EVIDENCE FOR SUCCESSFUL OVERWINTERING OF DIAMONDBACK MOTH, PLUTELLA XYLOSTELLA (L.) (LEPIDOPTERA: PLUTELLIDAE), IN ALBERTA

Abstract

Diamondback moth, Plutella xylostella (L.), commonly occurs at relatively low population densities in areas of canola (oilseed rapes, Brassica rapa L. and Brassica napus L.) production in western Canada, but occasionally can reach outbreak densities (Madder and Stemeroff 1988). The most severe outbreak of P. xylostella in recent years occurred in Alberta and Saskatchewan in 1985 when approximately 467 860 ha were treated with insecticide, at a cost of approximately $11.9 million (Madder and Stemeroff 1988).Damage to canola is the result of larval feeding. Leaves are the preferred feeding sites, and plants can withstand substantial damage before yield is affected (Philip and Mengersen 1989). However, late in the season when the leaves become senescent, larvae feed on pods and this can result in significant yield reductions. Plutella xylostella is multivoltine, capable of completing at least three generations per year in Alberta (Philip and Mengersen 1989), and four to five in Ontario (Harcourt 1986).