Efekti insekticida prirodnog porekla na Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) / Effets of insecticides of natural origin on lasser grain borer (Rhyzopertha dominica Fabricious Coleoptera: Bostrichidae) and quality of stored small grains

In this study was examined the potential of synthetic insecticides of the natural origin of spinosad, abamectin and three diatomaceous earths - DEs (two originated from Serbia designated as S-1 and S-2 and one commercial formulation Protect-It) on Rhyzopertha dominica in small grains. The research was conducted in three rates/doses for every tested insecticide and the effect of their application, as well as the effect of infestation of R.dominica on certain physical and chemical traits of small grains, was also examined. Moreover, rheological properties of flours of wheat, triticale and rye obtained from three groups of grains (treated with DEs; treated and infested; non treated, but infested with R. dominica) were evaluated through the application of Glutopic and Mixolab. With an application of synthetic natural insecticides spinosad and abamectin in doses of 0.25, 0.5 and 1.0 mg/kg, the percentage of mortality R. dominica was 100%, after 21 days exposure. In addition, it wasn't noted the emergence of progeny, as well as no impact on particular chemical traits (moisture, protein and ash contents). The efficacy of applied DEs (S-1, S-2 and Protect-It) on the mortality percentage of R. dominica has differed according to exposure period, type of grain and application rate. In the relation to the type of grain, the lowest efficacy was recorded in triticale and rye treated with 0.5 g/kg. The present study showed that DEs from Serbia achieved efficacy of 94-100% against R. dominica exposed for 21 days to the highest application rate of 1.5 g/kg in alltest grains, and that efficacy was either not significantly different or only slightly different from the efficacy of 1 g/kg of Protect-It, such that DE S-1 may be considered as having good insecticidal potential. Efficacy of DE S-2 was at the same significance level, but only in wheat and barley. High levels of progeny reduction of ≥ 95% were found in small grains treated with 1.0 and 1.5 g/kg of Protect-It, and 1.5 g/kg of DEs from Serbia. The lowest dockage weight were found in all grains at treatment rates of of 1.0 and 1.5 g/kg of three DEs, and the highest in wheat and rye treated with 0.5 g/kg DEs from Serbia. The highest adherence on kernels of all three DEs was found in wheat and oats, from 95 to 83%, while the lowest adherence was found in rye and triticale, from 77 to 59%. Significant reduction in hectolitre mass after treatments with DEs was detected in all grains. Protect-It caused the highest reduction (3,6%-8,8%). The changes in grain moisture, protein or ash contents are not caused by DEs, these are due to the activity of R. dominica. Values of the wet gluten and the gluten index were unchangeable within tested wheat varieties, while these values were changed for triticale because of application of DEs. In case of determination of rheological behavior of samples applied to Glutopic, is not established significant impact of DEson value of maximum resistance, while the impact of DEs on time forming maximum pik was different in relation to the species (wheat and triticale grains), but also in a relation to the variety. Dough testing of grain samples with Mixolab has shown that the effect of usage of DEs was different in relation to the species, as in relation to variety within the same species. In samples with a smaller quantity and lower quality of gluten, the impact of DEs is more pronounced on Mixolab parameters which determine rheological characteristics of proteins. The effect of the application of DEs on parameters which determine rheological traits of starch is not recorded for the wheat variety Planeta, unlike other tested varieties and species. Untreated grain samples, infested with R. dominica, in relation to the other tested samples, had shown the biggest change in technological features of tested species and varieties.