population fluctuation of the economically important boring insect pest Ptosima undecimmaculata (Coleoptera: Buprestidae), attacking orange trees were monitored at Sharkia governorate during the two successive years 2015 and 2016. P. undecimmaculata prevailed from late March / early April to late October / early November. Three peaks were recorded during 2015, during 2nd half of June (0.28 beetle/tree), the 1st half of August (0.29 beetle/tree) and the 2nd half of September (0.18 beetles / tree). Only two peaks were recorded in 2016, during the 1st half of July (0.31 beetles/tree) and the 1st half of September (0.36 beetles / tree). Summer months recorded the maximum flight (1.23 and 1.63 beetles), followed by spring (0.69 and 0.58 beetle), then autumn (0. 09 and 0.12 beetle) /tree, and nearly stopped during winter (0.٠0 and 0.01 beetle) / tree in 2015 and 2016, respectively. The total numbers per year were 2.01 and 2.34 beetles/tree in 2015 and 2016, respectively. The respective means per tree / month were 0.17 and 0.20 beetles / tree / half a month. It had two broods of beetles' activity and the beetle's activity averaged 7.8 months. Effect of weather factors on the borer activity was mostly positively significant with day maximum, day minimum, and day mean temperatures but negatively and insignificantly with day mean relative humidity. The infestation was almost doubled for only one year, thus needed urgent integrated control.