1985 Volume 36 Issue 4 Pages 289-294
Studies were conducted using a laboratory colony of Chironomus yoshimatsui (Diptera : Chironomidae) to investigate the tube-forming ability of the larvae that were experimentally cultured in 11 different materials. A preliminary examination was performed to establish criteria for judging larval mortality due to larvicidal effect. Among the 11 materials used during tubular formation, the larvae constructed tubes in the least amount of time using mud particles (30-150 mesh) collected at their natural habitat, followed by larvae using 0.1,0.2 and 0.3mm glass beads, respectively. Materials containing fine particles, such as silica powder (150,300 mesh) and kaolin (300 mesh) proved to be unsuitable for tubular formation. The larvae failed to construct tubes of glass fiber. Further, water temperature was found to influence tubular formation; lower temperatures (5-20℃) significantly retarded formation as opposed to a higher temperature of 25℃. Laboratory evaluations of 13 organophosphorus (OP) insecticides used against C. yoshimatsui was performed with larval mortality judged on the basis of the success or failure of tubular formation within 48 hours after chemical treatment by using the standard material (0.1mm glass beads). Among the five most active OPs, phoxim (LC_<50>=0.00271ppm) was found to be the most active, followed by chlorpyrifos (LC_<50>=0.0032ppm), chlorpyrifos-methyl (LC_<50>=0.00562ppm), temephos (LC_<50>=0.0112ppm), and finally ethylisoxathion (LC_<50>=0.0136ppm). The water temperature influenced the efficacy of some insecticides : chlorpyrifos-methyl and temephos were significantly more active at 20℃ than at 5℃, whereas the efficacy of fenthion and fenitrothion was not noticeably affected by the water temperature.
