Larvicidal activity of inhibitors of DOPA decarboxylase on the Australian sheep blowfly, Lucilia cuprina.

Inhibitors of DOPA decarboxylase, the key enzyme in the formation of the sclerotizing agent (N-acetyl dopamine) of the blowfly cuticle, have been tested for larvicidal activity against L. cuprina. A significant level of DOPA decarboxylase activity has been shown to be present throughout larval life in this species. Four potent in vitro inhibitors of L. cuprina larval DOPA decarboxylase (carbidopa, benserazide, methyl tyrosine and methyl DOPA) have been shown to be effective larvicides when fed to first- or second-instar larvae. However, no correlation is seen between the apparent Ki and LD50 values for these compounds. Treated larvae are observed to die at the next moult but death can be averted by the addition of N-acetyl dopamine to the food. Thus the toxic effects of the DOPA decarboxylase inhibitors appear to result from an inhibition of the formation of the sclerotizing agent in the cuticles of treated larvae.