捕食者对空心莲子草叶甲种群的生物胁迫

Biotic stress of predators on population of alligator weed flea beetle,Agasicles hygrophila( Col.: Chrysomelidae)

广食性捕食者广泛捕食植食性昆虫,常被用于有害生物的生物防治,也因此影响植食性昆虫对杂草的生物效果。空心莲子草叶甲(Agasicles hygrophila)(鞘翅目:叶甲科Chrysomelidae)作为入侵恶性杂草空心莲子草(Alternanthera philoxeroides)(苋科:莲子草属Alternanthera)的专性天敌,从美国的弗罗里达州引入中国,在释放地防治空心莲子草取得了较好的防治效果。虽然空心莲子草叶甲在引入地均已建立田间种群并有一定程度的自然扩散,但丰富的食物资源,并未使空心莲子草叶甲的自然种群数量变得繁荣,因此其未能有效抑制空心莲子草的扩散蔓延。在野外调查时发现空心莲子草生境中存在大量广食性捕食者。这些广食性捕食者是抑制空心莲子草叶甲种群数量扩张的生物胁迫因子吗?为此,选择捕食性昆虫龟纹瓢虫(Propylaea japonica)(鞘翅目:瓢虫科Coccinellidae)、蜘蛛类捕食者拟水狼蛛(Pirata subpiraticus)(蜘蛛目:狼蛛科Lycosidae)与斜纹猫蛛(Oxyopes sertatus)(蜘蛛目:猫蛛科Oxyopidae)为捕食者,分别以空心莲子草叶甲各虫态为猎物,构建简单的捕食者-猎物系统,在室内检测了上述3种捕食者对空心莲子草叶甲各虫态在不同密度下的日捕食量,以期了解捕食者对空心莲子草叶甲的捕食作用,客观评估空心莲子草叶甲的生物防治效能。研究结果表明:捕食者龟纹瓢虫、斜纹猫蛛与拟水狼蛛均捕食空心莲子草叶甲的卵粒及1龄、2龄幼虫,斜纹猫蛛与拟水狼蛛捕食3龄幼虫,捕食者的捕食量均随着猎物密度的升高而增加,寻找效应降低。三者均不捕食成虫。除拟水狼蛛对3龄幼虫的捕食用Holling II模型拟合不呈显著相关关系外,其余捕食反应均拟合Holling II模型并显著相关。通过拟合方程得出捕食者对空心莲子草叶甲卵粒的理论日最大捕食量为:斜纹猫蛛10.9粒,拟水狼蛛为6.2粒,龟纹瓢虫为5.6粒;对1龄幼虫的理论日最大捕食量为:斜纹猫蛛为17.1头;拟水狼蛛为35.8头,龟纹瓢虫为10.4头;对2龄幼虫的理论日最大捕食量为:斜纹猫蛛为6.6头,拟水狼蛛为11.2头,龟纹瓢虫为2.9头;对3龄幼虫的理论日最大捕食量为:斜纹猫蛛捕食12.3头,拟水狼蛛为1.1头。研究结果证实了捕食者可通过捕食作用降低空心莲子草叶甲种群密度,削弱空心莲子草叶甲对空心莲子草的控害效能,是空心莲子草叶甲种群存活的生物胁迫因子。建议在提高空心莲子草叶甲田间种群数量,达到对空心莲子有效的持续控制效果方面开展进一步研究。

Generalist predators are often applied in biological control of pests. Sine generalist predators often prey on herbivorous insects unselectively, they also influence biological control of weeds with herbivorous insects. The alligator weedflea beetle, Agasicles hygrophila （Coleoptera： Chrysomelidae） is acted as a specific biological control of the alligator weed Alternanthera philoxeroides （Amaranthacese ：Alternanthera）, and it had been introduced to China from Florida, USA. It has performed a good control effect on A. philoxeroides since the beetle was released in the areas invaded by A. philoxeroides. Although the population of A. hygrophila had been established and spread to adjacent regions from the release sites, the population abundance of the beetle maintains only a lower level. Thus, it can not suppress effectively the population expansion and spread of A. philoxeroides. We found that many generalist predator species such as spiders and predatory insects live in the habitat of A. philoxeroides. Whether the generalist predators are a biotic stress factor for suppressing the population expansion of the beetle.＇？ To demonstrate this problem, a predator-prey system including predators, i.e. lady beetle Propylaea japonica （Coleoptera： Coccinellidae ）, spider Oxyopes sertatus （Araneae： Oxyopidae ） and Pirata subpiraticus （Araneae： Lycosidae）, and host preys, i.e. egg, Ist-3nd instar larva and adult of A. hygrophila was built. Then the daily eating number of the above three predators on different immature stages and adults of A. hygrophila was observed in the laboratory. This aim to understand the biotic stress of predators on A. hygrophila in a natural ecosystem that may evaluate objectively the biological control efficiency of A. hygrophila on A. philoxeroides in the field. The results showed that P. japonica, 0. sertatus and P. subpiraticus could feed on eggs as well as 1St--2nd instar larvae of A. hygrophila. Both O. sertatus and P. subpiraticus could feed on 3nd instar larvae of A. hygrophila. The predatory capacities of P. japonica, 0. sertatus and P. subpiraticus to eggs and larvae of A. hygrophila increased, but searching efficiency of the predators decreased with the increasing densities of prey. However, the three predators did not prey on adult A. hygrophila in this experiment. The predatory function responses of P. japonica and P. subpiraticus on eggs, l st-2nd instar larvae, and of 0. sertatus on eggs, lst-3nd instar larvae of A. hygrophila fitted to the disc equation of Holling II. With the exception of the predatory function response of P. subpiraticus on 3rd instar larvae of A. hygrophila, there were a significant correlation between predator and host prey that were fitted by the disc equation of Holling II. The maximum theoretical number of eggs, 1 st insar and 2nd insar larvae of A. hygrophila captured by O. sertatus, P. subpiraticus and P. japonica per day was 10.9, 6.2 and 5.6 eggs, 17.1, 35.8 and 10.4 1s＇ insar larvae, and 6.6, 11.2 and 2.9 2nd insar larvae, respectively. The maximum theoretical number of 3rd insar larvae of A. hygrophila captured by O. sertatus and P. subpiraticus was 12.3 and 1.1 larvae, respectively. The results of our present study suggest that the predation of predators can decrease the population density of A. hygrophila, which weakens the control efficiency of A. hygrophila on A. philoxeroides in the field. Therefore, the predators are an important biotic stress factor that affects survival and development of A. hygrophila in the field. Another further study should focus on how the biocontrol efficiency of A. philoxeroides are enhanced via increasing the population density of A. hygrophila in the field.