VZDRŽEVANJE POPULACIJE (Diabrotica virgifera virgifera  Le Conte) V POLJSKIH IN LABORATORIJSKIH RAZMERAH

D. INDJIĆ, Z. KLOKOČAR ŠMIT, Š. ALMAŠI, M. VUJAKOVIĆ, K. VIOGLAVIN, T. BJELJAC, I.  FELBAB

Institut za zaštitu bilja i životne sredine “Dr Pavle Vukasović”, Poljoprivredni fakultet, Novi Sad

Koruzni hrošč (Diabrotica virgifera virgifera Le Conte) je bil vnesen v Srbijo leta 1990. V letu 2000 smo na številnih koruznih njivah našli od 1 do 50 imagov na koruzno rastlino. Glede na to, da se škoda zaradi koruznega hrošča iz leta v leto povečuje, da je izbor insekticidov (bifentrin in terbufos) za njegovo zatiranje majhen in da se v prihodnosti načrtujejo obsežne raziskave te vrste, smo si postavili za cilj optimizirati razmere za shranjevanje in vzdrževanje osebkov za laboratorijske raziskave. Hrošče smo zbrali na lokaciji Klek (Zrenjanin). Gojili smo jih na dva načina: v plastičnih škatlah in v škatlah iz žice s po 100 osebki v vsaki in v razmerju 40 samic : 60 samcev. Zračenje v plastičnih škatlah je bilo slabo za razliko od žičnatih, kjer je bila dobra. Poskusi so potekali: v poltermostatu pri konstantni temperaturi 5, 12, 20 in 25 ^oC, v laboratorijskih razmerah na sobni temperaturi 19-25 ^oC in na prostem v poljskem poskusu pri temperaturi 20 – 25 ^oC. Poskusi so trajali od 13. do 28. julija. Vsakih 24 ur, skozi 10 dni, smo beležili mortaliteto hroščev (v %) pri različnih načinih shranjevanja. Rezultate smo izrazili kot dnevno dinamiko smrtnosti z lt-p črtami in vrednostmi LT₂₅ (25 % mortaliteta je zgornja dovoljena meja za vključitev populacije v biotest).

Imagi koruznega hrošča so med 10 dnevnimi opazovanji umirali z različno dinamiko, v odvisnosti od temperature. Pri temperaturi 5 ^oC so pri obeh variantah poginili po 7 dneh vsi hrošči (100 %), pri temperaturi 12 ^oC pa po 8 dneh v žičnatih posodah in po 10 dneh v plastičnih posodah. Pri temperaturi 20 ^oC je zabeležena 100 % smrtnost hroščev po 4 dneh ne glede na način shranjevanja, pri 25 ^oC pa po 7 dneh. V laboratorijskih in poljskih poskusih smo zabeležili 100 % smrtnost hroščev po 6 dneh pri shranjevanju v plastičnih škatlah in po 9 dneh v škatlah iz žice. Pri temperaturi 12 ^oC so imagi poginjali najbolj izenačeno. Glede vpliva shranjevanja na vitalnost žuželk na podlagi vrednosti LT₂₅ ugotavljamo, da so se žuželke najdlje ohranile pri temperaturi 20 – 25 ^oC v naravnih poljskih razmerah v plastičnih škatlah, 25 % populacije je poginilo šele po 3 dnevnem shranjevanju. Poskuse s koruznim hroščem je treba postaviti takoj, ko se v ta namen zbere hrošče oziroma ne kasneje kot po 24 urah.

ABSTRACT

  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 °C, in laboratory under room temperature 19–25 °C, and in open field under 20 to 25 °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 LT₂₅ 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 °C mortality of adults reached 100% in cages and in plastic boxes after 7 days, At 12 °C the 100 % mortality was achieved in cages after 8 days and in boxes after 10 days. At 20 °C, regardless the containers 100% mortality occurred after 4 days, and at 25 °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 °C. Concluding upon LT₂₅ values, temperatures between 20 to 25 °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.