Peanuts, Arachis hypogaea L., have been grown experimentally in Ontario since 1970, with the ultimate objective of commercial production. The pests of this new Canadian crop have been surveyed and the most important one has been identified as the potato leafhopper, Empoasca fabae (Harris) (Ellis and Roy 1979). This pest is native to North America and disperses into Ontario from the south in early June; it attacks a number of crops including potatoes, alfalfa, beans, and peanuts. Feeding by E. fabae interferes with translocation and results in yellowing of the tips of peanut leaves, followed by necrosis, a condition called hopper bum. Reported here are experiments on the injury of this pest to peanuts in 0ntarioT