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Summary The population growth of the green rice leafhopper,Nephotettix cincticeps, in the paddy field was analyzed based on the life table data accumulated for six years.
The paddy field population, which stems from the invading adults of the first generation (G-I), repeats two complete generations,
and the hatchlings of the fourth generation (G-IV) enter diapause and overwinter as the fourth instar nymphs in fallow paddy
fields. It was clarified that the density dependent reduction in the mean longevity and oviposition rate of adult females
in G-II and III played a primary role in stabilizing the annual population densities. The annual average of the mean longevity
of G-II females (3.9 days) was much shorter than that of G-III ones (7.7 days) and thus the density dependent reduction in
the mean longevity induced a more prompt regulatory effect on the oviposition of G-II females compared with G-III ones. As
the result, two equilibrium densities of eggs were obtained,e.g., ca 100 and 700 eggs per hill in G-III and IV, respectively. Density dependent decrease in the proportion of mature females in
the adult population was especially conspicuous in G-II, and this was closely associated with the density dependent reduction
in the mean longevity and fecundity. Thus, the density dependent dispersal (emigration) of the adult females by flight in
G-II and III was the most convincing factor in the process of population regulation. The density dependent dispersal of the
adult females is effective in avoiding the deleterious effects of nymphal crowding in a breeding habitat unit (a paddy field),
and may result in a more even distribution of the population over a continuous habitat units in a locality than otherwise. 相似文献
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Summary Two experiments on the nymphal predation ofPodisus maculiventris were conducted usingSpodoptera 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. 相似文献
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Summary A simple experiment of simulation was done to analyze the natural mortality process of young larval colonies and egg masses
of the southern green stink bug. In this experiment, a degree of contagiousness
was allowed in regard to the action of a mortality factor, and
was defined as the mean number killed per a colony or an egg mass by the mortality factor within a unit time and the number
killed per a colony was assumed to follow the Poisson series with the mean
. Thus each component of the Poisson series was opposed to each colony or egg mass which was taken at random from 162 egg
masses, 135 and 117 colonies of the first and the second instar larvae, respectively.
It was revealed that mortality factors in the field did not act with a small degree of contagiosness, e. g.
, on all colonies or egg masses, but acted with a large degree of contagiousness, e. g.
, on some of the colonies or egg masses. Thus differential survival somewhat in all or none way occurred among the insect
colonies irrespective of their initial sizes. These results were well explained by taking actual mortality factors into account. 相似文献
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Summary Population behaviour of adults and 5th-instar nymphs ofNezara viridula L. was analysed by means of the marking-and-recapture method in an early-planted paddy field. The field contained five varieties
of rice which differend in growth states. It was estimated that a total of more, than 7,000 adults of the first generation,
in which at least 3,000 were females, invaded the field from early July to middle August. Egg-mass census data, however, indicated
that only 10 per cent or less of the females participated in egg-laying. This was largely due to the, low rate of adult survival.
The adults preferred younger plants, for both feeding and oviposition.
The method described byIwao
et al. (1966) permitted estimate that 3,300–3,400 of the 5 th-instar nymphs and 1,100–1,200 of the adults of the second generation
were produced from 298 egg-masses (25, 700 eggs); while 95–6 per cent of the individuals were thought to have died before
reaching adulthood. Most of the 5 th-instar nymphs moved less than 4 m in three days as long as the condition of food plants
remained suitable, but they tended to move more towards younger plants when those on which they lived became too mature. The
apparent survival rate of the second generation adults was very low, probably due both to a rapid emigration and a high mortality
of newly-emerged adults. 相似文献
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