BIOLOGY AND CONSERVATION OF TIPHIA WASPS, PARASITOIDS OF TURF-INFESTING WHITE GRUBS

White grubs, the root-feeding larvae of scarab beetles, are serious pests of athletic turf in the United States. We found two parasitic wasp species, Tiphia vernalis Rohwer 1924 (Hymenoptera: Tiphiidae) and Tiphia pygidialis Allen 1966 (Hymenoptera: Tiphiidae), to be abundant in central Kentucky and important as biological control agents for Japanese beetle (Popillia japonica Newman 1838, Coleoptera: Scarabaeidae) and masked chafer (Cyclocephala spp.) grubs, respectively. Little was known about these beneficial wasps before our studies revealed details of their life history, and some ways that their benefits can be conserved. Monitoring with pan traps and dilute sugar sprays revealed that T. vernalis adults are active in May and June, whereas the flight period of T. pygidialis is mid-August through early October. Parasitism rates ranged from 15 to 58% at turf field sites. Choice tests showed that each Tiphia species can discriminate between body odor trails and frass from host and non-host grubs, and that these cues are used to locate their specific hosts in the soil. The process by which Tiphia wasps subdue and oviposit on their victims, and development of the ectoparasitic larvae are described. Once parasitized, grubs cease feeding and move deeper into the soil. This should be taken into account when monitoring for the occurrence of parasitism. Gardens of flowering plants established near turf sites were ineffective in attracting T. pygidialis, whereas large numbers of T. vernalis were observed visiting and feeding on nectar produced by peonies. While it is yet to be determined if incorporating such flowering plants into a landscape can increase parasitism rates, applying dilute sugar sprays to the grass resulted in higher grub parasitism in nearby turf. Applying imidacloprid insecticide in May was shown to interfere with the ability of T. vernalis to locate and parasitize P. japonica grubs. Postponing preventive grub treatments until June will help to conserve beneficial Tiphia populations.