Aratchige Nayanie S, Sabelis Maurice W, Lesna Izabela
Section Population Biology, Institute for Biodiversity and Ecosystem Dynamics (IBED), University of Amsterdam, Kruislaan 320, Amsterdam, The Netherlands.
Exp Appl Acarol. 2007;43(2):97-107. doi: 10.1007/s10493-007-9107-9.
Being minute in size, eriophyoid mites can reach places that are small enough to be inaccessible to their predators. The coconut mite, Aceria guerreronis, is a typical example; it finds partial refuge under the perianth of the coconut fruit. However, some predators can move under the perianth of the coconut fruits and attack the coconut mite. In Sri Lanka, the phytoseiid mite Neoseiulus baraki, is the most common predatory mite found in association with the coconut mite. The cross-diameter of this predatory mite is c. 3 times larger than that of the coconut mite. Nevertheless, taking this predator's flat body and elongated idiosoma into account, it is--relative to many other phytoseiid mites--better able to reach the narrow space under the perianth of infested coconut fruits. On uninfested coconut fruits, however, they are hardly ever observed under the perianth. Prompted by earlier work on the accessibility of tulip bulbs to another eriophyoid mite and its predators, we hypothesized that the structure of the coconut fruit perianth is changed in response to damage by eriophyoid mites and as a result predatory mites are better able to enter under the perianth of infested coconut fruits. This was tested in an experiment where we measured the gap between the rim of the perianth and the coconut fruit surface in three cultivars ('Sri Lanka Tall', 'Sri Lanka Dwarf Green' and 'Sri Lanka Dwarf Green x Sri Lanka Tall' hybrid) that are cultivated extensively in Sri Lanka. It was found that the perianth-fruit gap in uninfested coconut fruits was significantly different between cultivars: the cultivar 'Sri Lanka Dwarf Green' with its smaller and more elongated coconut fruits had a larger perianth-fruit gap. In the uninfested coconut fruits this gap was large enough for the coconut mite to creep under the perianth, yet too small for its predator N. baraki. However, when the coconut fruits were infested by coconut mites, the perianth-rim-fruit gap was not different among cultivars and had increased to such an extent that the space under the perianth became accessible to the predatory mites.
细须螨体型微小，能够抵达其捕食者难以进入的狭小空间。椰细须螨（Aceria guerreronis）就是一个典型例子，它能在椰果的花被下找到部分藏身之所。然而，一些捕食者能够进入椰果的花被之下并攻击椰细须螨。在斯里兰卡，植绥螨类的巴氏新小绥螨（Neoseiulus baraki）是与椰细须螨相关联的最常见捕食螨。这种捕食螨的横径约为椰细须螨的3倍。尽管如此，考虑到这种捕食螨扁平的身体和细长的体躯，相对于许多其他植绥螨类而言，它更能够进入受侵染椰果的花被之下的狭窄空间。然而，在未受侵染的椰果上，几乎从未在花被下观察到它们。受早期关于郁金香球茎对另一种细须螨及其捕食者的可达性研究的启发，我们推测椰果的花被结构会因细须螨的损害而发生变化，结果捕食螨更能够进入受侵染椰果的花被之下。我们在一项实验中对此进行了测试，在该实验中，我们测量了斯里兰卡广泛种植的三个品种（“斯里兰卡高种”、“斯里兰卡矮种绿椰”和“斯里兰卡矮种绿椰×斯里兰卡高种”杂交种）的花被边缘与椰果表面之间的间隙。结果发现，未受侵染的椰果中，花被与果实的间隙在不同品种间存在显著差异：果实较小且更细长的“斯里兰卡矮种绿椰”品种，其花被与果实的间隙更大。在未受侵染的椰果中，这个间隙大到足以让椰细须螨爬到花被之下，但对其捕食者巴氏新小绥螨来说又太小。然而，当椰果受到椰细须螨侵染时，不同品种的花被边缘与果实的间隙没有差异，并且增大到了捕食螨能够进入花被之下空间的程度。
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