Phylloplane bacteria increase the negative impact of food limitation on insect fitness

Abstract

1. When populations of herbivorous insects increase in density, they can alter the quantity or quality of their food. The impacts of diet-related stressors on insect fitness have been investigated singly, but not simultaneously.2. Foliage quantity and quality of red alder, Alnus rubra, were manipulated together with the presence of non-entomopathogenic phylloplane bacteria to investigate their impacts, singly and in combination, on survival, pupal mass, growth rate, fecundity and egg quality of a cyclic forest insect, the western tent caterpillar, Malacosoma californicum pluviale.3. Food limitation (half food) had strong negative impacts on all life-history traits. When the larvae were fed continuously, however, neither ingesting phylloplane bacteria nor eating leaves from damaged branches (induced foliage) affected survival. In the half-food treatment, ingesting bacteria further increased mortality, while feeding on induced foliage improved survival.4. Growth rate and pupal mass of both sexes were reduced for larvae with food limitation compared with continuously fed insects and this was exacerbated when the larvae also ate bacteria-treated leaves. A combination of bacteria and induced foliage also reduced larval growth rate by 5% in the full-food treatment.5. Fecundity (eggs per egg mass) was 2.7 times greater in full-food than in food-limited treatments but neither phylloplane bacteria nor plant induction had an effect. Insects fed induced foliage produced smaller eggs. Overall, there was no evidence of a three-way interaction between the three stressors, although there were negative synergistic effects, primarily between food limitation and the ingestion of phylloplane bacteria.

Sub-lethal viral exposure and growth on drought stressed host plants changes resource allocation patterns and life history costs in the Speckled Wood butterfly, Pararge aegeria

“…In nature, therefore, maternal resource allocation to egg size (and hence transgenerational maternal effects) may play an important role in determining the capacity by which P. aegeria can cope with changes in host plant quality and disease prevalence expected with continued climate change. But, variation in food quality that influences egg size does not necessarily always affect offspring immunity (Shikano et al, 2016;Olson et al, 2017). Further studies would therefore be required to determine whether egg size plays a role in offspring immunity in P. aegeria.…”

A plant pathogen modulates the effects of secondary metabolites on the performance and immune function of an insect herbivore

“…On the other hand, the Toll pathway is associated specifically with fungal recognition (Rolff and Reynolds 2009), hence mildew infection of the host plant could also directly affect M. cinxia's immunity. Nonetheless, cases where insect immunity has been affected by ingestion of non-entomopathogenic generalist (Freitak et al 2007(Freitak et al , 2009) and plantspecific microbes (Shikano et al 2015, Olson et al 2017 have been reported in literature. In addition, cases of insects becoming infected with phytopathogens or acting as transmission vectors have also been reported (Kluth et al 2002, Medeiros et al 2004, Nadarasah and Stavrinides 2011.…”

Learning to starve: impacts of food limitation beyond the stress period

“…These results indicate that periods of stress could either act to exacerbate starvation or serve in priming animals to tolerate starvation more effectively. Importantly, revealing the dynamics between stress exposure and food limitation is crucial to understanding the impact of single or multiple starvation bouts under field conditions as food limitation is often accompanied by other environmental stressors (Olson et al, 2017).…”