Copepod predation on Anopheles quadrimaculatus larvae in rice fields

Cyclopoid copepods and mosquito larvae were surveyed in southwestern Louisiana rice fields. Almost every rice field had a natural population of Mesocyclops ruttneri, Acanthocylops vernalis, or Macrocyclops albidus. Judging from the abundance of pupae, 29% of the fields were responsible for virtually all Anopheles quadrimaculatus production, apparently because larval mortality suppressed production in the other fields. Mesocyclops ruttneri had the strongest negative association of naturally occurring copepod populations with An. quadrimaculatus larvae, though a few fields with M. ruttneri had substantial Anopheles production. Macrocyclops albidus, M. ruttneri, Mesocyclops edax, and Mesocyclops longisetus were introduced to experimental rice field plots. It took two months for the introduced copepods to build up their numbers; Anopheles larvae then disappeared from all treated plots while larvae continued to be present in the adjacent control field. Copepods were observed to kill the following number of first instar An. quadrimaculatus larvae in the laboratory: Mesocyclops ruttneri (36 larvae/day), Macrocyclops albidus (23 larvae/day), Mesocyclops longisetus (24 larvae/day), and Acanthocyclops vernalis (15 larvae/day). It is concluded that introducing select species of copepods and encouraging their populations offer possibilities for contributing to Anopheles control in rice fields.