Efficacy of collars with allomones on dogs to control Rhipicephalus sanguineus sensu lato infestations under field conditions.

Benzaldehyde and 2-hexanone are allomones produced by beagle dogs that reduce infestation by Rhipicephalus sanguineus sensu lato on these animals and on susceptible dogs which artificially release these repellents. These observations were obtained in previous laboratory tests or artificial infestations of susceptible dogs under controlled conditions. Here we evaluated the efficacy of collars delivering these repellents for suppressing the loads of R. sanguineus s.l. on naturally infested mixed-breed dogs under field conditions. Thirty dogs naturally infested with R. sanguineus s.l. were separated into two groups with 15 dogs each. The dogs from the treatment group received the collars with slow-release formulations of the allomones, and the dogs from the control group received collars without such compounds. Collar effectiveness tests were carried out over 30 days. All ticks found were removed from each dog, identified, and counted every collection day. The density of the different life stages of R. sanguineus s.l. varied greatly between groups and across evaluation times. Adult ticks were the stage most abundant and prevalent on infested dogs. The counts for larvae, nymphs and adults were similar between the control and the treatment groups within each tick collection day. Conversely, when we considered the total number of ticks over 30 days and gathered all life stages collected in the same animal, the dogs from the control group had significantly higher loads (35.3 ± 4.27) of ticks than the dogs from the treatment group (21.8 ± 2.96) (P < 0.01). In addition, the efficacy of treatment with repellent collars was high for adult ticks (30.8%) but was extremely low for reducing larval or nymphal infestation (0 or 2.6%, respectively). The present study demonstrates, for the first time, the efficacy of these volatile compounds on naturally infested dogs under field conditions. The development of a technologically enhanced device for slow release of the allomones tested here can be an advantageous alternative for reducing R. sanguineus s.l. infestation on dogs in residential environments.

Identification of a non-host semiochemical from miniature pinscher, Canis lupus familiaris, that repels Rhipicephalus sanguineus sensu lato (Acari: Ixodidae).

It is already known that the beagle breed of domestic dogs produces semiochemicals capable of repelling the brown dog tick, Rhipicephalus sanguineus sensu lato (s.l.). With a view to discovering new non-host semiochemicals as tick repellents, we compared the semiochemicals produced by a putative tick-resistant breed of dog, miniature pinscher, with known tick-resistant (beagle) and tick-susceptible (English cocker spaniel) breeds. Two non-host compounds produced by beagles, i.e. 2-hexanone and benzaldehyde, were shown to be present in samples collected from all three breeds. Furthermore, two compounds, 6-methyl-5-hepten-2-one and 1,2,4-trimethylbenzene, were found in higher amounts in samples collected from miniature pinscher dogs. The mean amounts of benzaldehyde, 2-hexanone and 1,2,4-trimethylbenzene were similar for beagles and miniature pinschers (P > 0.05) and higher than the means observed for cocker spaniels (P < 0.05), whereas the mean amount of 6-methyl-5-hepten-2-one produced by miniature pinschers was significantly higher (P < 0.05) than for the other breeds of dogs. In Petri-dish assays with adult R. sanguineus s.l., 6-methyl-5-hepten-2-one was repellent for all observation periods evaluated for the two highest concentrations (0.100 and 0.200 mg.cm-2, P < 0.01). The obtained results support our hypothesis that miniature pinschers are a tick-resistant dog breed and agree with previous observations of miniature pinschers being the breed least parasitized by ticks. Furthermore, the non-host semiochemical 6-methyl-5-hepten-2-one has potential to be developed for use as a repellent for the protection of susceptible dogs from R. sanguineus s.l. ticks.

Surface lipidome of the lone star tick, Amblyomma americanum, provides leads on semiochemicals and lipid metabolism.

