Influence of nutritional characteristics of selected corn genotypes on food utilization by the rice weevil (Coleoptera: Curculionidae)

The contents of protein, starch, fat, sucrose, glucose and fructose in the kernels of 22 maize genotypes were determined in laboratory studies in the USA and correlated with food utilisation parameters and indices determined for developing examples of Sitophilus oryzae (L.) reared on each genotype. The larval period was shorter and pupae were heavier on grain with high glucose contents. Increased levels of protein reduced the amount of food consumed and increased the food utilisation efficiency. Larvae reared on pelletised germless kernels required longer to reach pupation and had lower pupal weights and food utilisation efficiencies than larvae reared on pelletised whole kernels. However, mortality was similar in both treatments, indicating that nutrients found in the germ were not essential. A homogenous distribution of nutrients in the food reduced larval development time and increased food utilisation efficiency.<new para>ADDITIONAL ABSTRACT:<new para>The grain composition of 22 maize genotypes, on which Sitophilus oryzae was reared, was analysed. Glucose content was negatively correlated with number of days required by the weevil to reach pupation and positively correlated with pupal weight. High protein content was associated with efficient use of food and low food consumption by the weevil. Starch content was positively correlated with number of days to pupation and amount of faeces excreted. Larvae reared on pelletized, germless grains took longer to reach pupation, had lower pupal weight and used food less efficiently than larvae reared on pelletized, whole grains. Larval mortality was similar on both diets. Hybrid genotypes had larger grains and endosperms than inbred lines and larvae fed longer on hybrids. Larvae feeding on inbred lines reached the germ sooner, consumed less food and reached pupation sooner than those feeding on hybrids.