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ABSTRACT Herbivorous insects tolerate chemical and metabolic variation in their host plant diet by modulating physiological traits. Insect immune response is one such trait that plays a crucial role in maintaining fitness but can be heavily influenced by variation in host plant quality. An important question is how the use of different host plants affects the ability of herbivorous insects to resist viral pathogens. Furthermore, the transcriptional changes associated with this interaction of diet and viral pathogens remain understudied. The Melissa blue butterfly (Lycaeides melissa) has colonised the exotic legumeMedicago sativaas a larval host within the past 200 years. We used this system to study the interplay between the effects of host plant variation and viral infection on physiological responses and global gene expression. We measured immune strength in response to infection by the Junonia coenia densovirus (JcDV) in two ways: (1) direct measurement of phenoloxidase activity and melanisation, and (2) transcriptional sequencing of individuals exposed to different viral and host plant treatments. Our results demonstrate that viral infection caused total phenoloxidase (total PO) to increase and viral infection and host plant interactively affected total PO such that for infected larvae, total PO was significantly higher for larvae consuming the native host plant. Additionally,L. melissalarvae differentially expressed several hundred genes in response to host plant treatment, but with minimal changes in gene expression in response to viral infection. Not only immune genes, but several detoxification, transporter, and oxidase genes were differentially expressed in response to host plant treatments. These results demonstrate that in herbivorous insects, consumption of a novel host plant can alter both physiological and transcriptional responses relevant to viral infection, emphasising the importance of considering immune and detoxification mechanisms into models of evolution of host range in herbivorous insects.
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Feeding on an exotic host plant enhances plasma levels of phenoloxidase by modulating feeding efficiency in a specialist insect herbivore
Background: Exotic plant species represent a novel resource for invertebrates and many herbivorous insects have incorporated exotic plants into their diet. Using a new host plant can have physiological repercussions for these herbivores that may be beneficial or detrimental. In this study, we compared how using an exotic versus native host plant affected the immune system response and feeding efficiency of a specialist lepidopteran, the common buckeye ( Junonia coenia : Nymphalidae, Hübner 1822). Materials and Methods: In a lab experiment, larvae were reared on either the exotic host plant, Plantago lanceolata (Plantaginaceae), or the native host plant, Mimulus guttatus (Phrymaceae). Beginning at second instar feeding efficiency data were collected every 2 days until fifth instar when immune assays were performed. Immune assays consisted of standing phenoloxidase activity, total phenoloxidase activity, and melanization. Results: Interestingly, we found that all three immune system parameters were higher on the exotic host plant compared to the native host plant. The exotic host plant also supported higher pupal weights, faster development time, greater consumption, and more efficient approximate digestibility. In contrast, the native host plant supported higher efficiency of conversion of ingested and digested food. The relationship between immunity and feeding efficiency was more complex but showed a large positive effect of greater host plant consumption on all immune parameters, particularly for the exotic host plant. While not as strong, the efficiency of conversion of digested food tended to show a negative effect on the three immune parameters. Conclusion: Overall, the exotic host plant proved to be beneficial for this specialist insect with regard to immunity and many of the feeding efficiency parameters and continued use of this host plant is predicted for populations already using it.
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- Award ID(s):
- 1929522
- PAR ID:
- 10454178
- Date Published:
- Journal Name:
- Frontiers in Physiology
- Volume:
- 14
- ISSN:
- 1664-042X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.3389/fphys.2023.1127670
