Ngah Norhayati, Thomas Rebecca L, Shaw Michael W, Fellowes Mark D E
People and Wildlife Research Group, School of Biological Sciences, University of Reading, Whiteknights, Reading, Berkshire RG6 6AJ, UK.
Fakulti Biosumber dan Industri Makanan, Universiti Sultan Zainal Abidin, Besut Terengganu 22200, Malaysia.
Insects. 2018 Jul 6;9(3):80. doi: 10.3390/insects9030080.
Plant pathogens can profoundly affect host plant quality as perceived by their insect herbivores, with potentially far-reaching implications for the ecology and structure of insect communities. Changes in host plants may have direct effects on the life-histories of their insect herbivores, which can then influence their value as prey to their natural enemies. While there have been many studies that have explored the effects of infection when plants show symptoms of disease, little is understood about how unexpressed infection may affect interactions at higher trophic levels. We examined how systemic, asymptomatic, and seed-borne infection by the ubiquitous plant pathogen , infecting two varieties of the lettuce , affected aphids (the green peach aphid, ) and two widely used biocontrol agents (the parasitoid and the ladybird predator ). Lettuce varieties differed in host plant quality. Asymptomatic infection reduced chlorophyll content and dry weight of host plants, irrespective of plant variety. Aphids reared on asymptomatic plants were smaller, had reduced off-plant survival time and were less fecund than aphids reared on uninfected plants. Parasitoids showed reduced attack rates on asymptomatically infected plants, and wasps emerging from hosts reared on such plants were smaller and showed reduced starvation resistance. When given a choice in an olfactometer, aphids preferentially chose uninfected plants of one variety (Tom Thumb) but showed no preference with the second (Little Gem) variety. Parasitoids preferentially chose aphids on uninfected plants, irrespective of host plant variety, but ladybirds did not show any such preference. These results suggest that the reduced quality of plants asymptomatically infected by negatively affects the life history of aphids and their parasitoids, and alters the behaviors of aphids and parasitoids, but not of ladybirds. Fungal pathogens are ubiquitous in nature, and this work shows that even when host plants are yet to show symptoms, pathogens can affect interactions between insect herbivores and their natural enemies. This is likely to have important implications for the success of biological control programs.
植物病原体能够深刻影响寄主植物对于植食性昆虫而言的质量，这可能对昆虫群落的生态和结构产生深远影响。寄主植物的变化可能直接影响其植食性昆虫的生活史，进而影响这些昆虫作为天敌猎物的价值。虽然已有许多研究探讨了植物出现病害症状时感染所产生的影响，但对于未表现出症状的感染如何影响较高营养级之间的相互作用却知之甚少。我们研究了无处不在的植物病原体——感染两种生菜品种的 ，其系统性、无症状和种子传播感染如何影响蚜虫（桃蚜 ）以及两种广泛使用的生物防治剂（寄生蜂 和瓢虫捕食者 ）。生菜品种在寄主植物质量上存在差异。无症状感染降低了寄主植物的叶绿素含量和干重，与植物品种无关。在无症状植物上饲养的蚜虫体型较小，离株存活时间缩短，繁殖力也低于在未感染植物上饲养的蚜虫。寄生蜂对无症状感染植物的攻击率降低，从在这类植物上饲养的寄主中羽化出的黄蜂体型较小，饥饿抵抗力也降低。在嗅觉仪中进行选择时，蚜虫优先选择一个品种（拇指汤姆）的未感染植物，但对第二个品种（小宝石）没有偏好。寄生蜂优先选择未感染植物上的蚜虫，与寄主植物品种无关，但瓢虫没有表现出这种偏好。这些结果表明，被 无症状感染的植物质量下降对蚜虫及其寄生蜂的生活史产生负面影响，并改变了蚜虫和寄生蜂的行为，但没有改变瓢虫的行为。真菌病原体在自然界中无处不在，这项研究表明，即使寄主植物尚未出现症状，病原体也能影响植食性昆虫与其天敌之间的相互作用。这可能对生物防治计划的成功具有重要意义。
