Difference in the susceptibility to infection with nuclear- and cytoplasmic-polyhedrosis viruses and in the larval growth among the fall webworm larvae reared on the semisynthetic diet, and on artificial diet containing 25per cent and 50per cent mulberry leaf powder was investigated. Growth and developmental rate of larvae which had been reared on the semisynthetic diet were much inferior to those reared on the artificial diet containing mulberry leaf powder. Similar results were obtained on both pupation rate and pupal weight. On the other hand, the larvae reared on the semisynthetic diet were more susceptible to the oral infection with nuclear- and cytoplasmic-polyhedrosis viruses than those reared on the artificial diet containing mulberry leaf powder. Especially, the larvae reared on the semisynthetic diet before the oral infection showed the highest susceptibility.

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Population density of Locusta migratoria has reached a notably high level in sugar cane field of Minami-Daito Island, 360km east of Okinawa Island in 1972 and 1973. The larvae in the outbreak area were black in body colour and showed remarkable gregariousness. Group oviposition and small scale mass-flight of adults were observed in these years. Morphometric study showed that the ratio of the bend of upper ridge of pronotum to pronotum length of the adults collected in the outbreak areas was significantly lower than that of solitary adults from Honshu, Kyushu and Okinawa Island. Thus, the phase-transformation at least to the phase transiens, is considered to have taken place in Minami-Daito Island.

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To elucidate the effective range of traps baited with virgin females (VF-trap) on the suppression of mating of Spodoptera litura, preliminary experiments were carried out by using tethered females in the field. Mating of the females located at 3 and 30m apart from VF-traps was apparently suppressed in May, June, or November, when the population of the moth was in low density. However, no suppression of the mating was observed in higher population during August to September. Mating of the tethered females was also suppressed when they were surrounded with four VF-traps. However, the mating suppression was seriously affected by the distance between two adjacent traps and by the mean temperature from the sunset to the midnight, when the moth copulated. Critical temperature for mating behavior was found to be near 10°C. The most effective suppression effect of VF-traps was observed at temperatures between 11°C and 15°C. At the temperature higher than 1°C, the effectiveness of VF-traps remarkably decreased.

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Stimulative activity of nutrient chemicals including 9 sugars, 20 amino acids, 9 vitamins, 2 sterols, 4 lipids and 4 salts on the feeding of Gallerucella vittaticollis BALY was investigated. Of the sugars tested, sucrose and D-fructose appeared to be active feeding stimulants. D-Glucose showed slight stimulative activity. D-Fructose and D-glucose were determined in leaves of Rumex obtusifolius and Fragaria chiloensis, hosts of this insect, but sucrose did not occur in these plants. From these results, D-fructose and D-glucose seemed to be the stimulants in the feeding of host plants in this insect. Among the amino acids, L-alanine alone was inactive but slightly active as feeding stimulant in the presence of sucrose, whereas other amino acids were inactive with or without sucrose. The quantitative determination of free amino acids in the leaves of R. obtusifolius and F. chiloensis showed that L-alanine content was much higher than any other amino acids. It is noteworthy that L-alanine stimulating the feeding of this insect was the most abundant amino acid in these host plants. Vitamins, sterols, lipids and salts were showed to be inactive with or without sucrose.

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In order to get a basic knowledge on the forecasting of seasonal change of population density, yearly trapping of Microtus montebelii was made in a pasture in Iwate Prefecture. It was revealed from the yearly trapping data obtained in 1972 that the population density was clearly high in pasture area as compared with that in forest area. The seasonal change in population density was shown by a curve with 2 peaks which appeared at early summer and late autumn. Seasonal change in reproductive activity directly reflected to the type of seasonal change in population density. Since the overwintered individuals died out by summer, the majority of overwintering population consisted of individuals born in autumn. The type of seasonal fluctuation in population density of each year was greatly affected not only by the increase or decrease in number of newborn individuals at that time, but by the density of overwintered population.

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