An Example in Washington: How Effective is Foray 48B?
In Washington state, a small infestation (29 acres, less than 80 moths in total trapped) of EGM in a rural town (Vader) was treated with Foray48B in the spring of 2001. Trapping data showed that the treatment was not completely effective – the infestation grew somewhat in size geographically. The Dept. of Agriculture’s answer is to aerially treat a square mile with the same Foray 48B again. Statistically, this might well be effective (and devastating to a number of insects outside of gypsy moths as well as possibly dangerous for the human population, not to mention costly to the taxpayers), but this incident shows that btk-based insecticides are fallible and probably perform no better than disparlure. By the WSDA’s own figures, since 1974 almost one in four aerial treatments has failed to eradicate gypsy moths in Washington.
It is actually quite possible that ballooning or bad timing of the application allowed this infestation to spread even though Foray 48B, which attacks the larval stage, was used. One could even postulate that had the WSDA used disparlure, this infestation might not have spread as it did, and certainly would be no worse than it is today.