Cover crop providing windborne pollen enhances the efficacy of biocontrol of multiple pests by Euseius sojaensis in citrus orchards

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.