Effects of Conspecific Presence on Oviposition Behavior in Egg-Raft Producing Mosquitoes

The selection of an appropriate oviposition site is crucial to the maternal fitness of eggraft producing mosquitoes. Females in this group of mosquitoes produce a single egg-raft during their lifetimes. All egg-raft producing mosquitoes are members of the subfamily Culicinae and include the medically important genera Culex and Culiseta. Egg-raft producing mosquitoes use several physical and chemical cues when selecting an oviposition site. One important chemical cue is the oviposition pheromone, (5R,6S)-6acetoxy-5-hexadecanolide. This chemical was first identified from egg-rafts in the early 1980’s and has since been found in all Culex mosquitoes. The oviposition pheromone is released from the tip of eggs immediately before larvae begin emerging. Early laboratory studies indicated that this pheromone was attractive to gravid females. Other studies have shown that females prefer to oviposit in pools of water that contain conspecific larvae or in pools of water that had previously contained conspecific larvae. Several hypotheses have been proposed as to why females prefer to oviposit in the presence of conspecifics. These hypotheses include; (i) conspecifics may alter the water surface and make it easier for females to oviposit, (ii) conspecific presence may signal a high quality habitat, (iii) the presence of active larval stages may indicate a habitat devoid of predators or offer protection against predators, and (iv) aggregation may coordinate emergence times and reduce the uncertainty of mate finding. However, there is evidence that intraspecific competition can be detrimental to egg-raft producing mosquitoes. Studies have shown that larvae raised in crowded containers have slower growth rates and lower fecundity as adults. Field studies have shown that the presence of conspecifics can have no effect or a detrimental effect on oviposition site selection by gravid females. This paper reviews oviposition behavior related to the presence of conspecifics and presents some of the proposed explanations for the apparent inconsistencies in oviposition site selection. Oviposition in egg-raft producing mosquitoes The choice of oviposition site is critical for mosquitoes (Diptera: Culicidae). Without exception, the juvenile stages of mosquitoes are confined to aquatic environments (Eldridge 2003). Since immature stages are unable to relocate if conditions become unfavorable and brood care is not practiced in mosquitoes, the maternal fitness of female mosquitoes is strongly based on their ability to choose appropriate oviposition sites (McCall and Cameron 1995). This is especially true for egg-raft producing