Acaricidal activity of symbiotic bacteria associated with entomopathogenic nematodes against the red palm mite Raoiella indica Hirst (Acari: Tenuipalpidae)
ABSTRACT The red palm mite Raoiella indica Hirst, 1924 (Acari: Tenuipalpidae) is an important invasive pest affecting tropical crops, particularly coconut and banana, in several countries. In Brazil, pest management is limited by the reduced availability of registered chemical control products, which may favor the selection of resistant populations. Symbiotic bacteria of entomopathogenic nematodes (EPNs), such as Xenorhabdus (Thomas and Poinar, 1979) and Photorhabdus (Boemare and Akhurst 2006), are known to produce metabolites with insecticidal and acaricidal activity, but their activity against R. indica has not been evaluated yet. In this study, an exploratory laboratory bioassay was conducted to assess the acaricidal activity of 15 bacterial isolates of Xenorhabdus and Photorhabdus through topical application to adult females of R. indica. Mortality was recorded over a six-day period and compared with water and culture-medium controls. Several isolates induced mortality rates exceeding 95%, and two isolates resulted in complete adult mortality. In addition, oviposition was strongly reduced by specific isolates. Females exposed to isolates CER144 and CER09 laid on average 0.03 and 0.15 eggs per alive female per day, respectively, compared with approximately 0.85 eggs per alive female per day in both controls, indicating a reduction of over 80% in egg production. Although preliminary, these findings provide the first evidence that EPN-symbiotic bacteria represent a promising and underexplored source of compounds for the biological control of R. indica, opening perspectives for sustainable pest management in tropical and subtropical systems.