Effects of baculovirus-killed cadavers on plant defenses and insect behavior

Authors: JONES, ASHER - Pennsylvania State University; SHIKANO, IKKEI - University Of Hawaii; Mason, Charles; PEIFFER, MICHELLE - University Of Hawaii; FELTON, GARY - Pennsylvania State University; HOOVER, KELLI - Pennsylvania State University

Submitted to: Arthropod-Plant Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/2024
Publication Date: 1/28/2025
Citation: Jones, A.G., Shikano, I., Mason, C.J., Peiffer, M., Felton, G.W., Hoover, K. 2025. Effects of baculovirus-killed cadavers on plant defenses and insect behavior. Arthropod-Plant Interactions. 19. Article 22. https://doi.org/10.1007/s11829-024-10129-7.
DOI: https://doi.org/10.1007/s11829-024-10129-7

Interpretive Summary: Baculoviruses (Baculoviridae) are a group of entomopathogenic viruses that are important natural enemies of insects, particularly lepidopteran larvae. We used the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) and host Trichoplusia ni caterpillars to study the effects of virus-killed cadavers on tomato plant defenses and T. ni behavior as well as the cadaver microbiome. We performed amplicon sequencing of the V4 region of the 16S rRNA gene to compare bacterial communities associated with virus-killed and uninfected (freeze-killed) cadavers. The most represented bacterial orders in these communities were Lactobacillales, Enterobacteriales, Pseudomonadales and Bacillales, in agreement with other studies in Lepidoptera. In terms of overall community composition and membership, there was no significant difference between tomato-fed virus-killed or freeze-killed cadavers. Culture-dependent plating indicated that virus-killed cadavers had significantly higher bacterial titers compared with uninfected cadavers. To examine the effects of cadavers on tomato defenses, we applied virus-killed cadavers, freeze-killed cadavers, or water to undamaged or mechanically wounded plants. We found that virus-killed cadavers suppressed plant defense proteins in damaged plants. Cadavers did not influence plant defenses induced by healthy or infected T. ni herbivory. When applied to intact plants, virus-killed or freeze-killed cadavers did not influence T. ni oviposition, larval choice, or larval consumption, indicating these insects did not discriminate cadaver cues.

Technical Abstract: Baculoviruses (Baculoviridae) are a group of entomopathogenic viruses that are important natural enemies of insects, particularly lepidopteran larvae. At the end of the virus infection cycle, host tissues rupture, releasing occlusion bodies (OBs) and bacteria from liquified cadavers. An important component of baculovirus transmission efficiency is the frequency with which hosts encounter patchily distributed OBs on plants. Little is known about the ecology and bacterial composition of these cadavers. We used the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) and host Trichoplusia ni caterpillars to study the effects of virus-killed cadavers on tomato plant defenses and T. ni behavior. To provide an initial characterization of cadavers, we used high-throughput Illumina amplicon sequencing of the V4 region of the 16S rRNA gene to compare bacterial communities associated with virus-killed and uninfected (freeze-killed) cadavers. The most represented bacterial orders in these communities were Lactobacillales, Enterobacteriales, Pseudomonadales and Bacillales, in agreement with other studies in Lepidoptera. In terms of overall community composition and membership, there was no significant difference between tomato-fed virus-killed or freeze-killed cadavers. Comparison of virus-killed cadavers from two separate experiments revealed significant differences in bacterial community composition, suggesting that host plant could play a more important role in shaping bacterial communities than virus infection status. Culture-dependent plating indicated that virus-killed cadavers had significantly higher bacterial titers compared with uninfected cadavers. To examine the effects of cadavers on tomato defenses, we applied virus-killed cadavers, freeze-killed cadavers, or water to undamaged or mechanically wounded plants. We found that virus-killed cadavers suppressed polyphenol oxidase (PPO) activity, an important plant defense protein, in damaged plants. Although cadavers did not influence plant defenses induced by healthy or infected T. ni herbivory, this study provides the first evidence that baculoviruses could influence plant defenses through host cadavers. When applied to intact plants, virus-killed or freeze-killed cadavers did not influence T. ni oviposition, larval choice, or larval consumption, indicating these insects did not discriminate cadaver cues. Virus-killed cadavers could play important roles in mediating interactions between plants, herbivores, and other trophic levels, with potential implications for viral transmission dynamics.