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The responses of Irodes scapularis (Acari: Ixodidae) nymphs and adults to extracts of cast larval skins were tested in a Petri dish bioassay. Assembly was elicited in nymphs and adults in the presence of skins, exudate from ticks, and filter paper exposed to ticks compared to untreated controls. Assembly was noted by 1 hr after exposure with little change between 1 and 24 hr. The assembly response increased in the presence of an increased number of skins. Similar assembly was elicited in nymphs and adults in the presence of cast larval skins and a saline (0.95% NaCl) skin extract. Methanol and hexane extracts were not attractive. When chemical standards were tested against nymphs, they responded to guanine, uric acid, hypoxanthine, xanthine, inosine, and hematin. Adults were tested against guanine, inosine, and xanthine, and all elicited significant assembly. Responses of nymphs increased significantly with increase in dose of uric acid and guanine. Responses of nymphs to a mixture of guanine, xanthine, and adenine (25:1:1 ratio) were similar to responses to cast skins. This study provides the first evidence of an assembly pheromone in I. scapularis.

Ticks and mites respond to a limited spectrum of stimuli in their search for hosts and mates. Airborne chemical signals include carbon dioxide, ammonia, organic acids, terpenoids, 2,6-dichlorophenol, and other phenolic compounds. These are detected primarily by sensilla in and adjacent to Haller's organ. Most ixodid species examined have one or more multiporose sensilla that detect such volatiles. These olfactoreceptors enable the ticks to respond to remote volatile chemicals from hosts and from the other ticks, e.g., sex pheromones. Other sensilla, probably mechanogustatory in function, also occur on the tarsi. Gustatory sensilla on the palps detect assembly pheromones that enable ticks and mites to respond to conspecific or heterospecific chemical stimuli in their environment. Responses to those stimuli in ticks result in clustering, i.e., arrestant behavior. Arrestant behavior also occurs in certain mites. Finally, cheliceral chemosensilla enable ticks to recognize specific phagostimulants in host blood, e.g., ATP and glutathione, that stimulate feeding. InDennacentor variabilis andD. andersoni, these same cheliceral chemosensilla recognize species-specific genital sex pheromones in the vulvae of conspecific mates, without which they do not copulate.

Evidence is presented indicating the presence of the tick sex pheromone, 2,6-dichlorophenol in lipid droplets in the foveal glands ofDermacentor variabilis (Say) andDermacentor andersoni Stiles. The pheromone appears to be dissolved in the lipid droplets. The droplets consist of neutral lipids, mostly triacylglycerides and cholesterol esters. The esterified fatty acid profiles of foveal gland triacylgylcerides are different from those of other tissues examined or reported for other ticks. The percentage of shorter chain, mostly saturated fatty acids were decreased, while the longer chain polyunsaturated fatty acids were increased. The biological advantages of lipid solution for storage, translocation, and release of the sex pheromone from the female tick are discussed.

Administered monoamines affected sex pheromone activity in the foveal glands of the tick,Dermacentor variabilis (Say). Flooding the tissues of the female tick with reserpine, α-methyl-m-tyrosine methyl ester hydrochloride, and pilocarpine prior to feeding led to reductions in female sex attractant activity during engorgement. Similar treatments with cyclic AMP, dopamine, serotonin, 6-hydroxydopamine, and acetylcholine had no apparent effects on the attractiveness of feeding females. Assays (by gas chromatography) demonstrated substantial reductions in 2,6-dichlorophenol content following treatment with α-methyl-m-tyrosine methyl ester, pilocarpine, and, in most cases, with reserpine. Reserpine was effective only when administered in near-lethal concentrations to unfed females. In contrast, treatment with dopamine led to elevated 2,6-dichlorophenol content in most trials. X-ray microanalysis corroborated the evidence with reserpine and dopamine. These and other findings reported elsewhere implicate monoamines, presumably catecholamines, in the regulation of sex pheromone secretion in this species. The significance of these findings for understanding the physiological mechanisms involved in the regulation of sex pheromone secretion and biosynthesis is discussed.

The occurrence of a genital sex pheromone in the anterior reproductive tract of partially fed femaleDermacentor variabilis was demonstrated by extraction and bioassay. A new type of bioassay, the "neutered" female assay, was developed to test the potency of extracts or chemically defined fractions to stimulate males to copulate. Electrophysiological tests confirmed the ability of males to detect the pheromone with sensilla on their cheliceral digits. Males of bothD. variabilis andD. andersoni exhibited neuronal excitation when stimulated with extracts of theD. variabilis reproductive tissues. The pheromone, which is soluble in methanol, was fractionated and found to contain at least two fractions that stimulated copulation by sexually excited males. Evidently, the pheromone is a mixture of two or more compounds. Histologic, ultrastructural, and histochemical studies suggest the vestibular vagina as the site of genital sex pheromone occurrence, presumably from secretions of the surrounding lobular accessory gland. The identity of the compounds that comprise the pheromone remains unknown.

No detectable sex pheromone, 2,6-dichlorophenol (2,6-DCP), was found inDermacentor variabilis engorged nymphs, teneral females, replete females, or unfed males. The amount of 2,6-DCP present in unfed females of different ages was extremely variable; no relationship between age and 2,6-DCP content in these unfed females was observed. Partially fed virgin females had less 2,6-DCP than unfed females, but there was no change in pheromone content during the course of feeding. Sex pheromone was also found in partially fed males.

2,6-Dichlorophenol (2,6-DCP) is the major volatile sex pheromone component in the extracts ofHyalomma dromedarii (35 ng/female) andHyalomma anatolicum excavalum (20 ng/female). The GC fraction containing essentially pure 2,6-DCP, as well as an equal amount of synthetic 2,6-DCP, elicits from the male of each species a hierarchy of responses culminating in attempted copulation.

MaleDermacentor variabilis andD. andersoni respond to an unknown chemical or chemicals present on the body surfaces of partially engorged conspecific female ticks. Following contact, the males mount the females and apply their mouthparts and legs against the female dorsal body surface. Then, the males turn with these appendages still in close contact and crawl to the female's venter, whereupon they locate the gonopore, probe the vulva, and copulate. Similar responses are elicited by heterospecific as well as conspecific females. However, the response is lost when the female cuticle is cleaned (delipidized) with organic solvents. It can be restored by applying hexane extracts prepared from female cuticle to the previously cleaned females. Males do not use surface texture as the primary stimulus for mate recognition. Male ticks also respond to hexane extracts applied to spherical inanimate objects, ("dummy" female), suggesting that a chemical or chemicals soluble in organic solvents has been transferred to these objects. These findings suggest the existence of a previously undescribed pheromone, the mounting sex pheromone (MSP). This contact sex pheromone enables males excited and attracted by 2,6-dichlorophenol to identify the female as a potential mating partner. The MSP is the second in the series of three sex pheromones guiding the hierarchy of behavioral responses which constitute tick courtship behavior.

Treatment ofD. variabilis-infested dogs with formulations of the sex pheromone, 2,6-dichlorophenol, significantly reduced mating by the attached ticks. Aqueous emulsions of a gelatin microcapsule-xylene slurry and a pheromone-loaded, molecular-sieve powder were used. Concentration was an important variable influencing product efficacy. Such formulations combined with an acaricide may prove effective in reducing tick populations on livestock and pets.