Long-term reduction of cold hardiness following ingestion of ice-nucleating bacteria in the Colorado potato beetle, Leptinotarsa decemlineata

We investigated the effect of ingestion of ice-nucleating bacteria on the s upercooling capacity and cold hardiness of the Colorado potato beetle (Lept inotarsa decemlineata Say), a freeze-intolerant species that overwinters as adults in shallow, terrestrial burrows. Ingestion of ice-nucleating bacter ia (Enterobacter agglomerans, Pseudomonas fluorescens, Pseudomonas putida, Pseudomonas syringae), fed on slices of potato tuber, caused an abrupt decr ease in supercooling capacity. No change occurred in the supercooling capac ity of beetles fed Escherichia coli, as this species lacks ice-nucleating a ctivity. Ingestion rates showed that tubers treated with different species were equally palatable. During diapause induction beetles evacuated food fr om their guts, but nevertheless retained sufficient ice-nucleating bacteria to diminish supercooling. Beetles fed P, fluorescens and P. putida exhibit ed reduced supercooling even after an 8-wk exposure to simulated winter con ditions. Furthermore, P. fluorescens was isolated 10-wk post-ingestion from diapausing beetles. Our data suggest that ingested bacteria may be retaine d by insects during entry into diapause and that the cold hardiness of cand idate crop pests, such as L. decemlineata, may be reduced by feeding them i ce-nucleating bacteria prior to winter diapause. (C) 1998 Elsevier Science Ltd. All rights reserved.