The laboratory assessment of the inherent susceptibility of maize varieties to post-harvest infestation by Sitophilus zeamais Motsch. (Coleoptera, Curculionidae)

Abstract

A biological technique for assessing the susceptibilities of varieties of maize to post-harvest infestation by Sitophilus zeamais Motsch. has been developed. The effects of the age and population density of the parent insects upon the results obtained were investigated, and the possible effects of insect selection due to breeding upon particular maize varieties were looked at. Twenty-five Malawi, two Colombian and three Indonesian maize varieties were tested for susceptibility, and the results obtained were summarized using an ‘Index of Susceptibility’ which took into account both the F 1 progeny developing during the tests and a measure of the average development period of these progeny. The effects of the proportion of floury endosperm in the maize kernels, the mean kernel weight, the 70% r.h. equilibrium moisture contents of the varieties, and the amylose contents of the varieties upon susceptibility were investigated using regression techniques. It was concluded that the hardness of the kernels, as estimated by the proportion of floury endosperm was related to susceptibility, and that the hardness was closely correlated with amylose content. However amylose may have a small effect upon susceptibility in addition to that associated with hardness. Egg plugs placed in the kernels of different varieties during standard susceptibility tests were counted, and no evidence was found that there was any relationship between the numbers of eggs laid and susceptibility. Therefore it was concluded that susceptibility was determined in these varieties by factors operating after oviposition.