A 16-YEAR STUDY ON THE BIVOLTINISM OF ANOMALA-FLAVIPENNIS (COLEOPTERA, SCARABAEIDAE) IN MEXICO

Seasonality and abundance of the scarab beetle Anomala flavipennis Bur meister were studied using a black light trap in Rio Bravo, in norther n Tamaulipas, Mexico, from 1979 to 1994. A bivoltine life cycle in A. flavipennis was evident throughout the period of study as shown by 2 d istinctive night periods: one from mid-April to mid-May (spring or ove rwintering generation) and the other from late August to late Septembe r (fall generation). Bivoltinism of A. flavipennis in northeastern Mex ico, as compared with univoltinism of this species in the United Stale s (e.g., Georgia, Kansas, Nebraska), is attributed to the warmer, subt ropical climate of the former, where annual heat units nearly double t hose accumulated in northern parts of the range of this beetle. An ave rage of 1,174 and 3,509 accumulated heat units (>10 degrees C) startin g 1 January was required for 50% adult emergence in the spring and fal l generations, respectively. However, heat units resulted in a more va riable parameter than did Julian dates for predicting emergence of A, flavipennis. Although rainfall appeared to trigger A. flavipennis adul t emergence during the fan, the influence of rainfall was not as clear during the spring, probably because of the irrigation practices in th is region during the spring growing season. Captures were generally gr eater during the fall than the spring, with a maximum of 21,444 adults having been captured on 7 September 1994. Abundance (total captures d uring spring or fall) of A. flavipennis was not associated with temper ature and precipitation. Abundance of A. flavipennis during the spring season depended on the adults captured during the previous fall. Howe ver, fall generation did not depend on abundance of adults emerging du ring the previous spring.