Paul J. Homsher

A re-evaluation of relationships in the Metastriata (Acari: Parasitiformes: Ixodidae)

A systematic analysis of generic/subgeneric relationships in the ixodid lineage Metastriata was conducted based on 82 structural and developmental characters, 15 of which have multiple states. Results of the analysis show considerable agreement with current classifications of the Ixodidae, including good support for monophyly of the Metastriata, the genera Ixodes and Haemaphysalis, and the grouping of Hoogstraals Rhipicephalinae and Hyalomminae, and fair support for the genus Hyalomma. Our results differ from these classifications most notably by rejecting monophyly of the genera Aponomma and Amblyomma. Instead, the analysis provides weak support for a hypothesis in which the basal two to three lineages in the Metastriata are all composed of Aponomma species, and in which a fourth lineage within that genus, Aponomma elaphense, clusters with Amblyomma quadricavum to form a more derived lineage. Resolution is insufficient to support or reject monophyly of the genera Dermacentor and Rhipicephalus, or to resolve the position of the genus Haemaphysalis relative to the other Metastriata. Overall resolution within the Rhipicephalinae/Hyalomminae is quite good, but it is quite poor among the Amblyomminae and Haemaphysalinae. These results are similar to the results of recent 16S and 18S rDNA based molecular analyses. There are few indications of host specificity among the lineages analysed. The basal metastriate lineages contain a large number of squamate associates, but the pattern is not sufficiently clear to reject the hypothesis that these ticks will feed on all available vertebrate hosts. On the other hand, nearly all of the basal taxa are Australian. This suggests a possible origin of the Metastriata in Australia, with subsequent dispersal to other parts of the world.

Foveal glands, source of sex pheromone production in the ixodid tickDermacentor andersoni stiles

The foveal glands of the Rocky Mountain wood tick,Dermacentor andersoni Stiles, are the sex pheromone glands from which the sex pheromone is released via the foveae dorsales. The sex pheromone, 2,6-dichlorophenol, was recovered from extracts of these glands by GLC. Other evidence of the role of these glands in sex pheromone production is described. A36Cl-labelled volatile compound (or compounds) was (were) collected from partially engorged femaleD. andersoni fed in36Cl-labelled hosts, but no labelled compounds were collected when the foveae dorsales were blocked. X-ray analysis revealed unusual concentrations of chlorine in the foveal glands compared to other tissues. Autoradiography also revealed significant accumulations of radiochlorine in the vicinity of these glands.Presumably, the foveal glands of the American dog tick,Dermacentor variabilis (Say), are the sex pheromone glands of that species also, since a36Cl-labelled volatile was collected from female ticks fed on a36Cl-labelled host. However, attempts to recover 2,6-dichlorophenol from gland extracts or volatile emissions fromD. variabilis were unsuccessful.

Dermacentor variabilis and Dermacentor andersoni: genital sex pheromones.

Abstract There is evidence for the existence of a previously undescribed sex pheromone (or pheromones) in the ticks Dermacentor variabilis and D. andersoni . In addition to 2,6-dichlorophenol, which attracts mate-seeking males, a pheromone released on the cuticle of the female genital area enables the sexually excited male to locate the gonopore. The compound (or compounds) appears to act as a contact pheromone; male copulation responses are greatly reduced when the female genital surface is washed with solvents, especially hexane. It is also a potent excitant; males will puncture or dislodge barriers placed over the gonopore to copulate. However, the response is eliminated if the genital area is washed (hexane or acetone) prior to sealing the gonopore, suggesting the reproductive system as the source of the pheromone. A species specific copulation-eliciting pheromone appears necessary to excite the male to form and implant its spermatophore in the vulva of a conspecific female. Males encountering trans-specific females probe their gonopores, but mating attempts are almost always aborted within 5–10 min. The copulation-eliciting pheromone may be the same, or similar, to that used to locate the gonopore. Physical differences in the shape of the female gonopore in the two species, although slight, may contribute to the males ability to identify conspecific females. Using this pheromone-guided process of attraction and identification, females present in mixed species populations will almost always be distinguished and inseminated by conspecific mate-seeking males.

