Role of a parasitoid with a low fecundity,Praestochrysis shanghaiensis (Hymenoptera: Chrysididae), in the population dynamics of its host |
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Authors: | Yoshihiro Yamada |
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Abstract: |
1. |
Analysis of life tables of the oriental moth,Monema flavescens, obtained for 8 generations over 4 years, disclosed that the cocoon parasitoid,Praestochrysis shanghaiensis, acted as a density-disruptive factor.
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The density of the host cocoon remained stable (max./min.=3.2), whereas that of the host adult varied (max./min.=14.3) although
both showed similar fluctation patterns.
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3. |
Stability of the host population was associated with the density-dependence in the ratio of first generation cocoons to overwintered
generation moths, which was the key factor for the rate of change throughout the year. Chrysidid parasitism among the first
generation cocoons ranged from 37.7 to 70.1%, and that among the second generation cocoons from 16.7 to 63.2%, each showing
an inverse density-dependence and acting as the main determinant (key-factor) of the between-year variation in the density
of the adult moths.
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4. |
The density-dependence of the rate of change from overwintered generation adults to first generation cocoons was so strong
that the parasitism on the second generation hosts had not effect on the cocoon density of the first generation. On the other
hand, the density-dependence of the rate of change from first generation adults to second generation cocoons was weak, and
the parasitism on the first generation hosts became the key factor for the between-year variation of the second generation
cocoons.
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5. |
It is suggested that the stability of the parasitoid-host system will be disrupted without three parasitism-restricting factors:
asynchrony in the parasitoid attack on the second generation hosts, high mortality among parasitoid larvae of the second generation,
and the high proportion of those first generation parasitoids that enter diapause. These factors are considered to be effective
only in cooler parts of the distribution of the parasitoid.
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Keywords: | |
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