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University of Zimbabwe (2013)

Nouvel articleTemporal population dynamics of stored maize insect pests and efficacy of safer grain protectants in the smallholder sector of Zimbabwe

Machekano, H.

Titre : Temporal population dynamics of stored maize insect pests and efficacy of safer grain protectants in the smallholder sector of Zimbabwe

Auteur : Machekano, H.

Université de soutenance : University of Zimbabwe

Grade : MASTER OF SCIENCE IN TROPICAL ENTOMOLOGY 2013

Résumé partiel
The overall objective of the study was to establish the efficacies of different inert dusts alone and in combination with safer levels of a synthetic pyrethroid or a bio-pesticide as grain protectants. Parallel on-station ecological studies at the Institute of Agricultural Engineering (IAE), Harare, were conducted to establish sources of primary infestations that are responsible for most grain damage incurred seasonally. Results from both were integrated to advocate for the combination of the use of safe grain protectants with grain handling practices that minimise or eliminate resident infestations. The efficacies of new food grade imported diatomaceous earths (DEs) (A2 and A3), imported new DE (MN51), registered imported DE (Protect-It®) and local raw DE (Chemutsi®) combinations with spinosad (Spintordust® 0.125%) and reduced quantities of deltamethrin were tested against Prostephanus truncatus (Horn), Sitophilus zeamais (Motsch.) and Tribolium castaneum (Herbst) under controlled conditions of 27±1oC and 60±5% relative humidity. Shumba Super® dust (fenitrothion 1% + deltamethrin 0.13%) applied at 0.5 g/kg and untreated grain were used as positive and negative control treatments, respectively. Cumulative mortality data were recorded at 7, 14 and 21 days, while F1 progeny emergence was recorded at 49 (S. zeamais) and 70 (P. truncatus and T. castaneum) days after treatment. Protect-It® gave significantly higher (P < 0.001) insect mortalities than all the other DEs across all test species. Chemutsi was equally efficacious against S. zeamais with significant differences (P < 0.001) from other DE treatments except Protect-It®. In combination treatments, except for spinosad 0.5 mg/kg + Chemutsi 0.05% w/w that gave low mortality, there were no significant differences between all the treatments and the positive control (Shumba Super® dust 0.5 mg/kg) on all the three test insects. There were no significant differences in P. truncatus F1 progeny emergence across all the DE treatments. However, there were significant differences (P < 0.001) between Deltamethrin 0.05 mg/kg + Chemutsi 0.1% (w/w) and other cocktail treatments in S. zeamais progeny emergence. Out of the 31 laboratory-tested materials, Protect-It® 0.1% (w/w), Spintordust® 1 mg/kg, Spintordust® 0.3 mg/kg + Protect-It® 0.1% (w/w), Deltamethrin 0.05 mg/kg + Protect-It® 0.08% (w/w), Deltamethrin 0.05 mg/kg + Chemutsi 0.1% (w/w), Deltamethrin 0.1 mg/kg + Chemutsi 0.08 % (w/w), Deltamethrin 0.1 mg/kg + Protect-It® 0.08 % (w/w), Spintordust® 0.5 mg/kg + Chemutsi® 0.05 % w/w were further tested for 24 weeks at IAE . These treatments were compared with Shumba Super® 0.5 g/kg and untreated control. Grain damage and weight loss in the untreated control were significantly higher (P < 0.001) compared to all other treatments. On-farm trials were conducted in Musami Communal Area, Murehwa district, using five best combination treatments selected from the laboratory bioassay results. The treatments were : Chemutsi 0.08% (w/w) + Deltamethrin 0.1 mg/kg, Chemutsi 0.05% (w/w) + Spinosad 0.5 mg/kg, Chemutsi 0.1%(w/w) + Deltamethrin 0.05 mg/kg, Protect-It® 0.05% (w/w) + Deltamethrin 0.1 mg/kg, Protect-It® 0.1 % (w/w) and were compared with Chikwapuro® 0.4 g/kg (pirimiphos-methyl 2.5% w/w + deltamethrin 0.1% w/w) and untreated control. At 24 weeks after treatment, grain damage (22.5 %) and weight loss (1.96 %) in the untreated control were both significantly higher (P < 0.001) than in all other treatments.

Mots clés : grain pesticides storage structures fumigants biological phenomena topping maize storages ampling productivity

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