Immune defence strategies of generalist and specialist insect herbivores

Abstract

Ecological immunology examines the adaptive responses of animals to pathogens in relation to other environmental factors and explores the consequences of trade-offs between investment in immune function and other life-history traits. Among species of herbivorous insects, diet breadth may vary greatly, with generalists consuming a wide variety of plant families and specialists restricted to a few species. Generalists may thus be exposed to a wider range of pathogens exerting stronger selection on the innate immune system. To examine whether this produces an increase in the robustness of the immune response, we compared larvae of the generalist herbivore Heliothis virescens and the specialist Heliothis subflexa challenged by entomopathogenic and non-pathogenic bacteria. Heliothis virescens larvae showed lower mortality, a lower number of recoverable bacteria, lower proliferation of haemocytes and higher phagocytic activity. These results indicate a higher tolerance to entomopathogenic bacteria by the generalist, which is associated with a more efficient cell-mediated immune response by mechanisms that differ between these closely related species. Our findings provide novel insights into the consequences of diet breadth and related environmental factors, which may be significant in further studies to understand the ecological forces and investment trade-offs that shape the evolution of innate immunity.

The plastic response of Manduca sexta to host and non-host plants

“…Likewise, plant secondary metabolites can influence an insect's immune system, resulting in the differential expression of immune-related genes. Immune defense strategies might also vary with the breadth of an organism's diet (Barthel et al, 2014;Lee et al, 2008;Ponton et al, 2013). Similarly, differences in both types and densities of host plant-associated bacteria can have an impact on innate immunity in herbivorous insects (Freitak et al, 2007).…”

Immune modulation enables a specialist insect to benefit from antibacterial withanolides in its host plant

“…In the evolutionary divergence of these closely related species about two and a half million years ago10, immune competence has evidently also diverged. Although the host range of the common ancestor is unknown, it is likely that H. virescens or its ancestor evolved a more efficient immune response as its host range increased, exposing it to a greater variety of pathogens, in accordance with the predictions of ecological immunology30. However, it is also likely that the immune system in the H. subflexa lineage evolved as it developed its unique specialization on Physalis : it not only overcame the inhibitory effect of withanolides on its immune system, but also evolved the ability to be stimulated by withanolides, possibly by circumventing ecdysteroid antagonistic activities.…”

Come to the dark side! The role of functional traits in shaping dark diversity patterns of south‐eastern European hoverflies

“…Saproxylic hoverfly larvae, as well as phytophagous species that develop in bulbs and roots, are considered specialists (van Veen, 2004;Müller et al, 2011). Generalist species are widely regarded as being at an advantage compared with specialists in adapting to changing environmental conditions (Biesmeijer et al, 2006;Barthel et al, 2014). Generalist species are probably favoured under conditions of detrimental change and should constitute the majority of observed diversity, whereas specialists may be absent from impacted habitats and contribute towards dark diversity.…”