豚草卷蛾寄主专一性风险评价

Risk Analysis of Host Specificity for Epiblema strenuana (Lepidoptera: Tortricidae), a Biocontrol Agent Against Ragweed, Ambrosia artemisiifolia (Compositae)

在以往豚草生物防治研究的基础上 ,为评价防治恶性豚草的外来天敌昆虫的安全性 ,以及探索外来生防作用物的风险评价方法 ,以豚草卷蛾为案例 ,进一步对其寄主安全性进行了风险评估。基于与豚草的近缘关系及以往的研究结果 ,选用 9科 36种常见经济作物、观赏植物和杂草 ,采用室内非选择性取食测定、田间开放条件下多选择性取食测定和室外非选择性取食分龄接虫的生命表等研究方法 ,对豚草卷蛾的寄主专一性作了深入研究。 ( 1 )室内非选择性取食测定结果表明 ,豚草卷蛾仅能在豚草和苍耳上完成整个幼虫的发育 ;但在强迫将高龄幼虫 ( 4～ 6龄 )接入黄花蒿、菊花 (黄莲 )和向日葵 (白 97-1和天委 F2 )时 ,有少量幼虫能发育化蛹 ,但不发生取食 ,在这些植物上完成发育只是一种假象。 ( 2 )田间开放条件下多选择性取食测定结果表明 ,豚草卷蛾的寄主选择性随种群数量不同而异 ,当种群数量增大 ,受取食条件胁迫时 ,出现风险“扩散”现象。田间供试的 1 6种 (含品种 )植物中 ,第 2、3和 4代出现虫瘿 (被幼虫选择 )的供试植物依次为 :豚草(第 2代 ) ;豚草和苍耳 (第 3代 ) ;豚草、苍耳和黄花蒿 (第 4代 )。按产卵单因子选择性风险指数 ( SEFRI(1) )值分析表明 ,豚草卷蛾成虫产卵对豚草。

Epiblema strenuana is an important biocontrol agent against ragweed (Ambrosia artemisiifolia). This phytophagous insect was imported to China by the Chinese Academy of Agricultural Sciences as a potential candidate to control A. artemissifolia in 1990. Safety to flora in the northern region of China was a concern and the insect was not released until in 1993 on a small scale in Linxiang, Hunan province, China. However, no risk analysis or monitoring was conducted after its release. In order to evaluate its safety to native ecosystems, to expand its utilization and to advance methods of risk analysis for introduced biocontrol agents, we studied host specificity of E. strenuana. Thirty-six species of economic, ornamental and weedy species belonging to nine families were selected based on the centrifugal phylogenetic testing method. A no-choice test was conducted to evaluate E. strenuana larval feeding risk under laboratory conditions, by inoculating different instar larvae on the tested plants. A more realistic multiple-choice test was conducted for three successive generations under field conditions in three scenarios: (1) adult oviposition, (2) larval development, and (3) larval movement. Based on the probability theory, risks were analyzed in two ways. (1) Single Exposure Factor Risk Index (SEFRI) was introduced to quantitatively evaluate selection risk of E. strenuana to the tested plants. SEFRI for larval development and adult oviposition was divided into three categories: active selection risk (SEFRI≥ 0.01), random selection risk (SEFRI< 0.01) and no selection risk (SEFRI = 0). (2) A Combined Risk Index (CRI) was calculated to express the combined exposure factor risk on a tested plant, i.e. CRI = SEFRI (1)×SEFRI (2)...×SEFRI (n). Laboratory no-choice feeding test showed that E. strenuana could complete development only on A. artemisiifolia and Xanthium sibiricum. When introduced onto tested plants, all young larvae (1st～3rd instar) died; and only a few old larvae (4th～6th instar) could pupate on Artemisia annua, Dendranthema morifolium (cv. Yellow lotus) and Helianthus annuus but without any feeding. These three plants cannot be considered host plants for E. strenuana. Open field multiple-choice test showed that in all the 16 tested plants, (including A. artemisiifolia, X. sibiricum, 6 cultivars of H. annuus and 7 species/ cultivars of potted chrysanthemum), Single Exposure Factor Risk Index (SEFRI (1)) for adult oviposition from three generations was 0.76～1 on A. artemisiifolia, 0～1 on X. sibiricum, 0～0.06 on A. annua and 0～0.02 on Tagetes. erecta, only 0～0.004 on H. annuus (I-M1 and I-M2), and 0 on other tested plants. SEFRI (2) for larval survival of E. strenuana was 1 on A. artemisiifolia and 0.42 on X. sibiricum, and 0 on other tested plants. SEFRI (3) for capability of larval selection for tested plants in non-choice condition was 1 on A. artemisiifolia, 0.59 on X. sibiricum, 0.21 on A. annua, 0 on Helichrysum bracteatum and 0.03～0.15 on other tested plants. Thus, the combined host specificity risk index (CRI) was 0.76 for A. artemisiifolia and 0.25 for X. sibiricum (active selection risk), and 0 for the other tested plants (no selection risk), respectively. The population increase trend index of E. strenuana also showed the same results. We can conclude that E. strenuana has a very restricted host range, as it can only complete development on A. artemissifolia and X. sibiricum, and poses no risk to the other plant species tested. It can be considered as an ecologically safe bio-control agent against ragweed in China.