Laboratory Oviposition Choice of Aedes aegypti (Diptera: Culicidae) From Kenya and Gabon: Effects of Conspecific Larvae, Salinity, Shading, and Microbiome

The mosquito Aedes aegypti (L.) is the primary vector of several arboviruses. Mosquito control and surveillance are essential to restrict disease transmission, the effectiveness of which depends on our understanding of the mosquito's behaviors, including oviposition. Previous studies have identified a variety of oviposition cues. However, most of these studies involved only Ae. aegypti outside of the species' native range, Africa. Populations outside Africa differ in their genetics and some behaviors from their African counterparts, suggesting possibly different oviposition preferences. Within Africa, Ae. aegypti can be found in both ancestral forest habitats and domestic habitats. The African domestic populations may represent an intermediate state between the forest and the truly domesticated non-African populations. Comparing mosquitoes from these three habitats (African forest, African domestic, and non-African domestic) might provide insight into the evolution of oviposition behavior. In this study, I examined the oviposition choices of multiple Ae. aegypti colonies from all three habitats in laboratory settings. I applied a two-choice assay to test four oviposition cues: the preexistence of conspecific larvae, salinity, shading, and microbiome. A subset of African colonies showed similar oviposition choices as their non-African counterparts, whereas the rest show little response to the factors tested. Within the African colonies, oviposition choices of the domestic colonies were significantly different from the forest colonies in most experiments. Yet, their preferences were not always intermediate between that of mosquitoes from the other two habitats. Collectively, this study adds to our understanding of Ae. aegypti oviposition, especially in previously understudied African populations.

Attraction of the Larval Parasitoid Spintherus dubius (Hymenoptera: Pteromalidae) to Feces Volatiles from the Adult Apion Weevil Host

The behavioral response of the larval parasitoid Spintherus dubius (Hymenoptera: Pteromalidae) to volatile compounds derived from its Apion weevil hosts was investigated in two-choice bioassays. Odor source candidates were the larval and adult stages of weevils, clover flowers, and feces from adult weevils. Despite S. dubius being a larval parasitoid, the odor of weevil larvae isolated from the clover flowers was not attractive to female parasitoids. Surprisingly, S. dubius females were instead attracted by the odor from the feces of adult weevils. The female parasitoids were similarly attracted to the feces produced by the two main hosts, the red clover weevil (A. trifolii) and the white clover weevil (A. fulvipes). Chemical analysis of the volatile composition of feces produced by the two hosts revealed qualitatively similar odor profiles, correlating with the observed attraction by the parasitoid towards both odor sources. Some of the identified volatile compounds are commonly present in clover plant headspace fractions and may function as a kairomone to facilitate orientation by S. dubius to Apion-infested clover flowers. Larval and adult weevils were not attractive for parasitoid females, whereas, for the white clover weevil-plant association, infested flowers were highly attractive. These data show the use by the clover weevil parasitoid of an alternative source of olfactory information for locating its host.