This document makes several citations in its discussion of neem's effect on various pests. It references the experiment done by Dimetry, N.Z. on spider mites as well as discussing how neem affects white flies.
http://www.colostate.edu/Depts/Entomology/courses/en570/papers_1994/sclar.htmlA good point is made here about pesticide resistance and neem. Since neem oil is composed of a variety of chemicals, a mutant pest which is resistant to some aspect of neem may not be resistant to another.
The above paper also explains why neem has to be applied over and over before it actually kills off a colony. It is the combined effects of decreased chitin production, biomass, and fertility rates that eventually cause the population to crash. Spider mites are the classic example of this. It would appear spider mites move on shortly after neem is sprayed, but really all that happened is their neurological pathways are temporarily short circuited from exposure. If neem application is stopped, the spider mites come right back after they regain their composure. Instead, if the application goes on for some time, the population eventually dwindles from not being allowed to fully mature sexually.
Even though they did spell bifenthrin wrong ("binfenthrin") in this paper, it is interesting that neem was found effective on the bifenthrin-resistant white flies... just like the kind here on the north coast.
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