Determination of efficacy of local diatomaceous earths collected from different regions of Turkey against stored grain insects

In this study, efficacy of local diatomaceous earths (DE) collected from different regions of Turkey was investigated against stored grain insects, rice weevil (Sitophilus oryzae (L.), the confused flour beetle (Tribolium confusum du Val.) and the lesser grain borer (Rhyzopertha dominica (F.)). For this purpose, biological tests were carried out at concentrations of 500 and 1000 ppm (mg DE / kg wheat) of 9 local diatomaceous earths and one commercial diatomaceous earth, namely Silicosec® as positive control at 25 ± 1 ° C temperature and 65 ± 3% relative humidity in wheat. In addition, the studies on some of the chemical and physical analysis of the tested diatomaceous earths (silicon dioxide (SiO2) ratio, particle size and adhesion rate on commodity) were also conducted. Laboratory analysis results showed that there were significant differences in the SiO2 ratio of the local diatomaceous earths collected from different regions of Turkey. The highest SiO2 ratio was obtained from the local diatomaceous earths collected from Aydın (FB2N-1) and Kayseri (BHN-1) provinces. The particle sizes of all local diatomaceous earths except FBN-1 ranged from 12.31 to 20.05 μm, while the particle size of the commercial formulation Silicosec® was 12.51 μm. Adherence rates of FB2N-1, ACN-1, BHN-1, CCN-1 and Silicosec® on wheat kernels were found to be 89% or <89% while adherence rates of AGCN-1 and FBN-1 diatomaceous earth ranged from 80% to 89%. In the adherence test none of the diatomaceous earths had an adherence rate below 75%.In biological tests conducted at 500 ppm concentration for 7 days of exposure in wheat, the highest mortality rates of S. oryzae and R. dominica adults were obtained from CB2N-1, AGN-1 and CCN-1 while the highest mortality rates of T. confusum were recorded in CB2N-1, AGN-1, ACN-1 and CCN-1. After 14 days of exposure at 500 ppm concentration, the highest mortality rates (97 to 98%) of S. oryzae adults were recorded in CB2N-1, AGN-1 and BGN-1, while the highest mortality rates of T. onfusum adults were obtained from only AGN-1 and BGN-1. In the case of R. dominica, the highest mortality rate (64.4%) was recorded only in CB2N-1. At concentration of 1000 ppm for 7 days of exposure in wheat, mortality rates of S. oryzae adults ranging from 92% to 100% were found in CB2N-1, AGN-1, CCN-1, ACN-1, AG2N-1 and BGN-1 while mortality rates of T. confusum adults ranging from 86% to 98% were detected in AGN-1, CCN-1 and AG2N-1. After 14 days of exposure at 1000 ppm concentration, 100% mortality of S. oryzae adults was observed in all tested local except FB2N-1 and Silicosec while mortality rates of T. confusum adults ranging from 95% to 100% were obtained in all tested local diatomaceous earths except FB2N-1, FBN-1 and Silicosec. In the case of R. dominica adults, mortality rates ranging from 80% to 93% were recorded in CB2N-1, CCN-1 and AG2N-1. In this study, it was determined that S. oryzae adults were more susceptible to tested diatomaceous earths than T. confusum and R. dominica adults, whereas the susceptibility of T. confusum and R. dominica to tested diatomaceous earths was found to be mostly similar.In conclusion, laboratory bioassays indicated that CB2N-1 and BGN-1 local diatomaceous earths had high efficacy against S. oryzae, T. confusum and R. dominica adults and thus could be a potential grain protectant for successfully control of stored grain insect pests.