Overcrowding Factors of Mosquito Larvae12

Third-instar larvae of the southern house mosquito Culex Pipiens quinquefasciatus Say, raised under overcrowded conditions (5-7 larvae/ml) produced chemical factors which were highly toxic to 1st-instar larvae of this species. In addition to being highly toxic to younger larvae, overcrowding factors slowed down growth and development of younger larvae and produced morphological aberrations in larvae exposed to suspension of extracts of these factors. Overcrowded cultures of larvae maintained under septic and aseptic conditions, showed approximately similar activity when supernates from the cultures were evaluated against younger larvae. Infusions of larval food (without any larvae), under septic and aseptic conditions also produced some toxic factors, but the nature and quantity of these factors produced were different from those elaborated in overcrowded larval cultures. Tap water control and less crowded larval cultures were devoid of these factors. The toxic overcrowding factors were ether extractable, but some factors also were extracted in the aqueous layer as determined by bioassay techniques. Ether extract of larval homogenates was free of toxic overcrowding factors. Overcrowding factors isolated from cultures of C. p. quinquefasciatus and streaked on thin layer chromatograms showed 2 zones where biological activity was most obvious. Ether eluate from I of these 2 zones was further streaked on a thin layer chromatogram using a 2nd solvent system. The most active materials were located at the solvent front. Material from this zone as well as 2 other zones showed quick killing action and residual activity against 1st-instar larvae. In some tests, the overcrowding factors manifested biological activity for as long as 22 days. Overcrowding factors of C. p. quinquefasciatus showed considerable activity against 1st-instar larvae of Culex tarsalis Coquillett; the yellow. fever mosquito, Aedes aegypti (L.); and Anopheles albimanus Wiedemann. In 1 experiment overcrowding factors from a larval culture of A. aegypti were extracted with ether. This material showed high activity against larvae of C. p. quinquefasciatus. Ethanol elution of concentrated ether extract showed considerably higher biological activity than water suspensions of the same materials. It is postulated that ethanol either synergizes the factors or increases their availability to the larvae.