Treatment of cattle with Steinernema riobrave and Heterorhabditis floridensis for control of the Southern Cattle Fever Tick, Rhipicephalus (=Boophilus) microplus (Acari: Ixodidae)

Authors: Goolsby, John; SINGH, NIRBHAY - Guru Angad Dev Veterinary & Animal Sciences University; Shapiro Ilan, David; Miller, Robert; Moran, Patrick; Perez De Leon, Adalberto - Beto

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2018
Publication Date: 6/1/2018
Citation: Goolsby, J., Singh, N.K., Shapiro Ilan, D.I., Miller, R., Moran, P.J., Perez De Leon, A.A. 2018. Treatment of cattle with Steinernema riobrave and Heterorhabditis floridensis for control of the Southern Cattle Fever Tick, Rhipicephalus (=Boophilus) microplus (Acari: Ixodidae). Southwestern Entomologist. 43:295-302.

Interpretive Summary: Cattle fever ticks (CFT) Rhipicephalus (=Boophilus) microplus and Rhipicephalus 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 vectors of bovine babesiosis, a lethal disease causing high mortality particularly in susceptible European breeds of cattle and severely affecting 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 from wildlife and stray cattle. In recent years, there has been an increase in CFT infestations outside of the PQZ in Texas. Entomopathogenic nematodes are a promising alternative for tick control, especially to protect wildlife. Nilgai (Boselaphus tragocamelus) is an exotic Asian antelope and an alternative wildlife host species for CFT in South Texas. Insect and tick killing parasitic round worms (nematodes) are under evaluation for eradication of CFT on cattle and nilgai. Since they are native to the Rio Grande Valley, non-toxic to mammals, and available commercially, six nematode species were tested in the laboratory for control of CFT. Two species Steinernema riobrave and Heterorhabditis floridensis performed well in lab tests and were selected for further testing on live cattle infested with CFT. In these tests, S. riobrave and H. floridensis when applied directly to infested cattle, affected all life stages of the tick (larvae, nymphs and adults), and caused 14.5 and 25.4% mortality of adult engorged female ticks from one single application of the nematodes. To our knowledge this is the first study of nematodes applied directly to cattle or other mammals for control of CFT. Higher rates of nematodes, ie. more nematodes per gallon of spray solution could significantly increase the control of CFT and warrants further testing.

Technical Abstract: Entomopathogenic nematodes are a promising alternative for tick control, especially to protect wildlife. Two entomopathogenic nematode species Steinernema riobrave Cabanillas, Poinar, and Raulston and Heterorhabditis floridensis Nguyen, Gozel, Koppenhöfer, and Adams were tested for in-vivo efficacy against southern cattle fever tick, Rhipicephalus (=Boophilus) microplus Canestrini. Twelve heifer calves were experimentally infested three times at 1-week intervals with 125 mg of larvae of southern cattle fever ticks on days 0, 7, and 14. On Day 21, the animals were randomly divided into three treatment groups and sprayed with water only (check) or 5,000 infective juvenile S. riobrave or H. floridensis nematodes per milliliter. Number of ticks dropped, reproductive index, percentage of inhibition of oviposition, and hatching rate were calculated. S. riobrave and H. floridensis affected all life stages of the tick, and caused 14.5 and 25.4% reduction in production of adult engorged female ticks during the first 21 days post treatment. The nematodes significantly affected the reproductive parameters of treated ticks, but not egg hatchability. To our knowledge this is the first study to show a negative impact on ticks by entomopathogenic nematodes applied directly to the mammalian host of the tick. But, additional research is needed, especially higher rates, to enhance tick control using entomopathogenic nematodes. Novel formulations that enhance penetration or survival by nematodes should be investigated.