双斑截尾寄蝇对寄主种类及草地螟幼虫龄期和寄生部位的选择性

Host species,instar and position preference of a tachinid parasitoid,Nemorilla maculosa (Diptera:Tachinidae)

双斑截尾寄蝇Nemorilla maculosa Meigen是草地螟和其他鳞翅类昆虫的重要寄生天敌,但国内外对其寄生行为知之甚少。为了明确双斑截尾寄蝇的寄生行为特征及其对草地螟种群动态的影响,在22℃,光照16h的条件下就其对不同寄主种类及草地螟幼虫龄期、寄主部位的选择性进行了研究。结果显示:在草地螟、甜菜夜蛾和粘虫3种幼虫同时存在的条件下,双斑截尾寄蝇对草地螟的寄生率显著高于甜菜夜蛾和粘虫,而对甜菜夜蛾的寄生率又显著高于粘虫。另外,幼虫被寄生的平均次数也呈现相同的趋势,表明双斑截尾寄蝇喜选择草地螟。在3,4,5龄草地螟幼虫同时存在时,双斑截尾寄蝇对5龄幼虫的寄生率和平均寄生次数均显著高于4龄和3龄幼虫的,表明该寄蝇主要选择5龄幼虫为其寄主。在被寄生的草地螟幼虫中,胸部被寄生的比率(66.4%)和次数(4.2)显著高于头部(23.4%,1.0)和腹部(10.9%,1.1),而腹部及头部被寄生的比例及卵粒数没有显著差异,表明双斑截尾寄蝇主要选择幼虫的胸部进行寄生。最后,就双斑截尾寄蝇对产卵寄主选择的原因和机理进行了讨论。

The tachinid fly, NemoriUa maculosa Meigen （Diptera： Tachinidae） is an important parasitoid of the beet webworm, Loxostege sticticalis L. （Lepidoptera： Pyralidae） in China's Mainland. Females of N. maculosa lay heavy-shelled macrotype eggs on the last-stadium host larvae of L. sticticalis and other lepidopterous larvae. Little has been studied and understood so far in the host species and instar preference, and parasitic position of N. maculosa. Studies were therefore designed to investigate and understand the host preference of this parasitoid under laboratory conditions （22℃, LI6：D8）. The results indicated that N. maculosa could parasitize the beet webworm L. sticticalis, the beet armyworm Spodoptera exigua Hiibner （Lepidoptera ： Noctuidae）, and the oriental armyworm Mythimna separata （Walker） （Lepidoptera ： Noctuidae） when the final instar of the three host larvae were presented simultaneously. However, the parasitism rate for L. sticticalis was significantly higher than that for the beet armyworm, which in turn was significantly higher than that for the oriental armyworm. Besides, the number of tachinid eggs per host larva received also followed the trend of parasitism rate in these three species, indicating that N. maculosa was more likely to select L. sticticalis larvae as its host. The parasitoid mainly selected the last instar larvae as its host when 3rd, 4th, and 5th instar larvae of L. sticticalis were mixed together. The parasitism rates for these three instars of larvae were increased as the larval instar increased. The tachinid eggs were mainly located on the thorax （66.4 % ）, followed by on the head （23.4%） and the abdomen （ 10.9% ） of the host larvae. The number of tachinid eggs on the thorax was significantly greater than that on the head and abdomen of the host larvae, while the eggnumbers between the head and abdomen were insignificantly different. Mechanisms underlying the host instar, position and species preference of N. maculosa were finally discussed.