Comparative efficacy of entomopathogenic nematodes against multi-acaricide resistant strain of cattle fever tick, Rhipicephalus microplus (Acari: Ixodidae)

Authors: Goolsby, John; SINGH, NIRBHAY - Guru Angad Dev Veterinary & Animal Sciences University; SHAPIRO, DAVID - US Department Of Agriculture (USDA); Miller, Robert; Perez De Leon, Adalberto - Beto

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2019
Publication Date: 3/1/2019
Citation: Goolsby, J., Singh, N.K., Shapiro, D.I., Miller, R., Perez De Leon, A.A. 2019. Comparative efficacy of entomopathogenic nematodes against multi-acaricide resistant strain of cattle fever tick, Rhipicephalus microplus (Acari: Ixodidae). Southwestern Entomologist. 44:143-153. https://doi.org/10.3958/059.044.0116.
DOI: https://doi.org/10.3958/059.044.0116

Interpretive Summary: Cattle fever ticks (CFT) Rhipicephalus (=Boophilus) microplus and Rhipicephalus annulatus, are livestock pests that are endemic in 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 vectors for bovine babesiosis, a disease causing high mortality particularly in susceptible European breeds of cattle that can severely impact the beef cattle industry. Efforts to eradicate CFT from the United States have been successful. However, a permanent quarantine zone (PQZ) is maintained between Texas and Mexico to prevent incursions of CFT. In recent years, there has been an increase in CFT infestations outside of the PQZ in Texas. One of the alternate wildlife hosts for CFT in South Texas are nilgai (Boselaphus tragocamelus), an exotic species related to cattle. Nilgai are highly mobile with large home ranges and are implicated in the spread of CFT through the landscape. Currently, there are no methods for control of CFT on nilgai other than culling. Insect and tick killing parasitic round worms (entomopathogenic nematodes) are under evaluation for eradication of CFT on nilgai. Nematodes could be applied as a water-based spray to nilgai as they move through fence crossings and use latrines. Since the nematodes are native to the Rio Grande Valley, non-toxic to mammals, and some are available commercially, six nematode species were tested in the laboratory for control of not only CFT, but a highly acaricide resistant strain of CFT from the Yucatan in Mexico. Further, all the entomopathogenic nematodes produced significant mortality to the engorged resistant ticks and the effect of the nematodes increased with higher concentrations of the nematodes. The results of the current study were similar to recent studies evaluating the nematodes against acaricide susceptible cattle fever ticks and demonstrate the potential of entomopathogenic nematodes for effective control of tick populations resistant to various classes of chemical acaricides. To our knowledge this is the first study exploring the use of entomopathogenic nematodes for eradication of acaricide resistant CFT.

Technical Abstract: The current study was undertaken to evaluate the comparative efficacy of entomopathogenic nematode infective juveniles of Steinernema riobrave Cabanillas, Poinar, and Raulston (355 strain), S. carpocapsae (Weiser) (All strain), S. feltiae Filipjev (SN strain), Heterorhabditis bacteriophora Poinar (VS strain), H. indica Poinar, Karunakar, and David (HOM1 strain), and H. floridensis Nguyen, Gozel, Koppenhöfer, and Adams (K22 strain) against engorged adult females of the multi-acaricide resistant Yucatan strain of Rhipicephalus microplus (Cannestrini). Engorged female ticks were exposed to different concentrations of infective juveniles (1250, 2500 and 5000 per Petri dish) for 72 h in Petri dishes. The effects on mortality, egg mass weight, reproductive index, percent inhibition of oviposition and hatching percentage were assessed. A dose-dependent mortality response was recorded in ticks for all entomopathogenic nematodes except S. feltiae. Among the two genera of nematodes used, minimum LC50 (95% CL) values of 3180.2 (2957.9-3419.3) and 490.9 (462.1-521.5) nematodes per dish were estimated for S. riobrave and H. floridensis, respectively. Further, all the entomopathogenic nematodes produced significant reduction (p<0.05) on the reproductive index of the engorged ticks and the effect was also dose-dependent (except for S. feltiae) as higher concentrations produced maximum reduction. No effect on egg hatchability was recorded in infective juvenile exposed groups. The results of the current study demonstrate the high potential of entomopathogenic nematodes for effective control of tick populations resistant to various classes of chemical acaricides.