Abstract:Larch casebearer(C．Dahurica)is a serious pest of larches(Larix spp)in nor rheastern China．The number of needles infested and fed by a casebearer larva in．Different instars were determined．The pest has four-instars in larvae stage and overwinters as a 3rd-instr larva (a few as a 2nd-instar)．The average number of needles infested were 4—7，by a larva at the instar of 1-3 in summer and fall and 39.7 by a last-instar larva in spring，with a max．Of 48.5．The length and weight of ne-dles fed by the insect in 24 hours were measured on sixteen full-grown larvae．On the average，3.88 needles were infested by a full-grown larva，the fed length was 24.13mm，41.18％of total infested needles，and the fed weight was 6.65mg，3.22 times heavier than the larva’s weight and 55.74％of the total weight of the infested needles．It was found that the fourth-instar larvae and the pupae of larch casebearer were attacked by its parasites and no larvae in their 1-3 instar were Parasitized．To protect parasites．The chemicals to eontrol the pest should be applied in summer or fall．