AbstractLevels of dopamine (DA) and its precursor 3‐(3,4‐dihydroxyphenyl)alanine (DOPA) in adult bulb mitesRhizoglyphus echinopus(Fumouze and Robin), after exposure for 1 and 24 h in vials precoated with an acetone solution (1.0 mg ml−1) of the amidines chlordimeform, clenpyrin, or flubenzimine, were measured by high‐performance liquid chromatography with electrochemical detection and compared with those of untreated controls. When mites were exposed to the formamidine chlordimeform, there was an initial increase in levels of DA and DOPA; after 24 h, DOPA levels were still increased, but there was a significant decrease in the levels of DA. Exposure of mites to the cyclic amidines clenpyrin and flubenzimine resulted in decreased levels of DA and DOPA at both time intervals. The effects of amidines and anilides on the metabolism of 2‐phenylethylamine (PEA) by whole homogenates of bulb mites were also examined. Degradation of PEA was inhibited by chlordimeform and some of the other formamidines, but not by the cyclic amidines clenpyrin and flubenzimine. Formanilides, that are degradation products of certain formamidines, were the most potent inhibitors of PEA metabolism. These studies provide direct evidence for the interaction of amidines with mite biogenic amines and their regulatory m