Imidacloprid, BAY NTN 33893, 1-[(Chloro-3-pyridinyl)methyl]-4,5-dihydro-N-nitro1H-imidazol-2-amine, is an insecticide being developed worldwide by Bayer AG and in the U.S. by the Mobay Corporation (Anonymous 1990). This nitromethylene compound is a broad-spectrum, systemic insecticide which has shown activity against sucking insects such as Homoptera and some Coleoptera, Diptera and Lepidoptera. It also has shown excellent potential in seed and soil applications (Schmeer et al. 1990, Dewar & Read 1990). Imidacloprid has no known activity against phytophagous mites or nematodes (Elbert & Overbeck 1990). Mobay anticipates registration of imidacloprid on many commodities including vegetables, field crops, fruit, turf and ornamentals. Imidacloprid is a category 3 or 4 compound, depending upon formulation, and is relatively non-toxic to mammals (Elbert & Overbeck 1990). The systemic properties of imidacloprid may be useful with respect to activity against pests and selectivity to beneficial species. However, control of many target pests will require foliar applications which may also affect beneficial arthropods. The objective of this study was to determine the toxicity of imidacloprid to selected beneficial arthropods commonly found in agroecosystems. The 240 FS formulation (240 g ai/liter) of imidacloprid, obtained from Mobay Corporation, was used in the bioassays. Dilutions tested varied by predator response (Table 1), and 127.4 ppm active ingredient, the recommended concentration for foliar application, was used as the 1X rate. Laboratory tests of the toxicity of imidacloprid residues to the following predatory species were conducted: adults of the mirid, Deraeocoris nebulosus (Uhler); larvae in the last instar and adults of the coccinellid, Olla v-nigrum (Mulsant); adults of the coccinellid, Hippodamia convergens (Guerin-Meneville); adult females of the phytoseiid mites, Neoseiulus collegae (De Leon), Phytoseiulus macropilis (Banks), and Proprioseiopsis mexacanus (Garman); eggs and adults of the chrysopid, Chrysoperla rufilabris (Burmeister) from a Georgia colony and adults from a Texas colony; and adults of the lygaeid, Geocoris punctipes (Say). Some of the predators were collected in the field; however, the predatory mites and C. rufilabris were obtained from laboratory cultures. The female mites were from a one-year-old colony and had been adults for approximately 5-10 days. The Georgia C. rufilabris were from a one-year-old colony and had been adults for 15-30 days when tested. C. rufilabris from Texas were from a 2to 3-year-old colony and were approximately 5 days old when tested. Predators were provided water, a 1:1:1, honey:glycerin:water solution and/or wheast before and during the tests. All predators collected in the field were tested within 3 h of collection. Tests were conducted by exposing the predators to plastic petri dishes or diet cups with lids (29.6 ml) dipped in solutions of water + imidacloprid + Triton 1956 (0.1 mllliter)