豚草卷蛾与苍耳螟的资源生态位研究

Resource use overlap between Epiblema strenuana and Ostrinia orientalis: two biocontrol agents against Ambrosia artemisiifolia and Xanthium sibiricum

引进的豚草卷蛾和本地的苍耳螟是取食豚草的重要天敌昆虫。为了进一步明确两种天敌种间的竞争作用 ,定量研究了豚草卷蛾和苍耳螟在寄主植物种类和空间上的生态位指数。结果表明 ,在寄主植物种类上 ,豚草卷蛾只取食豚草和苍耳 ;苍耳螟可取食豚草、苍耳、黄花蒿、向日葵、万寿菊、国庆菊、菊芋、麦杆菊 ;苍耳螟的生态位宽度指数 ( Hurbert标准值 0 .2 2 8)明显大于豚草卷蛾 ( 0 .0 69) ,两者的食物资源生态重叠程度较小 ( Horn's指数 0 .31 8) ;豚草卷蛾和苍耳螟对常用资源的利用率分别为 93.5 % (豚草 )和 5 9.3% (苍耳 )。在相同寄主植物上 ,两种天敌的空间生态位表现为 :随着寄主植物的生长发育 ,两种天敌的生态位重叠程度减小 ;高龄幼虫的生态位宽度指数大于低龄幼虫。在食物生态位上 ,豚草卷蛾主要取食新发生的幼嫩枝 ,并且一旦蛀入形成虫瘿后很少发生转移 ,而苍耳螟除低龄幼虫喜蛀食幼嫩枝外 ,高龄幼虫的取食部位常常发生转移 ,从枝型较细的幼嫩枝转向枝型较粗的老龄枝。两种天敌对豚草和苍耳实际选择作用以及对常用资源利用率存在明显差异 ,因此 ,形成竞争的程度较小 。

The imported ragweed borer Epiblema strenuana (Lepidoptera: Tortricidae) and local Siberian cocklebur stem borer Ostrinia orientalis (Lepidoptera: Pyralidae) are important biocontrol agents against ragweed ( Ambrosia artemisiifolia ) and have similar feeding characteristics In order to evaluate interspecific interactions between these two biocontrol agents, food and spatial overlap were evaluated quantitatively in 2001 in the Field Experimental Station of Hunan Agricultural University, Changsa City, Hunan province, Central China. In this area, E. strenuana had 5 generations (peak periods for the 2nd～4th generations were middle to late June, middle to late July and middle to late August, respectively) and O. orientalis had 4 generations (peak periods for the 2nd and 3rd generations were middle to late July and middle to late August, respectively). The first generation of E. strenuana occurred one month earlier than O. orientalis . The two insect species overlapped temporally from middle June to early September. Populations of the first one to two generations of both species were relatively low. For the field survey, 9 plant species (including 6 varieties of Helianthus annus and 4 cultivars of Dendranthema morifolium ) from the family Compositae were tested. D. morifolium were potted (three plants per pot, 35～40cm in height) and put between the ragweed plant lines. Other plants were transplanted or seeded into 30 randomly distributed plots (2~3 plots per species, 20 ~50 m 2/plot, depending on the amounts of plant seeds or seedlings available) during May～June. During the whole growing season, galls caused by the two insect species on the 17 test plant species and other surrounding weed plants were recorded at 7 day intervals from middle June to early September. At the same time, 3 plants of both A. artemisiifolia and X. sibiricum were taken back to the laboratory and dissected to check the presence of the two insect species in different sized stems and branches. For the spatial overlap, only 7 samples, collected between 11 July and 22 August were taken into account, during which both species were present at high densities and developmental stages of both species overlapped. From the 9 Composite species (including varieties and cultivars) and other surrounding weeds plants, E. strenuana only utilized A. artemisiifolia and X. sibiricum as host plants. O. orientalis could feed on 8 host plant species: A. artemisiifolia, X. sibiricum, Artemisia annua, Helianthus annus, Tagetes erecta, Dendranthema morifolium (cv. Guoqing), Helianthus tuberosus , and Helichrysum bracteatum . These two insect species had significantly different preferences on the tested plant species. E. strenuana preferred A. artemisiifolia and 93 5% galls were found on ragweed. O. orientalis preferred X. sibiricum, with 59 3% galls distributed on cocklebur and others on the other 7 plant species. The Hurlbert's niche width index of O. orientalis was 0 228, higher than that of E. strenuana (0 069). Horn's niche overlap index value between the two insects was relatively small (0 318). Body size and feeding behavior of the two insect species were different. Larval E. strenuana was smaller and mainly fed on newly grown twigs from its early age, and it seldom transferred to other twigs after a gall was formed. However, old larvae of O. orientalis were bigger and usually changed feeding sites from small, newly grown twigs to fully grown branches. When feeding on ragweed, E. strenuana larvae mainly feed on tender branches of no more than 6mm in diameter. Old larvae (5th^6th instar) distributed wider (niche width value 0 34) than young 1st^4th instar larvae (0 25). Young O. orientalis larvae (1st^3rd instar) mainly feed on tender ragweed branches of no more than 8mm in diameter, while its old larvae (4th^5th instar) mainly on branches of more than 12mm in diameter. Old larvae also distributed wider (niche width value 0 37) than youn