Nanoemulsion of eucalyptus oil: An alternative to synthetic pesticides against two major storage insects (Sitophilus oryzae (L.) and Tribolium castaneum (Herbst)) of rice

Abstract

The residue of chemical pesticides used against storage insects may cause health hazards. Hence, alternative management of storage insects of rice is the need of the hour and eucalyptus oil (EO) is one of the safer alternatives. The study proposes to prepare EO nanoemulsions to improve its efficacy. Different combinations of EO, surfactant (Tween 80) and water, were homogenized at high speed to obtain nanoemulsion. Based on centrifugation, thermodynamic stability, heating and cooling, freezing and thawing experiments, two combinations, 1:2 and 1:2.5 (EO: Tween 80) of 6% EO concentration were optimum to formulate nanoemulsions. The droplet sizes of nanoemulsions were 4.04 nm and 2.27 nm and poly dispersity index (PDI) were 0.37 and 0.77 and zeta potential were 6.20 mV and 7.69 mV, respectively for these two combinations. Lethal concentration (LC50) of 1:2 and 1:2.5 formulated nanoemulsion eucalyptus oil against Sitophilus oryzae were 0.56 and 0.45 μL/cm2, respectively and against Tribolium castaneum, it was 1.11 and 0.89 μL/cm2, respectively. Whereas, LC50 of eucalyptus oil was 0.795 and 4.178 μL/cm2 against Sitophilus oryzae, Tribolium castaneum, respectively. The formulated nanoemulsions were superior over eucalyptus oil and it can be recommended as an innocuous alternative to harmful chemical pesticides against stored grain pests.