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

Abstract

The crapemyrtle bark scale (CMBS), Acanthococcus lagerstroemiae, is an important pest of crapemyrtles, Lagerstroemia spp. 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 seasons, evaluate their pathogenicity to CMBS, and determine optimum temperature for spore germination. Commercial formulations of the fungal biopesticides Isaria fumosorosea PFR97, Beauveria bassiana ANT-03, and the bacterial biopesticides Burkholderia rinojensis A396 and Chromobacterium subtsugae PRAA4-1 T were tested in greenhouse settings and did not have significant treatment effect on immature 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. When treatments were applied in winter, scale survivorship was significantly lower in the B. bassiana ANT-03 treatment compared to the control. When treatments were applied in spring, no treatment effect was observed. During another trial conducted in autumn using container-grown crapemyrtles, B. bassiana GHA treatment reduced scales survivorship when compared to the control. Pathogen re-isolation assays confirmed that scales collected in the spring trial were had all pathogens delivered; in addition, B. bassiana ANT-03 was the most 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 can be included in the toolbox for CMBS control, provided that climate and product coverage are considered.