Laboratory Studies on Developmental Responses of the Filarial Vector Mosquito, Culex pipiens pipiens (Diptera: Culicidae), to Urea Fertilizer

Abstract

Filariasis threatens the health and economic well-being of more than a billion people worldwide. Yet, the environmental factors that condition the abundance of its principal vector, i.e., Culex pipiens pipiens, is poorly understood due to the greater emphasis placed on anopheline vectors of malaria. Cx. p. pipiens mosquitoes breed profusely in rice-farming wetlands, where urea is commonly used as fertilizer; which has been controversially reported as having varied effects on the biology of the mosquito. In order to elucidate the potential contributions of application urea, to the production of Cx. p. pipiens mosquitoes from rice-growing wetlands, Laboratory studies were carried out to determine the influence of urea fertilizer on survival and development of immature life stages of the mosquito. Day-old 1st instar larvae of the mosquito species were raised in urea-treated media of concentrations ranging from 2.50-15.00 g L-1 and monitored daily for immature life stage survival rate and duration of development. The results showed dose-dependent mortality and developmental responses of the mosquitoes to urea treatments. Total Immature Survival (TIS) reduced significantly (p<0.05) from 90.38±6.52% in the control mosquitoes to 65.55±28.92% among those reared in 5 g L-1 urea-water. Generally, mean larval survival rates were significantly lower than those of the pupal stage. Survival rates of the larval instar stages significantly reduced from L1 to L4, with few exceptions. Similarly, the duration of Total Immature Development (TID) was significantly (p<0.05) extended by urea from 11.57±0.20 days in the control mosquitoes to 17.44±0.94 days among mosquitoes raised in 10.00 g L-1 urea-water. The duration of larval instar stages (i.e., L1 to L4) also varied significantly among the treatments, with larval development terminating at L3 in the 12.50 and 15.00 g L-1 urea-water treatments. However, for treatments 5.00 to 12.50 g L-1 urea-water, the duration of the L1 larval instars did not follow the usual dose-dependent effects of urea characteristic of the results of this study. The epidemiological implications of these results were highlighted and it is hoped that the findings will facilitate the development and integration of fertilizer-application best practices in to rice-farming activities