Toxicity of photorhabdus luminescens and xenorhabdus bovienii bacterial metabolites to pecan alhids (hemiptera: aphididae) and the lady beetle harmonia axyridis (coleoptera: coccinellidae)

Authors: WU, SHAOHUI - University Of Georgia; TOEWS, MICHAEL - University Of Georgia; Cottrell, Ted; SCHMIDT, JASON - University Of Georgia; Shapiro Ilan, David

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2022
Publication Date: 8/16/2022
Citation: Wu, S., Toews, M., Cottrell, T.E., Schmidt, J., Shapiro Ilan, D.I. 2022. Toxicity of photorhabdus luminescens and xenorhabdus bovienii bacterial metabolites to pecan alhids (hemiptera: aphididae) and the lady beetle harmonia axyridis (coleoptera: coccinellidae). Journal of Invertebrate Pathology. 194 : 107806. https://doi.org/10.1016/j.jip.2022.107806.
DOI: https://doi.org/10.1016/j.jip.2022.107806

Interpretive Summary: Broad spectrum chemical insecticides can cause harm to humans and the environment. Therefore alternatives are needed for sustainable insect pest control. Beneficial nematodes (small round worms) are natural biopesticides that are effective and environmentally friendly. These nematodes kill insect pests due to their association with mutualistic bacteria. The metabolic toxins (byproducts) of these bacteria have been found to suppress plant pathogens causing diseases in plants, and a few studies have reported their toxicity to insect pests. However, the insecticidal activities of these bacterial metabolites have been underexplored. Also, for potential use as biopesticides in pest management, the metabolite’s impact on beneficial natural enemies (such as lady beetles) should be considered. We tested the metabolic toxicity of two bacterial species to the black pecan aphid and the blackmargined aphid (both are significant pests of pecan trees), and evaluated their potential impact on the multi-colored Asian lady beetle, which is an important predator of pecan aphids. We found that both bacterial metabolites were toxic to pecan aphids, especially against the blackmargined aphid; the metabolites just as effective as a chemical insecticide that was included in the study. Both bacterial metabolites were safe to the lady beetles. These findings suggest that it is promising to use the bacterial metabolites as novel biopesticides in pest management for pecan orchards, or conceivably in other crops.

Technical Abstract: Toxicity of the metabolites of two bacteria, Photorhabdus luminescens and Xenorhabdus bovienii, symbionts of entomopathogenic nematodes, were tested in the laboratory against the multicolored Asian lady beetle, Harmonia axyridis, the black pecan aphid, Melanocallis caryaefoliae, and the blackmargined aphid, Monellia caryella. Both bacteria demonstrated high levels of toxicity equivalent to the pyrethroid insecticide bifenthrin and caused higher insect mortality than tryptic soy broth plus yeast extract (TSY) (blank control) against M. caryella; P. luminescens was more effective than TSY against M. caryaefoliae. At the levels tested, the metabolites were not toxic to H. axyridis.