Parasitism of Lygus bugs by native Peristenus species in southern Alberta, Canada.
1Lethbridge Research Centre, Agriculture and Agri-Food Canada, Lethbridge, Alberta, Canada
2ECORC, Agriculture and Agri-Food Canada, Ottawa, Ontario, Canada
3Beaverlodge Research Farm, Agriculture and Agri-Food Canada, Beaverlodge, Alberta, Canada
Correspondence: carcamoh@agr.gc.ca
Managing Lygus bugs in field crops of the Canadian prairies relies on insecticides as no alternatives are available. For example in 1998 over one million acres of canola were sprayed to reduce yield losses from an outbreak in Alberta. Seed alfalfa fields are prophylactically sprayed for Lygus and alfalfa plant bugs before releasing leafcutter bees. Encouraging results with biological control of Lygus bugs in northeast U.S.A. using introduced Peristenus wasps, have sparked interest in this group in Canada. The objective of this southern Alberta study were to (i) determine the suite of Peristenus species that attack Lygus bugs in and around crops, (ii) obtain baseline data on the levels of parasitism caused by these parasitoids, and (iii) document the basic seasonal distribution of the parasitoid species. Three Peristenus species were reared from Lygus nymphs: P. carcamoi, P. broadbenti and P. braunae with a putative fourth species to be confirmed. Peristenus braunae is rare in the first generation of Lygus in southern Alberta although it is commonly caught in sticky cards in grassy field margins in early May and may be more common in Adelphocoris spp. or other Miridae. By far the dominant species on the first Lygus generation was P. carcamoi which was collected from early June into late July suggesting that occasionally it attacks the second generation at low levels. Peristenus broadbenti was collected from mid-July into early August from the second generation nymphs. Total development times for each species were 350 and 352 days for P. carcamoi for males and females, respectively and 362 for both sexes of P. broadbenti. The number of days from adults to emergence from pupae after transferring them to 22 deg C from overwintering storage, were 4–7 for P. carcamoi but over 24 for P. broadbenti. Preliminary analysis of a no-choice laboratory oviposition study on L. keltoni (common host) and L. lineolaris (rare in the area) suggested that both Peristenus species have no preference for either Lygus bug host. Rates of parasitism from nymphal dissections ranged from zero up to around 60 % at some sites on some collection dates. Ongoing studies are focusing on quantifying the temporal dynamics of parasitism rates in alfalfa and canola grown adjacently to determine the potential for native Peristenus to reduce Lygus bugs from reaching pest status in crops.
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