Abstract: Erannis defoliaria, a spring-feeding moth, was reported for the first time in Tunisia in 2009. Important defoliations caused by this pest were observed in different cork oak forests of northwestern Tunisia with two peaks in 2009 and 2018. This study was carried out from 2009 to 2018 in a native cork oak (Quercus suber) forest ‘Ain El Baya’. Every spring, larval densities were monitored weekly. Larval mortality and parasitism were also calculated.The average number of larvae per branch varied significantly between years, ranging from 30.6 ± 3.14 larvae/branch in 2018 to 2.06 ± 0.4 larvae/branch in 2015. Differences in mortality and parasitism of caterpillars were highly significant among years. Pupal weight varied from 34.5 mg in 2018 to 44.7 mg in 2012.