Foreign mosquito survivorship in the pitcher plant Sarracenia purpurea-the role of the pitcher-plant midge Metriocnemus knabi

摘要

There are few reports of mosquito larvae other than those of the species-specific mosquito Wyeomyia smithii (Coq.) c 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 the 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. ~eomyia smithii larvae had high percent survivorships 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 then 2% when present in the culture plates. Based on these findings, we suggest that M. knabi larvae prevent non- ~eomyia mosquito taxa from exploiting the resources of S. purpurea leaves, thereby maintaining it as an exclusive mosquito niche for W. smithii. 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 mandibles of the M. knabi larva. Application of these findings to other mosquito-plant associations is suggested.