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United States Department of Agriculture

Agricultural Research Service

Title: Ovarian Physiology and Age-Grading in the Rice Weevil (Coleoptera: Curculionidae)

Authors
item Perez Mendoza, Joel
item Throne, James
item Baker, James

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 11, 2002
Publication Date: October 1, 2003
Citation: PEREZ MENDOZA, J., THRONE, J.E., AND BAKER, J.E. 2003. OVARIAN PHYSIOLOGY AND AGE-GRADING IN THE RICE WEEVIL (COLEOPTERA: CURCULIONIDAE). JOURNAL OF STORED PRODUCTS RESEARCH 40: 179-196.

Interpretive Summary: The rice weevil, Sitophilus oryzae, is one of the most destructive pests of stored grains in the U.S. and in tropical and warm temperate regions of the world. Determination of the age of individual adult weevils in a population can improve our understanding of the potential population growth of this species in bulk grain. We developed a method for determining age of female weevils based on changes in reproductive organs as the weevils aged. This method of determining weevil age will be useful in improving the accuracy of simulation models developed to predict outbreaks of pests in response to environmental changes. These more accurate models will improve the effectiveness of integrated pest management programs for stored grain.

Technical Abstract: Physiological and morphological changes in the ovarian system in rice weevils, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), reared on wheat seeds were studied as a function of adult age, mating status, and nutrient availability. X-ray analysis was used to determine time of adult eclosion and the duration of development of pre-emergent weevils within the seeds, a process that lasted ca. 4 days at 25°C and 60% r.h. There was no follicular differentiation in pre-emergent weevils. Oocyte maturation began after adults emerged from the seeds and started to feed. There was a significant increase in mean germarium length and size of proximal follicles within the first 5 days when newly emerged weevils were mated and fed ad lib. Maximum number of follicles and mature eggs per ovariole in mated females occurred between 5 and 40 days of age. The number of mature eggs decreased in 60-day-old weevils, at the same time that adult mortality increased. Development of the ovarian system was much slower in unmated females than in mated females. Although there was follicle development in unmated females, ovulation never occurred and no eggs were oviposited. Starvation of mated females resulted in an immediate reduction in number of follicles and mature eggs, probably as a result of oosorption. Females were categorized into two nulliparous and three parous stages according to ovarian development and the degree of accumulation of follicular relics. Parity was directly correlated with both weevil age and number of progeny produced and was the physiological basis used to construct an age-grading model for this species. The model will be useful for determining structure and reproductive potential of rice weevil populations in the field.

Last Modified: 8/27/2014
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