Climatic and cultivar effects on phytoseiid species establishment and seasonal abundance on citrus

The structure of phytoseiid communities on citrus varies among orchards and seasons, with potential implications for biocontrol services. Such variation may be driven by meteorological conditions and cultivar-specific traits. We conducted an outdoor seedling experiment to determine the effects of different cultivars on the establishment of introduced predatory mites (Euseius stipulatus and E. scutalis) and colonization by naturally occurring phytoseiids (Amblyseius swirskii, Iphiseius degenerans, and Typhlodromus athiasae) across seasons. Euseius stipulatus persisted through the spring only where it was released, regardless of cultivar, and reduced colonization by I. degenerans. In early summer (hot and dry conditions), nearly all phytoseiid species essentially disappeared, and after that only the naturally occurring A. swirskii and T. athiasae re-established. In mid-summer, A. swirskii colonized cultivars differentially, especially where pollen was provisioned, and was negatively related with the colonization of T. athiasae, which is known as its intraguild prey. Additionally, we performed laboratory experiments that simulated daily temperature fluctuations typical to spring and mid-summer seasons, measuring key demographic parameters of A. swirskii and E. stipulatus on leaf disc arenas of two citrus cultivars. Simulated spring temperatures resulted in higher total reproductive output in E. stipulatus than in A. swirskii, whereas mid-summer temperatures resulted in the opposite pattern. Both results are consistent with the seasonal patterns observed in the outdoor experiment. Together with the phytoseiid dynamics observed previously in commercial orchards, these findings emphasize the role of meteorological conditions and cultivars in the structure and function of phytoseiid communities.