Evaluation of the efficacy of Steinernema riobrave against Rhipicephalus microplus larvae at semi-field conditions

Authors: Goolsby, John; Maestas, Lauren; Adamczyk, John

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2024
Publication Date: 11/4/2024
Citation: Goolsby, J., Maestas, L.P., Adamczyk Jr, J.J. 2024. Evaluation of the efficacy of Steinernema riobrave against Rhipicephalus microplus larvae at semi-field conditions. Southwestern Entomologist. https://doi.org/10.3958/059.049.0116.
DOI: https://doi.org/10.3958/059.049.0116

Interpretive Summary: Cattle fever ticks (CFT) are invasive livestock pests that are endemic to Mexico and invasive along the Texas – Mexico border. Pesticide resistance, alternate wildlife hosts, and pasture weeds that help ticks survive all present challenges for sustainable eradication of this pest in the U.S. CFT are the vector for bovine babesiosis, a lethal disease causing high mortality particularly in cattle. Efforts to eradicate CFT from the United States have been successful; however, in recent years, there has been an increase in CFT infestations outside of the Permanent Quarantine Zone in Texas. New methods for management of cattle fever tick-infested white-tailed-deer and nilgai are needed especially along the Texas-Mexico border. This manuscript documents evaluates the use of entomopathogenic nematodes (round worms) to eradication of larval CFT on wildlife and larval CFT in infested pastures. Although the results show that the entomopathogenic nematode shows promise as a tool for controlling larval CFT in pastures, more research is needed to reduce the effect of UV light and rapid desiccation of nematodes once they have been sprayed on infested pastures. The adjuvant Barricade, which can be added to water in spray tanks, is suggested as way to reduce UV light and desiccation of nematodes.

Technical Abstract: The entomopathogenic nematode, Steinernema riobrave has a moderate impact on larval cattle fever ticks, Rhipicephalus microplus under semi-field conditions. Weekly foliar applications of in vitro reared S. riobrave (BASF – Nemasys-R) applied as spray on tick-infested potted buffelgrass caused significant mortality to R. microplus larvae. The use of a native nematode species, like S. riobrave, which occurs in the South Texas environment and would have few, if any, effects on native flora/fauna is favored by conservation focused organizations, especially in certain areas, inhabited by threatened or endangered species. Additional research is proposed to evaluate the impact of Nemasys-R under pasture conditions. An effective pasture treatment for questing R. microplus larvae is critical to support the USDA-APHIS Cattle Fever Tick Eradication program in South Texas.