ÜBER DEN SAISONDIMORPHEN ENTWICKLUNGSZYKLUS UND DIE AUFHEBUNG DER DIAPAUSE BEI ALEUROCHITON COMPLANATUS (BAERENSFRUNG) (HOMOPTERA, ALEYRODIDAE) *

Das Bestehen des von H aupt (1934) flüchtig beschriebenen Saisondimorphismus der an Spitzahorn ( Acer platanoides ) lebenden Aleyrodide Aleurochiton complanatus (Baerensprung) wird durch Beobachtungen an 14‐tägigen Stichproben aus Freilandpopvdationen geprüft. Die fast rein bivoltine Art bildet in der ersten Generation im Juli überwiegend rasch schlüpfende, zarte Sommerpuparien, in der zweiten (ab September) fast ausschließlich massive Winterpuparien, die eine echte Diapause aufweisen. Sie schlüpfen bei 20° C gar nicht, bei 15° nur teilweise und verzögert, nach mindestens einmonatiger Behandlung mit niederen Temperaturen (8°, 5°, 0°) zunehmend rascher und zu hohem Prozentsatz, im Freien erst im nächsten Frühjahr. Zu einem geringen Prozentsatz entstehen auch Winterpuparien in der ersten und Sommerpuparien zu Beginn der zweiten Generation. Der Saisondimorphismus ist also an die Diapauseinduktion geknüpft und nicht rein alternativ entwickelt. Die Verhältnisse bei dem auf Acer campestre lebenden Aleurochiton acerina Hpt. und bei dem auf Acer pseudoplanatus brütenden Nealeurochiton pseudoplatani (Visnya) werden vergleichsweise kurz beschrieben. Summary ON THE SEASONAL DIMORPHIC DEVELOPMENT AND THE TERMINATION OF PUPAL DIAPAUSE OF ALEUROCHITON COMPLANATUS (BAERENSPRUNG) (HOMOPTERA, ALEYRODIDAE) The developmental cycle of the aleyrodid Aleurochiton complanatus was studied at fortnightly intervals during 1961 in a wild population on Norway leaves ( Acer platanoides ) from a park in Quedlinburg. The seasonal dimorphism of the puparia. previously described by H auft in 1934, from a few observations, was confirmed. The species is almost completely bivoltine and forms two different puparial types: teneral, almost colourless summer puparia, which develop immediately, and mors sclerotised, dark‐coloured winter puparia with white wax patterns and strongly marked dormancy. Summer puparia are found during July, predominating in the first generation produced by the spring adults hatching from the over‐wintering puparia. A small proportion of summer puparia are also found in the next generation. The winter puparia develop mainly during late summer and are produced in the second generation. However, up to 10% of the first generation pupae are of the over‐wintering type. The winter puparia were examined for development and hatching at 20° C after exposure to 0°, 5°, 8°, 15°, and 20° for different periods. The results demonstrated the typical features of a diapause; i.e. almost complete check of development at 20° C, strong retardation and reduced hatching rate at: 15° C, rapid and complete hatching after chilling for at least one to two months at the lower temperatures. Chilling to 0° C for this period was most effective. Only when the chilling period lasted more than five months was there a significantly increased mortality. Seasonal dimorphism is thus connected with a facultative diapause. Nevertheless some individuals in each generation behave abnormally and there is some tendency to a monovoltine and a trivoltine cycle in addition to the normal bivoltinism. Breeding Aleurochiton acerina Hpt. in nylon bags on Field Maple ( Acer campestre ) showed similar results. However, under the same conditions Nealeurochiton pseudoplatani (Visnya) formed only one generation on its host, sycamore ( Acer pseudoplatanus ), due to the slow speed of development in the climate of Central Germany. It is probable that offspring of the few summer puparia, formed in the first (summer) generation, are seldom able to finish their development before the leaves wither in autumn. The normal latent seasonal dimorphism may be developed fully where favourable conditions are provided, including long day illumination and a healthy host plant, with an adequate environmental temperature.