BEHAVIOR OF APHIDIUS-COLEMANI SEARCHING FOR APHIS-GOSSYPII - FUNCTIONAL-RESPONSE AND REACTION TO PREVIOUSLY SEARCHED APHID COLONIES

Understanding the searching strategy of Aphidius colemani Viereck (Hym enoptera: Braconidae), might gain insight into the mechanisms by which control of Aphis gossypii Glover (Homoptera: Aphididae) is obtained i n glasshouses, and provide information on how to improve the biologica l control of aphids. The functional response of A. colemani in Petri d ishes is described, as well as its behaviour on returning to a previou sly visited leaf disk with aphids. The number of aphids attacked durin g the first visit followed a sigmoid functional response. The increase of the parasitization rates was dearest at densities of lip to 10 aph ids/leaf disk. The duration of the first visit to a leaf disk increase d with increasing aphid density. After re-entering a recently visited leaf disk, the parasitoid stayed for a much shorter time than on the f irst visit, and no effect of host density on the duration of the visit was observed. No evidence of patch marking was found, so the reductio n of visiting times was probably caused by encounters with parasitized hosts.