Preovipositional behaviors of Tiphia pygidialis and Tiphia vernalis (Hymenoptera: Tiphiidae), parasitoids of White Grubs (Coleoptera: Scarabaeidae)

The events leading to oviposition by Tiphia pygidialis Allen and Tiphia vernalis Rohwer on their host Cyclocephala spp. and Popillia japonica Newman grubs, respectively, were compared and quantified using videotaped recordings. Mean (±SE) duration of the oviposition process was 49.3 ± 2.9 min for T. pygidialis and 31.5 ± 2.2 min for T. vernalis. Behaviors included stinging, moving soil from around grubs, host kneading, host examination, host feeding, and scraping of the grub's cuticle. Sequence of behavioral events was translated into a first-order (Markovian) contingency table to construct flow charts of the oviposition process for both species. T. pygidialis spent more time kneading and scraping the cuticle of grubs than did T. vernalis, whereas T. vernalis performed more stinging and soil-moving events. These behaviors most likely serve to move the grubs into a suitable position for oviposition. Scraping of the host's cuticle where an egg was to be laid took more time than any other behavior. Compared with nonparasitized grubs, cuticle from parasitized grubs contained numerous grooves filled with cement used to anchor the parasitoid egg. Scanning electron microscopy revealed peg-like structures, similar in size to the grooves made in the cuticle of parasitized grubs, on the ovipositor sheath of female wasps. These structures are thought to be used in making the grooves in the cuticle, whose postulated function is to increase the surface area of the host cuticle to facilitate egg attachment. This is the first study to implicate such use of the ovipositor sheath by a parasitoid.