Evaluation of selected Botanicals and Diatomaceous Earth as Maize Protectant against Sitophilus Zeamias Motsch.

Abstract

The ever increasing world population requires high increase in food production andgreat assurance of food security. The food insecurity is a global crisis and FAO haswarned of increase in food prices. In Eastern and Southern Africa alone, food losses arevalued at $1.6 billion per year, or about 13.5 percent of the total value of grain production.About 35% of crops all over the world are destroyed by insect pests. Losses occur whengrain decays or is infested by pests, fungi or microbes, and physical losses are onlypart of the equation. Losses can also be economic, resulting from low prices and lackof access to markets for poor quality grain, or nutritional, arising from poor quality orcontaminated food. Maize is the main staple food in Kenya, averaging 80 % of the totalcereal. Postharvest losses in maize due to storage insect pests are generally estimated torange between 20 to 30% of which 10 to 20% of the weight losses have been by themaizeweevilSitophiluszeamaisafter 3 months storage on the farm. Attempt to control theinsectusing conventional insecticides has caused problems. They are known to leave toxicresidues,pollutes the environment and wild life coupled with high cost of production. In thisstudy,diatomaceous earth (DE) and five plants were investigated for their bioactivityagainstS. zeamais. The plants investigated include; Tagetesminuta, Chenopodium album, Artemisia absinthium, Tarchonanthuseomphoratus, Sorghum bieolorhusk and Sorghum bicolorleaves. Experiments were conducted both in the laboratory and designed on-farm trials in order to assess the insecticidal potency of botanical products. Insecticidal toxicityagainst S. zeamaisby powdered plant materials, solvent extracts (hexane, dichloromethane(DCM), and methanol), essential oil of the plants and DE was evaluated. Repellence ofthe essential oils of T. minuta, C. album, A. absinthiumand T. comphoratuswas alsoinvestigated. Further experiments were conducted on the efficacy of mixture of DE andessential oil of A. absinthium (DE/AB) against S. zeamais. The effect of the diatomaceousearth, solvent extract and essential oil on the viability of maize grains wag al~odetermined.The weight loss of the treatment was assessed in tbelaboratory after 62 days and on the fieldin 12 months period. Tbi~study has revealed that most powdered plant materials causedmortalities againstS. zeamaisless than 50% after 8 days of treatment at both 5% and 10%dose level and were significantly different from the positive control, actelic super'". Thehexane extracts of most plants displayed mortalities above 50% against S. zeamaisafter120 hours at a dose of 1.0%. DCM and methanol extracts of the plants caused mortalitiesless than 20% after 120 hours at both 0.5% and 1.0% dose level. The DE caused mortalityabove 90% against S. zeamaisat both 5% and 10% dose level both in the laboratoryand in the field trails. The weight loss of the grains treated with the actelicsuperl" was not significantly different (a = 0.05) with those of the DE, DEOITM and DEO/A.abutsignificantly different from the untreated control. The germination of the maize seeds was not affected by the treatment of the grains with DE, hexane extract and essential oils. All the germinations were significantly different (a = 0.05) from the untreated control. Theessential oil of; T. minuta, A. absinthium, C. album and T. comphoratusshowed significantrepellent activity against S. zeamaisat dose level of 0.5%. The major constituents of theessential oils T. minuta, A. absinthium, C. album and T. comphoratuswas determined byGC-MS. Thujone present in essentia~ oil of A. absinthiumand borneol in essential oil ofT. comphorarushave been reported to have bioactivity against S. zeamais. The plants aretherefore promising alternatives to the conventional insecticide for the control of storedproductpest, S. zeamais.