The Effect of Phenoloxidase Activity on Survival Is Host Plant Dependent in Virus-Infected Caterpillars

Abstract

An important goal of disease ecology is to understand trophic interactions influencing the host–pathogen relationship. This study focused on the effects of diet and immunity on the outcome of viral infection for the polyphagous butterfly, Vanessa cardui Linnaeus (Lepidoptera: Nymphalidae) (painted lady). Specifically, we aimed to understand the role that larval host plants play when fighting a viral pathogen. Larvae were orally inoculated with the entomopathogenic virus, Junonia coenia densovirus (JcDV) (Parvovirididae: Densovirinae, Lepidopteran Potoambidensovirus 1) and reared on two different host plants (Lupinus albifrons Bentham (Fabales: Fabaceae) or Plantago lanceolata Linnaeus (Lamiales: Plantaginaceae)). Following viral infection, the immune response (i.e., phenoloxidase [PO] activity), survival to adulthood, and viral load were measured for individuals on each host plant. We found that the interaction between the immune response and survival of the viral infection was host plant dependent. The likelihood of survival was lowest for infected larvae exhibiting suppressed PO activity and feeding on P. lanceolata, providing some evidence that PO activity may be an important defense against viral infection. However, for individuals reared on L. albifrons, the viral infection had a negligible effect on the immune response, and these individuals also had higher survival and lower viral load when infected with the pathogen compared to the controls. Therefore, we suggest that host plant modifies the effects of JcDV infection and influences caterpillars’ response when infected with the virus. Overall, we conclude that the outcome of viral infection is highly dependent upon diet, and that certain host plants can provide protection from pathogens regardless of immunity.

Use of an exotic host plant shifts immunity, chemical defense, and viral burden in wild populations of a specialist insect herbivore

“…Junonia coenia densovirus (hereafter, JcDV) is a non‐enveloped, single‐stranded DNA virus in the family Parvoviridae ( Densovirinae : Lepidopteran protoambidensovirus 1 ). Though first identified in Junonia coenia (Nymphalidae), JcDV is capable of infecting Lepidoptera in the Bombycidae, Erebidae, Noctuidae, and Nymphalidae in a laboratory setting (Mutuel et al, 2010; Resnik & Smilanich, 2020; Rivers & Longworth, 1968). Larvae become infected by JcDV through ingestion of contaminated food, after which viral particles cross the midgut and replicate in tracheae, hemocytes, visceral muscle, and epidermis (Mutuel et al, 2010; Wang et al, 2013).…”

Use of an exotic host plant reduces viral burden in a native insect herbivore

“…As diet-mediated variation in development and immunity provided limited explanation, additional research will be necessary to elucidate how A. jatrophae reared on Plantago are able to suppress viral burdens and increase their likelihood of surviving infection. As the specific routes through which the immune response contributes to defence against JcDV are unclear (Muchoney et al, 2022;Resnik & Smilanich, 2020;Smilanich et al, 2018), it is possible that immune parameters that were not measured are enhanced in larvae consuming Plantago. In addition, the role of phytochemistry warrants consideration.…”

Experimental removal of extracellular egg‐associated microbes has long‐lasting effects for larval performance

“…Previous literature reviews have found complex relationships between host plant diet and immune response in lepidopterans (Lampert, 2012; Singer et al, 2014). In some cases, larval consumption of the novel, low‐quality host plant resulted in a weakened immune response compared to consumption of the typical, high‐quality host plant (Diamond & Kingsolver, 2011; Resnik & Smilanich, 2020). In other cases, consumption of the alternative, lower quality host plant actually resulted in a stronger immune response (Klemola et al, 2007; Yang et al, 2008).…”