Intraspecific competition in the Parthenium beetle Zygogramma bicolorata (Coleoptera: Chrysomelidae): effect of larval crowding on life-history traits

The effects of larval crowding on growth, development and reproductive output of the Parthenium beetle Zygogramma bicolorata Pallister were investigated. Experimental manipulations of larval densities indicated that crowding creates intraspecific competition among the larvae, which negatively affected their growth and development. Larvae at high densities grew more slowly and exhibited longer larval periods compared with those at lower densities. Best-fit curves of developmental rates against larval densities were drawn, which revealed maximum theoretical density for 95% (6 or 15 larvae/63.6cm 2) and 50% developmental rate (1.75 larvae/63.6cm2), respectively. The reproductive potential of the beetle reared at different larval densities was also observed, but no effect of increased larval densities was observed. © 2009 ICIPE.