2005 Volume 40 Issue 2 Pages 273-282
A study carried out across 33 weeks in a patch of taro, Colocasia esculenta L., quantified demographic parameters and density-dependent processes for a population of melon aphid, Aphis gossypii Glover. Variation in relative density of aphids per cm2 of leaf tissue between consecutive weeks declined with the initial density of aphids, indicating that density dependent processes regulate populations of A. gossypii on taro. High abundance of aphids on large leaves suggest that host attributes affect the rates of colonization or reproduction of adults. Even though the incidence of winged aphids was consistently low throughout the experiment, between plant dispersal by aphids still homogenizes their spatial distribution within an array of plants, as indicated by similar relative densities of aphids on established plants and on sentinel (initially uninfested) plants 60 days following their introduction in the patch. The proportion of aphids parasitised by Aphidius colemanii Viereck and Aphelinus spp. was low (<3%), which may be attributed to a high level (>95%) of hyperparasitism. Mortality caused by two entomopathogens, Neozygites fresenii Nowakowski and Verticillium lecanii Zimmerman, averaged 12%. The proportion of fungal infection increased with the density of aphids, both on a spatial and temporal scale. However, the population of A. gossypii on taro was most likely not regulated by entomopathogens, because the proportion of diseased aphids did not influence variations of population density between consecutive weeks. The lower proportion of fungal infection on sentinel plants than on established plants suggests a limited impact of entomopathogens on taro plants recently colonized by aphids.
