Distribution of Rhipicephalus (Boophilus) microplus and Rhipicephalus (Boophilus) annulatus (Acari: Ixodidae) infestations detected in the United States along the Texas/Mexico border.

Species identification and global positioning system coordinates of infestations of cattle fever ticks, Rhipicephalus (Boophilus) annulatus (Say) and Rhipicephalus (Boophilus) microplus (Canestrini), were determined for 790 specimens submitted to the National Veterinary Services Laboratory between 1 October 1999 and 30 September 2010. Cattle fever tick specimens obtained by personnel of the United States Department of Agriculture-Animal and Plant Health Inspection Service-Cattle Fever Tick Eradication Program from infested cattle and wildlife along the Texas/ Mexico border were submitted for identification, as required by the program. A geographic information system database was developed that incorporates location, collection, and infestation records. Submitted ticks came from 11 Texas counties and were comprised of 19.5% R. (B.) annulatus and 80.5% R. (B.) microplus. Maps produced from this study locate and define the parapatric boundary between R. (B.) annulatus and R. (B.) microplus.

Evidence for role of white-tailed deer (Artiodactyla: Cervidae) in epizootiology of cattle ticks and southern cattle ticks (Acari: Ixodidae) in reinfestations along the Texas/Mexico border in south Texas: a review and update.

From 1907 when the fever tick eradication campaign began until 1933, the tick eradication methods of dipping cattle in an acaricide or "pasture vacation" were enormously successful in eradicating southern cattle ticks [Rhipicephalus (Boophilus) microplus (Canestrini)], until failures began to occur in some areas of Florida. Regarding the failures in Florida, the consensus was that populations of white-tailed deer [Odocoileus virginianus (Zimmermann)] infested with southern cattle ticks were responsible. After numerous deer in several counties were killed, eradication was achieved in Florida. As in Florida, in Texas increasing numbers of failures of the pasture vacation approach to tick eradication from the 1970s to the present are known to be related to the abundance of white-tailed deer and perhaps other wild ungulate species. A sizable body of evidence confirms the hypothesis that white-tailed deer support the dispersal and maintenance of both cattle ticks [Rhipicephalus (Boophilus) annulatus (Say)] and southern cattle ticks (cattle fever ticks) within the permanent quarantine or buffer zone in South Texas along the Rio Grande, as well as in the so-called free ("cattle fever tick-free") area north and east of the buffer zone and extending to the east coast of the United States. As of August 2009, in addition to the permanent quarantine zone of approximately 2233 km2, three temporary preventative or blanket quarantines were established. Currently, only two methodologies exist to control ticks feeding on white-tailed deer: (1) a systemic treatment method involving dispersal of ivermectin-medicated corn, Zea mays L.; and (2) two topical treatment methods, '4-poster' deer treatment bait stations and '2-poster' deer treatment feeder adapters, both of which passively apply topically active acaricide to deer for the eradication of populations of cattle fever tick associated with white-tailed deer. This study presents and summarizes confirmational support for the role of white-tailed deer derived from historical accounts, circumstantial evidence from review of recent infestations, and cattle fever tick infestations on white-tailed deer that were live-captured and examined specifically for cattle fever ticks.

Variation in general esterase activity within a population of Haematobia irritans (Diptera: Muscidae).

Control of the horn fly, Hematobia irritans (L.), is generally dependent on chemical insecticides. However, the biology and behavior of the horn fly favors rapid development of insecticide resistance. To prolong the effectiveness of the insecticide option, information is required regarding the mechanisms of insecticide resistance. Metabolic hydrolysis of insecticides by esterases is a detoxification mechanism in many insect species. Measurement of general esterase activity within populations of horn flies may provide a diagnostic tool for resistance management. In this study we evaluated the amount of variation in general esterase activity within female and male horn fly samples from a population that had not been exposed to insecticides for 8 yr. We found considerable variation in general esterase activity within samples of each sex, with females demonstrating the greater variation. The observed variation is thought to be the result of age-structure dynamics within the population. The amount of inherent variation makes it difficult to detect small mean differences between populations, thus limiting the utility of general esterase assays. Thus, effective diagnosis of esterase-mediated resistance mechanisms can only be achieved by the identification of specific detoxification esterases and the design of assays, either biochemical or molecular, for their detection and measurement.

Evaluation of horn flies (Diptera: Muscidae) from a pyrethroid susceptible colony for general and permethrin esterase activities.

In this study we describe a nonradioactive single-fly microassay for permethrin hydrolysis. We used this assay with a microplate assay for general esterase activity to evaluate the permethrin hydrolyzing and general esterase activities of aging pyrethroid-susceptible male and female horn flies, Haematobia irritans (L.). We found substantial gender- and age-related differences regarding general esterase activity, permethrin sensitivity, and permethrin hydrolyzing activity within the colony. Extracts of female flies collected 48 h after receiving their first blood meal yielded significantly greater esterase activity than male extracts. Aging female flies were more tolerant of permethrin than were male flies. In addition, a positive correlation was found to exist between the general esterase activity of aging females and their ability to hydrolyze permethrin.

Role of the kdr and super-kdr sodium channel mutations in pyrethroid resistance: correlation of allelic frequency to resistance level in wild and laboratory populations of horn flies (Haematobia irritans).

The kdr and super-kdr point mutations found in the insect sodium channel gene are postulated to confer knockdown resistance (kdr) to pyrethroids. Using an allele-specific PCR assay to detect these mutations in individual horn flies, Haematobia irritans (L.), we determined the allelic frequency of the kdr and super-kdr mutations in several wild and laboratory populations. Wild populations with very similar allelic frequencies had resistance levels that ranged widely from 3- to 18-fold relative to a susceptible population. Conversely, the kdr allele frequency in a lab population with 17-fold resistance was nearly double that found in a heavily pressured wild population with 18-fold resistance. We conclude that, although the kdr mutation confers significant levels of pyrethroid resistance, a substantial component of resistance in insecticidally pressured populations is conferred by mechanisms that are PBO-suppressible. High super-kdr allele frequencies were detected in two resistant lab populations, but in wild populations with equivalent resistance the super-kdr allele frequency was very low. Interestingly, in over 1200 individuals assayed, the super-kdr mutation was never detected in the absence of the kdr mutation.