Overcrowding Factors of Mosquito Larvae. 2. Growth-Retarding and Bacteriostatic Effects of the Overcrowding Factors of Mosquito Larvae13

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Abstract
LT50, values of the overcrowding factors based on continuous exposure of 1st-stage larvae of Culex pipiens quinquefasciatus Say were 1.4, 5.6, and 6.4 days for 1, ½, and ¼ unit of the factors, respectively, while LD50 was 0.31 unit. The overcrowding factors also retarded larval growth; 1 unit of these factors facilitated only 0.6% of the 1st instars to pupate on the 16th day from the start of the exposure, whereas 68.2% of the untreated larvae pupated, and the median pupation time was reached on the 10th day. First and 2nd instars were more vulnerable in terms of growth delay as well as mortality. Reduction in sizes of the egg rafts laid by females resulting from treated larvae also was noticed. Bacteriostatic or bactericidal activity of the overcrowding factors was shown by determining the number of bacteria in the treated waters and by testing the factors against Bacillus thuringiensis Berliner on nutrient agar. The rate of heartbeat was depressed markedly in larvae treated with these factors as compared with untreated larvae. Reduction in bacterial numbers in the treated water and reduced rates of heartbeat of mosquito larvae are partly responsible for high mortality and growth retardation.

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