How Polarized Light and Semiochemical Cues Influence Oviposition Site Selection Behavior in Chironomid Midges (C. riparius)

Chironomidae (non-biting midges) use polarized light cues to locate and select bodies of water to deposit jellied egg ropes. The role that semiochemical cues play in where females choose to lay their eggs (oviposit) is far less understood in relation to closely related genera of insects such as mosquitoes, which have been observed responding to the presence plant matter, organic repellents, and predator cues when selecting where to lay their eggs. Additionally, some Diptera have been observed avoiding polarized light cues when organized in vertical stripe patterns of high and low polarized light reflectivity contrast. The purpose of this study is to determine when polarized light cues are effective in influencing where Chironomus riparius choose to oviposit, as well as if C. riparius will respond to non-visual cues when selecting where to lay their eggs. Lab raised C. riparius were tested using two choice bioassays within a lab environment where water filled tubs were presented as the only available oviposition sites. These tubs were paired using either visual or semiochemical treatments. Independent sample t-tests were used to analyze the data in all experiments where a normal distribution of data was gathered. A Wilcoxon rank sum test was used for non-parametric data. It was concluded that lab midges would respond to polarized light cues when the visual treatment of each tub only extended to the water line. C. riparius also responded to both solid white and vertical black-white stripe patterns in similar manners when given the option to instead oviposit in a black tub, suggesting that polarized light uniformity plays a role in influencing midge behavior outside of the total percentage of polarized light reflected. None of the semiochemical cues tested produced any significant or conclusive effects, suggesting that C. riparius relies primarily on visual cues when selecting an oviposition site.