Long-term Dynamics of Phytophagous Lady Beetle Populations under Different Climate Conditions in Sumatra and Java, Indonesia.

Abstract

Since 1990 we have studied population dynamics of the phytophagous lady beetles, Epilachna vigintioctopunctata, E. enneasticta and Epilachna sp. 3 (aff. emarginata), (Coleoptera: Epilachninae) in Padang, Sukarami (West Sumatra), Bogor (West Java) and Purwodadi (East Java), Indonesia. These sites have distinctly different climate conditions, e.g. Padang has a typical tropical rainforest climate without a clear alternation of wet and dry seasons, while Purwodadi has a strong dry season of 6-7 months. We have conducted censuses at 3-7 day intervals, including mark-recapture of beetles and construction of life tables for up to 9 consecutive years in order to clarify the seasonal change in abundance and mortality of the populations. In most populations the adult number changed greatly with the formation of high peaks from time to time at intervals of 6-12 months. Their increase or decrease was gradual, progressing over 3-5 months. Even under conditions with sufficient amount of rainfall in Padang, Sukarami and Bogor, oviposition intensity, number of the following immature stages and, as a result, adult emergence frequently showed discrete peaks at a fixed interval. These “generation cycles” were especially clear during the phase of population increase. There was no simple relationship between the seasonal change in rainfall and that of the beetle populations. We also discussed the impacts of the strong droughts in 1994 and 1997-1998 caused by El Nino, and the degree of synchronization in the trends of the populations among the adjacent study sites.