Genital sex pheromones of ixodid ticks: 1. Evidence of occurrence in anterior reproductive tract of American dog tick,Dermacentor variabilis (Say) (Acari: Ixodidae)

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.

Fine structure of the foveal glands and foveae dorsales of the American dog tick, Dermacentor variabilis (Say).

The ultrastructure of the foveae dorsales and pheromone glands (foveal glands) of both feeding and unfed female Dermacentor variabilis (Say) was studied. Each pore of the fovea contains a pore tube, with cells surrounding a lumen that can be opened or closed. Each pore tube extends below the fovea and expands to form a cone-shaped ampulla, into which a duct of the foveal gland is inserted. Each duct is lined with microvilli, except near its insertion into the ampulla where the lumen is lined with a brush border. In the feeding female, numerous vesicles and lipid droplets accumulate in and around the ducts. However, in the unfed female, the ducts are free of vesicles or droplets. A nerve, the foveal nerve, occurs in the vicinity of the ducts. Neurosecretory vesicles occur in some of the nerve fibers in the feeding tick. Microorganisms, of unknown identity, were found near the ducts of the pheromone gland in feeding females, but not in unfed females. The secretory lobes of the pheromone glands, representing the major part of these organs, contain large cells which appear to comprise one type. In the feeding female, lipid droplets of varying size occur in vesicles or, more frequently, free in the cytoplasms. The may be clustered or scattered throughout large areas of the cell cytoplasm. Accumulations of vesicles and lipid droplets are especially abundant at the ends of the cells, near the junction with the ducts, where they may occur in a single large membrane-bound enclosure. In the unfed female, the lipid droplets occur only within vesicles, distributed more or less uniformly throughout the gland cells.

Ultrastructure of the foveal glands of the ticks, Dermacentor andersoni Stiles and D. variabilis (Say).

The foveal glands of Dermacentor variabilis appear to consist of 2 cell types. The outer cells (Type I) are active, with large areas of abundant finely granular material, apparently precursors of the mature secretory granules. The inner cells (Type II) are apparently storage cells. They are highly vacuolated and contain coarsely granular material as well as presumably mature secretory granules. The foveal glands of D. andersoni contain only Type II cells with extensive accumulations of presumably mature secretory granules.

QUINONE INHIBITION OF SEX PHEROMONE ACTIVITY IN THE TICKS DERMACENTOR ANDERSONI STILES AND DERMACENTOR VARIABILIS (SAY)

Disruption of sex pheromone activity in female Rocky Mountain wood ticks, Dermacentor andersoni Stiles, and American dog ticks, Dermacentor variabilis (Say), was achieved by treatment with the quinones para-benzoquinone and menadione. The most effective treatments were those administered by inoculation to unfed, mature, adult females prior to feeding. Inoculation of p-benzoquinone was also effective when administered to feeding ticks, from 2 to 5 days after they had attached, though not to the same extent as when it was given to unfed ticks. Decreases in sex pheromone activity were also observed with D. andersoni females, but not D. variabilis females, allowed to feed on rabbits receiving menadione daily by oral administration. Histochemical studies and electron microscopy revealed loss of neutral lipid secretory droplets in the pheromone glands, but no damage to gland structure, following treatment with p-benzoquinone. Elemental analysis revealed more than four times as much chlorine in pheromone glands of p-benzoquinone-treated D. variabilis females than in pheromone glands from control specimens. An extract of partially fed D. variabilis females treated with p-benzoquinone before feeding contained much more 2,6-dichlorophenol than an extract of untreated, partially fed females. Evidently, the quinone affects the neutral lipid component of the female sex pheromone gland, disrupting secretion and release of pheromone to the external body surface.

Studies on possible role of catecholamines in regulation of sex pheromone gland activity in American dog tick,Dermacentor veriabilis (Say)

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.

DNA studies of a Chesapeake Bay population of the tunicate Molgula manhattensis (DeKay) (Ascidiacea)

Gonadal development and total gonadal DNA of M. manhattensis were studied. Evidence of atrophication and of phagocytosis of residual gametes was found during histological examination. Colorimetric estimations of gonadal DNA indicated that at least two spawning peaks occurred during the summer and suggested that egg release was suppressed by water temperatures above 20 C.