Study on structure and dynamics of useful arthropods fauna of field crops in central Transylvania in order to minimize the insecticidal treatments

Under the specific conditions of Central Transylvania, during April-September 1991 and 1992, comparative research work was carried out on the Arthropods fauna in different cereal field crops. The comparison was made between two agroecosystems (represented by winter wheat, maize, clover, two-row spring beans barley fields, marginal herbs and protective forestry edges) in two intensive productive farms at Turda and Boldut, at the Agricultural Research Station Turda. The results were obtained by means of pitfall-soil traps, of adhesive sticky white plots traps and of 100 double sweep net catches in 3 samplings by every control sites. The captured were removed every 10 days. The traps (3/plot-field) were placed in one row in the centre of the field beginning with about 30 m from the edge, with 30 m distance from trap to trap. In the Arthropods fauna the captured phytophagus groups and the entomophagus are presented. The content of the insect group settlings on the studied crops was uniform whereas the dominance structure varied significantly on the two agroecosystems. The existing relationship between phytophagus and entomophagous stationary fauna is discussed beside the aspects regarding the dominance and abundance of different groups, in the biocenotic indices. The proof could be given for the presence and importance of entomophagous groups of: Neuroptera-Chrysopidae; Dermaptera; Heteroptera-Nabidae; Coleoptera-Cicindellidae, Carabidae, Cantharidae, Staphylinidae, Malachiidae, Coccinellidae: Diptera-Syrphidae, Tachinidae, Scatophagidae, etc., Hymenoptera and Arachnida. The predatory poliphagous species were captured in all the field crops according to the seasonal migration cycle. A large part of the captured insects consisted of entomophagous Arthropods groups, as follows: 24 percent in Turda agroecosystem (characterized by open area) were the beneficials represented: 13 percent in winter wheat fields, 41 percent in clover, 56 percent in beans and 42 percent in maize fields. By comparison in the agroecosystems with protective forestry edges in Boldut the percentage composition of species of trophic spectrum was different. There was pointed out the big weight of entomophagous groups: 31 percent, represented by 14 percent in winter wheat, 42 percent in clover, 26 percent in marginal herbs and 69 percent in forestry curtains. On this farm (existing from 1952) no pesticide interventions were used under normal conditions, because there was a real natural entomocenotic equilibrium here