Evaluation of Barricade® to enhance survival entomopathogenic nematodes on cowhide

Authors: Shapiro Ilan, David; Goolsby, John

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2021
Publication Date: 4/18/2021
Citation: Shapiro Ilan, D.I., Goolsby, J. 2021. Evaluation of Barricade® to enhance survival entomopathogenic nematodes on cowhide. Journal of Invertebrate Pathology. 184. https://doi.org/10.1016/J.JIP.2021.107592.
DOI: https://doi.org/10.1016/J.JIP.2021.107592

Interpretive Summary: Cattle fever ticks (CFT), Rhipicephalus microplus and R. annulatus, are invasive livestock pests that are endemic to Mexico and invasive along the Texas – Mexico border. Acaricide resistance, alternate wildlife hosts, and pathogenic landscape forming weeds 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. One of the alternate wildlife hosts for CFT in South Texas are nilgai (Boselaphus tragocamelus), an exotic Asian bovid. Nilgai are highly mobile with large home ranges and are implicated in the spread of CFT, through the landscape. Insect and tick killing parasitic round worms (entomopathogenic nematodes) are under evaluation for eradication of CFT on nilgai. Nematodes can be applied as a water-based spray to nilgai. A remotely activated field sprayer was developed for application of nematodes on CFT infested nilgai as they transit fence crossings. Nematodes have the potential to be transferred to tick-infested nilgai as they transit fence crossings and brush against vegetation and soil that has been wetted by the nematode suspension. Nematodes are sensitive to sunlight and dessication. We evaluated the fire suppression gel, Barricade®, to protect the nematode in the spray solution to reduce dessication and damage from sunlight. The test was done on cowhide to mimic an application made to a tick infested nilgai. Wax moth larvae were used as a substitute for cattle fever ticks due to regulations. Barricade® worked well to increase the longevity of the nematode, Steinernema riobrave, but not the other species, Heterorhabditis floridensis. Barricade® mixed in water with S. riobrave has the potential to increase the efficiency of the remotely operated nilgai sprayer and possibly for direct application of the nematode to fever tick infested pastures.

Technical Abstract: Entomopathogenic nematodes (EPNs), Steinernema riobrave and Heterorhabditis floridensis are under evaluation for eradication of the southern cattle fever tick, Rhipicephalus microplus infesting nilgai antelope, in South Texas. Remotely operated field sprayers have been developed to directly treat nilgai antelope with EPNs as they transit fence crossings and as they contact wetted foliage and soil from the surrounding area. EPNs are known to be susceptible to mortality from ultraviolet light (UV) and desiccation. A sprayable fire gel, Barricade®, has been reported to protect EPNs from UV and desiccation but has not been tested on animal hides. Barricade® at 1 and 2 percent rates was mixed with the water solution of S. riobrave and H. floridensis and applied to cowhides (to mimic direct treatment of nilgai) and filter paper and then these substrates were placed out of doors in 0, 30, 60 or 120 minutes of sunlight. Wax moth larvae were exposed to the cowhides and filter paper to determine efficacy of the EPNs. Efficacy of S. riobrave with 1 and 2% Barricade® gel applied to cowhides was significantly improved at 30 and 60 minutes as compared to the control. At 120 minutes mortality of the wax moth larvae was near zero for both the control and the treatments. Similar results were found with the filter paper test. In contrast, efficacy of H. floridensis with Barricade® applied to cowhides or filter paper was not significantly improved at 30, 60 or 120 minutes as compared to the water only control. Barricade® has the potential to improve the efficacy of S. riobrave and other EPNs by reducing mortality and desiccation, especially when used in the remotely operated sprayer developed for treatment of cattle fever tick infested nilgai.