Szűcs Marianna, Salerno Patricia E, Teller Brittany J, Schaffner Urs, Littlefield Jeffrey L, Hufbauer Ruth A
Department of Entomology Michigan State University East Lansing Michigan.
Department of Bioagricultural Sciences and Pest Management Colorado State University Fort Collins Colorado.
Evol Appl. 2018 Nov 27;12(3):470-481. doi: 10.1111/eva.12726. eCollection 2019 Mar.
The success rate of weed biological control programs is difficult to evaluate and the factors affecting it remain poorly understood. One aspect which is still unclear is whether releases of multiple, genetically distinct populations of a biological control agent increase the likelihood of success, either by independent colonization of different environmental niches or by hybridization that may increase the agent's fitness and adaptive ability. Since hybridization is often invoked to explain the success of unintentionally introduced exotic species, hybridization among biocontrol agents may be similarly important in shaping the effectiveness of biological control programs. In this study, we first evaluated intraspecific hybridization among populations of a weed biological control agent, the ragwort flea beetle, . These insects were introduced as part of a classical biological control program from Italy and Switzerland. We genotyped 204 individuals from 15 field sites collected in northwest Montana, and an additional 52 individuals that served as references for Italian and Swiss populations. Bayesian analysis of population structure assigned seven populations as pure Swiss and one population as pure Italian, while intraspecific hybrid individuals were detected in seven populations at frequencies of 5%-69%. Subsequently, we conducted a 2-year exclusion experiment using six sites with Swiss beetles and three with hybrid beetles to evaluate the impact of biological control. We found that biological control by Swiss beetles and by hybrid beetles is effective, increasing mortality of the target plant, , by 42% and 45%, and reducing fecundity of surviving plants by 44% and 72%, respectively. Beetle densities were higher and mortality of larger plants was higher at sites with hybrids present. These results suggest that hybridization of ragwort flea beetles at high-elevation sites may improve biological control of tansy ragwort and that intraspecific hybridization of agents could benefit biological control programs.
杂草生物防治项目的成功率难以评估，且影响其成功率的因素仍未得到充分理解。一个尚不清楚的方面是，释放多种基因不同的生物防治剂种群是否会增加成功的可能性，这可能是通过不同环境生态位的独立定殖，或者通过杂交来实现，杂交可能会提高生物防治剂的适应性和适应能力。由于杂交常被用来解释无意引入的外来物种的成功，生物防治剂之间的杂交在塑造生物防治项目的有效性方面可能同样重要。在本研究中，我们首先评估了一种杂草生物防治剂——千里光蚤蝇种群之间的种内杂交情况。这些昆虫作为经典生物防治项目的一部分从意大利和瑞士引入。我们对从蒙大拿州西北部15个野外地点采集的204只个体进行了基因分型，另外52只个体作为意大利和瑞士种群的参考。贝叶斯种群结构分析将7个种群判定为纯瑞士种群，1个种群判定为纯意大利种群，同时在7个种群中检测到种内杂交个体，频率为5%-69%。随后，我们进行了一项为期2年的排除实验，使用了6个有瑞士甲虫的地点和3个有杂交甲虫的地点来评估生物防治的效果。我们发现，瑞士甲虫和杂交甲虫的生物防治均有效，使目标植物——千里光的死亡率分别提高了42%和45%，并使存活植物的繁殖力分别降低了44%和72%。有杂交甲虫的地点甲虫密度更高，大型植物的死亡率也更高。这些结果表明，高海拔地区千里光蚤蝇的杂交可能会改善对千里光的生物防治，且生物防治剂的种内杂交可能会使生物防治项目受益。
