Triphenyl phosphate (TPP), a carboxylesterase
inhibitor, has synergized chlorfluazuron in the resistant strain of the black
cutworm but not in the susceptible strain. In vivo metabolism of ¹⁴C
– chlorfluazuron revealed that the amount of radiolabeled major metabolites
(2,6 – difluorobenzoic acid and 2,6 – difluorobenzamide) recovered from
resistant larvae  was four times higher
than susceptible larvae. Addition of TPP did not affect chlorfluazuron metabolism
pattern in the susceptible insects but it caused a significant reduction of the
amount of detected metabolites in the resistant insects. Cleavage of
chlorfluazuron molecule took place at one or both of the urea C-NH-C bonds which suggests the responsibility of
carboxyamidase enzyme for chlorfluazuron metabolism. In vitro assays
revealed that carboxyamidase activity was about four times higher in the
resistant larvae than the susceptible ones which supports the hypothesis of the
involvement of carboxyamidase in chlorfluazuron resistance in this insect pest.