Contents lists available at ScienceDirect Industrial Crops & Products journal homepage: www.elsevier.com/locate/indcrop Nanoemulsion of eucalyptus oil: An alternative to synthetic pesticides against two major storage insects (Sitophilus oryzae (L.) and Tribolium castaneum (Herbst)) of rice Totan Adak*, Nishant Barik, Naveenkumar Basanagouda Patil, Guru-Pirasanna-Pandi Govindharaj, Basana Gowda Gadratagi, Mahendiran Annamalai, Arup Kumar Mukherjee, Prakash Chandra Rath Crop Protection Division, ICAR-National Rice Research Institute (formerly Central Rice Research Institute), Cuttack, 753006, India ARTICLE INFO Keywords: Eucalyptus oil Nanoemulsion Sitophilus oryzae Tribolium castaneum Bio-efcacy test 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 al- ternatives. The study proposes to prepare EO nanoemulsions to improve its efcacy. Diferent 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 combi- nations, 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 (LC 50 ) of 1:2 and 1:2.5 formulated nanoemulsion eucalyptus oil against Sitophilus oryzae were 0.56 and 0.45 μL/ cm 2 , respectively and against Tribolium castaneum, it was 1.11 and 0.89 μL/cm 2 , respectively. Whereas, LC 50 of eucalyptus oil was 0.795 and 4.178 μL/cm 2 against Sitophilus oryzae, Tribolium castaneum, respectively. The formulated nanoemulsions were superior over eucalyptus oil and it can be recommended as an innocuous al- ternative to harmful chemical pesticides against stored grain pests. 1. Introduction For thousands of years, rice has been a staple food source for many parts of the world. Prolonged storage of rice is utmost important for future use and to maintain food security. Stored grain pests could cause 10% loss of harvest during storage (Shankar and Abrol, 2012). Scien- tifc storage methods can reduce these losses up to 1–2% (Kumar and Kalita, 2017). Generally, chemical pesticides are applied to manage these stored pests. But, their continuous application may arise few problems like, insect resistance, environmental pollution and handling hazards (Yuan et al., 2014; Meyer-Baron et al., 2015). There are also unintended poisoning threats to humans because of their incorrect use (Jones et al., 2014). Besides these, rice for export must be free from pesticide residue. So, novel alternatives to chemical pesticides are needed to meet new regulatory norms and consumers demand of safe food. Botanicals mainly, essential oils are being favoured for their high vapour pressure and they have broad spectrum efcacy against large number of insect-pests (Tapondjou et al., 2005; Batish et al., 2008; Rajkumar et al., 2019). Eucalyptus oil (EO) is efective against storage pests e.g. Sitophilus oryzae, Tribolium castaneum, Rhyzopertha dominica, Sitophilus zeamais etc. (Lee et al., 2004; Mossi et al., 2011). EO, especially E. globulus, is the most representative species in the international pharmacopeia (Bajaj, 1995). Pesticide property of EO is due to the presence of volatile compound “eucalyptol or 1,8-cineol”. The lethal dose (LD 50 ) of 1,8-ci- neole against S. oryzae adults were between 19.0–30.6 μL/L air and it was toxic to T. castaneum and R. dominica too (Lee et al., 2004). In another study, LD 50 s of EO were 0.36 μL/cm 2 against S. zeamais and 0.48 μL/cm 2 against T. confusum (Tapondjou et al., 2005). Despite its efcacy, use of EO is limited due to lack of better formulation. As EO is insoluble in water, it can only be used as emulsion to disinfect soil and surfaces. Particle size and stability of the emulsion is most crucial for its efcacy. The emulsions are generally susceptible to creaming, foccu- lation and phase separation due to Oswald ripening (Simonazzi et al., 2018). This study was carried out to prepare nanoemulsion of EO based on high speed homogenization technique. https://doi.org/10.1016/j.indcrop.2019.111849 Received 28 June 2019; Received in revised form 19 September 2019; Accepted 7 October 2019 ⁎ Corresponding author. E-mail addresses: totanadak@gmail.com, Totan.Adak@icar.gov.in (T. Adak). Industrial Crops & Products xxx (xxxx) xxxx 0926-6690/ © 2019 Elsevier B.V. All rights reserved. Please cite this article as: Totan Adak, et al., Industrial Crops & Products, https://doi.org/10.1016/j.indcrop.2019.111849