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Notes: [Abstract only.] The common method of forecasting insect abundance by means of temperature sums is not always sufficiently accurate, since the sum of effective temperature accumulated during a given instar varies from year to year. The effect of temperatures of 33, 28, 22, 19 and 17 degrees C (with a variation of 1 degree C) on the sums of effective temperatures for the development of Quadraspidiotus perniciosus (Comst.) on apple was investigated in the USSR. Results indicate that the sum of effective temperature is an indicator of development but it can be influenced by external factors and may be lower than normal after two favorable years.