Efficacy of natural diatomaceous earth products from Serbia against the fifth larval instar of Plodia interpunctella (Lepidoptera: Pyralidae)

Abstract: The aim of this study was to evaluate the insecticidal efficacy of natural diatomaceous earths (DE) from Serbia against the 5th larval instar of laboratory population of Plodia interpunctella (Hübner, 1813). We used two natural DE products mined in Kolubara region, S-1 (containing 78.8% of SiO2) and S-2 (containing 63.2% of SiO2). Registered product Protect-It® (containing 83.7% of SiO2) (Hedley Technologies Inc., Canada) was used for comparison. Evaluation of DEs efficacy was conducted on broken maize kernels, at 27 ± 1 °C and 60 ± 5% r.h., by following modified methods of OEPP/EPPO (2004). All three DE products were tested at rates of 0.5, 1.0 and 1.5 g/kg. Efficacy was evaluated after 2, 4, 7 and 14 days of larval contact with treated maize kernels. Two, four and seven days after the treatment, mortality was low (less than 10% in DE S-1 and S-2, and 30% in Protect-It® tests). The highest mortality was recorded 14 days after the treatment. Depending on application rate, it was found to range: 23.5-28.5% (DE S-1), 24.0-34.5% (DE S-2) and 34.0-66.0% (Protect-It®). The efficacy of tested DE products was affected significantly by exposure period, less by type of DE and the least by tested concentrations. Results indicate that two tested natural diatomaceous earth products from Serbia have low insecticidal potential for control of the 5th larval instar of P. interpunctella, due to fast larval change into the pupal stage, induced by the treatment.