First results of the monitoring of the resistant pollen beetles (Meligethes aeneus Fabricius 1775) occurrence in the Czech Republic

Abstract: Laboratory experiments were conducted to test effects of the active substances of two different pyrethroids on imagos of the pollen beetle (Meligethes aeneus Fabricius 1775) collected in various areas of the Czech Republic in 2008. The tested pyrethroids were: lambda-cyhalothrin as a specimen of the ester pyrethroids (type II) and etofenprox as a specimen of the other group of pyrethroids (type I, ether pyrethroids). An adult-vial-test (IRAC Susceptibility Test Method No. 11) was used.The pyrethroids were applied in the glass tubes (internal surface area: 37.97 cm2). The lambda-cyhalothrin was applied as four doses: 0 μg cm-2 (acetone only); 0.003 μg cm-2 (4% of the European field application rate of 7.5 g a.i. ha-1); 0.015 μg cm-2 (20% rate); 0.075 μg cm-2 (100% rate). The etofenprox was also applied as four doses: 0 μg cm-2 (acetone only); 0.016 μg cm-2 (4% of the Czech field application rate of 40 g a.i. ha-1); 0.080 μg cm-2 (20% rate); 0.400 μg cm-2 (100% rate). The collected insects were exposed to the dried residues of the insecticides for up to 24 hours. The response of beetles were assigned into one of four categories in accordance to their reactions to the insecticidal residues after 1, 5 and after 24 hours from the beginning of the tests. The active imagos without any symptoms of insecticide affect were assigned to category 4, imagos with slight symptoms (retained ability to move the legs) were assigned to category 3, severely affected beetles (immobility, tremor) were assigned to category 2 and dead imagos were assigned to category 1.Significant differences were found among the reactions of the pollen beetles originating from the compared localities to lambda-cyhalothrin applied at the 100% rate. The differences in the lambda-cyhalothrin effectiveness expressed in accordance to Abbott exceeded 50% among the different localities. Conversely, there were no significant differences between the reactions of the pollen beetles originating from the five compared localities to the etofenprox applied at the 100% rate. The differences in the etofenprox effectiveness expressed in accordance with Abbott (and in the pollen beetles mortalities) were minor between the compared localities. On the base of other analyses, it is also possible to conclude that the localities where the beetles showed significantly different reactions.