The potential of Croatian diatomaceous earths as grain protectant against three stored- product insects

The objective of this study was to determine the potential insecticide efficacy of several Croatian diatomite samples (as inert dusts) against Sitophilus oryzae (Linnaeus), Tribolium castaneum (Herbst) and Rhyzopertha dominica (Fabricius) adults and to compare their efficacy with the efficacy of the USA standard diatomaceous earth (DE) Celatom Mn 51. DE Mn 51 belongs to a group of DE with medium to increased efficacy for stored agricultural products insects. Six Croatian samples from three different locations (MA-4, MR-10, MR-10B, OP-4, OP-4A and PD-1) were selected and prepared for testing with fractions of particles ≤45 µm and applied at 500 mg/kg. Insect mortality was recorded after 7 and 14 days. The highest lethal effect after 7 and 14 days showed Croatian sample MA-4 with 97 % and 100 % mortality respectively for S. oryzae, 61.5 % and 99 % mortality respectively for T. castaneum and 26.5 % and 34 % respectively for R. dominica. In all treatments the efficacy of MA-4 was in the same range with the efficacy of the standard DE Mn 51. The other five tested samples had significant lower efficacy regarding to MA-4, although after 14 days mortality was 85.7 - 98 % for S. oryzae, 5 – 47 % for T. castaneum and 2 – 5 % for R. dominica depending on a different DE sample. These results show that Croatia has potential diatomite deposits with good and promising efficiency for tested insects.