Löhr B, Gathu R, Kariuki C, Obiero J, Gichini G
International Centre of Insect Physiology and Ecology, 00100 Nairobi, Kenya.
Bull Entomol Res. 2007 Aug;97(4):337-50. doi: 10.1017/S0007485307005068.
Diadegma semiclausum (Hellén) (Hymenoptera: lchneumonidae), an exotic diamondback moth parasitoid, was released in two pilot areas (Werugha in Coast Region and Tharuni in Central Province) in Kenya. Fifteen month before release, observations on the diamondback moth, Plutella xylostella (Linnaeus), and local natural enemy population dynamics and pest damage were initiated in both areas and continued for three years after release. The P. xylostella population was bimodal with higher records during dry seasons. At Werugha, the peak population of P. xylostella was 16.8 per plant (October 2001); at Tharuni it was 12.8 (February 2002). Populations at Werugha declined from three months after release and decreased from 5.4 per plant (before release) to 0.8 (year 3 after release). Concurrently, average damage (1.9 to 1.5) (on a 0-5 scale), proportion of attacked plants (72 to 31%) and proportion of plants in damage group >2 (plants with head damage) decreased (21.4 to 5.3%), while total parasitism increased from 14.4 (before) to 52.5% (year 3 after release, 90% due to D. semiclausum). At Tharuni, D. semiclausum was only recovered 3 months after release. Average populations of P. xylostella declined from 5.9 per plant (before release) to 2.4 (year 3 after release) and damage scores from 2.3 to 1.7. The proportion of plants in damage group >2 declined from 39.7 to 4.5% while overall parasitism increased from 4.2 to 40.6% (98.3% by D. semiclausum). Four species of indigenous parasitoids (Diadegma mollipla (Holmgren), Oomyzus sokolowskii (Kurdjumov), Apanteles sp. and Itoplectis sp., all primary parasitoids) were almost completely displaced by D. semiclausum. Possible reasons for the different parasitoid development between the two release areas and the displacement of the indigenous species are discussed.
半闭弯尾姬蜂（Diadegma semiclausum (Hellén)）（膜翅目：姬蜂科）是一种外来的小菜蛾寄生蜂，已在肯尼亚的两个试验区（海岸地区的韦鲁加和中部省份的萨鲁尼）释放。在释放前15个月，在这两个地区开始对小菜蛾（Plutella xylostella (Linnaeus)）、当地天敌种群动态和害虫危害进行观测，并在释放后持续了三年。小菜蛾种群呈双峰型，在旱季记录较高。在韦鲁加，小菜蛾的种群峰值为每株16.8头（2001年10月）；在萨鲁尼为每株12.8头（2002年2月）。韦鲁加的种群在释放后三个月开始下降，从释放前的每株5.4头降至释放后第3年的每株0.8头。与此同时，平均危害程度（从1.9降至1.5）（0-5级）、受攻击植株比例（从72%降至31%）和受损程度>2级的植株比例（头部受损植株）下降（从21.4%降至5.3%），而总寄生率从之前的14.4%增至释放后第3年的52.5%（90%归因于半闭弯尾姬蜂）。在萨鲁尼，半闭弯尾姬蜂在释放后3个月才被发现。小菜蛾的平均种群数量从释放前的每株5.9头降至释放后第3年的每株2.4头，危害评分从2.3降至1.7。受损程度>2级的植株比例从39.7%降至4.5%，而总体寄生率从4.2%增至40.6%（98.3%归因于半闭弯尾姬蜂）。四种本土寄生蜂（均为初级寄生蜂，分别是柔弯尾姬蜂（Diadegma mollipla (Holmgren)）、菜蛾啮小蜂（Oomyzus sokolowskii (Kurdjumov)）、小腹茧蜂属（Apanteles sp.）和艾托普姬蜂属（Itoplectis sp.））几乎完全被半闭弯尾姬蜂取代。文中讨论了两个释放区寄生蜂发育情况不同以及本土物种被取代的可能原因。
