Notes on the life-history of the balsam shootboring sawfly in the Maritimes region

Balsam shootboring sawfly (BSS), Pleroneura brunneicornis Rowher (Hymenoptera: Xyelidae), is a poorly understood insect pest of balsam fir ( Abies balsamea [L.] Mill. (Pinaceae)) in northeastern North America. Recent increases in BSS populations have raised concerns among commercial Christmas tree growers, prompting research on its emergence phenology, larval development, and parasitism. Ground emergence traps in New Brunswick (NB) and Nova Scotia (NS) indicated adults emerged from the soil immediately after snow had melted from beneath balsam fir tree crowns in mid to late April. Adults were collected from emergence traps for 2 weeks and remained active in or on trees until the end of May. Both mating and oviposition were observed and photographed up until the end of May in NB. Weekly shoot dissections from stands in NB indicated the presence of four larval instars. All larvae had exited shoots by the end of June, presumably to spin cocoons in the duff layer where overwintering occurs. Parasitoids caused mortality throughout the larval developmental period and appear to be a significant mortality factor for BSS, with 52% of fourth-instar larvae in NB showing signs of parasitism.