Effect of harvest on euphorine (Hymenoptera: Braconidae) parasitism of Lygus lineolaris and Adelphocoris lineolatus (Hemiptera: Miridae) in alfalfa.

摘要

Effective biological control of Lygus lineolaris and Adelphocoris lineolatus depends on the availability of appropriate host stages to sustain populations of euphorine parasitoids which are important in reducing pest populations. In Quebec alfalfa, crops are cut 2-4 times during the summer season, yet how this affects the host and parasitoid populations is poorly understood. A 3-year study conducted from 2000-2002 in southern Quebec demonstrated that overall, abundance of susceptible host stages (N2+N3) in cut alfalfa were less than half of those collected in uncut alfalfa, even after 4-5 weeks when the cut crop reached the same height as the uncut crop. Parasitism levels of N4+N5 nymphs in the cut crop were usually less than those in the uncut crop, although on several sampling dates the reverse was observed. Numbers of adult L. lineolaris and A. lineolatus were always lower immediately after harvest in the cut crop but numbers increased in the following weeks to equal those collected in the uncut crop. These results suggest that periodic harvest of alfalfa reduces available host stages for parasitism and subsequent levels of parasitism but does not cause elimination of parasitoid populations. Furthermore, dispersing adults likely contributed to an increase in abundance of susceptible host stages after habitat modification, thereby sustaining parasitoid populations.