Monitoring Pholetesor ornigis (Hymenoptera: Braconidae), a Parasite of the Spotted Tentiform Leafminer, Phyllonorycter blancardella (Lepidoptera: Gracillariidae): Effect of Sticky Trap Location on Size and Sex Ratio of Trap Catches

Abstract

The effect of trap location on the number and sex ratio of adult Pholetesor (=Apanteles) ornigis (Weed) caught on yellow sticky traps was examined in Ontario from 1982 to 1985 during the spring and first-summer activity periods in one experimental and five commercial apple orchards. In the first experiment, traps placed within the tree canopy in the peripheral zone caught significantly more P. ornigis than traps placed above, within, and below the tree canopy, as well as those placed between adjacent trees in the peripheral and interior zones of the orchard. Traps placed above the tree in both zones caught less than 1%of all parasites trapped. In the second experiment, traps placed within the tree canopy in the interior zone caught significantly more male, female, and total P. ornigis than traps placed below the tree in the interior zone and within and below the tree in the peripheral zone during both the spring and first-summer activity periods. The results suggest that the spatial distribution of male and female parasites changes between the spring and first-summer activity periods. Trap location did not significantly affect the sex ratio of trap catches; males constituted from 82.3 ± 13.6 to 87.2 ± 7.7% ($\bar x$ ± SD) of the catch. The percentage of males in trap catches from an orchard ranged from 75.6 to 96.4 during the two activity periods, whereas estimates of the percentage of males in the adult population from an orchard ranged from 40.0 to 63.0.