The impact of grain quantity on the biology of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae):: oviposition, distribution of eggs, adult emergence, body weight and sex ratio

Studies were conducted to observe the effect of grain quantity on the oviposition, distribution of eggs, adult emergence, adult body weight and sex ratio of Sitophihis zeamais, an important pest of maize. Three quantities of maize grains (200, 400 and 800 grains/glass jar of 11) were used under laboratory conditions (30degreesC and 70% r.h.). Twenty five male/female pairs of maize weevil were introduced into each glass jar for 12d. The greatest and lowest number of eggs was laid on batches of 800 and 200 grain kernels, respectively. The total number of grains attacked followed a similar trend. The aggregation of eggs expressed as a ratio of the variance to mean increased as the amount of maize grains was increased. The aggregation parameter k ranged from 2.35 on 200 grains to 4.49 on 800 grains. On average, a significantly higher proportion of grains were infested (90%) when less grain was present. Emergence of adult weevils was, however, maximal (472 individuals/glass jar) when the grain quantity was highest. The mean weight of the emerged adults was not significantly influenced by grain quantity, but female weevils were heavier than males (mean weight 3.16 vs. 3.05 mg) irrespective of maize quantity and eggs laid. Sex ratio (males/100 females) of emerged adults did not differ among treatments. The importance of grain quantity, and of oviposition, in internally feeding granivores and the possibility that there is an adaptive reproductive strategy are discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.