Chapter 9 - Oil in water nanoemulsion formulations of botanical active substances

Abstract

Water-based nanoemulsions of insecticidal botanical oils and extracts have advantages over emulsifiable concentrates and macroscopic emulsions, particularly due to the small droplet size (< 300 nm). In this chapter, we explain some concepts and present some examples of applications of nanoformulations of biopesticides. We also present some new data from our recent work on formulating plant essential oils and assessing them against the aphid species Myzus persicae (Homoptera: Aphididae). Lecithin nanoemulsions (1%, v/v) of geraniol, farnesol, and trans-anethole prepared by ultrasound maintained their activity after storage (Repellency Index = 59.6–71.6) and had Z-potential values of < 30 mV measured with a Zetasizer, indicating good stability. Repellent doses (RD50) were in the range of 0.47–2.06% (v/v). Nanoemulsions were prepared with a high speed rotor and tween80 as the surfactant. Citral gives a monodispersed nanoemulsion with 50–100 nm particles, even after dilution. Anise emulsions had at least two populations of particles, one of small sizes (20 nm in diameter) and another of 200–300 nm. When emulsified in water, cis-jasmone, the most active product, had particles of larger sizes (400 nm). Pyrethrum extract gave a reduction in RD50 from 0.131%–0.025% if a nanoemulsion was applied instead of a macroscopic emulsion in the choice laboratory bioassay with M. persicae. However, in greenhouse experiments, the number of aphids on pepper plants was not different between both treatments. Obviously, spraying pyrethrum had insecticidal effects in comparison with a control. On the other hand, the preventive application of citral or anise in pepper plants showed some repellence but only if the binary mixture at doses of 0.1%–0.2% was sprayed. A reduction in the number of aphids per plant was observed. Pyrethrum nano was less toxic to Aphidius colemani (LC90 = 0.064%) than the macroscopic pyrethrum emulsion (LC90 = 0.038%). Citral or anise was much safer for natural enemies (parasitoids) and had no residual contact toxicity up to 0.1%