Stages of the horn fly susceptible to methoprene.

Abstract

When 3rd-instars of Haematobia irritans (L.) were exposed to 0.2 ppm methoprene, an insect growth regulator, in cow manure (larval diet), emergence of adults was inhibited 94.5%. However, there was no effect when 1st-, or 2nd-instars or when pupae were exposed to the same treatment. Likewise, no accumulative effect was noted. Apparently, enough methoprene is absorbed by the 3rd-instars so that it is carried over and causes inhibition of adult emergence.