Insecticidal effects of the fast pyrolysis bio-oil against Spodoptera littoralis and Aphis gossypii insect pests

Abstract

The detrimental effects of agricultural pesticides on human and environmental health necessitate the development of alternatives to conventional pesticides. In the laboratory, the cotton leafworm (Spodoptera littoralis) and aphid (Aphis gossypii) insects were used to evaluate the insecticidal activity of bio-oil derived from olive cake. The application of bio-oil by leaf dipping against S. littoralis demonstrated no mortality at a concentration of 1 % bio-oil. In contrast, the bio-oil showed better results against A. gossypii by slide dip method with LC₅₀ = 1310.40 mg/l and LC₉₀ = 3117.40 mg/l. The combined activity of bio-oil and the biopesticide Beauveria bassiana (bio-oil/B.b) was comparable, with LC₅₀ = 1386.94 mg/L and LC₉₀ = 3142.05 mg/L. The field application (two sprays) of bio-oil, bio-oil/B.b, and a commercial insecticide (alpha super) on aphids revealed a reduction of 52 %, 74.33 %, and 74.67 % in the first spray and 59.67 %, 63.33 %, and73.67 % in the second spray for, bio-oil, bio-oil/B.b, and super alpha respectively. The bio-oil and bio-oil/B.b had significantly less effect on the population densities of two predators (predator mite Amblyseius swirskii and aphid lion Chrysoperla carnea) than the insecticide used. Analyses of bio-oil by gaschromatography–mass spectrometry (GC–MS) identified 30 compounds possibly have pesticidal activity. The most abundant compounds are 9 octadecenoicacid methyl ester, hexadecanoic acid, methyl ester, 6 octadecenoic acid, methyl ester and Phenol, 2methoxy. The pyrolysis byproduct (bio-oil) of olive cake biomass contains bioactive compounds that can be used as biopesticide.