Influence of ground cover management on diversity and density of phytoseiid mites (Acari: Phytoseiidae) in Guadeloupean citrus orchards.

The abundance and diversity of phytoseiid mites in the vegetal ground cover of a citrus orchard were surveyed by monthly samplings from October 2008 to July 2009. Six different vegetal cover management methods were studied: herbicide application without mowing (Gly), mowing without herbicide application (PV), mowing with herbicide application (AV), late mowing without herbicide application (LMV), cover crop (Neonotonia wightii, Fabaceae) without herbicide application (PNeo) and cover crop with herbicide application (ANeo). Eleven species were present in the ground cover, with Phytoseius rex and Proprioseiopsis mexicanus as major species. Species richness and densities (1.5 ± 4.5) in the Gly treatment were very low, except for one sample 4 months after herbicide treatment. The AV and PV treatments showed poor diversity and very low mite densities (1.2 ± 2.6 and 1.4 ± 1.5, respectively). The LMV treatment showed the highest diversity and high density of phytoseiid mites (6.9 ± 8.8). The ANeo and PNeo treatments also showed generally high diversity, but with variations in time and exhibited the highest density of phytoseiid mites (13.5 ± 12.7 and 13.4 ± 9.1, respectively). Neonotonia wightii as the cover crop seems to act as a reservoir of phytoseiid mites, sustaining abundant and diverse populations all year round. Some naturally occurring plant species such as Achyranthes aspera, Amaranthus dubius and Eleutheranthera ruderalis could also constitute favourable host plants for Phytoseiidae. Results are discussed in relation to the potential of collected phytoseiid species as candidates for biological control of phytophagous mites on Guadeloupean citrus orchards.