The sterile male approach to the control of the spruce budworm, Choristoneura fumiferana

Induction of dominant sterility by irradiation of male pupae or adults of Choristoneura fumiferana with 25-30 kR of 60Co irradiation reduced mating competitiveness and longevity. In laboratory populations, release ratios in excess of 10 sterile to 1 normal male were required to achieve even 80% reduction in fertility. Adult males sterilized with Thiotepa remained fully viable in the laboratory, and were very competitive, making 40% more first matings when tested against normal males. Release ratios of 5 sterile to 1 normal male reduced fertility of laboratory populations by 95%. However, adverse effects of Thiotepa treatment reduced the males' ability to respond to females and copulate successfully in the field. Treatment of males with 5-10 kR of 60Co irradiation reduced fertility by 12 to 75%, depending on the stage treated. Introduction of males irradiated with 5-10 kR into caged laboratory populations reduced fertility for up to three generations, after which recovery occurs at the lower dose. Additional effects of inherited semi-sterility included sex-ratios biased towards males by 2 or 3:1, reduced larval survival, full competitiveness of adult male offspring, and males and females were equally affected. Pheromone trapping was used to study dispersal of released insects, rate and pattern of emergence of field adults, and adult population density. Released males were detected in pheromone traps even when their numbers were low compared with native population levels. Dispersal of field-collected, laboratory-reared, irradiated or genetically marked males has been compared to determine effects of origin, treatment or phenotypic differences on the ability of released males to perform effectively in the field. Pheromone trapping methods are also being developed to monitor field emergence and predict when releases should begin