IMPACT OF EMIGRATING SEED CHALCID, MEGASTIGMUS SPERMOTROPHUS WACHTL(HYMENOPTERA: TORYMIDAE), ON SEED PRODUCTION IN A DOUGLAS-FIR SEED ORCHARD IN FRANCE AND MODELLING OF ORCHARD INVASION

Abstract

AbstractThe invasion of a Douglas-fir seed orchard by host-specific seed chalcids immigrating from the surrounding plantations of Douglas-fir has been monitored for a 10-year period. The orchard cone crop was entirely harvested every year to prevent the establishment of a resident chalcid population. Over the 10 years the percentage of infested seeds resulting from the immigration of seed chalcids ranged from 0.88 to 91.0%. A model to forecast the importance of annual seed orchard infestation by immigrating populations is proposed. This model is based on passive diffusion of females emerging in the surrounding plantations with a downwind drift. Only a few plantations located within a radius of 5 km from the orchard appeared to contribute significantly to orchard infestation. Settlement of Douglas-fir orchard in regions with low density of conspecific trees and annual harvest of cones are suggested to limit the importance and regularity of seed chalcid damage.