The reliability of colorado potato beetles (Leptinotarsa decemlineata Say) population density predictions based on phenological and overwintering data

On the basis of phenological observations and over-wintering mortality data in 2015/2016 we tried to predict the population density of Colorado potato beetle (Leptinotarsa decemlineata Say) (CPB) for the following season. Because of the late and cool spring in 2015, the beetles started to emerge from the soil at the end of May and, because of the low temperatures, did not start to reproduce immediately. The first egg clutches did not appear until the end of June. The low density of larvae and beetles in mid-summer lead us to expect low damage for the whole season. However, very warm weather in August and September induced the beetles to lay eggs and the population density increased sharply. A lot of the summer beetles managed to terminate their development in time and to dig into the soil for overwintering. Consequently, we expected the beetles to be abundant the following spring. However, a short, snowless, very cold period in January when air temperature fell to -30 °C and soil temperature to -6.6 °C nullified this prediction as over 90% of over-wintering beetles perished. In spring 2016, very few beetles were found on the field and the potato plants remained undamaged until the end of June. Then, due to south-east storms at the end of June, very large migrations occurred and, some weeks later, various development stages of CPB were very abundant in potato fields. Thus, none of our predictions came true. The main reason for this was our extremely unstable weather conditions during summer and the overwintering period and the unpredictable large migrations from southern regions