Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/12/2007
Publication Date: 10/20/2007
Citation: Day, W.H. 2007. Effect of Host Instar on Measuring Parasitism of Lygus spp. (Hemiptera: Miridae) Nymphs by Peristenus spp. (Hymenoptera: Braconidae). Environmental Entomology. 36:1154-1158. Interpretive Summary: The accurate measurement of the mortality of target insect pests is critical for determining the inadequacy of native parasites or diseases, and for evaluating the success of introduced parasites. However, during the past 115 years of classical biological control, surprisingly little attention has been devoted to critically evaluating the different measurement methods used. The author's previous publication showed that dissection, the less common of the two principal procedures used to measure parasitism, was far more accurate than rearing in determining the proportion of the pest insect that will be killed by either parasites or fungus disease. In the present paper, he shows that the instar (growth stage) of the immature insect selected for dissection is also very important--unselected (random) instars, early, and late instars all significantly underestimated mortality by parasites.
Technical Abstract: The accurate measurement of insect mortality by parasites is critical in biological control research - - both in baseline studies to determine the absence or inadequacy of native parasites, as well as in subsequent efforts to measure the effectiveness of introduced parasite species. Although rearing has been most frequently used to measure parasitism, dissection has been shown to be more accurate in several cases. Selection of the host instar, whether for rearing or dissection, was found in this study to also be important. In two species [Lygus lineolaris (Palisot) and L. hesperus Knight] parasitism by Peristenus digoneutis Loan and P. howardi Shaw, respectively, was highest in instars three and four. Parasitism was underestimated in instars one and two (due to reduced exposure time), and also in instar five (due to parasites killing the hosts in instar four).