小菜娥(Plutella xylostella Linnaeus)幼蟲寄生小繭峰(Apanteles plutellae Kurdjumov)之觀察

Abstract

小菜娥(Plutella xylotella Linnaeus)幼蟲寄生小繭蜂(Apaizteles pluella Kurdjumov)乃小菜蛾之主要天敵。在本省北部地區春季之田間情況下，其寄生率可達30%。本文從事其各期形態記述，發育經過及部份習性之觀察。各期之識別特徵為卵無色透明，長圓形，尾端有一刺。卵期二天。幼蟲期約為八天。第一齡幼蟲為尾顆型，初孵化時體節不甚明顯，頭大、大顆鍊刀狀，體具尾狀物。經二天後即蛻皮而達二齡。第二齡幼蟲為囊型，此時大頸不見，但見口部有三隆起，即上唇和一對小頸。前胸發達，腹部末端有膨大之圓形囊狀物。約經五天即蛻皮而成為第三齡幼蟲。此時幼蟲穿破寄主體膚外出。其體色淡黃帶綠、略彎曲、大顆與體節均明顯，但腹末之囊狀物消失。幼蟲一屆老熟，約經一天即成前蛹。前蛹體色談黃，腹部帶白色，有橙紅色之眼點。約經二天即化蛹。蛹體鮮黃色稍透明，複眼紅褐色，單眼三個均橙紅色。蛹期約五天。自卯之孵化，幼蟲發育，化蛹至成蟲羽化約需時十七天。成蟲羽化後以蜜水餵飼，其壽命可長達二十天。 Apanteles plutilac Kurd., of the family Braconidae, is an endoparasitic larval parasite of the diamond-back moth, Plitella xylostella L. (Plutellidae). It has been considered as one of the promising biological control agents of the moth in Taiwan. This investigation was aimed at to have a thorough understanding of the biology of the parasite, and carried out in Taipei under the laboratory conditions of approximately 20±2℃ temperature and 66~75% relative humidity. The average duration of the egg, larval, prepupal and pupal stages of the parasitewas 2, 8, 2 and 5 days respectively. The total time required for the completion of a life cycle starting from egg to adult emergence averaged 17 days. The preovipositional period was less than 24 hours. Both sex of adult fed on 25% bee honey could live for an average of 20 days. Larvae appeared to have 3 nstars, the first-, second and third-instar, and lasted 2, 5 and 1 day respectively. The fully grown larva came out from the host body and pupated inside silken cocoon beside the remains of its host. The morphological characteristics of different stages are also described and summerized as follows: Egg is transparent, elongate with a short stalk, about 0.2 x 0.04 mm in size when deposited into the host and becoming larger 24 hours after deposition. The first instar larva may be recognized as the caudate-mandibulate type, with body transparent, about 0.39-0.58x 0.08-0.14 mm in size, segmentation not clear, head larger, mandible distinct, and with a caudal projection. The second instar larva is semi-transparent about 2.1-4.2 x 0.63-0.84 mm in size, mouth parts three-lobed (labium and a pair of maxillae), segmentation of thorax and abdomen distinct, and caudal projection developed to a vesicle. The third instar larva is yellowish green, about 4.27x 0.84 mm in size, body slightly curved, with distinct mandible, pleura of 1st to 7th abdominal segments distinctly convex, and abdominal apex without apical vesicle. The prepupa is light yellow with ventral side in white color, about 2.6-3.0 x 0.77-1.0 mm in size. And a pair of orange red eye spots appeared. The pupa is bright yellow with seven visible abdominal segents, about 2.8x 0.9mm in size, with antenna, wings and legs transparent. Antenna 18-segmented. The exuviae of the third instar larva remains attached to its abdominal apex. The cocoon is white in color, elongate in shape and about 3.6x 1.5mm in size. The adult is black in color, about 3 mm in length. Forewing about 2.6mm long. Mandible light brown, palpi yellow, antenna black ordark brown, wings hyaline with pterostigma blackish and veins fuscous, legs light brown with coxae black except mid-coxa partially light brown, hind femur, tibia and front and middle tarsi partially dark, hind tarsus almost entirely dark, all legs of males usually darker than those of females. Antenna 18-segmented. Body densely punctate and with fine punctures on face, posterior half of the mesopleurum impunctate, propodeum coarsely densely punctated with a few distinct wrinkles which are more distinct in females. The first two abdominal tergites densely coarsely punctated, punctures on the other tergites are scarce, fine and weak or almost lacking.