Semi‑field experiments highlight the importance of maize and rice pollen on oviposition site choice and larval development in Anopheles arabiensis

Abstract

Background Members of the Anopheles gambiae complex, such as Anopheles gambiae sensu stricto (An. gambiae s.s.), Anopheles coluzzii and Anopheles arabiensis, are among the key malaria vectors in sub-Saharan Africa. These species are often abundant in areas of intense rice and maize farming with temporary water pools reflecting the dependence of their larvae on the pollen shed in such pools as food. In this study we explored the oviposition preference of wild-caught gravid An. arabiensis in response to maize and rice pollen in artificial aquatic habitats in a semi-field system. Methods Twelve experimental breeding habitats were established in each of the two large compartments of a semi-field system. Rice or maize pollen was added into eight randomly selected habitats in eachcompartment; the remaining four habitats of each compartment were used as control habitats without pollens. In the first experiment, 40 gravid An. arabiensis were released in each compartment and left overnight to choose egg-laying habitats, following which the eggs were sampled and counted. The second experiment differed from the first experiment only in that the counted eggs were returned to the respective habitat where the development of the resultant larvae was monitored and recorded until pupation. Results Pollen types strongly affected the oviposition behaviour of gravid An. arabiensis. Females preferred to lay eggs in habitats with rice pollen on the water surface over those with maize pollen, and in habitats with maize pollen on the water surface over pollen-less controls. The development of larvae was significantly affected by the type of pollen in the habitats. The highest total number of An. arabiensis offspring were produced in habitats with rice pollen compared to those with maize pollen and no pollen. However, larval development success was comparatively lower in habitats containing rice pollen than those with maize pollen and no pollen, suggesting that the habitats with rice pollen were overcrowded. Conclusion This study demonstrates that pollen types on the surface of aquatic habitats influence the oviposition site selection behaviour of gravid An. arabiensis and has carry-over effect on the developmental success of their offspring.