Reduction of Cold Tolerance of Stored-Product Insects by Ice-Nucleating-Active Bacteria

Abstract

Ice-nucleating-active bacteria, Pseudomonas syringae (strain 31a), applied as a freeze-dried powder on grain in laboratory tests, caused an increase in the ice-nucleating activity of the grain and an increase in the supercooling point of Cryptolestes ferrugineus (Stephens) adults. Sitophilus granarius (L.) and Oryzaephilus surinamensis (L.) also had increased mortality when placed on grain treated with ice-nucleating-active bacteria and held at -lO°C. Cold-acclimated C. ferrugineus , S.granarius , and O. surinamensis were more cold hardy than noncold-acclimated insects, but when these insects were held on grain treated with ice-nucleating-active bacteria, their mortality at -1O°C was increased. These results were confirmed in a simulated granary application when C. ferrugineus adults were placed in vials with 10 g of ice-nucleating-active bacteria-treated wheat before being placed in granaries containing 100 t of grain. Two of the three bins were aerated until the temperature had reached −9 or −15DC. Ice-nucleating-active bacteria increased insect mortality in the aerated bins at bacterial concentrations as low as 10 ppm. The potential of using ice-nucleating-active bacteria as a cold synergist that will make low temperature a more effective means to control stored-product and other insect pests is discussed.