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.
North America
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.
Bermuda
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.