Winter Cold Hardiness and Supercooling of Metzneria paucipunctella (Lepidoptera: Gelechiidae), a Moth Introduced for Biological Control of Spotted Knapweed

Abstract

The potential geographic range of Metzneria paucipunctella Zeller, a moth released from Europe into North America for the biocontrol of spotted knapweed, Centaurea maculosa Lamark, is limited by low winter temperatures. The moth larvae are often exposed to the extremes of winter air temperatures because they overwinter in the persistent capitula of the knapweed stems from the previous season, which usually remain standing throughout the winter. Supercooling points of larvae from 2 field colonies were recorded with a computerized data acquisition system in the laboratory. Periodic measurements of supercooling points were made on larvae from the primary field site during 1 complete winter and part of a 2nd winter. Mean supercooling points changed from October to April, reaching minimums near -30°C in December and January. During 2 subsequent extreme cold periods, mortality of the larvae at the field sites was consistently predicted from supercooling points measured in the laboratory and minimum air temperatures recorded at the field sites. Some larvae survived in capitula under snow cover. No delayed mortality was observed in surviving larvae exposed to field temperatures near the mean supercooling point and reared to adult stage. M. paucipunctella is probably unsuited to sites where minimum air temperatures reach -30°C without snow cover.