Cost effective production of Bacillus thuringiensis aizawai and their application against Spodoptera litura
Abstract
Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) was prevalent in many species of aquatic plants grown in Green Farms. This study was carried out to understand the production of Bacillus thuringiensis aizawai (Bta) using cost effective method to manage the pest biologically. Bta is being widely used in pest control programs. However, the production of this Bta is expensive due to the high cost of the production medium. In this study, an attempt has made to develop a cost-effective medium, based on a locally available raw materials namely coconut water which is available in plenty as waste product from coconut oil industry, coconut poonac, rice bran and coir dust. A standard conventional Luria Bertani medium was included in the assay for comparison. Media were assessed for the growth, sporulation and production of insecticidal properties of Bta. Coconut poonac extract and coconut water media produced higher spores than compare with conventional LBmedium. Maximum spore count of 25.0×1013 spores/mL was obtained with a 72 hold culture of this bacterium grown in coconut poonac extract. Larvicidal activity (LC50) of 8 ×106 spores/mL (coconut poonac extract) against early second-instar larvae of S.litura were obtained. This is almost similar to that obtained with LB (9 × 106 spores/mL) medium. Hence, coconut based culture medium is economical for the production of Bta and compared favorably with the standard. Cost-effective analyses have revealed that production of Bta from test media is highly economical. The cost of production of Bta with local media was significantly reduced by 88-293 fold. The use of nonconventional sources has yielded a new knowledge in this area as the process development aspects of small scale production have been neglected as an area of research. These studies are very important from the point of media optimization for economic production of Bta based agents in pest management programs.
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Introduction
Green Farms Ltd., being one of the biggest exports oriented floriculture industry in Sri Lanka. Recently larvae of S.litura emerged as a problem in one of the aquatic plant Ludwigia repens. This larva is polyphagous, larval stages caused severe damage on the other variety of aquatic plants. The occurrence of the larvae of S.litura on aquatic plants as reported first time in the farm and being new it caused significant damage to the plant resulting to an economic loss of the export section. S. litura also becomes resistant to many commonly used insecticides, resulting in failure of effective controls (Ahmad et al., 2007). Bacillus thuringiensis (Bt) is the most successful commercial biopesticide in the biological control market (Glare and Callaghan, 2000) accounting for 90% of all biopesticides sold allover the world. This bacterium is characterized by its ability to produce crystalline inclusions proteins have a great potential to control a great number of pest insects belonging to the order Lepidoptera, Diptera and Coleoptera (Vidyarthi et al., 2002).
Cost to grow and produce Bt, through highly refined laboratory bacterial culture medium, is comparatively high than other bio agents. The cost of Btproduction depends on many factors; however, the raw material cost is one of the most important criteria, which comprises more than 70% of the overall production cost (Ejiofor, 1991). In order to encourage the commercial production of biopesticides, utilization of less expensive raw material is advisable (Mummigatti and Raghunathan, 1990).
Conclusion
Bta was successfully grown on all selected locally available media such as coconut water, coconut poonac extract, ricebran extract and coirdust extract. Coconut water and coconut poonac extract media was produced higher spores compare to standard LBmedia.
The highest number of viable spores was reached after 72 hours of growth. According to this study, the highest spore count was recorded after 72 hours of fermentation in coconut poonac extract as 25.70 × 10 13 /mL. Next highest spores count was observed in coconut water was 22.10×10 13 /mL, followed by LB (18.17 ×10 13 /mL) and coir dust extract (11.23 ×10 13 /mL). Lowest spore count was recorded in rice bran extract as 1.97×10 13 /mL after 24 hours of fermentation. The concentrations required to kill 50% of the larvae (LC50) coconut poonac extract (8.1 × 106 spores/mL) indicated that locally produced Bta media compared favorably with conventional LB (9 × 106 spores/mL) in the S.litura assays. Cost-effective analyses have revealed that production of Bta from test media is highly economical. The cost of production of Bta with local media was significantly reduced by 88 to 293 fold.
