Influence of rearing medium on size and weight of adults of four Sitophilus populations and on weight loss of host kernels (Coleoptera: Curculionidae)

Four populations of Sitophilus (S. zeamais Motsch. from Mexico, S. zeamais from Arkansas, U.S.A., S. oryzae (L.) and S. granarius (L.) were studied. Hard red winter wheat (“Cloud” variety), brown commercial sorghum, and yellow and white “dent” maize (mixed varieties) were used to determine the effect of parent-and progeny-rearing media on the adult elytron length in each population. Kernel weight loss caused by individuals of each population and weevil weights were determined.Elytron lengths of S. oryzae progeny were significantly (P < 0.05) but only slightly longer, when parents were reared in wheat rather than sorghum or maize; otherwise parent-rearing medium had no effect. Progeny-rearing medium, not parent size, was most responsible for differences in elytron lengths. S. granarius progeny from wheat were significantly larger than those from maize or sorghum; progeny from all other populations were significantly larger from maize than from wheat or sorghum.S. oryzae caused less weight loss in kernels of wheat and sorghum, and were significantly lighter (P < 0.05) than other insects. The Arkansas S. zeamais was significantly heavier than Mexican S. zeamais in wheat, otherwise their weights were similar. Weight losses (actual and percentages) of kernels of all grains were similar for Arkansas S. zeamais and Mexican S. zeamais. S. granarius were heavier and produced greater weight loss in wheat kernels than other populations did.     

Influence of medium and physical disturbances during rearing on development and numbers of Sitophilus progeny

Four Sitophilus populations (Sitophilus zeamais Motschulsky from Mexico, S. zeamais from Arkansas, U.S.A., Sitophilus oryzae L., and Sitophilus granarius L.) were studied. Hard red winter wheat, sorghum, and maize were used to determine effects of rearing media on progeny production of insects from the four populations.Mechanically disturbing infested samples to remove newly-emerged adult weevils every 48 hr reduced numbers of progeny surviving to the adult stage, especially for Arkansas S. zeamais and S. granarius reared in any of the three grains.With one exception, reproduction for all populations in all three grains was highest when parents were reared in wheat; other differences are discussed. Also, progeny developmental periods for all four populations were shortest when parents were reared in wheat. Progeny of all four populations had the longest developmental periods when reared in maize regardless of the medium in which their parents were reared.In 250 g samples of wheat, and 125 g samples of sorghum, 50 parent S. oryzae produced statistically as many progeny as in 500 g and 625 g samples of wheat and 250, 500, and 625 g samples of sorghum, respectively. In maize, 625 g samples produced significantly more progeny than 500 g samples.Sex ratios of progeny from each grain were 1:1, except that females of S. oryzae reared in maize outnumbered males.