Distribution patterns of the larvae of the five tortricids, Choristoneura diversana, Lozotaenia coniferana, Archips issikii, Epinotia aciculana and Zeiraphera truncata, were analyzed by using IWAO'S ^*m-m method. The distribution patterns of the larvae, egg masses and pupae of C. diversana per 50cm branch as a unit fitted to aggregated distributions with α=0 and β>1, while at higher population levels the pattern for the larvae changed to a distribution with α>0 and β>1, which corresponds to a model of randomly distributed colonies. The distribution pattern of the larvae per branch of 1m as a unit (which approximates one whole branch) fitted also to a random distribution of colonies. The distribution pattern of the larvae of L. coniferana per 50cm branch as a unit fitted to a random distribution of colonies, and that per 1m branch to an aggregated distribution. The distribution pattern of the larvae of E. aciculana per 50cm branch as a unit fitted to an aggregated distribution with α=0 and β>1, and the remaining species to a model with α>0 and β>1, where the average size of the colonies distributes contagiously. The differences in patterns among these species were attributed to the deposition of egg masses, overwintering status, and the settling of larvae on shoots in certain parts of a branch.

View full abstract

The late second instar larvae of Scirtothrips dorsalis HOOD moved from the upper leaves of tea bush to the ground for pupation by crawling or falling. The falling behavior which was specific to these larvae was never observed during the first to early second larval period. It did not appear to be related to morphological or functional changes of the tarsal bladders, but could be regarded as an intentional behavior aimed at searching for a suitable place to pupate. The fall was selected when crawling was hampered. On the basis of the laboratory observations, the pupation place was usually a humid and dusky crack or space. In the tea fields, most of the mature larvae pupated in old leaves bound by the larvae of tea tortrixes, dead leaves hanging from the tea bush, cracks on the bark, moss and lichen on the tree trunk and leaf litter, whose amounts vary with the conditions of cultivation of tea.

View full abstract

Multiple regression models for predicting the arrowhead scale population densities were designed 2 years ago. These models were further improved by incorporating the data accumulated at the experiment stations of Kanagawa, Shizuoka, Hiroshima and Kumamoto during 5 years after the previous model had been constructed. The following 3 types of models comprised statistically and/or biologically significant variables. Type A: involved the stepwise forward regression method based on the smallest residual sum of squares; Type B: the same method was used based on the smallest prediction sum of squares; Type C: included fewer variables selected on the basis of biological consideration or by intuition.
Regression coefficients were determined by using the following 2 kinds of data sets: (i) each of 4 sets collected at the 4 respective experiment stations and (ii) the pooled data of the 4 experiment stations.
Compared with the previous models, the multiple correlation coefficients in the new models were a little smaller, although they reached a value of 0.75 and the multiple regression coefficients were more stable among the 4 stations than in the previous models. These new models were used for predicting the arrowhead scale population density in the year following the observations for model building. The results show that Type C model offered the highest predictability and Type B was as good as Type C. Predictability was high even in the case of the model for the respective station using their own data, but type A was not particularly adequate. Conclusions are as follows: if the sample size for constructing a regression model is adequate, reliable multiple regression coefficients can be obtained, and such multiple regression type models, especially based on the prediction sum of squares, are reliable enough for forecasting of population density.

View full abstract

The appearance of Cnaphalocrocis medinalis GUENÉE in early planted rice fields was investigated in Chikugo between 1976 and 1979. The leaf tip of rice plants was brushed with a rod and the number of the moths which had flown away from the plants was counted every day from June to July, while the numbers of eggs, larvae and pupae on the rice plants were monitored at three or four day intervals. The female moths collected in the field were checked for the number of spermatophores and mature eggs, and the amount of fat. The moth was found in paddy fields from the latter half of June every year and the average number of the moths was usually less than ten individuals per are with the number of females exceeding that of males. The moths found in the fields seemed to move from field to field. Nearly all the female moths had already mated and had mature eggs whenever they were collected in the fields. The moth was usually observed one day to three days later than the two species of rice pests, Sogatella furcifera HORVÁTH and Nilaparvata lugens STÅL, which are known to be long distance migrant planthoppers. However, when the interval between the landing and the finding of the moth in the field is taken into account, out of nine long distance migratory flights of the planthoppers during the test period, seven were thought to be associated with the moths. These findings strongly suggest that the moth might be a long distance migrant. None of the moths were captured by black light traps in June.

View full abstract

The ovarian development, copulation and oviposition of the white-spotted stink bug, Eysarcoris ventralis, were studied in relation to photoperiod and temperature. The ovary developed under photoperiods over 14L-10D. Photoperiods shorter than 13L-11D inhibited the ovarian development. This species diapaused by the effect of short day in the same way as adults with nondeveloped ovary. For the ovarian development of the diapausing autumn population, long day (over 13L-11D) and high temperature (over between 15 and 20°C) were required. The copulation was usually observed under conditions similar to those required for the ovarian development. Short day treatment did not affect further oviposition of the females, but oviposition was discontinued or the number of eggs laid under low temperature reach as 15°C decreased significantly. Oosorption appeared to occur in the females which did not complete oviposition. However, when the females were placed under favourable conditions oviposition resumed. The females which had laid eggs in the previous year could be traced in the field population of early spring

View full abstract

In Pseudaulacaspis pentagona TARGIONI, the eggs of uncopulated females were found to be underdeveloped along with the abonormal parasitic behavior of females leaving their shells. On the basis of the present investigation it was concluded that this species reproduces by amphigory. The ovary of uncopulated young adult females ceased to grow and gradually shrank. In that process the eggs became black like mulberry fruits and finally they collapsed. The uncopulated females secreted white body lipids like silk after leaving the shell, and died without oviposition. Oviposition of normal females was found to take place over a long period of time from the beginning of the adult stage until death.

View full abstract

In the course of studies on the chemical factors controlling host-selection in three species of planthopper (Nilaparvata lugens, Sogatella furcifera, and Laodelphax striatellus), attractant(s) for these planthoppers was detected in the rice plant. The two-way choice assay using the apparatus shown in Fig. 1 indicated that these planthoppers were significantly attracted to the rice plant. Since antennectomized N. lugens was not attracted to the rice plant, it was suggested that the attractant(s) may consist of volatile component(s) in the rice plant which could be detected by the antennae of the planthopper. The attractant(s) was extracted with ether and the activity was found in the neutral fraction. These data suggest that some volatile compound(s) in the rice plant plays an important role in the orientation of the planthopper to the host plant.

View full abstract

A new simple method was proposed to estimate total effective temperature from the maximum and minimum temperatures of a day. Lines connecting the minimum (5a.m.) and the maximum (1p.m.), temperatures of a day with minimum temperature of the next day formed a triangle. The effective temperature of a day was estimated from the area of the triangle which was above the threshold temperature for development. The total effective temperature was calculated by adding the daily effective temperature. This method was found to give more accurate estimation than others.

View full abstract