Desouhant Emmanuel, Debouzie Domitien, Menu Frédéric
UMR CNRS 5558 "Biométrie, Génétique et Biologie des Populations", Université Claude Bernard, 43, bd du 11 novembre 1918, 69622 Villeurbanne Cedex, FRANCE Fax: (33) 04 78 89 27 19 e-mail:
Oecologia. 1998 Apr;114(3):382-388. doi: 10.1007/s004420050461.
Frequency distributions of insect immatures per host are often fitted to contagious distributions, such as the negative binomial, to deduce oviposition pattern. However, different mechanisms can be involved for each theoretical distribution and additional biological information is needed to correctly interpret the fits. We chose the chestnut weevil Curculio elephas, a pest of the European chestnut Castanea sativa, as a model to illustrate the difficulties of inferring oviposition pattern from fits to theoretical distributions and from the variance/mean ratio. From field studies over 13-16 years, we show that 20 out of the 31 yearly distributions available fit a negative binomial and 25 a zero-inflated Poisson (ZIP). No distribution fits a Poisson distribution. The ZIP distribution assumes heterogeneity within the fruit population. There are two categories of host: the first comprises chestnuts unsuitable for weevil oviposition or in excess relative to the number of weevil females, and the second comprises suitable fruits in which oviposition behavior is random. Our results confirm this host heterogeneity. According to the ZIP distribution, the first category of hosts includes on average 74% of the chestnuts. A negative binomial distribution may be generated by either true or false contagion. We show that neither interference between weevil females, nor spatial variation in the infestation rate exist. Consequently, the observed distributions of immatures are not the result of false contagion. Nevertheless, we cannot totally exlude true contagion of immatures. In this paper we discuss the difficulty of testing true contagion in natural conditions. These results show that we cannot systematically conclude in favour of contagion when fitting a distribution such as the negative binomial or when a variance/mean ratio is higher than unity.
通常将每个寄主上未成熟昆虫的频率分布拟合到传染性分布，如负二项分布，以推断产卵模式。然而，每种理论分布可能涉及不同的机制，需要额外的生物学信息来正确解释这些拟合。我们选择欧洲栗象Curculio elephas（欧洲栗Castanea sativa的一种害虫）作为模型，来说明从理论分布拟合以及方差/均值比推断产卵模式的困难。通过13 - 16年的田间研究，我们发现，在可获得的31个年度分布中，有20个符合负二项分布，25个符合零膨胀泊松分布（ZIP）。没有分布符合泊松分布。ZIP分布假定果实群体内存在异质性。寄主有两类：第一类包括不适合象虫产卵或相对于象虫雌虫数量过多的栗子，第二类包括产卵行为随机的合适果实。我们的结果证实了这种寄主异质性。根据ZIP分布，第一类寄主平均包括74%的栗子。负二项分布可能由真实或虚假的聚集产生。我们表明，象虫雌虫之间既不存在干扰，侵染率也不存在空间变化。因此，观察到的未成熟昆虫分布不是虚假聚集的结果。然而，我们不能完全排除未成熟昆虫的真实聚集。在本文中，我们讨论了在自然条件下测试真实聚集的困难。这些结果表明，当拟合负二项分布等分布或方差/均值比高于1时，我们不能一概而论地得出有利于聚集的结论。