Lipids extracted from the surface of the lone star tick, Amblyomma americanum, were analyzed by high resolution mass spectrometry. Prior to lipid extraction, the adult ticks were either unfed or fed on cattle, and the fed ticks were in groups either containing males and females together, or containing only males or females. Cholesteryl esters were found on the surfaces of fed females, and they may provide a more complete description of the composition of the mounting sex pheromone. Dihydrocholesteryl esters were detected on the surfaces of unfed males and females, suggesting a possible role in survival during host-seeking. Dehydrodeoxyecdysone, found on fed females, could be a component of the genital sex pheromone. The most abundant polar surface lipids detected were acylglycerides. High levels of sphingolipids and glycerophospholipids on males fed separately might be derived, in part, from sperm development. A high level of a 20:4 fatty acid, presumably arachidonic acid, was found on the surface of fed females, indicating that it may be a component of the genital sex pheromone. A high level of docosenamide was found on the surface of fed females. Wax esters were found on the surfaces of fed ticks but not on unfed ticks. These esters could be involved in elasticity of the cuticle of engorged females or in wax coating of eggs. N-acylethanolamines were found on the surfaces of male and female ticks fed together, and on male ticks fed separately, but were absent or at low levels on females fed separately and on unfed ticks. This pattern suggests a possible role as a metabolic coordination primer pheromone.

Better than DEET Repellent Compounds Derived from Coconut Oil.

Hematophagous arthropods are capable of transmitting human and animal pathogens worldwide. Vector-borne diseases account for 17% of all infectious diseases resulting in 700,000 human deaths annually. Repellents are a primary tool for reducing the impact of biting arthropods on humans and animals. N,N-Diethyl-meta-toluamide (DEET), the most effective and long-lasting repellent currently available commercially, has long been considered the gold standard in insect repellents, but with reported human health issues, particularly for infants and pregnant women. In the present study, we report fatty acids derived from coconut oil which are novel, inexpensive and highly efficacious repellant compounds. These coconut fatty acids are active against a broad array of blood-sucking arthropods including biting flies, ticks, bed bugs and mosquitoes. The medium-chain length fatty acids from C8:0 to C12:0 were found to exhibit the predominant repellent activity. In laboratory bioassays, these fatty acids repelled biting flies and bed bugs for two weeks after application, and ticks for one week. Repellency was stronger and with longer residual activity than that of DEET. In addition, repellency was also found against mosquitoes. An aqueous starch-based formulation containing natural coconut fatty acids was also prepared and shown to protect pastured cattle from biting flies up to 96-hours in the hot summer, which, to our knowledge, is the longest protection provided by a natural repellent product studied to date.

The chemosensory appendage proteome of Amblyomma americanum (Acari: Ixodidae) reveals putative odorant-binding and other chemoreception-related proteins.

Proteomic analyses were done on 2 chemosensory appendages of the lone star tick, Amblyomma americanum. Proteins in the fore tarsi, which contain the olfactory Haller's organ, and in the palps, that include gustatory sensilla, were compared with proteins in the third tarsi. Also, male and female ticks were compared. Proteins were identified by sequence similarity to known proteins, and by 3-dimensional homology modeling. Proteomic data were also compared with organ-specific transcriptomes from the tick Rhipicephalus microplus. The fore tarsi express a lipocalin not found in the third tarsi or palps. The fore tarsi and palps abundantly express 2 proteins, which are similar to insect odorant-binding proteins (OBPs). Compared with insect OBPs, the tick OBP-like sequences lacked the cysteine absent in C-minus OBPs, and 1 tick OBP-like sequence had additional cysteines that were similar to C-plus OBPs. Four proteins similar to the antibiotic protein microplusin were found: 2 exclusively expressed in the fore tarsi and 1 exclusively expressed in the palps. These proteins lack the microplusin copper-binding site, but they are modeled to have a significant internal cavity, potentially a ligand-binding site. Proteins similar to the dust mite allergens Der p7 and Der f 7 were found differentially expressed in female fore tarsi. A protein exclusively expressed in the fore tarsi has similarities to Neto, which is known to be involved in clustering of ionotropic glutamate receptors. These results constitute the first report of OBP-like protein sequences in ticks and point to several research avenues on tick chemosensory reception.

Biological parameters of ticks (Amblyomma cajennense Fabricius, 1787) under field and laboratory conditions in Pedro Leopoldo, State of Minas Gerais, Brazil.

This study evaluated the biological parameters of the duration of the pre-oviposition and egg incubation periods and maximum survival of unfed larvae, under field and laboratory conditions, with the aim of providing support for more rational measures for controlling Amblyomma cajennense. This study was conducted at the Experimental Farm of the Veterinary School of the Federal University of Minas Gerais. Every 14 days, from September 1997 to March 1998 and from October 1998 to April 1999, six netted tubes containing engorged females were kept on pasture of Brachiaria decumbens that was up to 60 cm high and another six were kept in a BOD glass chamber (27 degrees C, 80% relative humidity). For both groups, 84 and 72 females were used during the first and second observation periods, respectively. The duration of the pre-oviposition period was similar under both conditions (5-7 days). Significant differences were seen between the duration of the egg incubation period under field conditions (56 to 60 days) and under BOD conditions (34 to 39 days); and between the maximum survival of the unfed larvae under field conditions (14 months) and under BOD conditions (9.5 months). These suggest that behavioral diapause was occurring. The long survival of unfed larvae in pasture needs to be considered when implementing Amblyomma cajennense control programs.

