INSECTICIDAL POTENTIAL OF PLANT OILS OF THREE INDIGENOUS PLANTS AGAINST FIELD INSECT PESTS OF SOLANUM SPECIES

Abstract

Solanum species are part of the Nigeria’s agrobiodiversity, grown in diverse agroecology with potential for both dietary diversity and food security. Solanum species are prone to production constraints, notably field pest infestation, which ravage the crop from the seedling to the fruiting stage, and adversely limit productivity and fruit quality. This study investigated the insecticidal potential of oil extracts sourced from three medicinal plants; Acalypha godseffiana (A. Muerg), Annona muricata (L.) and Petiveria alliacea (L.) against vegetative pest and fruit pest complex of three Solanum species; Solanum melongena (L.), Solanum macrocarpon (L.) and Solanum aethiopicum (L.). The crops were planted in a Randomized Completely Block Design (RCBD) at a spacing of 0.7 m by 0.5 m. The pest profile of the crops was documented at pre-flowering, flowering and fruiting stage. Phytochemical attributes of the plant oils were determined using standard laboratory procedures. Sub-chronic oral toxicity of the aqueous extracts of the plants was also determined using albino rat, Rattus novergicus (Berk). Standard procedures were used to determine the proximate and food composition of the Solanum fruits. Major minerals composition of eggplant fruits was determined . Compounds contained in the plant oils were assessed through Gas Chromatography – Mass Spectroscopy (GC-MS) characterization. Results from the study showed that the plant oils, most especially P. alliacea oil compared favourably with Cypermethrin 2.5 EC in terms of fruit yield and reduction of fruit damage in the respective eggplant species. There was significant interaction between the plant oils and eggplant fruit yield in Akure and Ibadan while R 2 were 0.18 and 0.20 respectively. Shoot damage ranged between 4.93-21.79%, while fruit damage ranged between 0.1- 13.93 %. Nine (9) and eighteen (18) insect species were inventoried and documented on Akure and Ibadan experimental field respectively of which eggplant shoot and fruit borer, Leucinoides orbonalis (Guenee) and short horn grasshopper, Acrae spp were noted to be the most dominant pests. Phytochemical evaluation of the plant oils yielded important phytochemicals; notably terpenoid, tannin, flavonoid, saponin, cardiac-glycoside, and alkaloid. Gas Chromatography – Mass Spectroscopy (GC-MS) characterization of the of the pooled ethanol and ethyl acetate fractions of the respective plant oils identified 48 and 51 bioactive compounds in A. godseffiana oil, 18 and 22 compounds for A.muricata while P. alliacea oil yielded 38 and 58 bioactive compounds respectively. Some of the compounds detected in the oil extracts include Hexadecanoic acid, ethyl ester, Methyl p-coumarate, TMS derivative, 9,12- Octadecadienoic acid (Z,Z)-, 2-hydroxy-1-(hydroxymethyl)ethyl ester, Benzene, 1,2,3,5- tetrachloro-4,6-difluoro- , Phenol, 2,4-dibromo- and Squalene and possesses biological properties . Furthermore, higher numbers of the bioactive compounds were yielded in ethyl acetate (polar) than ethanol (non-polar) solvent component of the plant oils. Sub - chronic oral toxicity of aqueous extract of the plant materials was assessed on albino rats. There was significant increase in the serum activities of aspartate aminotransferase (AST), alkaline phosphatase (ALP), alanine aminotransferase (ALT), total protein, albumin, urea, creatine, globulin etc. with the increasing dosage of the plant aqueous extract in comparison to the control. Animal group dosed with 50 mg/kg body weight of the plant aqueous extract compared favourably with the non-treated animals in terms of biochemical parameters exhibited.