Evaluation of trunk injected systemic insecticides to control stem and leaf gall wasps, Josephiella species (Agaonidae, Hymenoptera) on Ficus microcarpa in Hawai’i

Chinese banyan, Ficus microcarpa (Moraceae) is a popular landscape tree in tropical regions of the world, including the Hawaiian Islands. These trees are severely infested by two host-specific insect pest species belonging to family Agaonidae (Hymenoptera: Chalcidoidea), the Chinese banyan leaf gall wasp (Josephiella microcarpae) and the stem gall wasp (Josephiella species, currently being described). Infestations by these insects result in gall formation on young leaves and shoots, premature leaf drop, new shoot death, poor tree health and eventually death of the tree. We evaluated the efficacy and longevity of systemic insecticides imidacloprid and emamectin benzoate, with or without phosphorous acid, delivered through trunk injection to control these two fig wasp species using 45 Chinese banyan trees for two years, on University of Hawaii at Manoa Campus, Honolulu, Hawaii. Our results suggested that only emamectin benzoate had an effect against stem gall wasp up to 14 months post treatment. Both systemic insecticides had an effect against leaf gall wasp for 18 months post treatment, but emamectin benzoate was more effective compared to imidacloprid. We did not observe any indirect benefit of phosphorous acid amendment for trees resist wasp infestations.