Increasing vineyard floral resources may not enhance localised biological control of the leafroller Epiphyas postvittana (Lepidoptera: Tortricidae) by Dolichogenidea spp. (Hymenoptera: Braconidae) parasitoids.

摘要

In agroecosystems, the efficacy of biological control exerted by many parasitoids is predicted to be enhanced where the availability of floral resources is increased. Such resources may attract parasitoids and enhance their longevity and fecundity. In Hawke's Bay, New Zealand, this prediction was tested by adding varying quantities of potted flowering alyssum (Lobularia maritima) to plots containing apple plants (Malus domestica) inoculated with larvae of the leaf roller, Epiphyas postvittana. In two replicated trials conducted in 2003, over 90% of the parasitoids from recovered larvae were Dolichogenidea spp. In both trials, increasing the percentage of alyssum did not result in a corresponding increase in the leaf roller parasitism rate. Instead, the primary influence on parasitism rates was due to Dolichogenidea spp. dispersing from a nearby orchard. A significant negative correlation was observed in leaf roller parasitism as a function of distance from this orchard. A vineyard to the north of the study site also influenced parasitism rates. The results suggest the orchard was a regional source population for this parasitoid, and the abundance of local resources such as alyssum did not influence parasitoid foraging. At the level of the entire study block, the effective area of resource provision was 0.1%. A level of resource provision higher than that used in this study may be necessary to test for a positive influence on local parasitism rates. From the results, it appears that for parasitoids with relatively high dispersal rates, the availability of local resources may not be as important as a regional source population..