2017 ASHS Annual Conference

Chinese banyan (Ficus microcarpa L. f.) and weeping banyan (Ficus benjamina L.) are common ornamental landscape trees grown in many tropical and subtropical regions of the world, including Hawaii. In Hawaii, a new invasive insect pest, lobate lac scale (Paratachardina pseudolobata Kondo & Gullan), first detected on Oahu in 2012, attacks F. benjamina. Damage includes twig and branch dieback, foliage thinning, sooty mold, and death of the entire plant when infestation is severe. Lobate lac scale, and two gall wasp species, the leaf gall wasp (Josephiella microcarpae Beardsley & Rasplus), and the stem gall wasp, an undescribed Josephiella species newly discovered in 2012 in Hawaii, attack F. microcarpa. Gall wasp damage includes progressive branch dieback that may eventually cause tree mortality. Considering the heavy infestations of both gall wasp species in Hawaii and lobate lac scale on Oahu, and high likelihood of these invasive species to spread to neighbor islands in Hawaii and other areas, it is critical to identify effective means to control these pests. No natural enemies of these pests been observed in Hawaii; thus, we focused on low-risk systemic insecticides for control. For gall wasps, we evaluated the efficacy and persistence of two systemic insecticides, imidacloprid and emamectin benzoate, with or without phosphorous acid amendment, delivered through trunk injection, using 45 F. microcarpa on University of Hawaii at Manoa campus. Although both systemic insecticides had some effect against leaf gall wasp for up to 18 months post treatment, only emamectin benzoate had effect and persisted against stem gall wasp for up to 14 months. Phosphorous acid amendment did not provide any benefits for F. microcarpa to mitigate wasp infestations. For lobate lac scale, we evaluated the efficacy and persistence of preventive treatment using imidacloprid and emamectin benzoate, delivered through trunk injection, using 45 F. microcarpa, and those of curative treatment using imidacloprid on ten F. benjamina. We found that imidacloprid delivered via trunk injection was very effective in preventing lobate lac scale infestation for at least 22 months post treatment, and also in reducing lobate lac scale infestation curatively for at least 20 months. In summary, trunk injection of emamectin benzoate could be a feasible strategy to control stem and leaf gall wasps on F. microcarpa, while trunk injection of imidacloprid is an effective preventive and curative strategy against lobate lac scale on F. microcarpa and F. benjamina.