Preserving adults of Diabrotica virgifera virgifera LeConte under field and laboratory conditions

Western Corn Rootworm (Diabrotica virgifera virgifera LeConte) was introduce in Yugoslavia in 1999. At present the populations density varies from 1 to 50 adults per plant. The population density is in permanently increasing with every new vegetation season. The number of plant protection products granted with permission for weevil control is small - only two products, insecticide bifenthrin and terbuphos. The situation is urgently demanding more detailed investigation in near future. Therefore the technique of preserving and rearing the insects are important to be developed. The aim of this investigation was to determine the optimum laboratory conditions for keeping and rearing this species. D. v. virgifera adults were collected in Klek, locality near Zrenjanin. Plastic vessels and wire cages were used for rearing 100 adults, sex ratio 40/60 - female/male. Wire cage permitted better aeration but lower air humidity. The rearing vessels were kept under different temperature conditions in control temperature chambers under 5, 12, 20 or 25 deg C, in laboratory under room temperature 19-25 deg C, and in open field under 20 to 25 deg C during period from 13th till 28 th of July. The effect on survival of adults was expressed as mortality percent every 24 hours during 10 days. Daily incidence of mortality, lt-p lines and LT-25 were determined, as 25% mortality is accepted as discriminatory limit for considering population suitable for biotest. The daily incidence and rate of mortality varied dependent on temperature. At 5 deg C mortality of adults reached 100% in cages and in plastic boxes after 7 days, At 12 degC the 100 % mortality was achieved in cages after 8 days and in boxes after 10 days. At 20 deg C, regardless the containers 100% mortality occurred after 4 days, and at 25 deg C after 7 days. Under laboratory and field conditions the mortality 100% was achieved after 6 days in boxes and after 9 days in cages. The most persistent increase in mortality was observed at 12 deg C. Concluding upon LT-25 values, temperatures between 20 to 25 deg C were most convenient enabling the longest preservation of insects under field conditions and when keeping them in plastic boxes. In fact 25% insects died only after three days. If the insects for experiments are to be kept in cages or under laboratory or control chamber conditions, they should be used in experiment within 24 h.