Larval pheromone disrupts pre-excavation aggregation of Cactoblastis cactorum (Lepidoptera: Pyralidae) neonates precipitating colony collapse

Authors: FITZGERALD, TERRENCE - State University Of New York (SUNY); Carpenter, James; Hight, Stephen

Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2019
Publication Date: 9/30/2019
Citation: Fitzgerald, T.D., Carpenter, J.E., Hight, S.D. 2019. Larval pheromone disrupts pre-excavation aggregation of Cactoblastis cactorum (Lepidoptera: Pyralidae) neonates precipitating colony collapse. Florida Entomologist. 102(3):538-543. https://doi.org/10.1653/024.102.0327.
DOI: https://doi.org/10.1653/024.102.0327

Interpretive Summary: The Argentine cactus moth is a non-native pest of prickly pear cactus in the southeastern U.S. The cactus moth continues to spread and will negatively impact the cactus biodiversity in the southwestern U.S. and Mexico, and the thousands of Mexican acres planted with prickly pear for fruit and vegetable consumption. No control measures are currently in use to manage the cactus moth. Scientists with the USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology, Tallahassee, Florida, and the University of New York, Cortland, New York, determined that a natural occurring pheromone sprayed on prickly pear plants interferes with the ability of young caterpillars to successfully penetrate the pads and survive. Caterpillars newly hatched from their eggs, lay down a pheromone trail so that they can follow one another and work together to cut a hole into the cactus pad, where they feed and develop. The trail-following pheromone was obtained from glands of large cactus moth caterpillars and sprayed on cactus plants, interrupting the ability of young larvae to orient to one another and successfully enter the pad. Production of an inexpensive synthetic pheromone could be sprayed on plantation prickly pear plants to prevent the establishment of destructive Argentine cactus moth caterpillars.

Technical Abstract: The newly eclosed larvae of Cactoblastis cactorum contained their activity to an arena that they form at the base of their eggstick, which they mark 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 four separate experiments, the average survivorship (15%) of C. cactorum larvae from cohorts on cladodes sprayed with the extract differed markedly from survivorship (80%) of caterpillar cohorts on cladodes treated with the solvent only or left untreated. This differential mortality was attributed to the elicitation of the independent dispersal of the caterpillars by 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.