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

Problems in reproducibility of results of the standard dip-leaf bioass ay using the subspecies tenebrionis of Bacillus thuringiensis Berliner on Leptinotarsa texana Schaeffer, indicated the necessity for develop ment of an alternative technique. The alternative technique is based o n the inverse relationship of dose and weight gain of starved L. texan a 3rd instars. Individuals avidly ingested a 2-mu l B, t, tenebrionis sucrose droplet and were reared on natural diet for 48 h. Linear regre ssion analysis estimated ED(50)s (effective dose for 50% response) com pared with weight gain of untreated individuals. Correlation coefficie nts > 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.