Bioactivity of brassica seed meals and its compounds as ecofriendly larvicides against mosquitoes

Abstract

Strategic, sustainable, and ecofriendly alternatives to chemical pesticides are needed to effectively control mosquitoes and reduce the incidence of their vectored diseases. We evaluated several Brassicaceae (mustard family) seed meals as sources of plant derived isothiocyanates produced from the enzymatic hydrolysis of biologically inactive glucosinolates for the control of Aedes aegypti (L., 1762). Five defatted seed meals (Brassica juncea (L) Czern., 1859, Lepidium sativum L., 1753, Sinapis alba L., 1753, Thlaspi arvense L., 1753, and Thlaspi arvense-heat inactivated and three major chemical products of enzymatic degradation (allyl isothiocyanate, benzyl isothiocyanate and 4-hydroxybenzyl isothiocyanate) were assayed to determine toxicity (LC₅₀) to Ae. aegypti larvae. All seed meals except the heat inactivated T. arvense were toxic to mosquito larvae. L. sativum seed meal was the most toxic treatment to larvae (LC₅₀ = 0.04 g/120 mL dH₂O) at the 24-h exposure. At the 72-h evaluation, the LC₅₀ values for B. juncea, S. alba and T. arvense seed meals were 0.05, 0.08 and 0.1 g/120 mL dH₂O, respectively. Synthetic benzyl isothiocyanate was more toxic to larvae 24-h post treatment (LC₅₀ = 5.29 ppm) compared with allyl isothiocyanate (LC₅₀ = 19.35 ppm) and 4-hydroxybenzyl isothiocyanate (LC₅₀ = 55.41 ppm). These results were consistent with the higher performance of the benzyl isothiocyanate producing L. sativum seed meal. Isothiocyanates produced from seed meals were more effective than the pure chemical compounds, based on calculated LC₅₀ rates. Using seed meal may provide an effective method of delivery for mosquito control. This is the first report evaluating the efficacy of five Brassicaceae seed meals and their major chemical constituent against mosquito larvae and demonstrates how natural compounds from Brassicaceae seed meals can serve as a promising ecofriendly larvicides to control mosquitoes.