DYNAMICS OF BOTHYNODERES PUNCTIVENTRIS GERM. POPULATION IN THE PERIOD FROM 1962 T0 1973 ON SUGAR BEET FIELDS IN BAČKA

Dynamics of Bothynoderes punctiventris Germ. population was observed from 1962 to 1973 in west Bačka on areas of Sugar prrocessing factory in Crvenka (north-eastern part of Yugoslavia). This species represented the most dangerous sugar beet pest in the mentioned region. Every year analyses were carried out on about 70 fields in average of socially owned sector with a total area of 3.700 ha of sugar beet. During September and October on every 2 ha a check was digged up of 50 x 50 cm (0,25 sq m) at the depth of 50 cm. On the basis of the data obtained by soil surveying we established the density of population of hibernating samples of this species. The population of hiberating samples of B. punctiventris Germ. varied by the individual years between 0,4 and 11,3 samples per sq m (the average for the whole period investigated was 3,6/sq m). The lowest population was recorded during falls of 1967, 1970 and 1973 and the highest during falls of 1962, 1963 and 1964 (Graph 1). The differences mentioned in the population of this species are the result of variation and climatic conditions during growing season, especially during April and May. In the period from 1946 to 1964 the majority of years had very high population of B. punctiventris Germ. Just from 1962 to 1964 we recorded from 6,5 to 11,3/sq m or an average of 8,9 sq m. Afterward, in the last nine years, a tendency of decrease in population of this species was established which varied from 0,4 to 4,4/sq m, with an average of 1,8/sq m. Several fastors affected ,the decrease in populations: more efficient control of imaga in spring, a frequent application of insecticides into soil for catipillars control, reduction of sugar beet areas, reduction of seed rates for sowing, improvement of cultural practice (wide application of herbicides, better soil tillage, frequent irrigation, etc.). The density of population of B. punctiventris Germ. in the individual localities (tab. 1), besides the amount of rainfall in spring and summer, depended also upon geomorphological elements and type of soil. It is highest on loess plateau, then loess terrace and the last place belongs to other regions. As regards different soil types the density of population of this species is highest on chernozem calcareus and calcareus black meadow soil. During the years of slight reproduction of B. punctiventris Germ. (0,4 -0,8/sq m) it was found in fall that 35,6% of fields ,in average were without this pest, 63,1% of fields attacked by this pest had population of 0,1-5/sq m and hardly 1,3% of fields had 5-10/sq m. During the years of mass reproduction of B. punctiventris Germ. (6,5-11,3/sq m) registered only 7,1% of fields without this species, 37,6% of fields with population of 0,1-5/sq m, 28,1% of fields with 5-10/sq m, and 27% of fields with density of over 107sq m (tab. 2). Everyday observation of the dynamics of fall population of B. punctiventris Germ. represents a basis for long term forecasting of the intensity of occurrence of this species in the following year while the analyses of the density of population per individual localites and fields enables the focus of pests to be disovered