Population field studies on the aphidophagous ladybird beetle Harmonia axyridis (Coleoptera: Coccinellidae): resource tracking and population characteristics |
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Authors: | N Osawa |
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Institution: | (1) Laboratory of Forest Ecology, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan Tel. +81-75-753-6077; Fax +81-75-753-6080 e-mail: osawa@kais.kyoto-u.ac.jp, JP |
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Abstract: | To clarify functional and numerical responses to temporal and spatial variations of resources (resource tracking), and the
population characteristics of the ladybird beetle Harmonia axyridis, I analyzed the results of a 3-year field observation at 24 sites (seven plant species) on eight species of aphids. The seasonal
changes in the number of beetles estimated by the Jolly–Seber method were significantly correlated with those of aphids in
the total area. The estimated values of population parameters suggested frequent immigration and emigration of the H. axyridis population, although reproductive rates between spring and summer were rather stable all 3 years (1.87–3.49). The staying
time and the daily number of adults and eggs at each site were influenced not only by a single factor but also by interactions
among time and quantity and quality of the prey. The adult movement showed two patterns, which corresponded with the movement
within and between the subpopulations when an assemblage of H. axyridis occurring on the plants of the same species or genus was regarded as a subpopulation. Adult movement intensely occurred within
a subpopulation, although the beetles moving between subpopulations had a significantly greater chance to reach the habitat
with a high aphid density. The habitats of H. axyridis could be categorized into a suitable habitat for survival and reproduction and a temporal refuge. The results obtained here
suggest that H. axyridis, with high ability of prey searching and reproduction, maintains a stable population in heterogeneous and temporal habitats
by its resource tracking mechanisms.
Received: March 8, 1999 / Accepted: April 25, 2000 |
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Keywords: | Aphid Polyphagous Population Dynamics Predator– prey interaction Habitat |
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