白蜡吉丁柄腹茧蜂的羽化和产卵与寄主之间的关系

Relationships between the emergence and oviposition of ectoparasitoid Spathius agrili Yang and its host emerald ash borer, Agrilus planipennis Fairmaire

白蜡窄吉丁是危害白蜡属树木的一种重要蛀干害虫,因其幼虫期高度的隐蔽性生活而极难检测和防治。白蜡吉丁柄腹茧蜂是新发现外寄生于白蜡窄吉丁幼虫的优势天敌种,对寄主害虫的控制作用较强,具有良好的生物防治利用前景。研究调查了白蜡吉丁柄腹茧蜂及其寄主白蜡窄吉丁越冬代成虫羽化的时序差异、不同时期林间的寄生率、寄主密度与寄生率的关系以及寄主幼虫大小与茧蜂产卵量的关系。结果表明,越冬后白蜡吉丁柄腹茧蜂的羽化时间比其寄主害虫白蜡窄吉丁的羽化要晚1个多月。2003年白蜡吉丁柄腹茧蜂越冬代成虫的羽化从6月中旬持续到8月中旬,羽化高峰期在7月份;寄主白蜡窄吉丁的羽化期在5月中下旬。2004年白蜡吉丁柄腹茧蜂越冬代成虫的羽化从5月下旬持续到7月下旬,羽化高峰期在6月下旬至7月上旬;寄主羽化期在4月中旬至5月中旬(室内)。越冬后天敌的羽化时间刚好适应最早寄主发育到可供寄生的龄期,这是二者长期协同进化的结果,也表明白蜡吉丁柄腹茧蜂很可能是一种专性寄生蜂。林间白蜡吉丁柄腹茧蜂对白蜡窄吉丁幼虫的自然寄生率随着时间的推移总体上是逐步上升的。自然条件下茧蜂决定是否产卵与寄主幼虫的大小即龄期有关,它仅在前胸宽和体宽1.5mm、体长12mm以上,即3～4龄的寄主幼虫体表产卵,但只要接受寄主并产卵,不同龄期寄主幼虫上的产卵量无显著的差异。

The emerald ash borer （EAB）, Agrilus planipennis Fairmaire （Coleoptera： Buprestidae ）, （ = A. marcopoli Obenberger）, is an important bark beetle attacking ash trees （ Fraxinus spp. ）. It is very difficult to detect and control because of its highly concealed life history. This pest mainly distributed in partial Asia countries （China, Japan, Korea, Mongolia） and Far East Russia, while in China it presented in Heilongjiang, Jilin, Liaoning, Shandong, Inner Mongolia, Hebei, Tianjin, Taiwan,etc. The important timber species F. mandshurica and gardening tree F. velutina were damaged severely in northern China.Spathius agrili Yang （Hymenoptera： Braconidae） is an important ectoparasitic wasp of the EAB larvae. This parasitoid has the potential to use as an excellent biological control agent for suppressing populations of EAB. We studied the differences of emergence date between overwintered S. agrili and its host, parasitism rates at different periods, relations between parasitism rates and host densities, and relationships between ovipositions of the braconid wasp and body sizes of host larvae using methods of regular surveys in forests and observations in laboratory. Results revealed that the emergence of S. agrili was more than one month later than that of its host, suggesting good synchrony between parasitoid emergence and host availability. The overwintered S. agrili emerged from mid June to mid August with the peak in July in 2003, and it was lasted from late May till late July with the peak during late June to early July. in 2004. While the EAB emergence period ranged in mid-late May in 2003, and in mid April through mid May in 2004 （in laboratory）. The emergence date of parasitoid asynchronously inosculated with the optimum developmental instars of the earliest host larvae, which was the results of a long-term co-evolution between the two species. It was also suggested that the parasitoid S. agrili could be a host-specificity parasitoid of EAB. The natural parasitism rates gradually increased in field on the whole at different periods. The body sizes of host larvae, i.e. larval instar, affected the decision of parasitoid S. agrili to lay eggs or not. Under natural conditions, this parasitoid usually oviposited only on those host larvae with a prontum and body width more than 1.5 mm, and a body length in excess of 12 mm, i.e. the 3rd to 4th instar larvae. But egg number deposited by female wasps showed no significant differences between. These findings would consequentially contribute to the further successfully biological control of the trunk borer.