THE EFFECT OF DIFLUBENZURON (DIMILIN) ON THE ECDYSTEROID TITER AND NEURONAL-ACTIVITY OF PERIPLANETA-AMERICANA (L)

The insecticide diflubenzuron (DFB) affected the larval-adult development of Periplaneta americana when administered by feeding or injection. Usually, the larvae died during adult ecdysis due to the inability to split their larval cuticle. In other cases, they did ecdyse partially or completely, but died during the first day after emergence. The duration of the larval instar after DFB treatment was prolonged. By radioimmunoassay the in vitro ecdysteroid production of the prothoracic gland as well as the ecdysteroid titer of the hemolymph in different periods of the last larval instar of P. americana was determined. It was shown that the first increase of the ecdysteroid production of the molting gland during the instar was unaffected by DFB in contrast to the second peak in the ecdysteroid production, which was missing. The dose-response relationship of the effect of DFB and dimethylsulfoxide (DMSO) as the solvent of DFB on the spontaneous neuronal activity of the frontal ganglion was studied in vitro. Administration of these substances resulted in a high stimulation of the spontaneous burst activity coming from the frontal ganglion and going via nervus connectivus to the somata in the protocerebrum. The action of DFB and DMSO seems to be a direct effect on the cholin-sensitive sites at synaptic regions in addition to the inhibition of the acetylcholinesterase (EC 3.1.1.7). © 1991.