Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Oviposition and development of Megastigmus spermotrophus (Hymenoptera: Torymidae) in unfertilized Douglas-fir seed.

Abstract

An exclusion study was conducted in Oregon during 1990 to determine the incidence of Megastigmus spermotrophus in unfertilized Pseudotsuga menziesii seed. Larvae were detected in seeds of cones, from which pollen was excluded, from all 14 test trees. Damage ranged from 6 to 79% in unfertilized seeds compared with 14-72% in control (untreated) 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 the development of larvae and adult emergence. It is concluded that future evaluations of chalcid effects on seed yields should recognize that some proportion of the seeds infested would have been empty at maturation.