Effect of larval density and cannibalism on growth and development of the Southwestern corn borer, Diatraea grandiosella, and the European corn borer, Ostrinia nubilalis (Lepidoptera: Pyralidae)

The effects of density and cannibalism on growth and development of the southwestern corn borer, Diatraea grandiosella, and the European corn borer, Ostrinia nubilalis, were examined. Larvae were grown on an artificial medium at densities of one, two, or four larvae per cup. D. grandiosella was reared under diapause-inducing and diapause-averting conditions, O. nubilalis was reared under diapause-averting conditions, and equal numbers of larvae of both species were reared together under diapause-averting conditions. D. grandiosella showed a higher rate of cannibalism than did O. nubilalis. In experiments with D. grandiosella, only rarely did more than one individual survive per container. Cannibalism may contribute to the increase in development time with density that was observed in these treatments. The survival of individuals that develop slowly is favored if individuals that grow more quickly have a higher risk of being cannibalized during larval molting cycles or as pharate pupae or pupae than do more slowly growing individuals. Since males develop more quickly than do females of D. grandiosella, this proposed relationship could also explain the low survival of males compared to females of this species. Furthermore, since O. nubilalis develops more quickly than does D. grandiosella, the proposed relationship could explain the low survival of O. nubilalis in mixed cultures. Competitive effects within and between species at higher density may also have contributed to the increased number of days to pupation, even though food was not limiting. A decrease in larval and pupal weights with density was observed in D. grandiosella and in females of O. nubilalis grown under diapause-averting conditions.