Larval competition between the invasive Anopheles stephensi and African native mosquitoes

The ecology of the invasive Anopheles stephensi in Africa remains poorly understood. Using laboratory strains, we conducted larval competition experiments between An. stephensi and African mosquito species under varying conditions of food availability and larval density. When An. stephensi was reared alone, high food availability did not influence adult emergence rates; however, emergence time was significantly prolonged at higher larval densities. The low food conditions and increased larval density led to both a significantly reduced emergence rate and a longer development time. When An. stephensi was co-reared with Anopheles arabiensis, its emergence rate was significantly reduced (31% reduction) compared with when reared alone; however, the decline in emergence rate was more pronounced in An. arabiensis (64% reduction). Similarly, co-rearing of An. stephensi and Anopheles gambiae sensu stricto only significantly reduced the emergence rate of adult An. gambiae (46% reduction). Across these experiments, changes in emergence time were generally not significant for either species. Larval competition between An. stephensi and Aedes aegypti had minimal effects on the emergence rate and development time of Ae. aegypti, however, it substantially reduced the adult emergence rate of An. stephensi under all experimental conditions (88% reduction, range 75-100%). Co-rearing An. stephensi with Culex quinquefasciatus had no significant effects on either emergence rates or development times for either species. The results suggest that An. stephensi may outcompete African malaria vectors but is strongly outcompeted by Ae. aegypti.