Data from: Host nutritional status mediates degree of parasitoid virulence

Parasitic organisms rely on the resources of their hosts to obtain nutrients essential for growth and reproduction. Insect parasitoids constitute an extreme condition since they develop in a single host from which they typically consume all available resources. As a result, the host is killed following parasitism. However, a few intriguing cases of host survival have been reported wherein hosts resume foraging and may even reproduce following parasitoid emergence. Yet, the ultimate and proximate mechanisms responsible for host recovery remain unresolved. We tested the impact of host nutrition on host fate and parasitoid fitness, using the association between Dinocampus coccinellae and the spotted lady beetle Coleomegilla maculata. Under laboratory conditions, we fed parasitized ladybirds on different aphid diets, with or without pollen. In the field, we followed the fate of parasitized ladybirds during seasonal variations in pollen and aphid abundance. We found that ladybirds fed on aphids or a combination of aphids and pollen recovered more frequently from parasitism (from 65 to 81%) than those eating only pollen (48%). Field data suggest that the fate of parasitized ladybirds is also related to food availability. On the other hand, when hosts fed on a combination of aphids and pollen, consequences for parasitoid fitness were often ‘all-or-nothing’: parasitoid emergence rate was the lowest of all host nutrition regimes (˜50%), but parasitoids that did emerge were larger than individuals emerging from other host nutrition regimes. Laboratory and field results concur to show that host nutritional status during parasitoid development significantly influences both host fate and parasitoid fitness.

寄生生物依赖宿主的资源，以获取生长与繁殖所需的必需营养物质。昆虫拟寄生者（insect parasitoids）则属于一类极端的寄生类型：它们仅发育于单个宿主体内，并通常会耗尽宿主内所有可利用的资源，因此宿主在被寄生后通常会死亡。不过已有若干引人关注的研究报道称，部分宿主在拟寄生者羽化后仍可存活，并能恢复觅食行为，甚至可进行繁殖。但目前导致宿主恢复的终极机制与近因机制仍未阐明。本研究以瓢虫茧蜂（Dinocampus coccinellae）与斑点瓢虫（Coleomegilla maculata）的寄生关联为实验模型，探究宿主营养状况对宿主存活结局与拟寄生者适合度的影响。在实验室条件下，我们为被寄生的瓢虫提供不同的蚜虫日粮，并设置添加花粉与不添加花粉两组处理；在野外环境中，我们追踪了随花粉与蚜虫丰度季节性变化的被寄生瓢虫的存活结局。研究结果显示，以蚜虫为食或同时取食蚜虫与花粉的瓢虫，其寄生后恢复率为65%~81%，显著高于仅取食花粉的个体（48%）。野外调查数据同样表明，被寄生瓢虫的存活结局与食物可获得性密切相关。另一方面，当宿主取食蚜虫与花粉的混合日粮时，拟寄生者的适合度往往呈现‘全有或全无’的特征：拟寄生者的羽化率在所有宿主营养处理组中最低（约50%），但成功羽化的拟寄生者体型却大于其他营养处理组的羽化个体。实验室与野外的研究结果一致表明，拟寄生者发育阶段宿主的营养状况，会显著影响宿主的存活结局与拟寄生者的适合度。