Oviposition and Development of Megastigmus spermotrophus (Hymenoptera: Torymidae) in Unfertilized Douglas-Fir Seed

Abstract

An exclusion study was done in Oregon to determine the incidence of Megastigmus spermotrophus Wachtl in unfertilized Douglas-fir, Pseudotsuga menziesii (Mirbel) Franco, seed. Larvae were detected in seeds of cones, from which pollen was excluded, from all 14 test trees. Damage ranged from 6-79% in unfertilized seeds, compared with 14-72% in control cones. Females were unable to distinguish between fertilized and unfertilized seeds for most or all of their oviposition period. Unfertilized seeds contained sufficient nutrition for larval development and adult emergence. Future evaluations of chalcid effects on seed yields should recognize that some proportion of the seeds infested would have been empty at maturation.