Larvicidal activities of limonoids from Turraea abyssinica (Meliaceae) on Tuta absoluta (Meyrick).
Preliminary screening of extracts of the leaves and stems of four Turraea plant species (Meliaceae) on second instar larvae of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) showed that the methanolic extract of Turraea abyssinica leaves possess good toxic potential with LD50 of 270.7 ppm. Fractionation of this extract led to isolation of a new limonoid derivative, 12α-diacetoxywalsuranolide (1) and three other known limonoids [1α,7α,12α-triacetoxy-4α-carbomethoxy-11β-hydroxy-14β,15β-epoxyhavanensin (2), 11-epi-21-hydroxytoonacilide (3), 11β,12α-diacetoxycedrelone (4)]. The structures of the compounds were established by IR, UV, mass spectrometry and 1D/2D NMR analyses, and in the case of the known compounds, also by comparison with reported data. All the isolates were tested for their larvicidal activities at different dose range against second instar larvae of T. absoluta. They were found to be more active (with LD50<7.0 ppm) compared to the reference compound azadirachtin (LD50 value of 7.8 ppm).