Acaricidal effect of cell-free supernatants from Xenorhabdus and Photorhabdus bacteria against Tetranychus urticae (Acari: Tetranychidae)

Abstract

The effects of secondary metabolites produced by the following symbiotic bacteria, Xenorhabdus szentirmaii, X. nematophila, X. bovienii, X. cabanillasii, Photorhabdus luminescens and P. temperata, associated with entomopathogenic nematodes, were investigated against various developmental stages of Tetranychus urticae (Acari: Tetranychidae) using cell-free bacterial supernatants in Petri dishes. In addition, the effects of the most active bacterial supernatant(s) found in Petri dish experiments were tested on T. urticae in pot experiments. All studies were conducted at 25 ± 1 °C temperature, 70 ± 5% relative humidity and a light cycle of 16 h in a climate room. The result of the Petri dish experiments showed that the supernatants had little or no effect on the egg stage, as less than 4% mortality was recorded. Depending on the bacterial supernatant, mortality in the other stages was 46-97% for larvae, 30-96% for protonymphs, 41-92% for deutonymphs, 92-100% for adult males and 46-93% for adult females. Control mortalities ranged from 1-7% for larvae, 2-9% for protonymphs, 4-10% for deutonymphs, 6-10% for adult males and 4-8% for adult females. Among supernatants tested, X. szentirmaii and X. nematophila were the most efficacious with mortality greater than 90% on the mobile stages of T. urticae. According to the results from pot experiments, the supernatants of X. szentirmaii and X. nematophila, singularly and in combination, significantly reduced the T. urticae population. However, the mixture of X. szentirmaii and X. nematophila supernatants did not increase efficiency to reduce T. urticae population compared to each supernatant alone. Further studies are warranted to find the active compound(s) in the supernatants of X. szentirmaii or and X. nematophila and assess whether the supernatant(s) has the potential of being a practical and economical control agent for T. urticae.

Keywords: Bacterial supernatant; Entomopathogenic nematodes; Photorhabdus; Tetranychus urticae; Two-spotted spider mite; Xenorhabdus.