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

Abstract

Incorporation of exotic plants into the diets of native herbivores is a common phenomenon, influencing interactions with natural enemies and providing insight into the tritrophic costs and benefits of dietary expansion. We evaluated how use of an exotic plant, Plantago lanceolata, impacted immune performance, development and susceptibility to pathogen infection in the neotropical herbivore Anartia jatrophae (Lepidoptera: Nymphalidae). Caterpillars were reared on P. lanceolata or a native plant, Bacopa monnieri, and experimentally infected with a pathogenic virus, Junonia coenia densovirus. We found that virus-challenged herbivores exhibited higher survival rates and lower viral burdens when reared on P. lanceolata compared to B. monnieri, though immune performance and development time were largely similar on the two plants. These findings reveal that use of an exotic plant can impact the vulnerability of a native herbivore to pathogen infection, suggesting diet-mediated protection against disease as a potential mechanism facilitating the incorporation of novel resources.

Exploring spatial and temporal patterns of viral infection across populations of the Melissa blue butterfly

“…Furthermore, we can speculate that JcDV-positive adults were not able to resist infection but either contracted the disease in a later larval stage just before pupation, or perhaps tolerated it through development (Roy & Kirchner, 2000). Because we know that larval infection causes increased pre-metamorphosis mortality from previous laboratory studies with other host species (Muchoney et al, 2023;Mutuel et al, 2010), the observation of live-caught adults that are JcDV positive suggests that sub-lethal infections could occur in this system. This might explain the persistence of JcDV at low prevalence and loads in certain populations, as covert or sub-lethal infection can still be horizontally transmitted or pass throughout generations by vertical transmission (Elderd, 2018).…”

“…This would be contingent upon infected individuals being reproductively viable, of course, and we did not test female reproductive capability in this study. However, a prior study found that adult white peacocks ( Anartia jatrophae ) harbouring JcDV are still able to reproduce (Muchoney et al, 2023), and additionally, the virus was detected on the surface of eggs oviposited by infected painted lady butterflies ( Vanessa cardui : Nymphalidae) (Smilanich et al, 2022 unpublished data). Because of this possibility and evidence of reproductive fitness increasing with infection in another densovirus system (Xu et al, 2014), it is conceivable that JcDV‐infected L. melissa adults may pass the virus to their offspring in later generations if they survive to adulthood (Fuxa, 2004).…”

“…Diseased hosts may become oxygen‐depleted and “stuck” between moults, often leading to death before pupation or adult emergence (Mutuel et al, 2010). Data on transmission strategies are not yet reported for JcDV, although recent data with white peacocks ( Anartia jatrophae : Nymphalidae) show that infected individuals that make it to the adult stage have survived infection, but still test positive for the virus (Muchoney et al, 2023). Vertical transmission from mother to offspring has been observed in several other insect‐densovirus systems (Altinli et al, 2019; Kittayapong et al, 1999).…”

“…Melissa blue populations are typically multivoltine, undergoing three to four overlapping generations throughout the flight season and overwintering as eggs. This suite of life history traits makes L. melissa unique from other lepidopteran families in which JcDV has been studied (Noctuidae, Mutuel et al, 2010; Nymphalidae, Smilanich et al, 2018; Nymphalidae, Muchoney et al, 2022, 2023). While L. melissa has been shown to be a viable JcDV host in laboratory settings (Yoon, 2021), the host–pathogen relationship has yet to be described for any densovirus infecting natural populations of L. melissa , nor have patterns of JcDV infection been described for any butterfly species in the family Lycaenidae.…”

When does spatial clustering in caterpillars influence the relationship between population density and contact rates?

“…Stein et al 2011). Another interesting step would be to build spatially explicit individual based models of this system (Tardy et al, 2018) once we know more about the biology of JcDNV transmission, its effects on larval survival, and the possibility of shared reservoir hosts (e.g., Rivers and Longworth 1972;Mutuel et al, 2010;Muchoney et al 2022;Muchoney et al, 2023).…”