Leaf epicuticular waxes effects egg parasitoid’s response to host adult footprint contact kairomone

Abstract

Chemical footprints left behind by true bugs are perceived as a contact kairomones by scelionid egg parasitoids. In the system Nezara viridula and its egg parasitoid Trissolcus basalis, previous studies have shown that the kairomone mediating such behavior is part of N. viridula’s cuticular hydrocarbons. In this study, the effect of epicuticular waxes of leaves of broad bean, Vicia faba, on wasp response to footprints of N. viridula females are investigated. Plants with intact waxes layer were used (1) without host chemical contamination, or (2) contaminated by host female footprints. Mechanically de-waxed plants were tested (3) without host chemical contamination, or (4) de-waxed a few minutes after being contaminated, or (5) de-waxed about 30 min before being contaminated by host female footprints. And, finally, female wasps were tested on the side of the gum arabic film that had been appressed to (6) the adaxial leaf surface of plants without host chemical contamination, and (7) to plants contaminated by host footprints. Direct contact solid-phase microextraction of the adaxial leaf surface of broad bean plants analyzed by GC/MS showed that epicuticular waxes contained high concentrations of hydrocarbons and alcohols, and low concentrations of aldehydes and esters. Scanning electron microscopy revealed that the epicuticular waxes occurred as a film densely crystallized as irregularly shaped platelets with spherical granules randomly distributed. These findings demonstrated that epicuticular waxes of broad bean leaves can mediate the foraging behaviour of T. basalis females by absorbing host adult footprints contact kairomone.