Passive transfer of Steinernema riobrave entomopathogenic nematodes with potential implications for treatment of cattle fever tick-infested nilgai

ABSTRACT

The entomopathogenic nematode, Steinernema riobrave is under evaluation for eradication of the southern cattle fever tick, Rhipicephalus microplus infesting nilgai antelope, in South Texas. Previous lab trials have shown that S. riobrave is effective against R. microplus. Remotely operated field sprayers have been developed to directly treat nilgai as they transit fence crossings. Mist from the sprayers also wets the surrounding foliage and soil at crossings. Studies were conducted to determine the potential for passive transfer of the nematodes from wetted foliage/soil and length of time nematodes remained viable in water droplets on leaves of Guineagrass. Wax moth larvae, Galleria mellonella were used as a facsimile for R. microplus due to regulatory constraints. Larvae exposed to S. riobrave under field conditions (misted by sprayer, hand misted, touched to misted Guineagrass leaves, drenched soil and misted soil) showed significantly lower levels of survival (0–42%). Larvae hand-misted and misted by the sprayer showed very low levels of survival (0–2%). Larvae in the three treatments which represented passive transfer of nematodes (nematode misted soil, drenched soil, and misted leaves) also showed low levels of survival at 42, 22, and 15% respectively. In contrast, larvae not exposed to S. riobrave showed high levels of survival (84–93%). In lab studies, S. riobrave remained viable in water droplets on leaves for up 180 min. These studies show the potential for direct and passive application of S. riobrave to infested nilgai for control of R. microplus as they transit the area around fence crossings.

KEYWORDS:

• Biological control
• livestock entomology
• entomopathogenic nematodes
• Steinernema riobrave

Acknowledgements

The authors thank Reyes Garcia (USDA-ARS, Edinburg, TX); Ann Vacek and Emma Sanchez, (University of Texas – Rio Grande Valley, Edinburg, TX), and Maurcio Cruz (Texas State Technical College, Harlingen, TX) for technical support; Diana Londoño and Boomer Cardinale of BASF, Inc (Raleigh, NC) provided the Nemasys-R used in the studies. We appreciate the support of the local ranching and wildlife community including Las Huellas, Brownsville, TX. We recognize the support of USDA-APHIS Veterinary Services and Texas Animal Health Commission, Cattle Fever Tick Eradication Program. Research reported here was supported through appropriated research project 3094-32000-042-00-D, Integrated Pest Management of Cattle Fever Ticks. This article reports results of research only and mention of a proprietary product does not constitute an endorsement or recommendation by the USDA for its use. USDA is an equal opportunity provider and employer.

Disclosure statement

No potential conflict of interest was reported by the author(s).