Influence of the biotic factors (food conditions, predators and parasitoides) on the population density of Aphis fabae Scop. in sugar beet stands
1998
Weismann, L. (Slovak Academy of Sciences, Ivanka pri Dunaji (Slovak Republic). Inst. of Experimental Phytopathology and Entomology)
Changes in population density of Aphis fabae and their dependence on amino-acid content in sugar beet leaves during plant development were studied. It was confirmed that sugar beet leaves offered the most suitable food conditions from the 2nd leaf stage of plant development up to the 12th leaf stage. During these stages, the beet leaves contain 19 amino acids and their amides. Consequently during the leaf stages between the 13th and 50th, the beet leaves form the essential amino-acids (asparagine, lysine and methionine) which successively decreases until complete downfall. These changes mean the beginning of the retrogradation of the aphids in sugar beet fields. The aphid population density and population density of its natural predators are compared. The value of predators and parasitoides in the reduction of pest frequency was proved only at a secondary infested level in sugar beet plants
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