Ocena liczebności pędraków Melolonthinae w pułapkach trocinowych w uprawach sosny zwyczajnej (Pinus sylvestris L.)

Root−feeding insects are an increasingly studied group of herbivores, whose impact on plant productivity and are some of the most damaging forest pests in Europe. Due to the mass feeding on the roots of seedlings and older trees in young plantation and stands, Melolonthinae larvae are classified as pests, which are the most dangerous on the land dedicated to afforestation. The research was located in the Wyszków Forest District (52°43'15' N; 21°39'03' E) on the mixed coniferous and mixed deciduous forest habitats. This study evaluated sawdust traps as the method for assessing abundance of Melolonthinae larvae in Scots pine plantations established artificially from open nursery, container production, and from natural regeneration. In spring 2015 i) ‘small sawdust pits’ in rows between seedlings, and ii) pits without soil in adjacent inter−rows as control were prepared. In spring and autumn 2016, and in spring 2017 sawdust and soil from both variants of pits were sieved and Melolonthinae larvae were counted and compared. The obtained results were analyzed in two ways. The first analysis compared the occurrence of grubs in small pits with or without sawdust, while the other one analysed influence of the time of making small pits, independently for the variant with or without sawdust. The final stage was to compare the number of Melolonthinae larvae in small pits between the origin of the seedlings. We found a greater number of grubs in spring assessment than in autumn. Both kinds of small pits showed higher number of Melolonthinae larvae when compared to traditional method of ‘great pits’. The number of Melolonthinae larvae was significantly higher on the plots with container seedlings than the others. The conceptual assumptions of this alternative and environmentally safe method of ‘sawdust traps’ seems to be optimistic.