bacillus thuringiensis shelf life

[Dan Jones]

We've been plagued with squash vine borers both this year and last, and I've 
been trying to exterminate them using "Safer Caterpillar Killer", a product 
containing bacillus thuringiensis (B.t.) var. kurstaki.  I've tried both 
injecting it into the stems and spraying it onto the plants, and neither has 
been successful.

What I'm wondering about is, since this is a biological agent, how long is 
it effective?  The package has no expiration date on it.  One mixes it with 
water before use.  How long is it effective once mixed with water?

Please reply by email as well.

Thanks,

Dan Jones