Constant high temperature regime (30, 34, 37, and 40°C) for 1–5 h decreased mean survival of nymphal and adult stages ofMonelliopsis pecanisBissell andMelanocallis caryaefoliae(Davis) with increasing temperature and time of exposure. Constant low-temperature regime (0, 6, 12, and 15°C) decreased aphid survival with decreasing temperatures and increasing time of exposure. A temperature by aphid interaction was observed, with the greatest mortality being at the extreme high (37 and 40°C) and low (0 and 6°C) temperatures. Aphid stages showed differences in tolerance to all temperature levels. Third and fourth ins tars and adults of both species withstood a wide range of temperatures better than first and second instars under either regime.M. pecanistolerated low temperatures better thanM. caryaefoliae, but at high temperatures,M. caryaefoliaewas more tolerant. Air temperature fluctuations within a pecan tree were measured during July with temperature probes. Air temperature was slightly higher at the edge of the tree crown than near the trunk, otherwise temperatures were very uniform within the tree crown for a given hour of the day.