Dataset: Resource limitation has a limited impact on the outcome of virus-fungus co-infection in an insect host

Infection by pathogens is strongly affected by the diet or condition of the prospective host. Studies that examine the impact of diet have mainly focussed on single pathogens; however, co-infections within a single host are thought to be common. Different pathogen groups might respond differently to resource availability and diverse infections could increase the costs of host defence, meaning the outcome of mixed infections under varying dietary regimes is likely to be hard to predict. We used the generalist cabbage looper, Trichoplusia ni and two of its pathogens, the DNA virus T. ni nucleopolyhedrovirus (TniSNPV) and the entomopathogenic fungus, Beauveria bassiana to examine how nutrient reduction affected the outcome of mixed pathogen infection. We challenged insects with a low or high effective dose of virus, alone or combined with a single dose of fungus. We manipulated food availability after pathogen challenge by diluting artificial diet with cellulose, a non-nutritious bulking agent, and examined its impact on host and pathogen fitness. Reducing diet quantity did not alter overall or pathogen-specific mortality. In all cases, TniSNPV-induced mortality was negatively affected by fungus challenge. Similarly, B. bassiana-induced mortality was negatively affected by TniSNPV challenge, but only at the higher virus dose. Dietary dilution mainly affected B. bassiana speed of kill when mixed with a high dose of TniSNPV, with an increase in the duration of fungal infection when cellulose was low (high quantity). One pathogen dominated the production of transmission stages in the cadavers and co-infection did not affect the yield of either pathogen. There was no evidence that co-infections were more costly to the survivors of pathogen challenge. In conclusion, dietary dilution did not determine the outcome of mixed pathogen infection, but it had more subtle effects, that differed between the two pathogens and could potentially alter pathogen recycling and host-pathogen dynamics.病原体感染极易受潜在宿主的饮食状况或生理状态影响。以往探究饮食对病原体感染影响的研究多聚焦于单一病原体，但学界普遍认为单一宿主内的共感染现象极为常见。不同病原体类群对资源可获得性的响应存在差异，而多重感染可能会提升宿主的免疫防御成本，这意味着不同饮食条件下混合感染的结局往往难以预判。本研究以广食性寄主甘蓝夜蛾（*Trichoplusia ni*）及其两种病原体——DNA病毒T. ni核型多角体病毒（nucleopolyhedrovirus, TniSNPV）和虫生真菌（entomopathogenic fungus）球孢白僵菌（*Beauveria bassiana*）为实验材料，探究营养限制对混合病原体感染结局的影响。我们以低、高有效剂量的病毒单独或联合单剂量真菌侵染试虫，并在病原体侵染后，利用非营养性填充剂纤维素稀释人工饲料以调控食物可获得性，进而探究其对宿主及病原体适合度的影响。饲料总量的缩减并未改变宿主整体死亡率或病原体特异性死亡率。在所有实验条件下，TniSNPV诱导的宿主死亡率均会受到真菌侵染的负向抑制。同理，球孢白僵菌诱导的宿主死亡率也会受到TniSNPV侵染的负向调控，但该效应仅在高病毒剂量处理组中显现。饲料稀释主要在高剂量TniSNPV联合侵染时影响球孢白僵菌的致死速率：当纤维素添加量较低（即饲料总量较高）时，真菌侵染的病程会显著延长。罹病虫尸中仅有一种病原体主导传播体的产生，且共感染并未改变两种病原体的增殖产量。此外，未发现共感染会加重病原体侵染后存活宿主的生理成本。综上，饲料稀释并未直接决定混合病原体感染的结局，但会通过两种病原体的差异化响应产生更为细微的影响，进而可能改变病原体的循环传播过程与宿主-病原体互作动态。