It has been established that a prolonged copulatory period of 3-4 hours is necessary for maximal insemination to occur in the western corn rootworn (WCR). This complete mating period has been suggested to speed ovarian development. The purpose of this study was to determine the relationship between copulation and ovarian development in the WCR. Using 11 and 12 day postemergence virgin WCR beetles, four female groups of varying copulatory duration were established: (1) 15 min. in copula (2) 1 hr. in copula (3) 2 hrs. in copula (4) a control group mated until natural completion. After copulation, these beetles along with a control group of unmated females were placed in isolated cage vials. Frequency of egg-laying and post-copulation change in female weight was recorded up until the time of dissection. The beetles were then sacrificed between 21-24 days post-copulation and the effects on ovarian development were evaluated with the following criteria: (1) reproductive status (an ovarian rating system) (2) morphometric analysis of ovarian area (using an Olympus C-R Research Image Analyzer with an IBM/PC Microcomputer). The presence of spermatozoa in the spermatheca was also noted at the time of dissection. The results demonstrate significantly larger mean ovarian area and greater mean reproductive status rating (P<0.05) in the control group of mated until completion females compared with the control group of unmated females. Egg-laying frequency and mean post-copulation change in weight reflected fully developed ovaries present in the mated until completion beetles and not in the unmated beetles. The results with the groups of varying copulatory duration suggest that spermatozoa may play a role in the development of fully maturated ovaries. In addition, it appears that directly after copulation some factor other than spermatozoa is responsible for significant increases in reproductive development. This other factor appears relatively transient and does not maintain a significantly developed reproductive state past approximately 14 days post-copulation.



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