Response of the neonate larvae of Cactoblastis cactorum to synthetic cactoblastins, a newly identified class of pheromonally-active chemicals found in the caterpillar’s mandibular glands

Abstract

The pre-excavation activity of the neonate larvae of Cactoblastis cactorum (Lepidoptera: Pyralidae) is typically confined to an arena that encircles the base of their egg stick. If the caterpillars are unable to penetrate the host plant within the arena, they strike off en masse in search of a more favorable site, marking their pathway with secretions from their mandibular glands. One component of this secretion, 4-hydroxy-2-oleoylcyclohexane-1,3-dione (an acylcyclohexanedione, ACHD), has been previously shown to function as a trail pheromone. In this paper, we report the characterization, synthesis, and bioassays of a family of 3-acyl fatty acid methyl esters (which we named cactoblastins), a chemically distinct group of mandibular gland compounds that also elicit trail following behavior. The relative effectiveness in eliciting trail following of the ACHD and six, chemically distinct, synthetic cactoblastins was determined. The most bioactive of the cactoblastins was also compared to whole mandibular gland extract to assess its ability to disrupt the aggregative behavior of the neonates and to serve as a biorational alternative to pesticides for managing invasive populations of the caterpillar.