Efficacy of Spinosad and Abamectin against Different Populations of Red Flour Beetle (Tribolium castaneum Herbst) in Treated Wheat Grain

Abstract

The efficacy of spinosad and abamectin against T. castaneum adults from a laboratory population with normal susceptibility to contact insecticides and against malathion-resistant populations from Nikinci and Jakovo was tested in the laboratory (25±1ºC and 60±5% r.h.). The insecticides were applied to 500 g of untreated wheat grain for each of the following application doses: 0.25, 0.5, 1.0, 2.5 and 5.0 mg a.i./kg. After treatment, wheat was divided into three equal subsamples and 50 T. castaneum adults from each of the three test populations were released the next day into jars for each dose. Mortality was evaluated after 7, 14 and 21 days of exposure to treated wheat grain. Generally, higher concentrations and longer exposure periods resulted in higher efficacy of both insecticides, but abamectin was significantly more effective than spinosad against all three tested populations. After 7 days of exposure, mortality did not exceed 30% in any test variant. Fourteen days after treatment with the highest dose (5 mg/kg) of spinosad, mortality was highest (75%) in the laboratory population, while treatment with the same dose of abamectin achieved the highest mortality (58%) in the laboratory and Jakovo populations. After 21 days, spinosad applied at the rate of 5 mg/kg was most effective (97% mortality) in the laboratory population, while 88% efficacy was recorded in Jakovo population and 87% in Nikinci population. Abamectin doses of 2.5 and 5 mg/kg caused high adult mortality of 94-100% in the laboratory and Jakovo populations, and a significantly lower mortality in Nikinci population (75 and 86%, respectively). Statistically significant differences in the efficacy of spinosad, and particularly of abamectin, were detected among the three tested populations, the greatest difference being between the laboratory and Nikinci populations, which clearly indicates that resistance of T. castaneum adults to malathion had a significant influence.

U laboratorijskim uslovima (25±1ºC i 60±5% r.v.v.) je ispitivana efikasnost spinosada i abamektina za adulte kestenjastog brašnara iz laboratorijske populacije, normalno osetljive na kontaktne insekticide, i populacija Nikinci i Jakovo, rezistentne na malation. Za sve testirane populacije insekticidi su naneti na po 500 g netretirane pšenice u zrnu u istim dozama: 0,25; 0,5; 1,0; 2,5 i 5,0 mg a.m./kg. Posle nanošenja insekticida tretirana pšenica je deljena na tri jednaka dela da bi sutradan u svaku ispitivanu količinu, posebno, bilo ubacivano po 50 adulta kestenjastog brašnara svih testiranih populacija. Smrtnost je utvrđivana posle 7, 14 i 21 dana izlaganja u tretiranoj pšenici u zrnu. Generalno, sa povećanjem doza i intervala izlaganja povećava se efikasnost oba insekticida, s tim da je abamektin značajno efikasniji od spinosada za sve tri testirane populacije. Posle 7 dana izlaganja ni u jednoj ispitivanoj varijanti nije utvrđena smrtnost veća od 30%, dok je posle 14 dana najveća smrtnost utvrđena kod laboratorijske populacije (75%), u pšenici tretiranoj najvišom dozom (5 mg/kg) spinosada, dok je tretman istom dozom abamektina najveću smrtnost (58%) prouzrokovao kod laboratorijske i populacije Jakovo. Posle 21 dana spinosad je najveću smrtnost ostvario primenom doze od 5 mg/kg kod laboratorijske populacije (97%), a zatim kod populacija Jakovo (88%) i Nikinci (87%). Abamektin je u dozama 2,5 i 5 mg/kg prouzrokovao visoku smrtnost (94-100%) adulta iz laboratorijske i populacije Jakovo i statistički značajno nižu smrtnost adulta iz Nikinaca (75 i 86%). Utvrđene statistički značajne razlike u efikasnosti spinosada i posebno abamektina, između testiranih populacija, gde su najznačajnije razlike utvrđene između laboratorijske populacije i populacije Nikinci, jasno pokazuju da rezistentnost adulta kestenjastog brašnara na malation značajno utiče na efikasnost spinosada i, posebno, abamektina.