【概 述】甜菜夜蛾学名Laphygma exigua（Spodoptera exigua）Hubner鳞翅目，夜蛾科，别名贪夜蛾。是一种世界性的害虫。在我国许多地方暴发成灾，危害遍及20多个省、市。除危害十字花科蔬菜以外，还严重危害玉米、花生、大豆、棉花、烟草、花卉、果树等170多种作物和植物。
【为害特点】幼虫取食叶片，仅留叶脉和叶柄，还可蛀食甜椒和番茄的果实，造成腐烂和脱落。
【形态特征】成虫体长10～14毫米，翅展25～30毫米，体灰褐色。前翅中央近前缘外方有肾形斑1个，内方有环形斑1个，外缘线由一列黑色三角形组成。卵圆馒头形，白色，表面有放射状的隆起线。卵粒重叠，多层，呈块状。幼虫老熟时体长约22毫米，体色多变，腹部体侧气门下线为明显的黄白纵带，直达腹末，有时带粉红色，每体节的气门后上方各有一明显白点。大龄幼虫有假死性。蛹黄褐色。
【生活习性】成虫白天躲在土缝、杂草丛、枯草下及植株茎叶浓荫处，夜晚8～11时活动最盛，进行取食、交尾和产卵。趋光性强而趋化性弱。卵多产在叶背面其上茎有白色绒毛。每雌可产卵100～600粒，多者可达1700粒。卵期3～6天。1～2龄幼虫群集在卵块附近，吐丝多。3龄后分散，4龄昼伏夜出，为害加剧， 5～6龄食量占幼虫期食量的90%左右。老熟幼虫入土化蛹。各虫态耐高温力较强，幼虫易产生抗药性。
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卵块（上为放大图）
Beet armyworm egg mass |
甜菜夜蛾成虫
Beet armyworm adult |
Beet Armyworm
(Spodoptera exigua? Hubner)
Description
Beet armyworm originated in Southeast Asia. Adult wingspan is about 1 inch. Forewings are mottled gray or brown with a pale spot near the center. Hind wings are white with dark veins and a fringelike border. Larva green or black, with a dark head, five pairs of prolegs, and sometimes three lightly colored stripes running the length of the body. On the second segment behind the head, there is a small black spot on each side of the body. This spot usually becomes visible to the field observer when the caterpillar reaches about 1/3 of an inch. The spot may be difficult to see on a dark caterpillar. Squeezing the caterpillar from the rear may make the spot more apparent. Larvae range from less than 1/10 of an inch when newly emerged to about 1 inch when fully grown.
Host Plants
The beet armyworm has a wide host range, occurring as a serious pest of vegetable, field, and flower crops.
Damage
Larvae feed on both foliage and fruit. It is regarded as a serious defoliator of flower crops and cotton, though much of the injury is induced by insecticide use that interferes with natural enemy activity. Young larvae feed gregariously and skeletonize foliage. As they mature, larvae become solitary and eat large irregular holes in foliage. They also burrow into the crown or center of the head on lettuce, or on the buds of cole crops.
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