Ips typographus juponicus is the most devastating pest of Picea jezoensis and P. glehnii in Japan. In endemic condition, egg gallery density under bark seemed to have an upper limit at about 200-300. In outbreaks after a strong ty hoon, beetles produced in windfalls attacked and killed trees. In those beetle-killed trees, egg galtry density reached a high level of 700-1100 and both body size and reproductive rate of the population was remarkably reduced. The change in the upper limit of attack density, which must be caused by the behavioural changes of free-living adult beetles at high density levels, seems to play an important part in bringing the population back down to an endemic level.

The autumnal population of the maple aphid, Periphyllus californiensis Shinji starts in October when aestivating larvae become active. The aphid utilized the key‐fruits of maple trees in October, the leaves in November and the twigs in December. Winged females appeared in November and dispersed. This dispersal spreaded the autumnal population over almost all host trees on which the aphid population had disappeared in the previous summer. Though the aphid is autoecious, some individuals on such trees that shed their leaves before mid‐November had to disperse to other trees in order to produce oviparae after mid‐November. Many winged females reproduced offspring on the trees whose foliage was orange‐yellow in hue, but while only a few reproduced on the trees whose foliage was red. The autumnal color of maple trees is an important factor which keeps some maple trees free from aphid infestation in autumn. Zusammenfassung Wirtswahl und Populationsdynamik bei einer Herbst‐Population der Ahorn‐Blattlaus, Periphyllus californiensis Shinji (Hom., Aphididae) P. californiensis beginnt ihre Populationsaktivität im Oktober mit den Larven der Aestivales. Die Blattläuse saugen an den Ahornfrüchten im Oktober, den Blättern im November und den Zweigen im Dezember. Geflügelte Weibchen erscheinen im November und breiten sich aus. Der Dispersionsflug verteilt die Herbst‐Population nahezu über alle Wirtsbäume, von denen die Blattlauspopulation im vorangegangenen Sommer verschwand. Obwohl die Blattlaus autök ist, müssen einige Individuen von solchen Bäumen, die ihre Blätter vor Mitte November verlieren, zu anderen Bäumen gelangen, um in der zweiten Novemberhälfte Oviparen bilden zu können. Viele geschlüpfte Weibchen erzeugen Nachkommen auf Bäumen mit orange‐gelb gefärbten Blättern, sehr wenige jedoch auf Bäumen mit roten Blättern. Die Herbstfärbung der Ahornbäume bildet einen wichtigen Faktor, um manche Bäume im Herbst von der Blattlausbesiedelung freizuhalten.

Flying Ips typogruphus juporzicus from Hokkaido (Japan) carried 12 species of phoretic mites, three of which were not previously recorded in Europe. The mite biologies were diverse, including specialists feeding on microorganisms, beetle eggs, and nematodes which were common under beetle elytra. Hyperphoretic on these mites were seven distinct species of fungal spores, plus an undetermined number identifiable only as conidia. The spores stuck anywhere on the mite bodies with no special carrying structures evident. Ophiostomu hicolor was the most common species, with the pathogenic Cerutocystis polonicum present in small numbers.