Effects of Sublethal Doses of Contact Insecticides on Offspring Production of Different Granary Weevil Populations

Abstract

The effects of prior contact of granary weevil (Sitophilus granarius L.) parents from a laboratory population, a Belgrade Port population (selected with LD70 pirimiphos-methyl) and a Bijeljina population (selected with LD70 deltamethrin) with filter paper treated with sublethal doses (LD20 and LD50) of the insecticides dichlorvos, malathion, chlorpyrifos-methyl, pirimiphos-methyl and deltamethrin on offspring production of the surviving insects in F1 generation (after 10 weeks) and F2 generation (after 16 weeks) in untreated wheat grain was examined under laboratory conditions. Offspring reduction of laboratory weevils was highest at 96% in the F1 generation after parents’ contact with LD50 dichlorvos, and lowest in F2 generation after contact with LD50 pirimiphos-methyl with 84% more insects than in the control. The highest offspring reduction of selected weevils from Belgrade Port, 83%, was recorded in F1 generation after treatement with LD50 dichlorvos and chlopyrifos-methyl, and the lowest in F1 and F2 generations after contact with LD50 pirimiphos-methyl, around 44%. The highest offspring reduction of the selected weevils from Bijeljina, 100%, was found in F1 and F2 generations after contact with LD50 dichlorvos, malathion and deltamethrin, and the lowest again in F1 and F2 generations after contact with LD20 chlorpyrifos-methyl, in which case insect numbers were some 130% higher than in the control. The results indicate that sublethal insecticide doses, apart from a significant decrease in their efficacy against treated granary weevil populations, may also provoke an increase in insect numbers in the following generations.

U laboratorijskim uslovima su ispitani efekti prethodnog kontakta adulta – roditelja žitnog žiška (Sitophilus granarius L.) iz tri populacije: laboratorijske, Luke Beograd (selekcionisana sa LD70 pirimifos-metila) i Bijeljine (selekcionisana sa LD70 deltametrina), sa filter-papirima tretiranim subletalnim dozama (LD20 i LD50) insekticida dihlorvosa, malationa, hlorpirifos- metila, pirimifos-metila i deltametrina, na produkciju potomstva preživelih jedinki u netretiranoj pšenici u F1 (posle 10 nedelja) i F2 (posle 16 nedelja) generaciji. Najveća redukcija potomstva laboratorijskih žižaka je zabeležena u F1 generaciji nakon prethodnog kontakta adulta - roditelja sa LD50 dihlorvosa, 96%, a najslabija u F2 generaciji posle kontakta sa LD50 pirimifos-metila, gde je u odnosu na kontrolu brojnost bila veća 84%. Najveća redukcija potomstva selekcionisanih žižaka iz Luke Beograd je zabeležena u F1 generaciji prethodnim delovanjem LD50 dihlorvosa i hlorpirifos-metila, 83%, a najmanja u F1 i F2 generaciji posle kontakta sa LD50 pirimifos-metila, oko 44%. Najveća redukcija potomstva selekcionisanih žižaka iz Bijeljine zabeležena je u F1 i F2 generaciji posle prethodnog kontakta žižaka sa LD50 dihlorvosa, malationa i deltametrina, 100%, a najmanja, takođe, u F1 i F2 generaciji posle kontakta sa LD20 hlorpirifos-metila, gde je brojnost u odnosu na kontrolu bila veća oko 130%. Dobijeni rezultati pokazuju da subletalne doze insekticida, pored značajnog smanjenja njihove efikasnosti u suzbijanju tretirane generacije žitnog žiška, mogu biti i uzročnici povećanja brojnosti u budućim generacijama.