Eline W. DE VOS, Joop J.A. VAN LOON*
Department of Entomology, Wageningen Agricultural University. P.O. Box 8031, 6700 EH
Wageningen, The Netherlands
The predatory bug Perillus bioculatus Fabricius (Pentatomidae: Heteroptera) is a specialized natural enemy of chrysomelid beetles, such as the Colorado potato beetle (CPB), Leptinotarsa decemlineata Say (Chrysomelidae: Coleoptera) We studied the locomotory behaviour of P. bioculatus in response to different stimuli using an automated locomotion compensator. Males or females were exposed to a stream of clean air (speed 0.25 m/s), to air carrying the odours of intact or mechanically damaged potato plants and to air passed over infested plants with or without feeding CPB larvae.
Air passed over intact potato plants evoked locomotory responses sumilar to clean air. Air passed over the potato-CPB complex elicited distinct orientation responses from P. bioculatus, characterized by significantly higher values of upwind fixation (a measure for upwind orientation i.e. upwind length divided by track length) than those displayed in response to volatile blends from intact potato plants or clean air. P. bioculatus responded to odours emitted by mechanically damaged plants in a way similar to the CPB-potato complex, but this response disappeared within 1 hour after damage was inflicted. In contrast, feeding damage produced oriented locomotion for several hours after removal of CPB.
Gas chromatographic analyses of headspace volatiles emitted by intact potato plants and plants damaged either mechanically or by feeding CPB, showed that several volatiles are emitted only after feeding by CPB and that the release of these compounds is sustained for several hours after removal of CPB larvae. No consistent differences in locomotory behaviour were found between the sexes.