Cold tolerance of the bean weevil, Acanthoscelides obtectus

The bean weevil, Acanthoscelides obtectus, is one of the most destructive insect pests of stored pulses globally. Cold treatment is a method used for controlling many insect species that are pests of stored-products. To understand if cold treatment can be used to control A. obtectus, we evaluated its cold tolerance at -5°C and its supercooling point. We measured the survival time of eggs, early instars, late instars, pupae, and adults at -5°C using non-cold-acclimated insects, originally collected in Florida, USA. We measured the survival time of late instars and adults at -5°C using the strain from Florida and Canada, comparing cold acclimation. To acclimate insects, they were placed for two weeks at 15°C followed by 10°C. The Florida strain had a slightly greater survival than the Ontario strain at -5°C. Results show that at -5°C, for non-cold-acclimated insects from the Florida strain, the most cold-sensitive stages were the eggs and the pupae, whereas the late instars (LT50 of 4.0-4.8 d and LT95 of 8.2-8.7 d) were the most cold hardy stage. Cold acclimation increased insect survival time at -5°C by several days. The egg was the stage with the lowest freezing point (SCP of -27.7°C). These results show that cold treatment can be used to control A. obtectus, particularly in Canada and other northernly regions where winter temperatures can be sustained below -5°C for months and aeration fans can be used to blow cold ambient air into bins of stored pulses.