Side effects of fungicides on the abundance and the species diversity of the natural populations of Drosophila and their hymenopterous parasitoids in orchards

Within entomophagous insects, hymenopterous parasitoids are important regulators of natural populations of insects including pests. Pesticide treatments are largely used in orchards for economic reasons. These treatments allow for greater productivity, but they may also impact upon non-target insect populations. Drosophila and their hymenopterous parasitoids are abundant in orchards and are not direct targets of pesticide treatments. In this work, natural populations of Drosophila and their parasitoids were monitored from June to November, and their abundance was reported from two types of orchards. One type was under conventional pesticide treatments, mostly fungicides (“Treated plot”), and the other was under low-input treatments (“Low-input plot”). Five Drosophila species and five parasitoid species were present in both types of orchards. A time effect on abundance was found with two peaks of abundance, one in August and the other in autumn (October), corresponding to a fluctuation of numbers depending on the availability of resources. When comparing insect abundance between the two types of plots, the abundance in the Treated plot was found to be lower than or equal to that in the Low-input plot. Furthermore, a significant decrease in the abundance of two scarce parasitoid species ( Leptopilina heterotoma and Asobara tabida ) that could lead to their disappearance was also observed. The results are discussed in the context of the diverse lethal and sub-lethal effects of pesticides on the development and reproduction of natural populations of insects and their importance as natural enemies.