Bionomics of Crapemyrtle bark scale (Acanthococcus lagerstroemiae)

Abstract

Crape myrtle bark scale (CMBS, Acanthococcus lagerstroemiae) is an invasive pest of crape myrtles (CM, Lagerstroemia) used in ornamental landscapes throughout the United States. Infestations of CMBS diminish the aesthetic value of CMs and heavy infestations of CMBS can kill young trees. This pest also affects the nursery industry due to increased management costs. First reported in the US 20 years ago, there are still gaps in the knowledge of bionomics of CMBS, specifically crawler activity and survival. Observing these gaps, these experiments noted various traits and reactions of these scale insects both on and off host to better understand CMBS phenology. Over multiple years, crawler movement in areas of known infestations were observed at locations in north and south Alabama. The first major peaks occurred in late April at Baldwin County in 2019 and mid-May at Madison County in 2020 with highest activity occurring between April and June at both locations. To predict peak crawler hatch, degree-day models were assessed revealing that the sine wave method with a base temperature of 1.7°C provided the lowest coefficient of variation (CV) across both counties. Relative humidity (RH) and temperature heavily impacted CMBS survival, with highest survival observed at 100% RH and 25°C, while low RH significantly reduced survival. No significant difference in crawler mortality was found between sealed and open bags in phytosanitary tests, but the presence of gravid females and newly hatched crawlers skewed results. This suggests the need for longer bagging durations of CM clippings to prevent future infestations. These findings provide better understanding of CMBS activity patterns, survival strategies, and effective disposal practices, which help enhance management strategies for this pest. Further research is recommended to explore the effects of solarization and temperature on CMBS mortality in outdoor disposal settings.