Diprion pini L. (Hymenoptera, Symphyta, Diprionidae) population dynamics in the Low Dnieper region

Pine sawflies (Hymenoptera, Symphyta, Diprionidae) are the most spread foliage browsing insects of pine forests in Europe, especially monovoltinous European pine sawfly Neodiprion sertifer (Geoffroy, 1785) and common pine sawfly Diprion pini (Linnaeus, 1758), which develops in one or two generations per year depending on weather. The outbreaks of both pine sawflies are the most frequent and intensive in the Steppe zone of Ukraine, especially in the Low Dnieper region, where pine forest (Pinus sylvestris Linnaeus and Pinus pallasiana D. Don) was planted on moving sands in the sixties of the 20^th century. This research is aimed at the evaluation of the parameters for D. pini outbreak dynamics in the Low Dnieper region.

Outbreak severity, specific foci area and mean score of stand threat by D. pini were evaluated from the regional statistical reports. In the regional scale for 1979–2017, notable outbreaks of D. pini were registered in 1982, 1993, 2002, 2006 and 2017. An interval between maximums was from 4 to 11 years, in average 9 years. The growth of foci area in 1979–1998 as compared to 1999–2017 as well as correlation between pine stand area and annual area of this pest’s foci in different forests was not statistically significant. Graphical analysis of dynamics of D. pini focal area for 2010–2017 was done based on individual threat levels. Our study confirms the fact of three outbreaks for this period in three forest and hunting enterprises (FHE), two outbreaks in one FHE and one outbreak in one FHE. An interval between the outbreaks makes three or six years. The causes of such shortening of interval are discussed.