EVALUATION OF RELEASE RATIOS OF Rhantus elevatus SHARP (COLEOPTERA, DYTISCIDAE) AS A PROMISING BIOLOGICAL CONTROL AGENT AGAINST Culex pipiens L. (DIPTERA, CULICIDAE) UNDER LABORATORY CONDITIONS.

This study was outlined to declare the effect of release of Rhantus elevatus (larvae and adults) at different predator: prey ratios (P: p) to control the larvae and pupae of mosquito, Culex pipiens under laboratory conditions. Effective control of second mosquito larvae was gained after one day from introducing the first instar larvae of predator when the P:p ratio was 1:25 or 1:50. After releasing the first instar larvae, a completely reduction in the third mosquito larvae was 100% after four days at P:p ratios 1:100, 1:125 and 1:150. Completely decreased of fourth instar mosquito larvae was occurred after two days at P:p ratios 1:25 and 1:50, respectively. After one day of releasing the first predator larvae against pupal mosquito stage, the reduction rate was 21.00, 12.50, 8.33, 5.00, 5.60 and 4.00% at P:p ratios 1:25, 1:50, 1:75, 1:100, 1:125 and 1:150, respectively. Release of first instar predator larvae against mixed mosquito larvae recorded one hundred reduction percentage after one day at P:p ratio 1:25. A complete control after one day was achieved at P:p ratios 1:25 and 1:50 when releasing of second instar larvae of predator against the second instar larvae of mosquito. Releasing the second instar larvae of R. elevatus against third instar larvae of C. pipiens showed a complete control after one day at P:p ratio 1:25. When using the second instar larvae of predator to control the fourth instar larvae of mosquito, the results indicated that an effective control of mosquito larvae was observed after four days at P:p ratio 1:150. Second instar larvae of predator showed a complete reduction in pupal mosquito stage at P:p ratios 1:25 and 1:50 after one and two days, respectively. After two days, the reduction rate was 41.50, 51.40, 62.50, 86.00 and 100.00% at P:p ratios 1:150, 1:125, 1:100, 1:75 and 1:50, respectively. One hundred reduction rate was recorded after one day of releasing second instar predator larvae against mixed mosquito larvae at P:p ratios 1:25 and 1:50. When the third instar larvae of predator was released against the second mosquito larvae, a complete reduction was occurred after one day at P:p ratios 1:25, 1:50, 1:75 and 1:100. A completely reduction of third instar mosquito larvae was achieved after one day at P:p ratios 1:25 and 1:50. A control percentage of fourth instar larvae of mosquito was 80.00 and 59.50% after one day at P:p ratios 1:75 and 1:100, respectively. Third instar larvae of predator showed a complete reduction against pupal stage at P:p ratios 1:25 and 1:50 after one day. A completely control of mixed mosquito larvae was achieved after one day at P:p ratios 1:25, 1:50, 1:75 and 1:100. Results of releasing adults with the predator: prey ratio of 1:100 showed that the predator adults were successfully eliminating the third instar of mosquito larvae after two days from the release. The number of mosquito larvae decreased by 60.25, 37.33, 27.75, 23.70 and 19.75% for 1:100, 1:150, 1:200, 1:250 and 1:300 ratio, respectively. When releasing the predator adults against the fourth instar mosquito larvae, the reduction rate was 65.67, 49.87, 41.10 and 33.34% at P:p ratios 1:150, Abdel-Salam, A. H. et al. 570 1:200, 1:250 and 1:300, respectively after two days. During pupal stage of mosquito, the reduction percentage was 29.75, 20.50, 13.86, 13.30 and 10.25% after one day of releasing pedator adults at P:p ratios 1:100, 1:150, 1:200, 1:250 and 1:300, respectively. When releasing R. elevatus adults to control mixed instar larvae of C. pipiens, a completely control was observed after two, three, four and five days at P:p ratios 1:100, 1:150, 1:200 and 1:250, respectively. According to regression analysis between P: p ratios of R elevatus (larvae and adults) and reduction percentage of larvae and pupae of mosquito, there were negatively high relationship of predator, which means that the reduction rate was increased with lower P: p ratios and vice versa.