Larval spongy moth transcriptomic response to ingestion of broad-versus narrow-spectrum insecticidal Chromobacterium species

Authors: Sparks, Michael; HERAGHTY, SAM - Oak Ridge Institute For Science And Education (ORISE); KUHAR, DANIEL - US Department Of Agriculture (USDA); FARRAR JR., ROBERT - US Department Of Agriculture (USDA); Bartholomew, Holly; Blackburn, Michael; Gundersen, Dawn

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2025
Publication Date: 3/8/2025
Citation: Sparks, M., Heraghty, S.D., Kuhar, D.J., Farrar Jr., R.R., Bartholomew, H.P., Blackburn, M.B., Gundersen, D.E. 2025. Larval spongy moth transcriptomic response to ingestion of broad-versus narrow-spectrum insecticidal Chromobacterium species. Scientific Reports. 15. Article e8106. https://doi.org/10.1038/s41598-025-92113-6.
DOI: https://doi.org/10.1038/s41598-025-92113-6

Interpretive Summary: Two insecticidal species of bacteria previously identified by the Invasive Insect Biocontrol and Behavior Laboratory, Chromobacterium subtsugae and Chromobacterium sphagni, exhibit differing toxicity properties depending on the types of insects that ingest them. C. subtsugae is a broad-spectrum agent, exhibiting oral toxicity against dipteran, coleopteran, lepidopteran, and at least some hemipteran insects, as well as other pests. C. sphagni is a more narrow-spectrum agent, toxic to fewer insects. What remains unknown is how a host insect responds to ingestion of these insecticidal bacteria at the gene transcriptional level. In this study, the authors examined gene expression profiles of larvae of European spongy (formerly gypsy) moth, Lymantria dispar, upon ingestion of these bacteria. Gene expression levels in healthy and treated insects were independently compared at the whole-insect and midgut-only tissue levels to characterize host-specific responses. This information will be used by scientists or entities interested in biological control or biopesticie bacteria.

Technical Abstract: The PRAA4-1T strain of Chromobacterium subtsugae was the first insecticidal bacterium to be registered by the U.S. Environmental Protection Agency for use in crop protection applications since approval for Bacillus thuringiensis was granted in 1961. C. subtsugae, a Gram-negative betaproteobacterium, exhibits oral toxicity against a broad range of important insects, including dipteran, coleopteran, lepidopteran, and at least some hemipteran and tetranychidan pests. Chromobacterium sphagni is a closely related bacterium exhibiting a distinctly narrower activity spectrum than that of C. subtsugae: it is toxic to lepidopteran, but not dipteran or coleopteran pest insects. The molecular mode of activity for either species is not well characterized at present, and it remains unclear whether these bacterial species affect insects similarly, notwithstanding their close evolutionary relatedness. In this study, synchronized third-instar larvae of the destructive lepidopteran forest pest, Lymantria dispar dispar (European spongy moth), were separately fed with cultures of C. subtsugae strain PRAA4-1T or C. sphagni strain 14B-1T and sampled after 24 h post infection. Gene expression levels in healthy reference versus treated insects were independently compared at the whole-insect and midgut-only tissue levels to characterize host-specific transcriptional responses to intoxication. Treatment induced up-regulation of such antimicrobial peptides as attacin and cecropin, of two cytochrome P450-encoding genes, and of gelsolin, a molecule involved in actin organization. Some differentially expressed genes were novel or uncharacterized, hence future work with lepidopteran species will be necessary to understand insect physiological responses to Chromobacterium infection.