Abstract:
Although many mosquito species develop within agricultural landscapes where they are
potentially exposed to agricultural chemicals (fertilizers and pesticides), the effects of
these chemicals on mosquito biology remain poorly understood. This study investigated
the effects of sublethal concentrations of four agricultural chemicals on the oviposition
site selection and on life history traits of Anopheles arabiensis and Culex
quinquefasciatus mosquitoes. Field and laboratory experiments were conducted to
examine how sublethal concentrations of four agricultural chemicals: an insecticide
(cypermethrin), a herbicide (glyphosate), and two nitrogenous fertilizers (ammonium
sulfate and diammonium phosphate) alter oviposition site selection, emergence rates,
development time, adult body size, and longevity of An. arabiensis and Cx.
quinquefasciatus. Both mosquito species had preference to oviposit in fertilizer
treatments relative to pesticide treatments. Emergence rates for An. arabiensis were
significantly higher in the control and ammonium sulfate treatments compared to
cypermethrin treatment (P = 0.009), while emergence rates for Cx. quinquefasciatus
were significantly higher in the diammonium phosphate treatment compared to
glyphosate and cypermethrin treatments (P = 0.007). For both mosquito species,
individuals from the ammonium sulfate and diammonium phosphate treatments took
significantly longer time to develop compared to those from cypermethrin and
glyphosate treatments (P < 0.001). Although not always significant, males and females
of both mosquito species tended to be smaller in the ammonium sulfate and
diammonium phosphate treatments compared to cypermethrin and glyphosate
treatments. There was no significant effect of the agrochemical treatments on the
longevity of either mosquito species (An. arabiensis (P = 0.21); Cx. quinquefasciatus (P
= 0.55).These results demonstrate that the widespread use of agricultural chemicals to
enhance crop production can have unexpected effects on the spatial distribution and
abundance of mosquito vectors of malaria and lymphatic filariasis.
