The present study was conducted with the aim of evaluating the effect of using three temperatures of 30, 40, and 50 °C and five exposure periods of 6, 12, 24, 48 and 96 hours/degree of temperature in reducing the residues of Lambda-cyhalothrin in water under laboratory conditions and measuring these residues using HPLC as well as Biological evaluation of these residues before and after thermal treatments. The HPLC readings of the residues of this pesticide showed that the highest general average of the degradation rate was at the concentration of 30 ppm / active substance (93.47%) and at the temperature at 30 °C (94.79%), while it was only for the exposure period. 48 hours significant effect (89.80%), and the percentage of deterioration in the effectiveness of the pesticide against adults of the insect T.confusum ranged between 96.72 and 99.22%, and the highest of these percentages was at a concentration of 10 ppm (99.22%) and at a temperature of 40 °C (98.33%). for the exposure periods 24 and 48 hours (98.29%). This may indicate the sensitivity of this pesticide to the temperatures used, which seemed to be high in its initial limit, while the highest rate of degradation was 89.08% at the 48-hour period, which differed significantly from The rest of the other averages, which reached 82.2, 85.26, 89.35 and 86.95% for exposure periods of 6, 12, 24 and 96 hours, respectively.