Will the application of biocontrol fungi disrupt predation of Acanthococcus lagerstroemiae by coccinellids?

Authors: MATOS FRANCO, GIOVANA - Louisiana State University; CHEN, YAN - Louisiana State University; DOYLE, VINSON - Louisiana State University; Rehner, Stephen; DIAZ, RODRIGO - Louisiana State University

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2021
Publication Date: 6/27/2022
Citation: Matos Franco, G., Chen, Y., Doyle, V.P., Rehner, S.A., Diaz, R. 2022. Will the application of biocontrol fungi disrupt predation of Acanthococcus lagerstroemiae by coccinellids? Journal of Invertebrate Pathology. 193:107789. https://doi.org/10.1016/j.jip.2022.107789.
DOI: https://doi.org/10.1016/j.jip.2022.107789

Interpretive Summary: Crapemyrtles are a key ornamental plant in southeastern U.S.A. that are under threat from the invasive crapemyrtle bark scale (CMBS), which has increased crapemyrtle management costs and spurred the search for natural integrated approaches to manage CMBS infestations. This research documented the prevalence of three species of coccinellid beetle predators of CMBS in Louisiana, investigated the impacts of mycopesticides on survival of CMBS predators by life stage, and determined whether entomopathogenic spores applied to crapemyrtles as mycopesticides for CMBS control are transferred to predators under field conditions. In laboratory assays, all three mycopesticides, based either on Beauveria bassiana or Isaria fumosoroseus, reduced survivorship of adult and larval beetles by over 50%. In field studies, mycopesticide spore formulations applied to crapemyrtle were re-isolated from coccinellids, confirming their transfer to these predators. Results from this project demonstrate the potential for negative interactions between applied mycopesticides and CMBS natural predators. suggesting that use of mycopesticides occur during winter and spring prior to the emergence and population growth of CMBS predators.

Technical Abstract: Insect predators are the most important natural enemies of the crapemyrtle bark scale (CMBS) in the USA. Mycopesticides (biocontrol fungi) are considered an IPM tool to increase CMBS mortality; however, their impacts on CMBS predators are unknown. The objectives of this study were to assess the abundance and diversity of CMBS natural enemies in Louisiana; evaluate the impacts of mycopesticides on survival of CMBS predators by life stage; and determine if entomopathogenic spores delivered to crapemyrtles are transferred to predators under field conditions. The mycopesticides Ancora® (Isaria fumosorosea PFR97), BioCeres® (Beauveria bassiana ANT-03), and BotaniGard® (B. bassiana GHA) were tested against the coccinellids Chilocorus spp. and Hyperaspis bigeminata under laboratory and field conditions. Adults and larvae of the coccinellids were treated with each mycopesticide and survival recorded over a 14-day period. The most common natural enemies on CMBS infested trees were the coccinellids Chilocorus cacti, C. stigma, and Hyperaspis bigeminata (Coleoptera: Coccinellidae). BotaniGard® reduced survival of adults and larvae of both genera by at least 57%. BioCeres® reduced the survival of Chilocorus spp. adults by 40% and Ancora® reduced survival of H. bigeminata larvae by 69%. Under field conditions, CMBS infestations were sprayed with the mycopesticides and coccinellids were collected every-other day for a two-week period. Spores of the delivered mycopesticides were recovered from the coccinellids; however, it is not known if infection occurred in the field trial or spores were delivered to CMBS infestations by the coccinellids. We conclude that mycopesticides negatively impacted the survival of coccinellids in laboratory trials, and coccinellids can transport pathogen spores under field conditions.