EFFECTS OF SORBIC ACID AND TEMPERATURE ON SURVIVAL AND REPRODUCTION OF WESTERN SPRUCE BUDWORM (LEPIDOPTERA, TORTRICIDAE)

A bioassay was used to determine how addition of sorbic acid (0.63 and 1.26% dry mass) to an artificial diet affected survival of Choristoneura occidentalis Freeman through all life stages of three generations. Development time of larvae and pupal weight were monitored. Development on diets with 0 or 1.26% sorbic acid was evaluated for insects that were held at 22 and 25-degrees-C. Experimental data were used to estimate population growth on the various diets tested. Addition of sorbic acid to the diet resulted in more rapid larval development and larger pupae, but survival through the pupal stage and viability of eggs were reduced. Decreasing the sorbic acid concentration from 1.26 to 0.63% greatly reduced the negative effects on survival, particularly in the F1 and F2 generations. Many of the pupae from the diet containing 1.26% sorbic acid exhibited morphological abnormalities characterized by deformed or missing wing pads. For diets with no sorbic acid, the 25-degrees-C temperature was clearly better than 22-degrees-C for C. occidentalis survival, development time, and pupal weights. However, population growth at 22-degrees-C was better on the 1.26% sorbic acid diet.