Egg parasitoids of Lygus bugs in southern Alberta
1Lethbridge Research Centre, Agriculture and Agri-Food Canada, Lethbridge, Alberta, Canada
2Canadian Forest Service, Ottawa, Ontario, Canada
Correspondence: carcamoh@agr.gc.ca
Biological control is a promising alternative for the management of Lygus bugs, an important pest of seed alfalfa and oilseed crops in western Canada. Recently, the native nymphal parasitoids have been described but very little is known about the egg parasitoids attacking Lygus in this region. The objectives of this study were (1) to determine which egg parasitoids attack Lygus bugs in Southern Alberta in both cultivated and non-cultivated habitats, during peak Lygus oviposition periods and (2) quantify rates of parasitism of the Lygus eggs to improve understanding of Lygus mortality factors. In 2005 and 2006, egg parasitism was examined using a combination of sentinel Lygus elisus or L. keltoni eggs, laid in the lab on sprouted potato tubers and canola, and sentinel Lygus eggs laid on caged plants in the field. We also exposed sentinel egg cards with Mediterranean flour moth eggs (Ephestia kuehniella) in the same sites, as potential alternative host for egg parasitoids. To supplement sentinel eggs, Lygus host plants (flixweed [Descurainia sophia], lamb's quarters [Chenopodium album], stinkweed [Thlaspi arvense], mustard [Sisymbrium altissimum]) and also potential host-plants (absinth [Artemisia absinthium], buffalo bean [Thermopsis rhombifolia], yarrow [Achillea sp.]) were surveyed for naturally occurring Lygus eggs. Sentinel eggs were exposed for between 2–3 days in the field. After field exposure sentinel and wild plants were collected and placed in cardboard emergence boxes. All emerging insects were collected in 70% EtoH for identification. Lygus did not oviposit on buffalo bean, yarrow or absinth. Sentinel egg cards with flour moth eggs and sprouted potato tubers did not produce any egg parasitoids indicating that these may not have been recognized as a host. Three parasitoids, Anaphes iole, Telenomus sp. and Polynema sp. were identified as putative Lygus egg parasitoids. Most egg parasitoids emerged from lamb's-quarter plants (N=11 Anaphes iole, N=3 Telenomus sp.), followed by mustard (N=7 Anaphes iole, N=2 Polynema sp.), flixweed (N=4 Anaphese iole, N= 3 Polynema sp.) and finally alfalfa (N=2 Anaphes iole, N=2 Polynema sp.). Overall numbers of parasitoids were very low and similar in the agricultural and non-agricultural sites (N =10, vs 12, respectively). Other insects (aphids, leafhoppers other plant bugs), managed to “contaminate” the field-caged plants at high numbers in some sites, preventing definitive associations between egg parasitoid and Lygus hosts; nevertheless, total egg parasitism rates, estimated from total nymphal emergence, were very low (<5%) suggesting that egg parasitoids do not cause significant mortality of Lygus bugs.
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