Phytophagous and predatory mites in the soybean-cowpea succession cropping system in Brazil – associations could promote sustainability?

Abstract: Improvement of a crop system is conditioned to increasing its productivity and sustainability. In this context pest control is a key factor. Some agricultural practices as weed removal or pesticides can cause a drastic reduction in natural enemies’ populations. Knowledge of mite assemblages and associations among its components can guide the adoption of sustainable practices and promote ecological services. Soybean-cowpea succession cropping system occupies extensive areas in Brazil. Phytophagous mites and small insects (whiteflies, thrips) have been considered as important pests in soybean crops and occasional pests in cowpea. Elimination of weeds in the soybean-cowpea cropping is the most common practice; however, the effect of this practice on mite communities is still unknown. This study aimed to know the phytophagous and predatory mite species occurring on the soybean-cowpea crop system, comparing communities in two systems (conventional and successional intercropping) and with and without weeding. Surveys were conducted in the States of Piaui and Maranhão, Northeast Brazil. In addition, field experiments were performed. Four treatments were evaluated (soybean-fallow, cowpea-fallow, soybean-cowpea, fallow-fallow) in two areas (weeding; not weeding). Phytophagous mites were found in high populations on soybean crop; however, on cowpea they were less abundant, confirming that this crop is not a host as favorable as soybean. Sixteen phytoseiid species were identified; however, the most abundant predator was the Blattisociidae, Aceodromus convolvuli. Weeds harbored a noticeable abundance and richness of predatory mites and scarce populations of phytophagous. Predatory mites were significantly more abundant on the not weeding area, while phytophagous mites were significantly lower. Results suggested that predatory mites play a key role as biological control agents in the system and that weeds favored predatory mite populations. Further studies should be performed to look into food webs involving predatory mites in this agrosystem.