Species of generalist phytoseiid mites in the genus Euseius are effective natural enemies of multiple arthropod pests in various types of orchards worldwide. Cover crops increase the densities of these predators and can help reduce pest densities, but their practical roles and effects in enhancing biological control have not yet been completely unveiled yet. Here, we examined the efficacy of biocontrol of Panonychus citri (McGregor) and Aculops pelekassi (Keifer) by naturally occurring Euseius sojaensis (Ehara) in commercial Japanese citrus orchards with cover crops of Lolium perenne L. (perennial ryegrass) managed in two different ways: flowering and mowing. In the flowering plots, the numbers of windborne pollen grains and phytoseiid mites were larger, P. citri populations were smaller, and rates of fruit injury caused by A. pelekassi were significantly lower than in mown plots. In early summer, the number of E. sojaensis in the flowering plots peaked following a peak in the abundance of windborne Poaceae pollen caught on the citrus trees. These results suggest that the windborne pollen supplied from cover crops of L. perenne boosts the populations of E. sojaensis inhabiting the citrus trees and enhances the efficacy of biocontrol of P. citri and A. pelekassi. The percentage of E. sojaensis females with eggs was higher in flowering plots than in mown plots. Therefore, in conservation biological control, a perennial ryegrass cover crop flowering in early summer would be beneficial for increasing the fecundity of this predatory mite, even when prey (pest) densities are low.

Euseius 属的多面手植物螨种是全球各种果园中多种节肢动物害虫的有效天敌。覆盖作物增加了这些捕食者的密度，可以帮助降低害虫密度，但它们在加强生物控制方面的实际作用和效果尚未完全揭示。在这里，我们检查了天然存在的 Euseius sojaensis （Ehara） 在商业日本柑橘园中对 Panonychus citri （McGregor） 和 Aculops pelekassi （Keifer） 的生物防治功效，这些覆盖作物以两种不同的方式管理 Lolium perenne L. （多年生黑麦草） 以两种不同的方式管理：开花和割草。在开花样地中，风传花粉粒和植物螨的数量更多，柑橘假单胞菌种群数量较少，由 A. pelekassi 引起的果实伤害率显著低于修剪样地。初夏时节，在柑橘树上捕获的风传禾本科花粉丰度达到高峰后，开花地中的 E. sojaensis 数量达到峰值。这些结果表明，由 L. perenne 覆盖作物提供的风传播花粉增加了栖息在柑橘树上的 E. sojaensis 的数量，并增强了 P. citri 和 A. pelekassi 的生物防治效果。开花地块中 E. sojaensis 雌性带卵的百分比高于修剪地块。因此，在保护性生物控制中，即使在猎物（害虫）密度较低的情况下，在初夏开花的多年生黑麦覆盖作物也有利于增加这种捕食性螨虫的繁殖力。