Development of entomopathogenic nematodes for control of cattle fever ticks on wildlife

 
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.  Field and lab 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 field 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 field sprayer treatments 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 Guineagrass leaves for up 180 minutes.  These studies show the potential for passive application of S. riobrave to nilgai for control of R. microplus as they transit fence crossings.