Mortality, Sex Ratio and Fecundity in Natural Populations of Large Carpenter Bees (Xylocopa Spp.)

Abstract

SUMMARY (1) Data on the sex ratio, fecundity, mortality caused by predators, parasites and unknown factors (probably mostly excessive dampness or dryness in the larval cell) and the availability of nesting substrates obtained by an extensive sampling method for fifteen Xylocopa species are analysed and discussed. (2) The sex ratio averaged 36 males to 64 females and average fecundity was 7.35 eggs per female. (3) Mean total mortality of immature stages was 44%. Parasitism tended to be lower where only univoltine Xylocopa species were present partly because of the absence of two parasites, Coelopencyrtus and Paralipsa, occurring with multivoltine species. (4) Destruction by man and predation by woodpeckers, baboons, small mammals and invertebrates such as ants was low on average but occasionally severe (over 50%). (5) Calculated multiplication rates persistently above x 1.00 per generation on the one hand and the observed light exploitation of nesting substrates on the other are incompatible except for relatively short periods. This indicates incompleteness of the data caused possibly by the missing of substantial mortality of prereproductive adults and the underestimation of predation.