Analysis of the number of hemimetabolous insects at variable wheat sowing densities – the role of nitrogen in the plant and soil

This work investigated the influence of nitrogen compounds on soil–plant–insect interactions. The study aimed to assess the effect that cultivation of two spring wheat cultivars (Triticum sphaerococcum Percival and Triticum persicum Vavilov) at various plant densities (400, 500 and 600 grains · m–2) under organic and conventional farming had on the abundance of mimetabolous insects in the context of selected chemical and biochemical soil properties. The soil was assayed for its content of organic carbon (SOC), total nitrogen (STN), nitrate (SNO3–) and activity of proteases (PRO) – an enzyme involved in N transformation. The aboveground part of spring wheat was assayed for the content of total nitrogen (TNC) and nitrate nitrogen (TNO3–). Spring wheat variety and plant density both determined the SOC and STN content. The tested soil was characterized by low SOC content. PRO activity was positively correlated with SOC and STN contents, which indicated the role of this enzyme in organic matter cycling. Thysanoptera, Aphididae and Miridae were found to prefer spring wheat grown under organic farming. However, the numbers of these pests did not pose a threat to the growth and development of the host plant. Hemimetabolous insects were far less abundant on T. persicum than on T. sphaerococcum.