The effect of diapause, cold acclimation and ice-nucleating bacteria on the coldhardiness of Plodia interpunctella.

Laboratory tests showed that over 50 d at 0°C, over 10 d at -5°C or 1 d at -10°C were required to control non cold-acclimated 5th instar larvae of Plodia interpunctella (Lepidoptera: Prylidae) (Indian meal moth). To control the most cold-hardy stage, diapausing cold-acclimated 5th instar larvae over 14 d at -10°C or 1 d at - 15°C were required. A freeze-out of a single floor of a seed warehouse was carried out from 23 December 1993 until 2 January 1994 by shutting off the heat and opening the windows. The lowest temperatures achieved varied with the size and location of the seed bulk. Seed packets, that had a few grams of seed, reached -17°C, whereas, the middle of a bag stack with forty 50-kg bags of maize only reached -9°C. By the end of the 10-d freeze-out all non cold-acclimated P. interpunctella larvae were killed in the packets, 90% of the diapausing cold-acclimated larvae were killed in a single bag and 65% were killed middle of the stack. Mortality in the freeze-out was higher than we would have predicted from the laboratory data. The supercooling points (temperature at which freezing begins) of the P. interpunctella larvae range from -7°C for the non-diapausing non-acclimated to -13°C for the diapausing acclimated. Keywords: Indian meal moth, Warehouse, Larvae, Supercooling poin