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.
Resumen
Las larvas recién nacidas de Cactoblastis cactorum Berg (Lepidoptera: Pyralidae) mantienen su actividad en una arena formada en la base del estipe del huevo, marcada con una feromona de la glándula mandibular. Se realizaron estudios de laboratorio y de campo para determinar si estas agregaciones antes de la excavación, que son esenciales para su penetración exitosa de la planta hospedera, podrían interrumpirse con el extracto de la glándula mandibular que hace que las colonias incipientes perezcan. Los cladodes o plantas enteras se rociaron con la feromona, obtenida mediante la extracción de orugas maceradas en hexano, solo hexano, o se dejaron sin pulverizar y la sobrevivencia de las orugas que nacieron de los huevos adheridos por el estipe a los cladodios registrados en una fecha posterior. En 4 experimentos separados, el promedio de la sobrevivencia de cohortes de larvas de C. cactorum sobre cladodios rociados con el extracto (15%) difirió notablemente de la sobrevivencia de los cohortes de orugas sobre cladodios tratados solo con solvente (84%) o sin tratar (80%). Esta mortalidad diferencial se atribuyó a la provocación de la dispersión independiente de las orugas por parte de la feromona de la glándula mandibular y su incapacidad de reagruparse en cantidades suficientes para organizar un ataque exitoso en la planta hospedera. Se discute el potencial para el manejo de poblaciones de plagas de orugas empleando esta alternativa específica a los pesticidas convencionales.
Key Words: Argentine cactus moth caterpillar; mandibular gland; pest control; prickly pear cactus; Opuntia spp.
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