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Variation in the summer-diapause expression of the ladybird beetle, Coccinella septempunctata, among local populations and years was investigated by field observation and dissection of sampled specimens, in Japan. Only non-diapausing adults were found in Hokkaido, northern Japan, whereas diapausing adults were observed at most sites in Honshu and southward in summer. However, the non-diapausing adults were also observed in northern Honshu and at high-altitudinal sites of central Honshu. The frequency of diapause expression in northern Honshu varied greatly among populations and years. The frequency of non-diapausing adults was significantly higher when average daily mean air temperature for July was relatively low. This indicated that the populations inhabiting northern Honshu have plasticity in diapause induction, primarily in response to temperature conditions. Moreover, the coexistence of diapausing adults and non-diapausing adults at the same site was often observed. This suggested that there might be genetic variation in diapause tendency within a local population.

Summary Two experiments on the nymphal predation of Podisus maculiventris were conducted using Spodoptera litura larvae as prey. First experiment: The predator nymphs divided into three groups were reared individually from second instar to adult in a small vessel. Each nymph in the groups 1, 2 and 3 was allowed to attack the serially growing larvae (these were supplied at the rate of one per day) from 3‐, 5‐ and 7‐day old after hatching, respectively. The first prey used for the group 1 was so small that it was not only insufficient to satiate the predator but also was difficult to be searched out. But these disadvantages were soon recuperated due to the rapid growth of the prey and all nymphs could survive to adults. The survival rate of third and fourth instar nymphs in the group 3 was severely affected by vigorous counterattack of older prey larvae. Second experiment: The predator nymphs were individually reared either in a small vessel or in a large one at various rates of food supply (the prey larvae of 7‐day old were used). The functional response curves obtained for each instar of the predator took a saturation type within a certain range of the prey density. The saturation level specific to each instar was generally higher for the predator reared in the large vessel than in the small one. The functional response of fourth and fifth instar nymphs was accelerated at a high prey density, viz. 16 larvae per vessel. Even at the low rate of food supply, viz. one larva per day per predator, the predator nymphs could survive to adults, but the size of resultant adults were abnormally small.

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