Relationship Between Flowering of Wild Rice and Larval Mosquito (Diptera: Culicidae) Abundance in California

Abstract

Densities of larval Culex tarsalis Coquillett and Anopheles spp. populations were monitored in experimental plots of white rice, Oryza sativa L., and wild rice, Zizania palustris L., in Lake County, CA, during the spring and summer of 1989. Plant height, floral debris drop, water quality, and bacterial counts were measured and contrasted between the two systems. Anopheles spp. and C. tarsalis populations in wild rice were 6 and 2.6 times higher, respectively, than in the white rice over the entire season. A significantly greater number of notonectids and hydrophilid larvae were sampled in the wild rice treatments and did not appear to be responsible for the difference in larval mosquito populations. A positive correlation was found between average larval density and plant height for Anopheles spp. in both wild and white rice and for C. tarsalis in wild rice during the early growing season. In the latter half of the growing season, only Anopheles spp. densities showed a significant correlation with plant height. A significant positive correlation was demonstrated between the number of shed wild rice anthers and larval densities for both Anopheles spp. and C. tarsalis. No significant differences were noted in either water quality factors or bacterial counts between white and wild rice treatments. In the field, development of C. tarsalis larvae was slower in wild rice than in white rice plots before flowering but faster during flowering. However, temperature-adjusted developmental times were significantly shorter for the wild rice group only during flowering. In the laboratory, C. tarsalis completed development from second instar to adult when fed only wild rice pollen. These results suggest that wild rice pollen serves as a nutrient source for larvae in the field. In addition, the floral components of wild rice may serve as an oviposition attractant and structural refuge for the immature stages.