Wasps in the genus Tiphia (Hymenoptera: Tiphiidae) are the primary parasitoids that attack scarabaeid grubs in the soil. Field observations suggested that parasitized grubs tend to be deeper in the soil than non-parasitized ones. We examined this phenomenon for both Tiphia pygidialis and T. vernalis, species that attack masked chafer (Cyclocephala spp.) or Japanese beetle (Popillia japonica Newman) grubs, respectively. Observation chambers resembling ant farms were constructed to observe differences in movement patterns between parasitized and non-parasitized grubs. Grub movement and depth were observed every 3 d for 3 wk following parasitism. Depth of grubs at various intervals after parasitism was further studied in PVC rings driven into the turf and soil. These experiments confirmed that parasitism causes grubs to move downward in the soil profile. Further tests were conducted to determine if this behavioral change is induced by venom injected by the female wasp, or from feeding by the parasitoid larva. In those tests, the Tiphia egg was removed before parasitized grubs were placed into the chambers. Significant differences were present only on the first two observation dates, suggesting an initial change in host behavior due to venom that is maintained by subsequent larval feeding. The physiological basis for altered grub behavior was examined by collecting hemolymph from grubs parasitized for 1d, 7d, and 14d as well as from non-parasitized grubs. Preliminary results suggest altered juvenile hormone levels in parasitized grubs. Implications for surveys of biological control by Tiphia spp. will be discussed.
Species 1: Hymenoptera Tiphiidae Tiphia pygidialis
Species 2: Hymenoptera Tiphiidae Tiphia vernalis
Species 3: Coleoptera Scarabaeidae (Japanese beetle, masked chafer)
Keywords: juvenile hormone, turfgrass
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