Pterostichus melanarius Ill. was the predominant ground beetle recovered in pitfall traps in three blocks of apple trees at Jordan Station, Ont. In one block, C, the number of mature fifth-instar larvae of Cydia pomonella (L.) seeking overwintering sites was related significantly (r2 = 0.5476, P < 0.05) to the number of P. melanarius caught, but was not related significantly (r2 = 0.1181, P > 0.10) to the proportion of beetles that were serologically positive. The proportion of larvae pupating also was not related significantly (r2 = 0.2014, P > 0.10) to the number of P. melanarius. The total number of all predators caught was related significantly (r2 = 0.4490, P < 0.05) to the number of larvae present, but the proportion of larvae that pupated was not related significantly (r2 = 0.3606, P > 0.05) to the total number of predators.
In block A, in 1983–1985, the number of mature larvae of C. pomonella seeking overwintering sites was not related significantly (r2 = 0.3763, 0.3619, and 0.5042, P > 0.05, respectively) to the number of P. melanarius taken in pitfall traps. In both blocks A and B, the number of serologically positive beetles was not related significantly (r2 = 0.3824 and 0.7921, P > 0.10, respectively) to the number of larvae seeking overwintering sites.
Amara aenea DeG., Anisodactylus sanctaecrucis F., Bembidion quadrimaculatum oppositum Say, Clivinia impressifrons LeC., Diplochaeila impressicolis (Dej.), Harpalus aeneus F., and Pterostichus chalcites Say also gave positive serological reactions to the antiserum against C. pomonella.
The occurrence of other species of Lepidoptera did not affect significantly the results obtained for C. pomonella.