Oviposition and larval establishment of Sitodiplosis mosellana (Diptera : Cecidomyiidae) on wheat (Gramineae) at different growth stages

The wheat midge, Sitodiplosis mosellana (Gehin), infests wheat, Triticum ae stivum L., heads only up to anthesis when pollination occurs. The terminati on of infestation might be due to a deterrence of oviposition or to a suppr ession of larval growth on developing seeds. These hypotheses were tested i n the laboratory by measuring oviposition preference, larval development, a nd larval preference for plants at different growth stages. Females showed no preference for ovipositing on heads at any stage from the onset of headi ng up to and including anthesis, and continued to lay eggs at a reduced rat e 10 days after anthesis. Survival of newly hatched larvae was reduced on s eeds 3-4 days after anthesis and survival and development was greatly reduc ed on seeds 5 or 6 days after anthesis. Larvae moved away from older seeds and fed on younger seeds in a choice test. Given a hatching time of 5-6 day s, a failure to infest wheat after anthesis is not due to oviposition deter rence at anthesis, but to suppression of larval growth and development whic h begins soon after anthesis.