SAWFLIES (Hymenoptera: Symphyta)
Henri Goulet
CONTAMINATION OF ADULTS BY PESTICIDES
I believe that adults of Tenthredo are more likely to be contaminated with pesticides than other sawflies. Because of the large acreage of land devoted to corn, adults sawflies of these genera feed on insects that could have been slightly contaminated while crossing and landing in distant corn fields. As predators, adults of Tenthredo would probably accumulate pesticide residues from their preys. These residues could at the least render them sterile. The main support for this hypothesis is the coincidence of the crash with the general spread of corn cultures through MWPE in the late 1960's.
The numerous collections from our region clearly show that adults of Tenthredo were quite easily collected up to the late 1960's. The number of students in universities was exceptionally high during the 1960's and the 1970's. This generally lead to greater collecting activities, but clearly much fewer specimens of these attractive insects were sampled. I suspect that at least some elements of both hypotheses are involved in these population crashes. I feel that there is a warning about the general quality of environmental conditions of our region as indicated by all common species of the most diverse genus.