Diapause-polymorphism
Guides
Megastigmus spermotrophus
Douglas Fir Seed Chalcidoid Wasp, Douglas-fir Seed Chalcid
Megastigmus spermotrophus is a seed-parasitic chalcid wasp native to western North America that has become invasive in Europe and other regions. It specializes in attacking seeds of Douglas-fir (Pseudotsuga menziesii), causing significant economic losses in seed orchards and natural forests. The species exhibits complex life history traits including facultative larval diapause lasting up to three years, which enables population persistence despite fluctuating cone crops. Females oviposit through cone scales into developing seeds, and the species shows preferences for larger cones with strongly arched exteriors and cone tips. Genetic polymorphism in diapause expression allows adaptation to varying environmental conditions.