Factors affecting refuge from parasitoid attack in a cynipid wasp, Aphelonyx glanduliferae |
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Authors: | M Ito N Hijii |
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Institution: | (1) Laboratory of Forest Protection, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan Tel. +81-52-789-4180; Fax +81-52-789-5518 e-mail: martin_i@agr.nagoya-u.ac.jp, JP |
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Abstract: | We examined seasonal patterns of gall morphology, growth, and survivorship of the agamic generation of a cynipid wasp, Aphelonyx glanduliferae, and discussed its mortality factors, especially from the point of view of refuge from parasitoid attack. Although the initiation
period varied greatly among individual galls, the larvae of A. glanduliferae grew rapidly and reached their maximum size within 3 weeks before pupating in late September to early October. This growth
period corresponded to the period when the gall walls became thinner. Parasitoid attack, which was the principal factor in
the mortality of A. glanduliferae in the tree crown, was concentrated around the pupation period of the cynipid. Gall walls were significantly thinner in galls
attacked by parasitoids than in those still containing a living cynipid. Therefore, the period available to parasitoids seems
to be limited by both gall wall thickness and cynipid size. Thus, the growth pattern of A. glanduliferae larvae can have significance in that it narrows the window of vulnerability to parasitoids to a particular period. Although
delaying gall initiation will also shorten the exposure period to parasitoid attacks, it was likely to increase the risk of
death from gall abortion caused by seasonal degradation in the quality of host plant tissues. Although many cynipids were
killed by disease in the galls that fell to the ground, the falling of mature galls to the ground may be another way to a
parasitoid-free space. It is thus suggested that a trade-off among life history traits against multiple factors operates in
the refuge of A. glanduliferae from parasitoid attack.
Received: May 15, 2001 / Accepted: February 1, 2002 |
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Keywords: | Gall morphology Life history traits Mortality factors Seasonal patterns Window of vulnerability |
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