Cold tolerance of Colorado potato beetle (Leptinotarsa decemlineata Say) adults and eggs

The cold tolerance of different seasonal groups (pre-diapause, diapauses and post-diapause) of Colorado potato beetle (Leptinotarsa decemlineata Say) was assessed by exposing them either to a constant temperature of -3°C for 48 to 624 h, or to -3, -4, -5, -6 or -7 °C for a constant 24 h.Cold survival was affected by the length of exposure, by the temperature rates and by seasonality.The least cold-tolerant were pre-diapause beetles in August with a mean lethal temperature (Ltemp50) of -4.4°C for 24 h exposure and with a lethal time (Ltime50) of 106.8 h at -3°C.Cold tolerance was significantly higher in the diapause group in January and in the post-diapause group in March; it did not differ significantly between these groups of beetle for 24 h exposure, the lethal temperature being -5.8°C for both groups.Seasonality had a greater influence on survival of these groups after longer exposure to constant mild sub-zero temperature (-3°C); in diapause group, all the beetles survived 624 h exposure, but in post-diapause group the survival limit decreased to 216 h and lethal time was 153.9 h.Colorado potato beetle eggs tolerated 24 h exposure to sub-zero temperatures from -3°C to -5°C or longer exposure at -3°C for 72 h without a reduction in hatchability.The mean lethal time for 50% mortality of eggs was 76.5 h and mean lethal temperature was -5.8°C.Thus, we conclude that night frosts common in northern regions do not damage Colorado potato beetle adults or eggs to the extent that might threaten the survival of the population.