[Study of foveae dorsales of nymphs and adults of four species of ticks (Acari: Ixodidae) by scanning electron microscopy]. / Estudo das fóveasdorsais de ninfas e adultos de quatro espécies de carrapatos (Acari: Ixodidae) por Microscopia Eletrônica de Varredura.

The foveae dorsalis, the external opening of the sex pheromone 2,6-dichlorophenol producer gland, of Amblyomma cajennense, Dermacentor nitens, Rhipicephalus (Boophilus) microplus and Rhipicephalus sanguineus was studied with scanning electron microscopy. At least three specimens from each stage: unfed larvae, nymphs, females and males, and females fed for 4 to 6 days were examined. The foveae dorsales were not observed in larvae and R. (B.) microplus males. The foveae dorsales were observed as paired depressions, below the scutum in nymphs and females. In males they appeared as paired subtle elevations, located (2/3) of the way along the idiosoma. Generally the larger structures with a higher number of pores were observed in A. cajennense. Males and nymphs showed foveae dorsales of similar sizes but smaller than those of females. After feeding, secretions were observed in D. nitens and A. cajennense foveae dorsalis. In R. sanguineus and R. (B.) microplus this kind of secretion was not observed. An attempt to connect the appearance of foveae dorsalis with the role of 2,6-dichlorophenol in tick copula has been made. The occurrence of D. nitens females with three foveae dorsales was described.

Quantification of sex pheromone from Anocentor nitens by gas chromatography-mass spectrometry-selected ion monitoring.

Two highly sensitive and selective methods based on gas chromatography coupled to mass spectrometry (GC-MS) in the selected ion monitoring (SIM) mode have been developed for the quantification of 2,6-dichlorophenol (2,6-DCP), a sex pheromone of the tick females of Anocentor nitens. Standard addition method and calibration curve techniques using 5-bromine-4-hydroxy-3-methoxybenzaldehyde (5-BrV) as internal standard (IS) afforded detection limit of 0.1ngml(-1). The calibration curve was linear over the concentration range from 0.5 to 500ngml(-1) for 2,6-DCP. Results show that the concentration range of sex pheromone in the extracts samples was 1.08-10.35ngml(-1). The methods developed provided reliable procedures to determine amounts of 2,6-DCP present in ticks.

The role of 2,6-dichlorophenol as sex pheromone of the tropical horse tick Anocentor nitens (Acari: Ixodidae).

The objective of this study was to evaluate the role of 2,6-dichlorophenol (2,6-DCP) as sex pheromone of Anocentor nitens. Sex pheromones were extracted by submerging 150 female fed for 6 days in hexane (3 ml) for two hours and sonicating them for 15 min. The extract was analyzed by GC-MS employing the Single Ion Monitoring (SIM) method. Identification of 2,6-DCP was based on the comparison of mass spectra with a computer search using the NIST library and by matching the mass spectrum of the peak at the retention time of 2,6-DCP from extracts and the synthetic product. In an olfactometer, males were released at 2.5 cm from females, control rubber septa and impregnated rubber septa with increasing concentrations of 2,6-DCP (50, 500 and 5000 ng). A higher percentage of orientation and higher frequencies of angles between 0 degrees and 10 degrees were observed for males tested with females than with controls. Attraction of males to dummies impregnated with 2,6-DCP was observed with highest response (100%) at 50 ng. There was a gradual decrease of responsiveness of males with increasing concentration of 2,6-DCP (70 to 75%). This compound stimulated a behavior of mounting and ventral positioning of A. nitens males at the lowest 2,6-DCP concentration whereas dummies impregnated with 2.6-DCP higher than 50 ng concentration inhibited these behaviors. Therefore, we can conclude that 2.6-DCP can elicit the complete behavior sequence of orientation, location, mounting and ventral positioning behaviors and plays a role as an attractant and, as a mounting sex pheromone in A. nitens.