LABORATORY STUDIES OF THE INTERACTIONS OF ENVIRONMENTAL-CONDITIONS ONTHE SUSCEPTIBILITY OF GREEN JUNE BEETLE (COLEOPTERA, SCARABAEIDAE) GRUBS TO ENTOMOPATHOGENIC NEMATODES

In the laboratory, four nematode species differed significantly in the percentage mortality that each caused in second-instar green June bee tles (grubs), Cotinis nitida (L.). Water suspensions of 1,000 infectiv e juveniles (IJ)/one grub/Petri dish each of Heterorhabditis bacteriop hora, Steinernema glaseri and S. feltiae caused 34, 22 and 18% grub mo rtality, respectively. These Values were significantly (P = 0.05) grea ter than the grub mortality caused by either S. carpocapsae(12%) or th e water check (0%) that were similar. Several factors affected third-a nd fourth-instar susceptibility in the laboratory when exposed to 10,0 00 S. carpocapsae or H. bacteriophora IJ in 75 g of soil (133 IJ/cm(3) soil)/plastic cup, Soil at 30% moisture by weight resulted in signifi cantly more (P = 0.006) dead grubs (6.6%) than at 10% soil moisture (2 .8%). Significantly more (P = 0.03) grubs died when at a grub density of 2 grubs/plastic cup (5.6%) than at 1 grub/plastic cup (3.8%). Signi ficantly more (P = 0.01) grubs were killed by either S. carpocapsae an d H. bacteriophora at a soil temperature of 25 degrees C (6.5%) than a l 12 degrees C (2.8%). There was also a significant interaction of tem perature and nematode species. Heterorhabditis bacteriophora killed si gnificantly more (P = 0.02) grubs at 25 degrees C (9.5%) than at 12 de grees C (1.9%) and more than S. carpocapsae killed at either 12 degree s C or 25 degrees C (<3.9%), More virulent nematode strains or species than these four nematode species must be identified if green June bee tles are to be controlled by nematodes.