Laboratory experiments were conducted in the laboratory of Economic Entomology Department, Faculty of Agriculture, Mansoura University to estimate the heat requirements as a tool for predicting the annual generation of Aphis craccivora Koch. and Nezara viridula (L.) attacking cowpea plants at Mansoura district. The obtained results revealed that the required time for developing nymphal instars of A. craccivora decreased as the temperature increased when this insect reared on cowpea plants. The results assured that, the developmental rate declined as temperature increased with significant differences between developmental rates for A. craccivora. The lower development threshold for the nymphal stage was 7.69, and the thermal units expressed as degree-days (dd's) required for nymphal stage were 118.30 ; 121.26; 112.69; 118.09 and 122.22 (dd's) at 15ºC; 20ºC; 25ºC; 30ºC and 35ºC respectively. The obtained results showed that the lower threshold of development for the adult stage of  A. craccivora was 15 ºC. The thermal units required for various development recorded 127.68, 154.76; 184.24, 206.64 and 213.12 (dd's) at 15ºC, 20 ºC, 25 ºC, 30 ºC 35 respectively. The results indicated that the lower development threshold (t₀) for the incubation periods of N. viridula (L.) was 35 ºC when reared on cowpea plants. The results revealed that the thermal units expressed as degree-days (dd's) required for the nymphal stage were 464.36; 422.08; 318.22; 298.25; 216.60 (dd's) at 15ºC; 20 ºC,25 ºC,30 ºC and 35 ºC respectively. the thermal units expressed as degree-days (dd's) required for incubation period were 917.29; 812.49; 664.27; 465.29 and 369.24 (dd's) at 15ºC; 20 ºC,25 ºC,30 ºC and 35 ºC respectively. The thermal units required for various development recorded  1387.36; 1324.83; 1222.98; 954.89 and 652.50(dd's) at 15ºC, 20 ºC, 25 ºC, 30 ºC 35 respectively.