The Study on the Regulatory System of the Population of the Southern Green Stink Bug, Nezara viridula L.(Heteroptera : Pentatomidae) under Semi-Natural Conditions

An attempt was made to know the factors which are responsible for the regulation of the population of Nezara viridula in 1962 and 1963. Each year, the experiment was started by introducing hibernant adults into the field cage. Censuses were made weekly to obtain data for building up the life tables. The key factor analysis revealed that the mortality of eggs and nymphs, that of adult and the prenatal mortality of ova, each contributed almost equally to the total mortality.The prenatal mortality was referred to as the reduction in fecundity from the potential to the realized fecundity. This involved the reduction due to the weight loss of female adult determined indirectly by the population density during the nymphal stages and the one directly induced by the adult interference. The reduction in fecundity was greater by far in the adult stage, that is, the interference among the adults. A considerable proportion of females died without laying their eggs. A devise was proposes to estimate the number of barren females in the population incorporating the life span of females and their mating frequency. It was suggested that 23-35 per cent of the females of the 1st and 2nd generations were barren. The egg mortality and the nymphal mortality from hatching to the end of the 4th instar occurred dependently on the population densities of eggs and hatchlings. The mortality of the 5th instars tended to be low when the mortality of nymphs prior to the 5th instar was high.A great variation in the mean fecundity of prolific females was noticeable among the generations : the highest one was 51/2 times as much as that of the lowest. It was concluded that the prenatal mortality contributes mostly to regulation of the natural populations of N. viridula.