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When the larvae of Porthetria dispar, Lymantria monacha and Boarmia bistortata were fed on a diet containing lethal doses of the moulting inhibitor, Dimilin (Diflubenzuron), no histological changes were detected in their internal tissues, mainly the mid gut, muscles, fat bodies and Malpighian tubules. The development of the testes and succession of spermatogenesis in L. monacha were not affected by this compound. Some histological effects were detected in the integument of the treated larvae of the 3 tested species. The endocuticle that was formed after treatment was not properly attached to the epidermis and showed globules of apparently coagulated material mainly protein. Chemical analysis of the integument in P. dispar indicated that the chitin deposition in the endocuticle was quantitatively reduced by about 33% after treatment with Dimilin. The lipid content increased in treated larvae which might reflect a reduced rate in the synthesis of glucose in the haemolymph to chitin. On the other hand, protein content was completely unaffected. These findings revealed that Dimilin has a specific mode of action which interferes with the rate of chitin deposition in the endocuticle. The newly formed cuticle becomes less rigid and therefore it cannot withstand the internal pressure during ecdysis or give sufficient support to the muscles involved in ecdysis and thus resulting in an inability to cast the exuviae and finally in death. The results proved that Dimilin at all tested concentrations did not resemble in properties the conventional insecticides. The symptoms induced to the larvae of the tested species after treatment with this compound were discussed. Lethal doses caused death of the treated larvae during ecdysis. At lower doses, the compound induced developmental retardation and few deformities and in this view it resembled to a little extent the juvenile hormone analogues. Zusammenfassung Über die Wirkungsweise von Dimilin als Häutungshemmer bei einigen Schmetterlingsarten Raupen von Lymantria dispar, Lymantria monacha und Boarmia bistortata wurden auf einem Kunstfutter gezüchtet, dem der Entwicklungshemmer Dimilin in letaler Dosis zugegeben war. Bei allen drei getesteten Arten war zu beobachten, daß die Mortalität ausschließlich während der Häutung auftrat. Doch waren zwischen den Arten einige Reaktionsunterschiede festzustellen, die im einzelnen näher beschrieben werden. Wie histologische Untersuchungen ergaben, konnten an den inneren Organen wie Mitteldarm, Fettkörper, Muskeln und Malipighischen Gefäßen keine Veränderungen beobachtet werden. Die Entwicklung der Keimdrüsen und die Spermatogenese wurde bei L. monacha, die daraufhin näher untersucht wurde, durch Dimilin nicht beeinträchtigt. Dagegen wurden einige histologische Veränderungen im Integument bei allen drei Arten festgestellt. Während die Epi‐ und Exocuticula nach Dimilineinwirkung keine Schäden zeigten, wies die neu gebildete Endocuticula einige pathologische Veränderungen auf. So waren Endocuticula und Epidermis voneinander losgelöst, w...

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Investigations into the flight behaviour of the male nun moth (Lymuntriu monucka L.) in different forest areas with the aid of electronic data recording equipment were carried out using pheromone baited traps. It was shown that according to the geographical area in which the observations were made, independent, however, from the type of forest, clear differences in the times of flight activity exist. These differences were maintained over an observation period of 2 years.