Factors affecting development and overwintering of second generation Colorado Potato Beetle (Coleoptera: Chrysomelidae) in Estonia in 2010

Abstract

We have established for the first time that Colorado potato beetle (CPB) (Leptinotarsa decemlineata Say) (Coleoptera: Chrysomelidae) produced a distinct second generation in 2010 in Estonia. This species has a history, in Estonia, of less than 50 years. Due to their great ability to adapt to variable environmental conditions, the beetles spread very quickly throughout the country and established a permanent population in the 1980s. Before 2010, CPB has been predominantly univoltine. The occurrence of the second generation was the result of rare coincidence of extremely favourable weather as the cumulative degree days (DD) of 927 exceeded the sum needed for two full generations. Constantly high temperatures from the beginning of May caused the formation of summer generation adults already by the end of July and the long day photoperiod, as well the availability of fresh food, kept the beetles in reproductive mode preventing the onset of diapause. Summer beetles continued to oviposit up to the second half of September, but a large proportion of the second generation was eliminated from the population in the pre-adult or adult stages as they failed to end their development in the favourable period. Successful overwintering with about 50% survivors occurred only in association with completed development which was restricted to August and the beginning of September. An abundant second generation has potential to reduce primarily the yield of late potato cultivars. However, the unpredictable weather conditions in Estonia does not allow exact prediction of the appearance of a second generation.