ALTERNATIVE BIOASSAY TECHNIQUE TO MEASURE ACTIVITY OF CRY-III PROTEINS OF BACILLUS-THURINGIENSIS

Problems in reproducibility of results of the standard dip-leaf bioassay using the subspecies tenebrionis of Bacillus thuringiensis Berliner on Leptinotarsa texana Schaeffer, indicated the necessity for development of an alternative technique. The alternative technique is based on the inverse relationship of dose and weight gain of starved L. texana 3rd instars. Individuals avidly ingested a 2-mu l B, t, tenebrionis sucrose droplet and were reared on natural diet for 48 h. Linear regression analysis estimated ED(50)s (effective dose for 50% response) compared with weight gain of untreated individuals. Correlation coefficients > 0.9 were always obtained. Reproducibility between bioassays was very high, despite the low number of treated individuals (10 per dose). Bioassay time was reduced from 4 d to only 48 h.