ENTOMOPATHOGENIC NEMATODES FOR CONTROL OF CODLING MOTH, CYDIA-POMONELLA (LEPIDOPTERA, TORTRICIDAE) - EFFECT OF NEMATODE SPECIES, CONCENTRATION, TEMPERATURE, AND HUMIDITY

The susceptibility of codling moth diapausing larvae to three entomopa thogenic nematode species was assessed in the laboratory using a bioas say system that employed cocooned larvae within cardboard strips. The LC50 values for Steinernema carpocapsae, S. riobrave, and Heterorhabdi tis bacteriophora were 4.7, 4.8, and 6.0 infective juveniles/cm(2), re spectively. When a discriminating concentration of 10 infective juveni les/ cm(2) of each of the three nematode species was evaluated at 15, 20, 25, and 30 degrees C, S. carpocapsae was the most effective nemato de with mortalities ranging from 66 to 90%. Mortalities produced by S. riobrave and H. bacteriophora at the four temperatures were 2-94 and 25-69%, respectively. Studies were also conducted to test infectivity at 10, 35, and 40 degrees C. No mortality was produced by any of the n ematode species at 10 degrees C. S. riobrave was the most infective ne matode at 35 degrees C producing 68% mortality which was more than twi ce that observed for S. carpocapsae or H. bacteriophora. Codling moth larvae treated with 10 infective juveniles/cm2 of S. carpocapsae and k ept in 95+% RH at 25 degrees C for 0-24 h followed by incubation at 25 -35% RH indicated that more than 3 h in high humidity was needed to at tain 50% mortality. Trials of S. carpocapsae, S. riobrave, and H. bact eriophora at 50 infective juveniles/cm2 against cocooned larvae on pea r and apple logs resulted in reductions of codling moth adult emergenc e of 83, 31, and 43%, respectively, relative to control emergence. Tri als of the three entomopathogenic nematodes at 50 infective juveniles/ cm2 against cocooned larvae in leaf litter resulted in 99 (S, carpocap sae), 80 (S. riobrave), and 83% (H. bacteriophora) mortality, respecti vely. Our results indicate good potential of entomopathogenic nematode s, especially S. carpocapsae, for codling moth control under a variety of environmental conditions.