Larval Pheromone Disrupts Pre-Excavation Aggregation of Cactoblastis cactorum (Lepidoptera: Pyralidae) Neonates Precipitating Colony Collapse

Abstract

Newly eclosed larvae of Cactoblastis cactorum Berg (Lepidoptera: Pyralidae) contain their activity to an arena formed at the base of their eggstick, marked with a mandibular gland pheromone. Laboratory and field studies were undertaken to determine if these pre-excavation aggregations, essential to their successful penetration of the host plant, could be disrupted with mandibular gland extract causing the incipient colonies to perish. Cladodes or whole plants were sprayed with the pheromone, obtained by extracting macerated caterpillars in hexane, hexane only, or left unsprayed, and the survivorship of caterpillars that eclosed from eggsticks attached to the cladodes recorded at a later date. In 4 separate experiments, the average survivorship of C. cactorum larvae from cohorts on cladodes sprayed with the extract (15%) differed markedly from survivorship of caterpillar cohorts on cladodes treated with the solvent only (84%) or left untreated (80%). This differential mortality was attributed to the elicitation of the independent dispersal of the caterpillars by the mandibular gland pheromone and their failure to reaggregate in numbers sufficient to mount a successful attack on the host plant. The potential for managing pest populations of caterpillars employing this target-specific alternative to conventional pesticides is discussed.