Abstract: The olive leaf gall midge Dasineura oleae (Diptera: Cecidomyiidae) is widespread in olive groves of Greece but its population levels are usually kept very low. However, in 2011 and 2012 there was an outbreak of this pest in certain areas of the island of Crete. In this study the population of D. oleae was recorded for 2 years, starting from May 8, 2012 to May 12, 2014, in two areas of Mirabello (Nisi Eloundas and Ampela), in North-East Crete. The number of galls per shoot was much higher in the olive grove of Elounda. In certain sampling occasions a really high number of galls per shoot was recorded showing a peak on the 7th of March 2013 when 32 galls were recorded per shoot, in average. As a consequence, the number of leaves developed on the infested shoots was much reduced. However, starting from the first sampling in 2013, parasitism was recorded. At the samplings from Elounda the parasitization rate reached to 89%. Most of the parasitoids belonged to Mesopolobus sp. (Hymenoptera: Pteromalidae). Mostly due to the suppressing effect of the parasitoids, the incidence of the pest was much reduced i.e. on August 5, 2013, only 1 larva was recorded per 10 leaves in samples of the olive grove of Elounda, where the pest had developed high densities. These results indicate the significant role that native biological control agents play in the regulation of D. oleae outbreaks.