Facilitative ecological interactions between invasive species: Arundo donax (Poaceae) stands as favorable habitat for cattle ticks (Acari: Ixodidae) along the U.S.-Mexico border

Authors: Racelis, Alexis; Davey, Ronald; Goolsby, John; Perez De Leon, Adalberto - Beto; VARNER, KEVIN - Animal And Plant Health Inspection Service (APHIS); DUHAIME, ROBERTA - Animal And Plant Health Inspection Services (APHIS), National Wildlife Center

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2011
Publication Date: 2/28/2012
Citation: Racelis, A.E., Davey, R.B., Goolsby, J., Perez De Leon, A.A., Varner, K., Duhaime, R. 2012. Facilitative ecological interactions between invasive species: Arundo donax (Poaceae) stands as favorable habitat for cattle ticks (Acari: Ixodidae) along the U.S.-Mexico border. Journal of Medical Entomology. 49(2):410-417.

Interpretive Summary: The cattle tick is a key vector of protozoa that causes bovine babesiosis, also known as cattle fever, a disease in cattle that causes mortality and morbidity. Largely eradicated from most of the US over the last century, the cattle tick continues to infest south Texas along the Cattle Fever Tick Quarantine Zone, and recent outbreaks of the cattle tick in this area may signal a resurgence of this debilitating disease. An improved understanding of the dynamic ecology of cattle ticks along the U.S.-Mexico border is required to devise strategies for sustainable eradication efforts. Management areas of the southern cattle tick overlap considerably with dense, wide infestations of the non-native, invasive perennial grass known as giant reed (Arundo donax L.). Here we show that when compared to other nearby habitats (open grass pastures and closed canopy forests), giant reed infestations presented conditions such as temperature and humidity that favor cattle tick survival and persistence. In sites where temperatures were extreme, specifically grass pastures, fewer females laid eggs and the resulting egg masses were smaller. The overhead canopies of giant reed stands and natural riparian forests reduced daily high temperatures, which was the best environmental predictor of egg-laying by engorged females. The diversity and abundance of potential predators such as spiders and ants was highest in pastures and natural riparian forests, signaling a low potential for natural suppression of tick populations in giant reed stands relative to other nearby environments. The finding that the highly invasive giant reed infestations present environmental conditions that facilitate the survival and persistence of cattle fever ticks, as well or better than native riparian habitats, represents an alarming complication for cattle fever tick eradication efforts in the U.S.

Technical Abstract: The southern cattle tick, Rhipicephalus (Boophilus) microplus (Canestrini), is a key vector of protozoa that causes bovine babesiosis. Largely eradicated from most of the U.S., the cattle tick continues to infest the Cattle Fever Tick Quarantine Zone in south Texas. Management areas of the southern cattle tick overlap considerably with dense, wide infestations of the non-native, invasive, water-consuming perennial grass known as giant reed (Arundo donax (L). This study explores whether stands of A. donax are associated with abiotic and biotic conditions that are favorable to tick survival. Two-hundred and thirty-four engorged females of R. microplus were sealed in fine mesh bags and placed securely at nine sites among three adjacent habitats: Arundo donax infestations, open pastures of buffelgrass (Pennisetum ciliare) and riparian forests of mixed native vegetation. Individuals were collected after three and six weeks to examine egg mass and egg hatch, respectively. A total of 48 control ticks were kept in a laboratory incubator and examined at the same intervals. Pitfall traps were placed in each of the nine field sites to estimate potential tick predators. When compared to other riparian habitats (open grasslands and closed canopy forests), A. donax infestations presented favorable conditions for R. microplus survival and persistence. The overhead canopies of A. donax stands and natural riparian forests reduced daily high temperatures, which was the best abiotic predictor of oviposition by engorged females. In sites where temperatures were extreme, specifically buffelgrass pastures, fewer females laid eggs and the resulting egg masses were smaller. Egg mass and percent egg hatch were strongly correlated to temperature. The highest diversity and abundance of potential predators was found in buffelgrass and natural riparian forests. Arundo donax stands were relatively depauperate of these insect families, signaling a low potential for natural suppression of tick populations in these areas. The finding that the highly invasive Arundo donax infestations present environmental conditions that facilitate the survival and persistence of cattle fever ticks, as well or better than native riparian habitats, represents an alarming complication for cattle fever tick eradication efforts in the U.S.