PLANT NATURAL ENEMY ASSOCIATION IN THE TRITROPHIC SYSTEM COTESIA-RUBECULA-PIERIS-RAPAE-BRASSICACEAE (CRUCIFERAE) .2. PREFERENCE OF C-RUBECULA FOR LANDING AND SEARCHING

The responses of the parasitoid Cotesia rubecula to differently damaged cabbages were recorded during a series of choice tests. To determine if flying C rubecula can discriminate differences in the blend of volatiles emitted by cabbages damaged by different causes and how plant volatiles released from a distant source affect the searching behavior of C rubecula once searching on a plant, wasps were presented with a choice of plants located one behind the other and separated by a distance of 15 cm. The sources of damage were: cabbage damaged by the host (Pieris rapae), by a nonhost lepidopteran herbivore (Plutella xylostella). by a nonhost, noninsect herbivore (snail), and by mechanical means. The results showed that the site of first landing and the time spent searching on the leaves was influenced by the type of damage inflicted on plants. Wasps preferred to land on cabbages damaged by host and nonhost species of Lepidoptera over those damaged by snails and mechanical means. No preference was observed for first landing between cabbages damaged by the two species of Lepidoptera or between cabbages damaged by snails and mechanical means. Cabbage damaged by P. rapae was searched most intensively, followed by cabbage damaged by P. xylostella, cabbage damaged by snails, and cabbage damaged by mechanical means. C. rubecula differentiates between the volatile blends emitted by differently damaged cabbages, and it is attracted to volatiles related to recent lepidopteran damage. Wasps searched longer on freshly damaged than on leaves with older damage.