Progress 06/01/02 to 05/31/06
Outputs
Male Gulf Coast ticks, Amblyomma maculatum, were found to produce a pheromone at least as early as the 4th day of bloodfeeding on cattle. Pheromone production continued as long as males were attached. Phermone production declined within 2-4 hours of forced male tick removal, but was renewed when ticks were allowed to reattach to the host. Bloodfeeding by male ticks was required before pheromone was produced. The pheromone consisted of at least 9 volatile compounds, three of which were predominant, and there was variation in the pheromone produced between geographic strains from Texas and Oklahoma. Biological activity exhibited by female ticks was established using y-tube olfactometer and petri-dish selection bioassay techniques. These experiments showed synergistic responses from unfed female ticks to combinations of phermone from fed males and carbon dioxide, compared to either of these sources alone. An evaluation of archived field data of counts of male and female
ticks on cattle from June to October in Texas suggests that questing female ticks are able to select cattle with feeding male ticks over cattle without males. Attempts to release pheromone extract on CO2 tick traps to attract female ticks has not been satisfactory to-date, but remains a hopeful approach to tick suppression when technical details are solved. In separate studies of nymph aggregation and attachment inside stockinette cells on cattle, nymphs were 6 times more likely to aggregate and attach near feeding males than to feeding females, or in control cells without ticks. There was a corresponding decrease in nymph mortality and increase in complete feeding success for nymphs in cells containing feeding males. This project has verified the presence of an attraction-aggregation-attachment pheromone produced by feeding male Gulf Coast ticks, provided evidence of the components of the pheromone and evaluated the dynamics of its production in feeding males. The project has also
provided evidence that aggregation-attachment behavior of nymphs is impacted by feeding males. Further chemical analysis and development is needed before the pheromone will become a useful tool in IPM strategies. All evidence to date supports the hypothesis that the Gulf Coast tick male pheromone will provide useful tactics in tick IPM strategies. Three Master of Science theses have been completed, and several manuscripts are pending.
Impacts
Gulf Coast ticks cause substantial economic loss to cattle producers throughout its range and the potential role of this tick in heartwater transmission, a foreign animal disease now found in the Caribbean, poses significant risk to ruminants in the US. Results of these studies show that male ticks produce a pheromone that influences attraction to female ticks and that has potential attraction and attachment influence on nymphs. Incorporating male pheromone with CO2 could improve surveillance of trapping devices for off-host ticks, and incorporation of an acaricide with the pheromone could lead to attraction-killing devices for tick population suppression.
Publications
- No publications reported this period
|
Progress 01/01/05 to 12/31/05
Outputs
A randomized block experimental design was used to test whether feeding site aggregation and mortality of Gulf Coast tick nymphs placed on cattle was influenced by feeding adult males, feeding adult females, or absence of adult ticks (control). The experiment was conducted by confining 10 male, 10 female ticks, or no ticks inside six 2-inch stockinette cells adhered to six sites on the backs of bos taurus-type heifers. A larger 8-inch diameter stockinette cell was adhered to each site with the smaller inner cell at the inside center. On the 6th day, the smaller cells were removed and 30 nymphs were released within each of the large cells. On the 10th day, the attachment site of each nymph was recorded and a count of live nymphs determined. Statistical analyses revealed that type of treatment significantly influenced both mortality and aggregation of nymphs. The highest mortality and lowest overall attachment were found in the control and female tick treatment cells.
The lowest mortality and highest attachment were found in the male treatment cells. Nymphs were 6 times more likely to be found attached in close proximity to males inside the inner cell area than the other treatements. These results support earlier preliminary observations that nymphs aggregate near feeding male ticks of this species. Our previous studies show that male Gulf Coast ticks produce an attraction-aggregation-attachment pheromone (AAAP)detectable by GC analysis as early as the 4th feeding day and that this pheromone influences female behavior. It now appears that this pheromone may also encourage nymph aggregation and attachment, and consequently reduce nymph mortality in some circumstances. To further support the hypothesis of AAAP involvement by feeding male Gulf Coast ticks, host selection by questing female ticks to cattle with feeding male ticks was examined using archived data obtained from untreated free-ranging cattle pastured on native rangeland. Female ticks were
significantly more likely to be found on cattle with feeding male ticks than without (Chi Square Analysis, P<0.01). Data were fit by regression to establish prediction equations for the number of female ticks on a cow as a function of number of male ticks per cow. These field-based host-parasite interactions support our earlier laboratory observations of a synergistic effect on female attraction in olfactometry bioassays when the male AAAP is combined with carbon dioxide. These findings will further the identification and development of this AAAP for tick suppression tactics. Two additional Master of Science theses have been completed and manuscripts are forthcoming.
