Estimating Mortality Caused by Parasites and Diseases of Insects: Comparisons of the Dissection and Rearing Methods

Abstract

Because the measurement of insect mortality caused by parasites and disease is fundamental to biological control and related fields, accurate data are of great importance. Most studies rely on the rearing of hosts to determine the incidence of disease and parasitism, and the results are seldom compared with those determined by the dissection method. The examples in the current study show that parasitism measured by dissection was 12 to 44% higher than by rearing, and that dissections are much more accurate than rearing for measuring the effects of parasites and disease, because dissection data are not confounded by the disproportional mortality of parasitized hosts by disease and stress that occurs during the rearing process. Moreover, even parasitism data obtained by dissections underestimate mortality because a considerable proportion of hosts die of oviposition trauma, and in some species, after being fed upon by female parasites before they are sampled. The rearing method is useful for determining parasite species as well as other purposes, and these are listed along with the numerous advantages of dissections. Although dissections provide the most accurate mortality estimates, for the most comprehensive results, both rearing and dissection methods should be used concurrently.