Effects of acclimation on the cold tolerance of the pepper weevil

Abstract

The pepper weevil, Anthonomus eugenii, is a subtropical pest of pepper plants that appears to be expanding its geographic range as evidenced by its increasing occurrence and persistence in field and greenhouse pepper crops in temperate areas. Here, we investigated the cold tolerance of A. eugenii and its potential for winter survival in temperate areas by comparing non-acclimated (24 °C) and cold acclimated (10 °C) adults and larvae for their cold tolerance strategy, supercooling points, and lower lethal thermal limits. Acclimated larvae were treated with silver iodide to assess their survival in the presence of an ice nucleator. Survival of non-acclimated adults was measured following exposure to 0 °C for an extended period. We also tested whether non-acclimated adults and larvae could survive winter at three outdoor sites in southwestern Ontario (agricultural field, adjacent to unheated building, and inside an unheated building). Adults and larvae died at freezing and even pre-freezing temperatures. Acclimation improved adult cold tolerance, decreasing the LT₅₀ by 3 °C, with half of the non-acclimated adults surviving around 6 days at 0 °C. External inoculation increased larval supercooling points (SCPs), but did not improve cold tolerance. In winter field studies, survival was evident only in the first month, but no insect survived afterwards at any of the overwintering sites. We conclude that A. eugenii is chill-susceptible, and winter temperatures will restrict outdoor establishment in temperate areas, but that high winter temperatures in empty greenhouses encourage indoor establishment.