Invasion Ecology: testing for the impact of Aedes albopictus on native or resident mosquito populations
As Aedes albopictus occupies more and more habitat in the United States, it has potential impact on native container breeding species, such as the treehole mosquito Ochlerotatus triseriatus and the introduced Aedes aegypti in the gulf coast region and peninsular Florida. The impact of this invasion on Aedes aegypti was rapid and drastic– so sudden that there was no opportunity to study it carefully. We hoped that an analogous situation in Bermuda might enable us to look at the albopictus-aegypti interaction in more detail, and will describe that effort later on. The northern advance of albopictus has slowed, and our approach to testing for effects of albopictus on resident O. triseriatus populations is the object of the Labor Day Mosquito Count.
The rationale behind the Labor Day Mosquito Count is that by sampling in many places along the northern margin of albopictus, we can find places where the invader has not yet arrived, and comparable places where it has become established. Testing for an association between albopictus abundance on the rate of change in O. triseriatus (estimable from successive censuses) will enable us to quantify the impact of the invader at the population level. Previous experimental studies enable potential mechanisms of agonistic interactions to be identified, but do not demonstrate that the interaction actually occurs in natural conditions. This study is intended to see if that missing connection can be made.
Aedes aegypti occupied Bermuda during the slave trade, and thrived in cisterns under houses for centuries, until an intensive control effort eliminated this species in 1960. At least, it was not seen on the island until its reappearance (reintroduction?) in 1998. Concerns over the potential resurgence of aegypt prompted the Bermuda Health Department to establish an island-wide network of egg traps for surveillance and targeted control measures. Shortly thereafter, in 2002, Aedes albopictus was found.
The existence and continued monitoring of egg traps by Bermuda Health Department staff, combined with the identification of eggs by graduate students at Clark (Laran Kaplan and Camilo Khatchikian), provides the unusual opportunity to trace the progress of the albopictus invasion with considerable detail. A spatial and temporal analysis of this invasion reveals that the establishment of A. albopictus occurred simultaneously with the disappearance of A. aegypti. Based on the speed of extinction for A. aegypti, we suspect factors in addition to resource competition, and are currently exploring alternative mechanisms.