Description of the situation regarding pollen beetle resistance to insecticides in the Czech Republic and Slovakia
Abstract: Since 2006, the resistance of pollen beetle populations to pyrethroids has been considered as a serious problem in all European countries involved in oilseed rape production and each year the problem is getting worse. In 2017, pollen beetles were collected from 55 locations in Czech Republic and 21 locations in Slovak Republic. The susceptibility of populations was tested to five different insecticides according to IRAC Susceptibility Test Methods. The tested insecticides were lambda-cyhalotrin and tau-fluvalinate from the pyrethroid group, thiacloprid from the neonicotinoid group, chlorpyrifos-ethyl from the organophosphate group and indoxacarb from the oxadiazine group of insecticides. In 2017 most of the Czech and Slovak populations showed resistance (degree 4 according to IRAC) or high resistance (degree 5 according to IRAC) to lambda-cyhalotrin. Relatively high portions of the populations also showed resistance to tau-fluvalinate, the pyrethroid which is, in some cases, perceived as the most suitable pyrethroid for use in sitations where pyrethroid resistance is a problem. Some indications of a decrease in contact susceptibility of pollen beetles to thiacloprid have also been recorded in some regions of the Czech Republic and Slovakia. There are populations which have shown significantly different reactions to the active ingredient, which indicates that some of the populations are significantly less susceptible to contact effects of the insecticide. All of the tested populations have shown high susceptibility to indoxacarb – very low doses (mostly 0.20 g a.i./ha) of the insecticide have been fully effective against the Czech and Slovak populations after 24 hours of exposure. All of the tested populations in both countries also showed high susceptibility to chlorpyrifos-ethyl. In most cases doses of about 9 g of chlorpyrifos-ethyl / ha resulted in full mortality of tested populations.