Impacts
Gulf Coast ticks cause substantial economic loss to cattle producers throughout its range and the potential role of this tick in heartwater transmission, a foreign animal disease now found in the Caribbean, poses significant risk to ruminants in the US. Results of these studies show that male ticks produce a pheromone that influences attraction to female ticks and that has potential attraction and attachment influence on nymphs. Incorporating male pheromone with CO2 could improve surveillance of trapping devices for off-host ticks, and incorporation of an acaricide with the pheromone could lead to attraction-killing devices for tick population suppression.
Publications
- No publications reported this period
|
Progress 01/01/04 to 12/31/04
Outputs
Production of pheromones from male Gulf Coast ticks originating from two geographic locations (Texas and Oklahoma) were investigated. Volatile organic compounds were collected from feeding male ticks after removal from bovine hosts by solidphase micro-extraction technique and evaluated by gas chromotography. Nine volatile chemicals were separated by gas chromotography having peaks at retention times from 9.7 to 15.6 minutes. Three of the nine chemicals were prominent with the peak at 11.4 minutes being the most dominant. This composition of peaks was not captured from unfed male ticks. The three most prominent chemicals were present in both Oklahoma and Texas strains of ticks, but varied in amount of each individual compound. Production of these chemicals began to decline between 2 and 4 hours removal from the host, but could be renewed if males were allowed to re-attach to their hosts. Experiments measuring pheromone production from unfed males, males in contact with
bovine hosts but not allowed to feed, and 3- and 8-day fed males confirm that bloodfeeding is necessary to produce the organic chemicals thought to comprise the phermone. There were significant differences among the 3 predominant chemicals of interest identified by GC analysis above. Two of these chemicals were produced in significantly greater quantities by males fed 3-days compared to 8-day fed males; however the most dominant of these three chemicals was produced in significantly higher amounts by 8-day fed ticks. Biological activity of volatile compounds from 8-day fed males was confirmed by petri dish and Y-tube olfactometry bioassays. Significantly higher numbers of female ticks were attracted to fed male ticks compared to unfed males or empty test chambers in the petri dish bioassay for both Texas and Oklahoma strains. The olfactometry bioassay allowed females to make a choice response between two sources. Female responses to choices of purified air vs air+fed-male ticks, air
vs air+CO2, or air vs air+fed-males+CO2 showed that significantly more females were attracted to the combination of air+fed-males+CO2 than any other test combination. Preliminary experiments were completed to test design procedures for evaluating whether feeding males are attractive to unfed nymphs. Preliminary results show that nymphs tend to aggregate their attachment sites around feeding males compared to a scattered random attachment pattern when males are absent. One master of science thesis has been completed and three manuscripts will be submitted for publication review.
Impacts
Gulf Coast ticks cause substantial economic loss to cattle producers throughout its range and the potential role of this tick in heartwater transmission, a foreign animal disease now found in the Caribbean, poses significant risk to ruminants in the US. Results of these studies show that male ticks produce a pheromone that influences attraction to female ticks and that has potential attraction and attachment influence on nymphs. Incorporating male pheromone with CO2 could improve surveillance of trapping devices for off-host ticks, and incorporation of an acaricide with the pheromone could lead to attraction-killing devices for tick population suppression.
Publications
- No publications reported this period
|
Progress 01/01/03 to 12/31/03
Outputs
Pheromone extracts were obtained from fed Texas and Oklahoma strains of male gulf coast ticks. These phermones have been chemically characterized and found to be quite similar having the same principal components, but differ in relation to relative amounts of these components. The pheromones have been determined to be biologically active for female ticks in both a standard petri-dish test and in olfactometry tests. Olfactometry tests have revealed that female response to a combination of carbon dioxide and male pheromone is greater than that of either stimulant alone. Tests are now being conducted to incorporate the pheromone into inert matrix materials for testing in carbon dioxide traps and for on-animal applications.
Impacts
Incorporating male gulf coast tick pheromone with CO2 could improve surveillance potential of a trapping device for off-host ticks, and further incorporation of an acaricide into the mixture could lead to attraction-killing devices for tick population suppression. Application of the pheromone to slow-release devices used on cattle could also enhance tick suppression.
Publications
- No publications reported this period
|
Progress 01/01/02 to 12/31/02
Outputs
To date, graduate research assistants have been selected and work on pheromone extraction from feeding male ticks initiated. Separate pheromone extraction from ticks originating in Texas and Oklahoma will allow comparison of biological activity in CO2-trap and on-animal applications scheduled for spring-summer of 2003. Collabortion with a chemist, external to this project, will enable chemical characterization of the extracted pheromones.
Impacts
Incorporating the natural pheromone with CO2 would improve the surveillance potential of a trapping device for off-host ticks, and further incorporation of an acaricide into the mixture could potentially lead to an attraction-killing device to suppress tick populations. Application of the pheromone to slow-release devices used on cattle could also enhance tick suppression.
Publications
- No publications reported this period
|
|