Department of Plant Protection, Faculty of Agriculture, University of Tabriz, Tabriz, Iran.
J Insect Sci. 2010;10:78. doi: 10.1673/031.010.7801.
Trichogramma brassicae (Bezdenko) is the most important species of Trichogramma parasitoids in Iran. The cotton bollworm, Helicoverpa armigera (Hubner) is a polyphagous insect pest that attacks many crops including cotton, maize, soybean, tomato, etc. The bollworm egg is a suitable target for many Trichogramma species. Factitious hosts such as eggs of the flour moth, Anagasta kuehniella (Zeller) and cereal moth, Sitotroga cerealella (Hubner) are used for mass rearing purposes. But a problem that arises sometimes in laboratory cultures is the development of a tendency toward laboratory hosts following a few generations rearing with them. This may tend to a low efficiency on target pest in field conditions. In this study the possibility of declining efficiency of the parasitoid on target pest by developing such a preference to alternative hosts in previous generations were investigated when the flour moth or cereal moth uses as laboratory host. Two generations of T. brassicae were reared on each of the mentioned hosts and then transferred to H. armigera eggs for two further generations. The intrinsic rate of natural increase as well as other life table parameters were used for monitoring fitness of the parasitoid at successive generations. Even generations were included to determine if previously rearing host affected parasitoid performance. Results revealed that host shift from cereal moth to bollworm caused a sudden fall in population growth parameters (both intrinsic rate of natural increase and net replacement rate). Further rearing on bollworm eggs led to a relapse in both parameters. No similar effect was observed in cultures initiated with the flour moth. As a whole, cereal moth was a more suitable host than flour moth.
小菜蛾卵啮小蜂（Bezdenko）是伊朗最重要的小菜蛾寄生蜂种类。棉铃虫（Helicoverpa armigera）是一种多食性害虫，会攻击包括棉花、玉米、大豆、番茄等多种作物。棉铃虫卵是许多小菜蛾寄生蜂种类的合适目标。粉斑螟（Anagasta kuehniella）和玉米螟（Sitotroga cerealella）等人工饲养的寄主卵，被用于大量繁殖。但是，在实验室培养中有时会出现一个问题，即在几代饲养后，昆虫会对实验室寄主产生倾向。这可能会导致在田间条件下对目标害虫的效率降低。在这项研究中，当粉斑螟或玉米螟作为实验室寄主时，通过在之前几代中发展对替代寄主的这种偏好，研究了小菜蛾寄生蜂对目标害虫效率下降的可能性。在每个上述寄主上饲养了两代 T. brassicae，然后将其转移到 H. armigera 卵上进行另外两代的饲养。利用内禀增长率和其他生命表参数来监测寄生蜂在连续几代中的适应能力。同时包括偶数代，以确定之前饲养的寄主是否会影响寄生蜂的表现。结果表明，从玉米螟向棉铃虫的寄主转换会导致种群增长参数（内禀增长率和净替代率）突然下降。进一步在棉铃虫卵上饲养会导致这两个参数的恢复。在以粉斑螟开始的培养中没有观察到类似的效果。总的来说，玉米螟比粉斑螟更适合作为寄主。
