中華小繭蜂 (Bracon chinensis Szépl.) 之形態與生活史觀察

Abstract

中華小繭蜂(Bracon chinensis Szépligeti)寄生於稻作與甘蔗之螟蟲煩，乃常見之寄生性天敵。該蜂產卵於3~4齡螟蟲體上，營體外寄生。臺北稻田於7月下旬至8月中旬與10月下旬此蜂出現甚多。本文係以二化螟幼蟲為其寄主，觀察中華小繭蜂之形態，各期發育經過，交尾產卵行為，以及二化螟幼蟲之被寄生情況。該蜂自卵發育至成蜂之過程為卵期1天，幼蟲有5齡，共5天，擬蛹期與前蛹期共1天，蛹期5天，完成1世代約需12天。成蜂餵以蜜水壽命為3~14天，雌者常較雄者多活1~2天。成蟲羽化之當天即可交尾。交尾之後，雌蜂即在稻稈上尋求適齡之二化螟幼蟲產卵。每隻寄主螟蟲體外常見到1~11粒成堆之寄生蜂卵。雌蜂對於已產過卵之寄主螟蟲從不再次亡卵，而被寄生蜂產過卵，或被其產卵管刺過但未產卵之寄主昆蟲均呈麻醉狀態，失卻取食為害稻作之能力而終於死亡。 Bracon chinensis (Szépligeti), Braconidae is an ecto-.parasite of the larva of rice stem borers and sugarcane borers such as Chilo sutppressalis, Tryporyza incertellus, Chilo infuscatellus, Diatraea venosata and Sesamia inferens. It is widely distributed in the Oriental region including Korea, Taiwan, Mainland China (Foochow), India, Philippines and Java. In Taipei area, it commonly occurred from late July through mid-August and in late October associated with rice paddies. Overwintering initially occurred as hibernated larva in the cocoon during October or November. They would pupate and emerge synchronally with the first generation stem borer in the next spring. The biological studies of the parasite was conducted from 1968 to 1972 under conditions of temperature 30±2°C and relative humidity 65-75%. Life cycle of the parasits from the egg to adult required about 12 days. The egg, larva, prepupa and pupa lasted an average of 1, 5, 1, and 5 days, respectively. The lst-5th larvae averaged of 8, 9 , 8, 10 and 84 hours, respectively. The longevity of adult was 3-14 days by feeding with 25% honey plus water. The female usually survived 1 or 2 days longer than the male. The sting of the parasite always caused the host larva motionless and paralyzed. The pulsations of its dorsal vessel were abnormally slow and intermittent. The sting did not always associate with the oviposition. However, the larvae would be paralyzed and died whenever they were stinged by the parasite. The execution of oviposition generally took 1-2 minutes. Through the procedure of oviposition, 1-11 of parasite eggs were deposited on or near one host larva . After egg hatching, the newly hatching larva crawed everywhere and soon attached on the host insect, inserting its mandibles through the skin and begun to feed. Larva of the parasite grew rather rapidly and completed its juvenile development within 2 days. Matured larva usually rested quietly beside the host body about 12 hours then spined its cocoon inside the rice stem. The formation of cocoon usually took about 2 days. In general, larva begun to pupate shortly after the cocoon was woven except the hibernated larva which overwintered until next spring. Prepupa appeared soon after the cocoon was made and it could be distinguished as eonymphal and pronymphal phases, the pronymph was easily to he recognized by having slightly flatten body, orange eye spots and female ovipositor recurred toward the dorsad of abdomen. Pupation was done in the cocoon and lasted about 1 day or more. Pupa colored light yellowish brown and gradually became darker as well as the adult stage. At eclosion, the adult emerged by breaking the anterior end of the cocoon and gnawing a small round hole about 0.5-1.35 mm in diameter through the rice stem. Additionally, the morphological characteristics of the species are described and illustrated in this report.