INTRASPECIFIC COMPETITION IN ANOPHELES STEPHENSI (DIPTERA: CULICIDAE): II. THE EFFECTS OF MORE CROWDED DENSITIES AND THE ADDITION OF ANTIBIOTICS

Abstract

Anopheles stephensi Liston larvae were reared in food- and space-limited environments to which a mixture of penicillin G, chloramphenicol, and amphotericin B was added to suppress microbial populations. Under crowded conditions larvae took longer to develop, exhibited reduced survival, had an extended pupation period, and produced adults that were smaller. Under uncrowded conditions slightly more males than females emerged, whereas under crowded conditions proportionately fewer males than females emerged. Indirect evidence suggested that inhibitory compounds that slowed development and increased larval mortality were produced by crowded larvae. The addition of antibiotics did not suppress all microbial populations, but rather selected for resistant Pseudomonas-group bacteria which actually increased in number. The addition of antibiotics increased developmental rates at uncrowded, but not crowded densities, increased larval mortality, and increased the size of the emerging adults. Residual antibiotics increased development rates in a subsequent bioassay of the rearing media.