from 2015 to 2019 dropped following concerns about the effect of neonicotinoid chemicals on pollinating insects. In May 2019, the Environmental Protection Agency revoked approval for a number of products containing imidacloprid as part of a legal settlement, although some formulations continue to be available. Application to trees When used on trees, it can take 30–60 days to reach the top (depending on the size and height) and enter the leaves in high enough quantities to be effective. Imidacloprid can be found in the trunk, the branches, the twigs, the leaves, the leaflets, and the seeds. Many trees are wind pollinated. But others such as fruit trees, linden, catalpa, and black locust trees are bee and wind pollinated and imidacloprid would likely be found in the flowers in small quantities. Higher doses must be used to control boring insects than other types. Background On January 21, 1986, a patent was filed and granted on May 3, 1988, for imidacloprid in the United States (U.S. Pat. No. 4,742,060) by Nihon Tokushu Noyaku Seizo K.K. of Tokyo, Japan. On March 25, 1992, Miles, Inc. (later Bayer CropScience) applied for registration of imidacloprid for turfgrass and ornamentals in the United States. On March 10, 1994, the U.S. Environmental Protection Agency approved the registration of imidacloprid. On January 26, 2005, the Federal Register notes the establishment of the '(Pesticide Tolerances for) Emergency Exemptions' for imidacloprid. It use was granted to Hawaii (for the) use (of) this pesticide on bananas(,) and the States of Minnesota, Nebraska, and North Dakota to use (of) this pesticide on sunflower(s). Biochemistry Imidacloprid is a systemic insecticide, belonging to the class of chloronicotinyl neonicotinoid insecticides. It works by interfering with the transmission of nerve impulses in insects by binding irreversibly to specific insect nicotinic acetylcholine receptors. As a systemic pesticide, imidacloprid translocates or moves easily in the xylem of plants from the soil into the leaves, fruit, pollen, and nectar of a plant. Imidacloprid also exhibits excellent translaminar movement in plants and can penetrate the leaf cuticle and move readily into leaf tissue. Since imidacloprid is efficacious at very low levels (nanogram and picogram), it can be applied at lower concentrations (e.g., 0.05–0.125 lb/acre or 55–140 g/ha) than other insecticides. The availability of imidacloprid and its favorable toxicity package as compared to other insecticides on the market in the 1990s allowed the EPA to replace more toxic insecticides including the