Impacts of commercial biopesticides on crapemyrtle bark scale (Acanthococcus lagerstroemiae) and beneficial insects

Abstract

The crapemyrtle bark scale (CMBS), Acanthococcus lagerstroemiae (Kuwana) (Hemiptera: Eriococcidae), is an important pest of crapemyrtles, Lagerstromia spp. (Myrtales: Lythraceae) since its damage results in an unpleasant aesthetic. Current CMBS management methods depend heavily on pesticides which impact on beneficial insects. Biopesticides show potential for pest control, host specificity, and low impact towards non-target organisms. The objectives of my thesis were to determine (1) if biopesticides are effective against CMBS infestations when applied in different seasons, and (2) their effects towards coccinellids known to attack CMBS. To test the efficacy of selected biopesticides, treatments were delivered to potted plants or full-grown trees infested with CMBS in different seasons. The fungal treatments Ancora® (Isaria fumosorosea strain PFR97) and BioCeres® (Beauveria bassiana strain ANT-03), and bacterial products Venerate® (Burkholderia spp. A396 strain) and Grandevo® (Chromobacterium subtsugae PRAA4-1T strain) failed to control CMBS in greenhouse conditions. When BioCeres®, Ancora®, and BotaniGard® (B. bassiana strain GHA) were delivered in field settings, BioCeres® significantly increased proportion of dead to total scales on full grown trees in the winter trial; whereas BotaniGard® was more effective during the Fall trial on small potted plants. In the spring trial, biopesticides failed to control CMBS. Temperature impacted product efficacy in the field. According to laboratory studies, the highest fungal germination was achieved at 28°C, and highest germination rates were between 25 and 30°C. Therefore, products containing B. bassiana can be a good management tool for CMBS on cooler seasons. Susceptibility of natural enemies to biopesticides in laboratory conditions was assessed by submerging the insects in a biopesticide mixture and observing survival over time. BotaniGard® significantly reduced the survival of larvae and adults of both Hyperaspis bigeminata and Chilocorus spp. by at least 57%. Adults of Chilocorus spp. had survival also reduced by 40% when treated with BioCeres®; and Ancora® reduced the survival of H. bigeminata larvae by 69%. In field conditions, entomopathogenic fungi spores were collected from live coccinellids, ensuring contact but not pathogenicity. Results of this project provide a basic understanding of the impact of biopesticides for the management of CMBS.