▁spring , ▁often ▁pro tr ud ing ▁from ▁the ▁cell ▁before ▁the ▁adult ▁emer ges . ▁P up ation ▁usually ▁occurs ▁from ▁mid - May ▁to ▁early ▁June , ▁and ▁the ▁ 2 - wing ed ▁re dd ish - b rown ▁adult ▁m idge ▁emer ges ▁through ▁a ▁consp ic uous ▁hole ▁in ▁the ▁gall ▁formed ▁in ▁the ▁previous ▁year ’ s ▁shoot . ▁M ating ▁occurs ▁shortly ▁there after , ▁and ▁eggs ▁are ▁laid ▁on ▁the ▁newly ▁developing ▁sho ots ▁at ▁the ▁base ▁of ▁the ▁need les ▁( Smith ▁ 1 9 5 2 ). ▁As ▁many ▁as ▁ 1 0 0 ▁lar va e ▁per ▁shoot ▁have ▁been ▁reported . ▁Lar va e ▁bore ▁immediately ▁into ▁the ▁tw ig ▁and ▁form ▁cells , ▁the ▁g alls ▁forming ▁by ▁the ▁sw elling ▁of ▁t issues ▁surrounding ▁the ▁lar val ▁cells . ▁Gall ▁formation ▁becomes ▁notice able ▁within ▁ 1 0 ▁days ▁as ▁a ▁series ▁of ▁small , ▁semi - g lo bose ▁sw ell ings , ▁which ▁render ▁the ▁inf ected ▁tw ig ▁twice ▁its ▁normal ▁diameter . ▁G alled ▁tw igs ▁usually ▁remain ▁on ▁branches ▁for ▁several ▁years . ▁ ▁According ▁to ▁data ▁collected ▁in ▁ 1 9 9 3 ▁and ▁ 1 9 9 4 ▁during ▁an ▁out break ▁in ▁Al berta ▁and ▁the ▁North west ▁Territ ories , ▁g alled ▁current - year ▁sho ots ▁caused ▁by ▁spr uce ▁gall ▁m idge ▁displayed ▁a ▁negative ▁bin omial ▁distribution ▁described ▁by ▁the ▁mean ▁k p ▁= ▁ 5 .