Utilization of lablab bean (Lablab purpureus) and palm sugar (arengapinnata) as natural medium to grow Mataram indigenous isolateof entomopathogenic Bacillus thuringiensis for controlling Aedes aegypti larvae

Abstract

The purpose of the study was to grow Lombok Island indigenous isolate of entomopathogenic Bacillus thuringiensis using some combinations of lablab bean (Lablab purpureus) as protein source and palm sugar (Arengapinnata) as carbohydrate source and to test its toxicity against Aedes aegipty 3rd instar larvae. This study used entomopathogenic B. thuringiensis isolate Bt-TP2B, locally isolated from soil in Mataram City. Lablab bean was mixed with palm sugar and water to form liquid medium. The based concentration for lablab bean and palm sugar was 50 g/L each. The medium was made into four weight-based concentration combinations, which were 1:1; 1:3: 1:5 and 1:7, respectively. NYSM (Nutrient broth Yeast Extract Salts Medium) supplemented with Amoxicillin was used as standard medium. Six hundred of 3rd Aedes aegypti instar were used as target in toxicity test. The test was performed in 5 culture dilutions (10-1 to 10-5 dilutions) against A. aegypti larvae. Larvae mortality was recorded in 24, 48 and 72 hours observation. Lethal concentration values were calculated using Probit Analysis. The highest cell concentration was reached by B. thuringiensis grown in 1:1 combination medium (5.95 x 107 cell/mL). Almost all B. thuringiensis grown in natural and NYSM medium showed decreasing trend within 72 hours incubation. Only 1:1 combination medium showed increasing trend from 24 to 72 hours incubation. The highest endospore concentration was reached at 4.32 x 108 endospore/mL by 1:1 combination medium in 72 hours incubation. All medium showed increasing trend within 72 hours incubation. The lowest LC50 value was reached by 1:7 combination medium (1.44 x 105 cell/mL) and the lowest LC90 value was reached by 1:5 combination medium (9.06 x 105 cell/mL). We concluded that lablab bean mixed with palm sugar can be used to grow Lombok indigenous isolate of entomopathogenic B. thuringiensis to substitute standard/industrial medium with almost similar toxicity.