Dynamics of the Composition and Density of Insects on Aboveground Organs of Alfalfa in the Forest-Steppe of Samara Province

摘要

This paper presents analysis of the effects of the alfalfa crop age, sowing method, phenological development phases, and green mass mowing on the composition and density of insects and spiders on the aboveground organs of alfalfa grown in crop rotation without irrigation, pest control measures, and fertilizers. The main inhabitants of alfalfa crops comprised over 50 species, with prevalence of the chewing herbivores: alfalfa weevil Hypera postica , alfalfa seed chalcid Bruchophagus roddi , nodule weevils Sitona lineatus and S. inops ; the sucking herbivores: flower thrips Odontothrips sp., gorse shield bug Piezodorus lituratus , lucerne bug Adelphocoris lineolatus , plant bug Lygus pratensis , cowpea aphid Aphis craccivora , and pea aphid Acyrthosiphon pisum ; the predators: spiders, predatory bug Orius niger , predatory thrips Aeolothrips sp., and variegated ladybug Hippodamia variegata . The seasonal dynamics of the composition and density of dominant groups was more pronounced in the first-year crops than in 2–4 year old ones. In field crop rotations without the use of insecticides, plots with periodic green mass mowing during the budding and flowering phases of alfalfa seed crops should alternate with unmown plots, so that plots with blossoming plants should be present in the field throughout the summer. This measure would promote the development and maintenance of highly diverse insect complexes, attract predators and pollinators, provide additional feeding for parasitic Hymeno-ptera, and reduce the number and harmfulness of herbivores as the result of greater trophic competition between them as well as of the impact of entomophages.