Insecticidal action of the combined use of spinosad and deltamethrin against three storedproduct pests in two stored hard-wheat varieties.

The combined use of spinosad with deltamethrin against adults of Sitophilus oryzae, Sitophilus granarius and Tribolium confusum was evaluated in a series of laboratory bioassays in two hard wheat varieties (Athos and Sifnos). Two groups of bioassays were carried out. In the first group of bioassays, spinosad or deltamethrin were applied alone at the tested wheat varieties at the doses of 0.01, 0.1 and 0.5 ppm for spinosad and 0.125 ppm for deltamethrin. In the second group of bioassays, the tested wheat varieties were treated with the combination of the above spinosad rates with 0.125 of deltamethrin. In both series of bioassays, mortality of the tested species was evaluated after 7 d of exposure on the treated wheat varieties at 25oC and 65% r.h. Mortality for all species was always significantly higher in Athos than Sifnos. The highest mortality of S. oryzae (73 and 40% for Athos and Sifnos respectively) or S. granarius (88% and 58% for Athos and Sifnos respectively) was recorded in the cases that spinosad was applied alone at 0.5 ppm. On the contrary, in the case of T. confusum, 0.125 ppm of deltamethrin was significantly more effective than any of the application rates of spinosad either when applied alone or in combination with deltamethrin. Despite the fact that the highest mortality of S. granarius adults was recorded after exposure on the wheat varieties treated with 0.1 ppm of spinosad x 0.125 ppm of deltamethrin, in light of the results of the present study, the combination of spinosad with deltmethrin requires further investigation since in most of the tested cases of the present study, single application of spinosad or deltamethrin was more effective or of equal effectiveness than the respective combination of spinosad with deltamethrin. Keywords: Spinosad, Deltamethrin, Tribolium, Sitophilus, Wheat, Variety