TIME ALLOCATION OF THE PARASITOID APHIDIUS-COLEMANI (HYMENOPTERA, APHIDIIDAE) FORAGING FOR APHIS-GOSSYPII (HOMOPTERA, APHIDAE) ON CUCUMBER LEAVES

The time allocation of individual Aphidius colemani female parasitoids foraging for Aphis gossypii nymphs on cucumber leaves has been invest igated. Apart from experiences on the current leaf (such as density of hosts on the current leaf, density of hosts on a neighboring leaf and encounters with hosts on the current leaf), the effect of previous le af visits on the time allocation was studied. Behavioral records were analyzed by means of the proportional hazards model, to determine the tendency of leaving the current leaf The leaving tendency decreased on ly on leaves with a high host density (100 aphids), thus increasing th e giving up time since the latest encounter. Rejection of aphids had n o influence on the leaving tendency. To assess the effect of the numbe r of hosts encountered on the leaving tendency, we considered three cl asses: 0-30 encounters, 31-100 encounters, and 100 or more encounters with hosts. The effect of the number of hosts encountered differed at different aphid densities, When Sewer than 10 aphids were present the leaving tendency was much greater after 30 encounters than beforehand, At a density of 100 aphids the leaving tendency was lower than at the other aphid densities and increased only after 100 encounters. The de nsity of hosts on a neighboring leaf, ranging from 0 to 100 hosts, had a negligible effect on the leaving tendency. Repeated visits to leave s with 10 unparasitized aphids resulted in an increase in the leaving tendency after 10 visits. It is argued that the parasitoids have some innate expectancy of host availability and that they concentrate on hi gh-density patches.