Larvicidal activity of Copaifera sp. (Leguminosae) oleoresin microcapsules against Aedes aegypti (Diptera: Culicidae) larvae

Abstract

Studies have demonstrated the potential of Copaifera sp. oleoresin to control Aedes aegypti proliferation. However, the low water solubility is a factor that limits its applicability. Thus, the micro- or nanoencapsulation could be an alternative to allow its use in larval breeding places. The purpose of this study was to evaluate if achievable lethal concentrations could be obtained from Copaifera sp. oleoresin incorporated into polymers (synthetic or natural) and, mainly, if it can be sustained in the residual activity compared to the pure oil when tested against the A. aegypti larvae. Microcapsules were prepared by the process of emulsification/precipitation using the polymers of cellulose acetate (CA) and poly(ethylene-co-methyl acrylate) (PEMA), yielding four types of microcapsules: MicPEMA₁ and MicPEMA₂, and MicCA₁ and MicCA₂. When using only Copaifera sp. oleoresin, the larvicidal activity was observed at concentrations of LC₅₀ = 48 mg/L and LC₉₉ = 149 mg/L. For MicPEMA₁, the LC₅₀ and LC₉₉ were 78 and 389 mg/L, respectively. Using MicPEMA₂, the LC₅₀ was 120 mg/L and LC₉₉ > 500 mg/L. For microcapsules MicCA₁ and MicCA₂, the LC₅₀ and LC₉₉ were 42, 164, 140, and 398 mg/L, respectively. For a dose of 150 mg/L of pure oleoresin, the residual activity remained above 20% for 10 days, while the dose of 400 mg/L remained above 40% for 21 days. The MicPEMA₁ microcapsules showed a loss in residual activity up to the first day; however, it remained in activity above 40% for 17 days. The microcapsules of MicCA₁ showed similar LC₅₀ of pure oil with 150 mg/L.