PETERSEN, RAYMOND L.*, ANDREA FAUST, JACQUELINE NAGAWA, CHANDI THOMAS, and ANNICK VILMENAY. Biology Department, Howard University, Washington, DC 20059. - Foreign mosquito survivorship in the pitcher plant Sarracenia purpurea - the role of the pitcher-plant midge Metriocnemus knabi.
There are few reports of mosquito larvae other than those of the
species-specific mosquito Wyeomyia smithii(Coq.) in leaves of
Sarracenia purpurea L. We investigate why this might be so in
two sets of experiments. In the first set, we compare the percent
survivorship of W. smithii, Aedes aegypti (L.), and
Anopheles stephensi Liston larvae when reared in intact pitcher
plant leaves to in vitro rearings and we found that the
survivorship of the Aedes and Anopheles larvae was close
to zero when reared in intact pitcher plant leaves compared to 37% and
64%, respectively, when reared in fish-food medium and 78% and 82%,
respectively, when reared in pitcher-plant liquid. Wyeomyia
smithii larvae had high percent survivorship under all three
rearing conditions. In the second set of in vitro experiments,
we compared the percent survivorship of W. smithii and Ae.
aegypti larvae when reared in pitcher-plant liquid in the presence
and absence of the larvae of the pitcher-plant midge, Metriocnemus
knabi (Coq.) and found that the percent survivorship for W.
smithii was high (90%) whether M. knabi larvae were present
or absent. We also found that Ae. aegypti larval survivorship
was 82% when M. knabi larvae were absent and less than 2% when
present in the culture plates. Based on these findings, we suggest
that M. knabi larvae prevent non-Wyemoyia mosquito taxa
from exploiting the resources of S. purpurea leaves, thereby
maintaining it as an exclusive mosquito niche for W. smithi.
This is confirmed by visual observation of M. knabi attacking
and devouring Aedes and Anopheles larvae, while at the
same time leaving W. smithii larvae unharmed. Possibly the long
setae of the W. smithii larva may prevent access to its body
wall by the mandibiles of the M. knabi larva. Application of
these findings to other mosquito-plant associations is suggested.
Key words: Metriocnemus knabi, Wyeomyia smithi, Aedes aegypti, Anopheles stephensi, mosquito larvae survivorship, Sarracenia purpurea