Interspecific competition between sibling species larvae of Anopheles arabiensis and An. gambiae

Mosquito larvae of the sibling species Anopheles arabiensis Patton and An. gambiae Giles sensu stricto (Diptera: Culicidae) were investigated for inte rspecific competition. Single-species and mixed-species populations were re ared at 27 degrees C from the first instar to pupation at different densiti es (100, 200 or 400 larvae/200 cm(2) tray) with a constant amount of food, 0.2 mg/larva/day. Pupae obtained from mixed populations were identified to species using PCR. Both species had a 1 : 1 sex ratio at pupation. Developm ent time to pupation averaged about one day less for An. arabiensis compare d to An. gambiae, ranging from 0.93-1.49 d for males and from 0.44-0.84 d f or females in single populations. In mixed species populations the differen ce for males ranged from 0.99-1.58 d and for females from 0.93-1.62 d. Surv ival rates of An. gambiae s.s. were significantly higher than those of An. arabiensis in both the single-species and mixed-species populations. Mixed- species rearing did not have an effect on the survival of An. gambiae, wher eas the mortality rate of An. arabiensis was significantly higher in mixed populations than when only this species was reared at the same densities, s uggesting a competitive disadvantage for An. arabiensis in mixed population s. High proportions of larvae (4-35%) were lost during development; these l osses could not be accounted for by corpses found in the rearing pans. The possibility of cannibalism was investigated by rearing each species separat ely in small containers (five per 50 ml), inspected every 6 h, but no canni balism was detected at any stage of development in either species. It was c oncluded that, under these experimental circumstances, interspecific compet ition between both species did occur but with a detrimental effect on An. a rabiensis only. Relevance of these findings to the ecology of both species in the field is discussed briefly.