INTEGRATED VARIETAL RESISTANCE AND PLANT PRODUCTS IN THE MANAGEMENT OF Sitotroga cerealella (Olivier) (LEPIDOPTERA: GELECHIIDAE) INFESTATION IN RICE

Abstract

Twenty improved paddy rice varieties were subjected to infestation by Sitotroga cerealella (Olivier) in the Storage Technology Laboratory of Federal University of Technology, Akure, Nigeria at ambient temperature of 28±20C and relative humidity of 75±5%. Newly emerged (0- 24hours old) adult S. cerealella were used to infest the different paddy rice varieties. Morphological features of paddy rice varieties, proximate composition, anti-nutritional factors, phytochemical compositions, total phenol and amylose contents were determined according to standard procedures. Parameters such as susceptibility index, mean number of adults emerged, developmental period (days) and percentage weight loss in grains were also assessed to determine level of susceptibility. Two varieties, one from most susceptible variety category and another from moderately susceptible variety category were used to evaluate insecticidal potentials of three plant materials namely Ricinus communis, Aframomum melegueta and Helianthus annuus against S. cerealella. The plant materials of R. communis, A. melegueta and H. annuus against S. cerealella were evaluated in the laboratory by admixing leaf powders of three plants and seeds of A. melegueta (which was the only one available) and extracts with the selected two paddy varieties. The plant materials were extracted with four solvents namely ethanol, petroleum ether, acetone and n-hexane using soxhlet extraction method. Toxicity of the plant leaf and seed powders, and also the extracts were assessed daily for 72 hours based on adult insect mortality, percentage weight loss, developmental period (days) and mean number of emerged adults. Toxicological effects of the plants leaf powders of A. melegueta, R. communis and H. annus on liver and kidney function indices were assessed. Acetylcholinesterase inhibitory effect of the most potent plant, A. melegueta was carried out in an in-vivo experiment on adult S. cerealella with all leaf and seed extracts. Percentage inhibition and minimum inhibitory concentration were assessed. The result showed that the paddy rice varieties, Cisdane, FARO 36, FAROX-228-4-1-1 and BG 90/2 were least susceptible; NERICA 1, WITA 4, FARO 12, IRAT 133 and ITA 230 were most susceptible while IR-627-1-3-1-4-3-7, Sipi 692033, DE- GAULLE, TOS-103, FARO 30, MAKALIOKA 823, ITA 321, FARO 54, BG 79 and FARO 43 were moderately susceptible. Highest phytate, cyanide, oxalate, tannin, total phenol and amylose content values of 23.90 in BG 79, 0.27 in TOS-103, FAROX 228 – 4– 1 – 1, 0.46 in TOS-103, 0.82 in ITA 321, NERICA 1 and 25.58% in FARO 30 were observed in the different paddy rice varieties. All the plant leaf and seed powders significantly reduced the population of S. cerealella compared to the two controls (untreated and solvent treated controls). All the extracts at 5% concentration caused 100% mortality of adult moths after 72 hours of application in Sipi 692033 and WITA 4 paddy varieties. However, the application of the plant materials reduced the level of susceptible of WITA 4 (most susceptible) to S. cerealella with high mortality rate, reduced weight loss and increased developmental period (days) compared to the result obtained during the susceptibility experiment. There were no emerged adults in 4 and 5% petroleum ether, leaf extract of A. melegueta and 3, 4 and 5% petroleum ether extract of A. melegueta seed and 5% acetonic extract of A.melegueta seed. The plant powder and extracts could be ranked in order of effectiveness thus; A. melegueta > R. communis >H. annuus. Alkaloids, tannin, saponis, flavonoids and cardiac glycosides were among the phytochemicals present in the three plant materials. Toxicological assessment of plant materials on Albino rats showed that the group fed with 10% H. annuus inclusion of leaf powders had significantly increased values in liver biomarkers in the plasma of treated rats compared to the basal diet group (Group VII), 1 and 10% of A. melegueta, 1 and 10% R.communis. Some kidney function of Albino rats showed that urea and creatinine concentrations of rats in groups I- VI were significantly higher than those rats fed with 10% H. annuus. Histopathological sections of the treated livers and kidneys showed that rats fed with basal diets (Group VII), 1 and 10% A. melegueta, 1 and 10% R. communis and 1and 10% H annus had normal liver and kidney structure with sinusoids in place. Liver of rats fed with 10% H annuus showed distortion of the sinusoid, and slight hemorrhage while the kidney showed vacoulation of the kidney cells. Acetylcholinesterase inhibition of S. cerealella by A. melegueta leaf extracts revealed that of all the extracts used, petroleum ether leaf extract had 54.17 % inhibition at 3% concentration while at the same concentration in the seed extract, 60 71 % inhibition was observed. The effectiveness of A.melegueta extracts in inhibiting Acetylcholine in S. cerealella is rated thus: petroleum > acetone> h-hexane>ethanol It is suggested that 10% H. annuus should be used as protectant for paddy rice varieties basically meant for planting because of histopathological lesions observed at this concentration. However, since paddy rice will have to be processed through different stages before consumption, significantly low quantity of the plant powder will be found in the paddy varieties.