INFLUENCE OF TURFGRASS SPECIES AND TALL FESCUE ENDOPHYTE ON FEEDING ECOLOGY OF JAPANESE-BEETLE AND SOUTHERN MASKED CHAFER GRUBS (COLEOPTERA, SCARABAEIDAE)

Suitability of six cool-season turfgrasses, including tall fescue, Festuca arundinacea Schreb., infected or not infected by the endophyte Acremonium coenophialum Morgan-Jones & Gams, was studied for root-feeding grubs of the Japanese beetle, Popillia japonica Newman, and the southern masked chafer, Cyclocephala lurida Bland. Larval growth, survival, food use, effects of larval diet on adult weight and fecundity, and natural incidence of grubs were investigated in laboratory, greenhouse, and field assays. Hard fescue, Festuca ovina var. duriuscula L., endophyte-free tall fescue, and perennial rye-grass, Lolium perenne L., were generally more favorable than creeping bentgrass, Agrostis palustris (Huds.), for growth of C. lurida, whereas Kentucky bluegrass, Poa pratensis L., was a relatively poor host for both grub species. Variation in nitrogen content of roots is apparently too small to explain these differences. Roots of endophyte-infected tall fescue contained 93-mu-g/g N-formyl loline, a level previously shown to deter grub feeding on artificial medium. However, this study suggests that antixenosis may not occur in the presence of the stimulus complex in tall fescue roots. Survival or growth or both of neonate first instars were lower on endophyte-infected than on endophyte-free tall fescue. However, response of older instars was variable, and there was no measurable effect of endophyte on density or weight of grubs in field plots or on fecundity of P. japonica adults that emerged from endophyte-infected turf. Variation in susceptibility of cool-season turfgrasses to white grubs is probably affected more by differences in their ability to tolerate the feeding damage than by their inherent suitability as food.