Breeding centers of the star-tailed sawfly, Acantholyda posticalis, are expanding rapidly in the Bryansk region. From 2009 to 2024, the area of its foci increased 47 times. In Russia, A. posticalis is one of the widespread pests of pine stands. Its phenology and morphometric characteristics have distinctive features in different regions.

   The object of the study is the populations of A. posticalis in the pine plantations of the Bryansk Forestry State Institution.

   The observations were carried out on 64 test areas located in the breeding ground of the sawfly. The phenology of pest development was studied by periodically determining and accounting for the phases of development with a frequency of 5–10 days over two years (autumn 2023 – spring 2025). In total, 193 reference soil pits were laid and the parameters of more than 600 larvae were taken into account. In the territory of the Bryansk region, flight of insects begins in late April – early May, and the largest – in the second decade of May – June. The flight begins with an average daily air temperature above 13.3 °C. Egg laying takes place from May to June, eggs are laid for 2–3 weeks. Flight of A. posticalis starts much earlier in the Bryansk Region than in other regions. Larvae appear from the 1st week of May to July. In the Bryansk region, 99.8 % of wintering individuals are yellow. The pupal phase lasts 8–15 days. Generation is annual, and part of the population always goes into diapause. In the course of the work, a diagram of the annual development cycle of A. posticalis was drawn up in the conditions of the Bryansk region. The parameters of A. posticalis larvae recorded in the Bryansk region differ from previously published data for other regions. The average weight of females is 0.12 g, males – 0.06 g; the average length of females is 16.7 mm, males – 13.7 mm; the average width of the head capsule of females is 2.04 mm, males – 1.84 mm. This indicates the regional peculiarities of the larval body parameters