Effect of isomers and enantiomers of pinene on Ceratitis capitata males mating performance

Abstract

In the world of organic chemistry, isomerism and enantiomerism are chemical properties of organic molecules that defines different biological activities. Particularly, α-copaene shows different attractant activity according to its (+) and (?) configuration on Ceratitis capitata males. It is widely recognized that plant phytochemicals affect the sexual behaviour of Tephritidae fruit fly males. Males of C. capitata increases its mating success after exposure to the volatiles of different essential oils or some pure monoterpenes. However, the role of isomerism and enantiomerism on the reproductive behaviour of fruit flies had not been studied so far. The objective of this study was to evaluate the effect of exposure to isomers and enantiomers of pinene (2,6,6-trimethylbicyclo [3.1.1] hept-2-ene) on the mating success of C. capitata males. Males from a laboratory colony were exposed to α- or β-pinene enantiomers and its sexual performance was evaluated in a mating arena. Experiments consisted in different combinations of two competing males considering the four compounds available according to isomerism and enantiomerism: α (+); α (-); β (+), β (-), and non-exposed males. Then, 8 treatments were performed, males exposed to α/β (+) / (-) vs non-exposed males (4 possible treatments); males exposed to the same isomer but different enantiomer (2 treatments) and males exposed to the same enantiomer but different isomer (2 treatments). The number of mating pairs obtained by each type of male (mating success), the latency to mate and the duration of the copula were recorded for each treatment. The effect of volatiles exposure on male mating success was evaluated by means of a G test of goodness of fit to an equal proportion hypothesis whereas latency to mate and copula duration were compared by means of a Wilcoxon test. Results showed that males exposed to (-) α-pinene achieved more matings than non-exposed males. However, when confronted to (+) α-pinene exposed males they achieved less matings. Latency to mate was shorter for (-) β-pinene exposed males than (+) β-pinene when competing together. Males exposed to (-) α-pinene showed the same tendency when competed with non-exposed males. No statistical differences were found for copula duration. Our results show that isomerism and enantiomerism affects the mating performance of C. capitata males exposed to pinenes.