Onzo Alexis, Hanna Rachid, Sabelis Maurice W
Biological Control Centre for Africa, International Institute of Tropical Agriculture, 08 B.P. 0932, Cotonou, Benin, West Africa.
Exp Appl Acarol. 2003;31(3-4):225-41. doi: 10.1023/b:appa.0000010380.44408.05.
To determine the impact of an acarine predator guild on the abundance of a shared herbivorous prey and its principal exotic predator, a series of surveys were conducted in ca. 200 cassava fields in swamp and non-swamp areas in southwestern Benin, West Africa. For each field, the surveys provided data on the density of a pest arthropod, the cassava green mite Mononychellus tanajoa (Bondar), of an introduced and successfully established natural enemy, the apex-inhabiting predatory mite Typhlodromalus aripo DeLeon, and on occurrence of other predator species that inhabit the leaves and share the same prey. These other predators included one exotic species, Typhlodromalus manihoti Moraes, that is successfully established mainly in swamp areas, and two indigenous species, Euseius fustis (Pritchard and Baker) and Typhlodromalus saltus (Denmark and Matthysse), that are commonly found on cassava in Africa. Our aim was to assess the association between the density of M. tanajoa and that of T. aripo, the most successful predator in terms of establishment and abundance, and subsequently determine how this association was affected by the presence or absence of the other predator species. No obvious density-dependent relationship was found by inspecting the scattergrams of T. aripo versus M. tanajoa densities, but high T. aripo densities did not occur when M. tanajoa densities were low and--during the dry season in February--the densities of M. tanajoa steeply increased when T. aripo numbers were low. Given the establishment of T. aripo in all fields, the presence of other species of predatory mites (T. manihoti, both in swamp and non-swamp areas; T. saltus in absence--as well as presence--of T. manihoti in swamp areas; E. fustis in absence of T. manihoti in non-swamp areas) reduced the density of M. tanajoa by a factor 2-3. Thus in all these cases, the presence of an exotic or indigenous species of predatory mite in addition to T. aripo was associated with lower M. tanajoa density. The density of T. aripo was usually positively affected by the presence of other predator species except for T. saltus in presence of T. manihoti that negatively affected the density of T. aripo in swamp areas, an effect likely mediated by either intraguild predation or competition for food. Path analysis showed that indigenous phytoseiid species were more important in suppression of M. tanajoa populations in cassava fields than previously thought. We suggest that the lack of negative effects of the predator species complex is likely due to differential niche use by the various species which reduces interference among the predators. Manipulative experiments are, however, needed to provide details on the relative importance in M. tanajoa suppression by each species within this acarine predator guild.
为了确定螨类捕食者群落对一种共享的食草猎物及其主要外来捕食者数量的影响，在西非贝宁西南部的沼泽和非沼泽地区约200块木薯田中进行了一系列调查。对于每块田地，调查提供了有关害虫节肢动物木薯绿螨（Mononychellus tanajoa (Bondar)）的密度、一种引入并成功定殖的天敌——栖息在叶尖的捕食螨（Typhlodromalus aripo DeLeon）的数据，以及关于栖息在叶片上并共享相同猎物的其他捕食者物种的出现情况的数据。这些其他捕食者包括一种主要在沼泽地区成功定殖的外来物种——马氏盲走螨（Typhlodromalus manihoti Moraes），以及两种在非洲木薯上常见的本土物种——尤氏真绥螨（Euseius fustis (Pritchard and Baker)）和盐沼盲走螨（Typhlodromalus saltus (Denmark and Matthysse)）。我们的目的是评估木薯绿螨密度与阿里波盲走螨（T. aripo）密度之间的关联，阿里波盲走螨是在定殖和数量方面最成功的捕食者，随后确定这种关联如何受到其他捕食者物种存在与否的影响。通过检查阿里波盲走螨与木薯绿螨密度的散点图，未发现明显的密度依赖关系，但当木薯绿螨密度较低时，阿里波盲走螨的高密度并未出现，并且在2月的旱季，当阿里波盲走螨数量较低时，木薯绿螨的密度急剧增加。鉴于阿里波盲走螨在所有田地中均已定殖，其他捕食螨物种（沼泽和非沼泽地区的马氏盲走螨；沼泽地区有或没有马氏盲走螨时的盐沼盲走螨；非沼泽地区没有马氏盲走螨时的尤氏真绥螨）的存在使木薯绿螨的密度降低了2至3倍。因此，在所有这些情况下，除阿里波盲走螨外，外来或本土捕食螨物种的存在与较低的木薯绿螨密度相关。阿里波盲走螨的密度通常受到其他捕食者物种存在的积极影响，但在沼泽地区，盐沼盲走螨在马氏盲走螨存在时对阿里波盲走螨的密度产生负面影响，这种影响可能是由种内捕食或食物竞争介导的。通径分析表明，本土植绥螨物种在抑制木薯田中的木薯绿螨种群方面比以前认为的更重要。我们认为，捕食者物种复合体缺乏负面影响可能是由于各种物种对生态位的不同利用，这减少了捕食者之间的干扰。然而，需要进行操纵实验以提供关于该螨类捕食者群落中每个物种在抑制木薯绿螨方面相对重要性的详细信息。
