIDOPTERA, PYRALIDAE)

Laboratory bioassays were conducted to determine pathogenicity of five entomopathogenic nematodes from the genera Steinernema and Heterorhab ditis against melon-worm, Diaphania hyalinata (L.). S. carpocapsae (We iser) (Mexican strain) was the most pathogenic nematode species, follo wed by H. bacteriophora (Poinar), S. feltiae (Filipjev), S. anomali (K ozodoi), and S. glaseri (Steiner), respectively. The LC50 for S. carpo capsae (Mexican) was 39.9 infective juveniles per milliter. The rate o f nematode invasion into insects was proportional to the overall patho genic effect of the various nematodes. The level of insect mortality a nd infectivity (the number of nematodes invading the insect) were dire ctly related to exposure time. First instars and pupae were significan tly less susceptible to S. carpocapsae infection than older larvae and prepupae. The number of nematodes found in the hemocoel increased wit h larval age. Mortality and infectivity were inversely related to nema tode size. In field trials, survival of S. carpocapsae (All strain) on squash plant foliage was reduced to 0.77% within 40 h in a trial unde r high humidity conditions and to 0.25% after 18 h in a trial under mo derate humidity conditions. Field applications of 5 billion nematodes per hectare produced infection rates of 52-55%.