Acaricidal and insecticidal activities of entomopathogenic nematodes combined with rosemary essential oil and bacterium-synthesized silver nanoparticles against camel tick, Hyalomma dromedarii and wax moth, Galleria mellonella.

Abstract

An innovative approach to ticks and insect pests management is necessary to mitigate the challenges posed by the indiscriminate use of chemical pesticides, which can lead to resistance development and environmental pollution. Despite their great potential, biological control agents have significant manufacturing, application, and stability limitations. Currently, using phytochemicals, biosynthesized nanoparticles, and bioagents to get rid of arthropods might be a good alternative that would make farmers less worried about residues and resistance. The present investigation was carried out to determine for the first time the in vitro acaricidal and insecticidal efficacies of endogenous two entomopathogenic nematodes (EPNs), Heterorhabditis indica and Steinernema sp. combined with either Proteus mirabilis-synthesized silver nanoparticles or Rosmarinus officinalis essential oil against the camel tick, Hyalomma dromedarii larvae and females, and greater wax moth, Galleria mellonella larvae as well. We also determined the potential effects of these treatments on the biological characteristics of H. dromedarii's engorged females. We further investigated R. officinalis essential oil (EO) profiling and nanoparticle (AgNPs) characterization. All the evaluated combinations demonstrated synergistic effects on the larvae of G. mellonella and H. dromedarii, as well as on engorged females. When H. indica was mixed with EO or AgNPs, it worked well than when Steinernema sp. was mixed with EO or AgNPs. This was shown by the highest number of tick and insect mortalities and the lowest lethal concentration (LC₅₀) values. One day after G. mellonella was exposed to H. indica (1,000 infective juveniles (IJs)) together with EO at 60 or 40 mg/mL, all tested individuals died. We obtained the same results when H. dromedarii females exposed to the same level of EPN with 60 mg/mL EO, and when H. dromedarii larvae treated with H. indica at 500 IJs + EO at 25 mg/mL. Treatments altered all biological parameters of engorged females, revealing extremely noticeable differences between the treated and untreated groups. Gas chromatography-mass spectrometry (GC-MS) analysis identified a total of 28 compounds in the R. officinalis EO. Visual observation showed a color change from yellow to dark brown for AgNPs biosynthesized from P. mirabilis; the transmission electron microscopy (TEM) image and ultraviolet-visible (UV-Vis) spectrum showed well-dispersed particles with a diameter of 5-45 nm; and the greatest surface plasmon peaked at 320 nm. The results demonstrated the high efficacy of combining EPN, H. indica, with EO to control tick and insect pests. This is due to its acaricidal activity on different stages of H. dromedarii, including larvae and engorged females, and its larvicidal effect on G. mellonella.