ARS | Publication request: INFLUENCE OF SEED SIZE ON EXPLOITATION BY THE RICE WEEVIL, SITOPHILUS ORYZAE

Submitted to: Journal of Insect Behavior
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 29, 2001
Publication Date: October 31, 2002
Citation: CAMPBELL, J.F. INFLUENCE OF SEED SIZE ON EXPLOITATION BY THE RICE WEEVIL, SITOPHILUS ORYZAE. JOURNAL OF INSECT BEHAVIOR 15(3): 429-445. 2002.

Interpretive Summary: The decisions that insects make about where and how many eggs to lay can have a major impact on their fitness, both in terms of number of offspring that survive to adulthood and the quality of those adult offspring. Female rice weevils, Sitophilus oryzae, lay eggs inside commodities such as wheat, rice, and corn. Because larvae develop to adult within a single kernel, the eresources available are determined by the behavior of the female parent an characteristics of the seed in which the egg was deposited. Females were demonstrated to lay more eggs in large than in small kernels. This is partly because they started laying eggs on the larger kernels sooner and because eggs laid in large kernels produced larger offspring, even though the probability of an adult progeny emerging did not increase with kernel size. Where females laid eggs on the wheat kernels also differed among the different wheat kernel sizes. Females laid more than one egg in a akernel primarily because they revisited the kernel multiple times, rather than because they laid multiple eggs during a single visit. The costs and benefits of laying eggs in different sized wheat kernels and of laying multiple eggs in a single kernel influence the behavior of individual rice weevils. The behavioral relationship between rice weevils and their environment influences their population dynamics and distribution and thus understanding these factors will ultimately improve our ability to manage this important pest species.

Technical Abstract: Oviposition decisions and their fitness consequences for the seed parasite Sitophilus oryzae (L.) (Coleoptera: Curculionidae) were investigated. Female S. oryzae lay eggs inside seeds such as wheat (Triticum aestivum (L.)). Because larvae develop to adult within a single seed, the resources available are determined by the behavior of the female parent and characteristics of the seed in which the egg was deposited. Females were demonstrated to lay more eggs in kernels > 20 mg. Females initiated the chewing of oviposition holes in shriveled kernels, but were less likely to oviposit in them. Progeny size increased with increasing seed size, but the probability of an adult emerging was not affected. Location of eggs in wheat kernels differed among kernel sizes. Dorsal center and dorsal posterior were preferred oviposition sites and eggs laid in the center region had a higher probability of adult emergence. Females accepted large kernels more quickly than small kernels and this contributed to increased oviposition in large kernels. The increase in the number of eggs per kernel appears to result from an increase in self-superparasitism rather than an increase in clutch size.