Trail following response of larval Cactoblastis cactorum to 2-acyl-1,3 cyclohexane diones

Authors: FITZGERALD, TERRENCE - State University Of New York (SUNY); KELLY, MICHAEL - State University Of New York (SUNY); POTTER, TYLER - State University Of New York (SUNY); Carpenter, James; ROSSI, FRANK - State University Of New York (SUNY)

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2015
Publication Date: 4/7/2015
Citation: Fitzgerald, T.D., Kelly, M., Potter, T., Carpenter, J.E., Rossi, F. 2015. Trail following response of larval Cactoblastis cactorum to 2-acyl-1,3 cyclohexane diones. Journal of Chemical Ecology. 41(4):409-417. doi: 10.1007/S10886-015-0567-9.

Interpretive Summary: The caterpillars of Cactoblastis cactorum, an invasive species in North America, secrete onto the surface of host cactuses droplets of an oily fluid that issues from the orifices of their paired mandibular glands. The fluid contains a series of 2-acyl-1,3 cyclohexane diones which, collectively, have been shown to elicit trail following behavior from the caterpillars. This study reports the results of bioassays to determine the ability of two specific compounds previously shown to be prominent components of the mandibular glands of pyralid caterpillars, 4-hydroxy-2-oleoylcyclohexane-1,3-dione and 2-oleoylcyclohexane-1,3-dione, to elicit trail following behavior from the larvae of C. cactorum. We also examined the biological activity of structural fragments of these molecules. We determined the relative effectiveness of the chemicals in eliciting trail following, the effect of varying concentration on the trail following response, the importance of specific functional groups to the trail following response, and the threshold sensitivity of the caterpillar to the pheromone were. The study showed that while all the tested compounds elicited some degree of trail following, they differed significantly in their effectiveness. The most effective of the compounds was 4-hydroxy-2-oleoylcyclohexane-1,3-dione which, on a per unit volume basis, was as effective as whole gland extract. The caterpillars secrete large quantities of fluid from the glands and the threshold response to 4-hydroxy-2-oleoylcyclohexane-1, 3-dione occurs at a relative high application rate compared to the trail pheromones of other social caterpillars and eusocial insects. This and the observation that the trail marker is secreted from the mandibular glands suggests that the use of 2-acyl-1, 3 cyclohexane diones as trail markers is derivative and that these compounds function primarily in some other as yet undetermined context.

Technical Abstract: The caterpillars of Cactoblastis cactorum secrete onto the surface of host cactuses droplets of an oily fluid that issues from the orifices of their paired mandibular glands. The fluid contains a series of 2-acyl-1,3 cyclohexane diones which, collectively, have been shown to elicit trail following behavior from the caterpillars. This study reports the results of bioassays to determine the ability of two specific compounds previously shown to be prominent components of the mandibular glands of pyralid caterpillars, 4-hydroxy-2-oleoylcyclohexane-1,3-dione and 2-oleoylcyclohexane-1,3-dione, to elicit trail following behavior from the larvae of C. cactorum. Also bioassayed were structural fragments of these molecules. The relative effectiveness of the chemicals in eliciting trail following, the effect of varying concentration on the trail following response, the importance of specific functional groups to the trail following response, and the threshold sensitivity of the caterpillar to the pheromone were determined. The study showed that while all the tested compounds elicited some degree of trail following, they differed significantly in their effectiveness. The most effective of the compounds was 4-hydroxy-2-oleoylcyclohexane-1,3-dione which, on a per unit volume basis, was as effective as whole gland extract. The caterpillars secrete large quantities of fluid from the glands and the threshold response to 4-hydroxy-2-oleoylcyclohexane-1, 3-dione occurs at a relative high application rate compared to the trail pheromones of other social caterpillars and eusocial insects. This and the observation that the trail marker is secreted from the mandibular glands suggests that the use of 2-acyl-1, 3 cyclohexane diones as trail markers is derivative and that these compounds function primarily in some other as yet undetermined context.