A comparison of molecular screening versus dissection and rearing methods to estimate parasitism of Lygus nymphs by Peristenus wasps: size matters

Abstract

Several broadleaf crops on the Canadian prairies suffer economic damage by Lygus bugs (Hemiptera: Miridae), populations of which are suppressed by parasitoids in the genus Peristenus (Hymenoptera: Braconidae). We used three different methods to assess levels of this parasitism for different instars of Lygus collected in southern Alberta, Canada. Screening Lygus for Peristenus DNA using a molecular polymerase chain reaction (PCR) method identified levels of parasitism ranging from 35 (second and third instars) to 47 (fifth instars) per cent. With dissection, parasitoids were recovered from 13 (second instars) to 44 (fifth instars) per cent of Lygus. For Lygus collected in the field and reared in the lab, Peristenus emerged from about 22 per cent of individuals. Our results show that use of PCR or dissection for fifth-instar larvae provides comparable estimates of parasitism. For earlier instars, PCR identifies levels of parasitism undetected using dissection – that is, 2.7-fold more for second instars in the present study. For the purposes of pest management and conservation biological control, dissection can provide adequate estimates of parasitism to inform a decision to reduce insecticides to protect Peristenus parasitoids.