Mortality of the crapemyrtle bark scale (Hemiptera: Eriococcidae) by commercial biopesticides under greenhouse and field conditions

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: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2022
Publication Date: 9/21/2022
Citation: Matos Franco, G., Chen, Y., Doyle, V.P., Rehner, S.A., Diaz, R. 2022. Mortality of the crapemyrtle bark scale (Hemiptera: Eriococcidae) by commercial biopesticides under greenhouse and field conditions. Biological Control. 175:105061.
DOI: https://doi.org/10.1016/j.biocontrol.2022.105061

Interpretive Summary: Crapemyrtles are an important ornamental plant in southeastern U.S.A. The crapemyrtle bark scale (CMBS) is an invasive species that has spread across southeastern U.S.A. CMBS has increased crapemyrtle management costs for nurseries and homeowners, thus an integrated approach is needed to manage CMBS infestations. Three fungal biopesticides were tested for efficacy against CMBS in greenhouse and field experiments. Biopesticides containing I. fumosorosea PFR97, B. bassiana ANT-03, and B. bassiana GHA were applied to mature crapemyrtles grown in the landscape and naturally infested with CMBS, and the scale survivorship was determined. When treatments were applied in winter, scale survivorship was significantly lower in the B. bassiana ANT-03 treatment (0.55 ± 0.0047; p= 0.0209) compared to the water control (0.72 ± 0.035). When treatments were applied in spring, no treatment effect was observed (0.58 ± 0.020; p= 0.2186). During autumn trials with container-grown crapemyrtles in greenhouses, B. bassiana GHA treatment reduced scales survivorship (0.27 ± 0.029; p= 0.0065) when compared to the water control (0.69 ± 0.023). Pathogenicity assays confirmed that scales collected in the spring trial were infected by all pathogens delivered; in addition, B. bassiana ANT-03 was the most commonly recovered pathogen. In a temperature-dependent spore germination assay, the optimum temperature range was between 22.5 and 30°C, with peak spore germination observed at 28°C for all three pathogens. Results from this project suggest that biopesticides containing strains of B. bassiana are a potential management tool in the development of an IPM program for CMBS of interest to home and commercial horticulturists and IPM managers.

Technical Abstract: Crapemyrtles, Lagerstroemia spp., are one of the most important ornamental plants in southeastern U.S. The crapemyrtle bark scale (CMBS), Acanthococcus lagerstroemiae (Kuwana), is an invasive species that has spread across southeastern U.S. and increased management costs for nurseries and homeowners. The scale impacts crapemyrtle’s aesthetical values and an integrated approach is needed to manage its infestation. Biopesticides are frequently used to control soft-bodied insects, however there is no information on their efficacy against CMBS. The objectives of this study were to test the use of selected biopesticides against CMBS under different environmental conditions, evaluate their pathogenicity to CMBS, and determine optimum temperature for effective biopesticide activity. Commercial formulations of the fungal biopesticides Isaria fumosorosea PFR97, Beauveria bassiana ANT-03, and the bacterial biopesticides Burkholderia rinojensis A396 and Chromobacterium subtsugae PRAA4-1T were tested in greenhouse settings. Results revealed that there was no treatment effect on scale mortality. Biopesticides containing I. fumosorosea PFR97, B. bassiana ANT-03, and B. bassiana GHA were applied to mature crapemyrtles grown in the landscape and naturally infested with CMBS, and the scale survivorship was determined in two trials at different seasons during a growing season. When treatments were applied in winter, scale survivorship was significantly lower in the B. bassiana ANT-03 treatment (0.55 ± 0.0047; p= 0.0209) compared to the water control (0.72 ± 0.035). When treatments were applied in spring, no treatment effect was observed (0.58 ± 0.020; p= 0.2186). During another trial conducted in autumn using container-grown crapemyrtles, B. bassiana GHA treatment reduced scales survivorship (0.27 ± 0.029; p= 0.0065) when compared to the water control (0.69 ± 0.023). Pathogenicity assays confirmed that scales collected in the spring trial were infected by all pathogens delivered; in addition, B. bassiana ANT-03 was the most commonly recovered pathogen. In a temperature-dependent spore germination assay, the optimum temperature range for I. fumosorosea PFR97, B. bassiana ANT-03, and B. bassiana GHA was between 22.5 and 30°C, with peak spore germination observed at 28°C for all three pathogens. Results from this project suggest that biopesticides containing strains of B. bassiana are a potential management tool in the development of an IPM program for CMBS.