The peanut culture is one of the most important of our country. However it is studied with very little intensity. The thrips Enneothrips flavens Moulton, 1941, the leaf beetle Diabrotica speciosa (Germar, 1824) and the red necked peanut worm Stegasta bosquella (Chambers, 1875), are insect pests often found in peanuts (Arachis hypogaea L.), in Jaboticabal, State of São Paulo, Brazil. The main proposal of this work is to study the variation of leaf area index, leaf area ratio, net assimilation rate and relative growth rate in an experiment in which one of the treatments consisted in the application of methyl parathion at 0,09% (E.C. 60%) and the other was a check in which no pesticide was applied. The results obtained during the plant life cycle were confronted. The increments of leaf area index and leaf area ratio were observed to be similar for both treatments, but both parameters were found to be practically always smaller for the check treatment. Finally, it was shown that the net assimilation rate and the relative growth rate was almost always slightly superior in the plot that received no treatment.