FORMATION OF COLORADO BEETLE POPULATION AND ITS HARMFULLNESS IN PREOBYE FOREST-STEPPE DEPENDING ON SCLEROTIA OF BARE PATCH CAUSATIVE AGENT AVAILABLE ON TUBER SETS
Colorado beetle was present on potato plantations through the entire vegetation colonizing and damaging them in a different way depending on the degree of tuber sets infestation with bare patch causative agent. The plants grown out of the tubers free from the infection onset show up a small amount of phytophage on the 33rd day after planting, but the plantations out of the tubers with bare patch sclerotia do 6 days later. The number of Colorado beetle imagoes was higher in the second case and made up 0.36 specimens per plant whereas in the first case it was by 1.3 less. Egg-laying began in the phase of complete shoots. The maximal number of egg-layings was observed in the plants grown out of healthy tubers, 0.29 egg-layings per plant, which is 1.2 times more than in the plantations out of the planting stock infected with bare patch sclerotia. The first larvae in the both cases emerged at the beginning of potato budding, but the number of the pests was close to and varied from 0.53 to o.57 pests per plant regardless the presence or absence of bare patch sclerotia on the planting stock. The peak number of larvae was observed in the phase of ripening: on the 50th day after planting and in the plants out of sclerotia-free tubers and on the 53rd day - in the plants out of sclerotized tubers. It was also established that in the first case potato was infested by the pest by 1.4 heavier than it was in the second case. The maximal number of summer generation imagoes was fixed in the phase of ripening. In this case the number of Colorado beetles on healthy plants was 1.2 times higher than that on the plantations out of bare patch sclerotized tubers. The crop attractiveness for imago in the field did not depend on bare patch presence on the planting stock. Larvae fed longer on the plants out of healthy tubers. The index was 1.8 times different. The intensity of leaf surface damage in potato bushes out of sclerotized tubers is by 11.2 % higher than in the plants out of healthy tubers. Tuber losses caused by Colorado beetle made up 29 %, by bare patch - 34 %, but the complex of harmful organisms concerned caused 46 % of the losses.