OCTOPAMINERGIC ACTION OF THE CARBODIIMIDE METABOLITE OF DIAFENTHIURON

DFCD or 3-(2,6-diisopropyl-4-phenoxyphenyl)-1-tert-butylcarbodiimide, a metabolite of the propesticidal thiourea diafenthiuron, stimulated adenylate cyclase activity in preparations from the bulb mite, Rhizoglyphys echinopus (Fumouze and Robin). Additivity studies with DFCD and octopamine at maximally effective concentrations suggested that both compounds were interacting with the same receptor. Cyproheptadine, chlorpromazine, phentolamine, metoclopramide, and mianserin were more potent inhibitors of DFCD- and octopamine-stimulated adenylate cyclase than were yohimbine and propranolol. DFCD had a threshold concentration of 1.0 nM and was a partial agonist with a Vmax 50% of that of octopamine. With a Ka of 0.2 μM, DFCD was 5, 40, and 500 times more potent than N′-(2,4-xylyl)-N-methylformamidine (XMF), octopamine, and N′-(4-chloro-o-tolyl)-N-methylformamidine (DMC), respectively. At high concentrations, DFCD was a partial antagonist of octopamine-stimulated adenylate cyclase activity with an EC50 of 350 μM. DFCD also caused light emission when applied to isolated male firefly, Photinus pyralis (L.), tails as did octopamine, XMF, and DMC. In firefly lantern homogenates, DFCD was a partial agonist with a Vmax 19% of that of octopamine and a Ka of 0.85 μM, a value 94 times lower than that of octopamine. Collectively, these data indicate that DFCD is an octopamine receptor agonist in some mite and insect preparations, an action that may play a role in the acaricidal and insecticidal activities of diafenthiuron. © 1991.