FLIGHT MANEUVERS USED BY A PARASITIC WASP TO LOCATE HOST-INFESTED PLANT

Cotesia rubecula Marshall (Hymenoptera: Braconidae) is a specialist la rval parasitoid of the butterfly Pieris rapae L. which itself feeds al most exclusively upon cruciferous plants. Female wasps are attracted t o the odour of host-infested plant (plant-host complex: PHC) and the p robability of flights in a wind tunnel depends on females' prior ovipo sition experience with the PHC and on the concentration of the PHC odo ur. This study considers the effect of both factors on characteristics of oriented flight upwind towards the PHC. The flight track parameter s that we measured and calculated were not significantly affected by t hese factors. C. rubecula females exhibited high average flight veloci ty and relatively straight flight tracks. There was a considerable var iability between individuals, however, in their odour-modulated upwind flight tracks. Some females generated a zigzagging upwind flight trac k similar to those commonly observed from male moths responding to fem ale sex pheromone. Other females flew along a straight track directly upwind. The flight tracks of most female wasps were intermediate betwe en these extremes. The full range of these flight performances was obs erved to all experimental treatments.