EFFECTIVENESS OF SOME BOTANICAL INSECTICIDES IN THE MANAGEMENT OF PLODIA INTERPUNCTELLA (HÜBNER) (LEPIDOPTERA: PYRALIDAE) IN MAIZE GRAINS

Abstract

This study investigated the effects of powders and ethanolic oil extracts of five plants, Cleistopholis patens (Benth.), Lantana camara (Linn.), Morinda lucida (Benth.), Plumbago zeylanica (Linn.) and Thevetia peruviana (Linn.) as contact and fumigant options in the management of Indian meal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) infesting stored maize grains. Pulverized powders from the plants were administered at 0.5, 1.0, 1.5, 2.0 and 2.5g dosages while the oils were administered at 5, 10, 15, 20 and 25 % concentrations. The powders and oils were set up in three replicates with a control sample in each case. Mortality rates were assessed at 24, 48, 72 and 96 h post treatment exposures at ambient temperature of 28±2ºC and 75±5% relative humidity in Completely Randomized Design. Column fractions from the selected plants were separated using column chromatography, then thin-layer chromatography to merge the similar fractions before subjecting them to GC-MS analysis. The column fractions from the botanicals were tested on the egg and larval stages of the moth in order to determine their insecticidal potentials. Further step was taken to examine the mode of action of the active compounds of the botanicals against some molecular targets in the moth using gene expression method. The mRNA expression of the target proteins were evaluated using reverse transcriptase PCR (RT-PCR) and the gene expressions/ bands resulting from agarose gel electrophoresis were quantified by image J software. An application of 1.0g of the stem powder of C. patens achieved 0% egg hatchability and adult emergence, 100% larval and adult mortalities at rates 1.5g after 96h post-treatment were also achieved. The contact toxicity of L. camara leaf powder achieved 82.81 and 84.11% respectively when used as powder and oil in the control of the larval stage of the moth. Leaf, stem bark and root bark of M lucida achieved 0.00% egg hatchability and adult emergence. Dosages ranging from 1.0 to 1.5g powder and 10 to 15% oil extract completely inhibited egg hatchability and yielded 100% larval and adult mortalities. A dosage of 2.0g of leaf powder achieved 0.00% egg hatchability and adult emergence. P. zeylanica root bark powder and oil extract achieved 0.00% hatchability and adult emergence at dosages ranging from 1.0 and 2.0g powder and 10 to 20 % oil extract, 100% larval and adult mortalities were also achieved at the same dosage range. T. peruviana contact powder treatment yielded 65.36% and 56.67% larval and adult mortalities respectively, while the fumigant oil treatment achieved 75.93 and 73.43% larval and adult mortalities respectively after 96h exposures. Results from GC-MS analysis of this study have revealed Caryophyllene, Humulene, Octadecanoic acid, Hexadecanoic acid, Neophytadiene, Azulene and Demacrene D (among others) which cut across the prominent botanicals as major active compounds responsible for the insecticidal activities of the botanicals. Fractions from C. patens, M. lucida and P. zeylanica completely inhibited egg hatchability and adult emergence. They also achieved 100% larva and adult mortalities between 24 and 48 hours post-treatment. The botanicals were observed to induce repellence, deterrence and reduced palatability. Findings from this study also shows that the active compounds displayed alteration of protein availability, enzyme inhibition and direct toxicity to the moth, resulting in the mortalities of the adults. The metabolites from C. patens, L. camara, M. lucida and P. zeylanica inhibited Calcium-independent phospholipase A2 pi-PLA2 enzymatic activities in the moth as revealed by mRNA gene/tissue expression profile using electrophoresis machine. Based on these results, it could be concluded that the plants used in this study are effective in the control of the developmental stages of Plodia interpunctella. It is therefore recommended that The Federal Government should educate and motivate the local farmers to cultivate the plants for pest management purposes.