Some factors affecting the infestation of wheat and maize by Sitophilus oryzae (L.) and Sitophilus zeamais Mots. (Coleoptera: Curculionidae)

Abstract

Cultures of various stocks of S. oryzae (L.) and S. zeamais Mots. were maintained for several generations at 25°C and 70% r.h. on both wheat and maize, on only one of these foods, or on rice. In every generation a subsample of adults was placed in a mixture of wheat and maize (equal weights of each) for 5 days, after which the two cereals were separated and incubated and the number of progeny counted. A substantial majority of S. oryzae and much less substantial majority of S. zeamais emerged from wheat. In both species the majority was a little less when the laying adults had passed their developmental stages upon maize or rice. In alternate generations the foods were presented to another subsample in separate piles 40 cm apart. The progeny distribution was very similar to that found with intermingled foods. In intervening generations the foods were presented to S. zeamais in suspended bags which could only be reached by flight. When this occurred, more emergences, in many cases over 90%, were found from maize than wheat. When the adults associated with the suspended bags were counted at the end of the 4-day experiment the numbers were as one would expect from the emergences. When similar counts were made daily, however, approximately equal numbers were found associated with each food and observations suggested that directional flight by females did not take place.