Evaluation of Barricade® to enhance survival of entomopathogenic nematodes on cowhide

Evaluation of the in vitro acaricidal effect of five organic compounds on the cattle fever tick Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

The cattle fever tick, Rhipicephalus (Boophilus) microplus, is the most economically important tick worldwide. Infestations with this tick can lead to direct damage and cattle mortality due to the transmission of potentially deadly pathogens. Management of this tick species has been focused on the use of synthetical acaricides; however, the emergence of acaricide resistance to single or multiple active ingredients has resulted in a need for novel acaricide compounds. Among potential avenues for the discovery of novel acaricides are plant-derived compounds. The efficacy of five organic compounds (nootkatone, Stop the Bites®, BioUD®, lavender oil, and cedarwood oil) was evaluated using larval immersion tests (LITs), repellency assays, and adult immersion tests (AITs). The results from the LITs indicate that three of the organic compounds (NootkaShield™, Stop the Bites, BioUD) led to significant mortalities at low concentrations (0.2, 0.02, and 0.08%, respectively). By comparison, lavender and cedar oil led to around 90% mortality at 10 and 1% concentrations, respectively. Similarly, NootkaShield, Stop the Bites, and BioUD had strong repellent properties with over 90% repellency at the two highest concentrations tested. Using the FAO 2004 guidelines, we evaluated the effectiveness of these organic compounds at reducing the fecundity of R. (B.) microplus and show that Nootkatone, Stop the Bites, and BioUD may significantly decrease tick populations (Drummond's index > 90% at concentrations of 5%), highlighting their potential as alternatives to synthetic acaricides for the control of cattle fever ticks.

Tolerance of Steinernema carpocapsae infective juveniles in novel nanoparticle formulations to ultraviolet radiation

Entomopathogenic nematodes (EPNs) are susceptible to abiotic environmental factors including ultraviolet (UV) radiation, which affects the survival and efficacy. This study evaluated nanoparticle (NP) formulations for protecting Steinernema carpocapsae infective juveniles (IJs) from UV radiation. First, silica-NH₂ NPs at oil-to-water ratios of 2:8, 3:7 and 4:6 were compared with Barricade Fire Gel (1 % and 2 %) and a water control (aqueous IJs) by exposing IJs to UV light (254 nm) for 0, 10 and 20 min. Barricade gel (especially 2 % Barricade) significantly improved IJs viability after UV treatment, while all three NPs had adverse effects on IJ viability after UV radiation. Subsequently, two silica (SiO₂ basic and advanced) and one titania (TiO₂) based formulations were tested with Barricade (1 % and 2 %) and a water control. The titania-NH₂ NPs provided the highest UV protection, and IJ viability and virulence were not reduced even after 20-min UV. Except TiO₂, only 2 % Barricade at 10-min UV and SiO₂ basic at 20-min UV had lower IJ mortality than the water control. Only TiO₂ formulated IJs caused higher insect mortality and infection levels than aqueous IJs after UV treatment. The UV tolerance of TiO₂ was further examined by assessing the number of nematodes invading the hosts. Consistent with virulence tests, the number of invading nematodes in titania-NH₂ NPs did not decrease after UV radiation for 10 or 20 min compared with the no-UV control. The anti-UV capability of titania-NH₂ NPs has promise as a tool to enhance biocontrol efficacy of EPNs under field conditions.