球形芽孢杆菌C_3－41对致倦库蚊的毒效及在蚊体内的再循环

EFFICACY OF BACILLUS SPHAERICUS C-3-41 ACAINSTCULEX QUINQUEFASCIATUS AND ITS RECYCLINCIN CADAVERS

球形芽抱杆菌Ｃ３－４１菌株（Ｂａｃｉｌｌｕｓｓｐｈａｅｒｉｃｕｓ Ｃ３－４１）对致倦库蚊（Ｃｕｌｅｘｑｕｉｎｑｕｅｆａ－ｓｃｉａｔｕｓ）幼虫有很高毒效，对２龄和３—４龄幼虫的半致死剂量（ＬＤ５０）分别为６３．１和８９．７芽孢／蚊幼虫。处理浓度越高，取食时间越长，蚊幼虫取食到的杀蚊活性物质量越多，死亡率越高。当蚊幼虫取食互致死剂量杀蚊活性物质后，球形芽孢杆菌在感染的活幼虫体内不增殖；但当蚊幼虫取食致死剂量杀蚊活性物质后，蚊幼死亡，球形芽抱杆菌在死蚊幼虫体内增殖明显，６天内芽抱从感染初期的１．８６×１０２／蚊幼虫增加到１．５９×１０６／蚊幼虫。芽抱在死蚊幼虫体内能正常荫发、生长、产孢和形成毒素。增殖的芽抱同样对致倦库蚊幼虫有较高毒力。

he efficacy of Bacillus sphaericus C3-41 to control the larvae of Culex quin-quelasciatus was evaluated in the laboratory. The result indicated that the strainC3-41 was a very effective control agent against the mosquito larvae. The 50 %lethal dosage (LD50) against the second to fourth larval instar were found to be63.1 and 89.7 sporesper larva respectively. The larvicidal substance ingested by lar-vae seemed to be directly proportional to the concentration of C3-41 and durationof feeding time. When larvae ingested sub-lethal dosage of B. sphaericus, its recyc-ling could not occur in the living larvae. However, when the laryae ingested lethaldosage, they died within 48 hours and recycling of the bacteria occurred immedia-tely. The number of spores increased from initial l.86 X 102 to l.59 X 106 sporesperlarva within six days after the death of the larvae. The spores germinated, multiplied, sporulated and forming toxin normally in larval cadavers. The spores yieldedin larval cadavers were highly toxic to the mosquito larvae.