DNA Diagnostic Tools for Detecting Beneficial Wasps to Help Control Cattle Fever Ticks and Tick-borne Zoonoses
Cattle fever ticks are a growing concern for livestock producers, property owners, and wildlife managers. Their presence on property, livestock and wildlife in Texas forces owners to quarantine their livestock and begin expensive treatments to eliminate ticks to prevent the onset of Texas cattle fever (also named bovine babesiosis), a highly fatal disease for infested animals.
A tick eradication program was developed in 1906 and after being considered successful in the southeast U.S., a quarantine zone was established across the Texas/Mexico border to prevent reestablishment. However, recent expansion of cattle fever tick infestations has resulted in quarantines in Texas counties away from the Mexico border that comprise the permanent fever tick quarantine zone. Increasing prevalence of tick hosts among native and exotic hoofed mammals, widespread tick pesticide resistance, and climate change undermine efforts to control bovine babesiosis. Biological control using small parasitoid wasps is seen as a potential complementary method of controlling cattle fever ticks.
Searching for cattle fever ticks parasitized by beneficial wasps using conventional methods is like looking for a needle in a haystack. These wasps are extremely small (1-mm) making them difficult to collect and quantify their impact. This leads to an underestimation of their presence and impact to tick populations. In addition, the prevalence of the wasps emerging from ticks, once they have completed their development, could be extremely low (3%), making the search for wasps very cumbersome and expensive.
Molecular methods have revolutionized the field of diagnostics, and today, application in the detection of wasp DNA within tick host DNA is a reality. However, current DNA-based methods for detecting and surveying wasps applied mainly to adult ticks and did not take much into account the juvenile ticks which are potentially highly parasitized. This could explain why the true parasitism may have gone unnoticed or underestimated.
To help alleviate this issue, European Biological Control Laboratory (EBCL) researchers attempted to optimize current DNA based methods. The most substantial recent milestone was real time monitoring of fluorescence during DNA amplification to detect early developmental stage of wasps, such as eggs, in tiny juvenile ticks. While this is still at the experimental stage, the method seems promising as it is possible to detect as little as one unit of wasp DNA mixed with 3,000 units of DNA of the juvenile ticks (Figure 1).Further testing is underway, specifically on cattle fever ticks collected in the Balkan region, which matches genetically with cattle fever ticks spreading in Texas. Once completely validated, this method would help to streamline the search of beneficial wasp populations to control cattle fever ticks and associated tick-borne zoonoses.
The European Biological Control Laboratory (EBCL) was established in 1991 near Montpellier, France. EBCL was created by the merger of the former European Parasite Laboratory, established in Paris in 1919, and the Biological Control of Weeds Laboratory in Rome. EBCL has a satellite laboratory in Thessaloniki, Greece. As the only USDA ARS-operated laboratory outside the United States, EBCL develops biological control technologies which can be used to suppress invading weeds and insect pests of Eurasian origin. EBCL researchers do this by searching for natural enemies (insects, mites, and pathogens) in their native habitat, determining their identity, testing their host specificity and potential impact in laboratory and field experiments, and shipping promising organisms to the U.S. for further testing as biological control agents. EBCL collaborates with scientists in many countries in Europe, Asia, and Africa to explore in regions of origin of the target weeds and insects.