Abstract
Stem borers (Chilo partellus) are important field insect pests of maize (Zea mays L.) and sorghum (Sorghum bicolor L.) in Africa. They account for more than 30% yield losses depending on the composition of the pest community. C. partellus larvicide like Bacillus thuringiensis have been widely and effectively used in C. partelluscontrol programs, but the industrial production of theses bacilli is expensive. Here we have attempted to develop three cost-effective media, based on legumes, potato, and whey. Growth and production of the insecticidal proteins from these bacteria were satisfactory; protein concentration yields of 27.60 mg/ml, spore counts of 5.60 × 108 CFU/ ml and first-instar Chilo partellus larvicidal activity (LC50) of 78 µg/l were obtained with a 72 h culture of this bacterium. Therefore, this investigation suggests that legume, potato and whey-based culture media are more economical and effective for the industrial production of B. thuringiensis insecticidal crystal proteins. Key words: Bacillus thuringiensis, larvicidal, Chilo partellus, insecticidal crystal proteins, LC50, optical density,sulphate polyacrylamide gel electrophoresis (SDS-PAGE), spore counts.
Highlights
In Kenya, the spotted stem borers (Chilo partellus) destroy an estimated 400,000 metric tons or 13.5% of farmers annual harvest of maize costing about >US$72 million (De Groote, 2002)
To derive full benefit from the Bt based biopesticides, there is a need for studying influence of carbon-source from cost-effective raw materials on growth, sporulation and crystal protein production by local Bt strains that would be used as biopesticides for the indigenous crops
Almost complete separation of the endotoxin protein crystals from the spores and cell debris was achieved by decantation of the frothy spent culture and high speed centrifugation at 10,000 rpm where the crystals formed a white pellet at the bottom of the tube leaving the spores and cell debris in the supernatant fraction
Summary
In Kenya, the spotted stem borers (Chilo partellus) destroy an estimated 400,000 metric tons or 13.5% of farmers annual harvest of maize costing about >US$72 million (De Groote, 2002). The management of C. partellus has largely been based on chemicals, which are rarely effective due to misuse and resistance development by the pest (Camilla, 2000). Bt synthesizes an insecticidal cytoplasmic protein inclusion during the stationary phase of its growth cycle (Pena et al, 2007). These crystalline inclusions comprise relatively high quantities of one or more glycoproteins known as delta-endotoxins or cryotoxins (Schnepf et al, 1998). To derive full benefit from the Bt based biopesticides, there is a need for studying influence of carbon-source from cost-effective raw materials on growth, sporulation and crystal protein production by local Bt strains that would be used as biopesticides for the indigenous crops
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