Phenology of Rhynchophorus palmarum and associated Phoenix canariensis mortality in Southern California

Abstract Rhynchophorus palmarum, an invasive palm pest in San Diego County California, has killed thousands of Phoenix canariensis. Over July 2016 to December 2022, this study tracked the population phenology of R. palmarum. Trapping data, derived from the capture of 8,262 weevils, of which 65% were female, indicated strong and predictable seasonal patterns in adult weevil activity, with trap captures increasing after March, peaking in July, before declining steadily towards December. Approximately 80% of weevils were trapped between April and October. This finding has important implications for the timing of management practices. Frond pruning should be done over November to March when weevil flight activity is low, and prophylactic insecticide applications should be made in March and June prior to increased weevil flight activity in April and July. Temperature and day length were strongly correlated with weevil capture rates, while precipitation, wind speed, and relative humidity were not. In urban areas over a 7-year survey period, August 2016 to August 2023, palm mortality rates, based on observations of 521 palms, indicated that 68% were killed. Drone surveys of 637 wilding P. canariensis in the Sweetwater Reserve exhibited a 73% rate of mortality over August 2016 to August 2023. Strong cardinal effects were observed for palm mortality in urban areas with west and east quadrants exhibiting higher rates of mortality in comparison to palms in north and south quadrants. In urban areas, weevil killed palms were removed on average, after 400 days, at an estimated average cost of $2,861 per palm.