Monitoring of rice weevil, Sitophilus oryzae, feeding behavior in maize seeds and the occurence of supernumerary molts in low humidity conditions

Rice weevils, Sitophilus oryzae (L.), complete their development from egg to early adulthood inside grains of wheat, rice or maize, but little is known about their feeding behavior within the seeds. An ultrasonic insect feeding monitor was used to characterize the feeding patterns of individual rice weevils as they developed in maize grains. Weevils reared in grains held at ca. 40% nh. took longer to develop from egg to pupation than those reared in grains kept at ca. 70% nh. Feeding patterns revealed that larvae developing in grains held at ca. 70% nh. had only four instars, whereas supernumerary molts (five instars) occurred in certain individuals reared in grain held at ca. 40% nh. The supernumerary molts may represent a response of the insect to stresses associated with low moisture levels in the seeds.