Cold hardiness of immature and adult stages of the Mediterranean flour moth,Ephestia kuehniella

Abstract: The cold hardiness profile of immature and adult stages of the Mediterranean flourmoth, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) was investigated in the laboratory.Supercooling point (SCP) of early instars, late instars, pupae and adults of E. kuehniella wasdetermined using a circulating bath with a cooling rate of 1°C/min. Mean SCP of pupae wassignificantly lower (-23.3°C) in relation to early and late instars (-16.1 and -19.5°C, respectively),but did not differ from adults (-21.6°C). Moreover, low temperature survival of eggs, earlyinstars, late instars, pupae and adults of E. kuehniella was estimated by cooling groups of 30individuals (three replicates of ten individuals for each treatment) to -7.5 and -10°C for 30, 60, 90and 120 min. Mean lethal time (LTime50) of eggs and early instars at -7.5°C was significantlyshorter (24.8 and 58.2 min, respectively) than that of late instars, pupae and adults (123.2, 143.6and 119.9 min, respectively). A similar trend was achieved at -10°C. Exposure to lowertemperature (from -7.5 to -10°C) resulted in shorter LTime50 values for all treatments, but thiswere significant only in late instars and adults based on non-overlapping confidence intervals.Freezing injury above the SCP was well documented for all stages of E. kuehniella indicating apre-freeze mortality. Our results suggest that the pupae are the most tolerant stage after exposureto sub-zero temperatures. Eggs and early instars appeared to be the most susceptible stages to lowtemperatures below 0°C while adults and late instars had a moderate resistance to sub-zerotemperatures.