Off-host aggregation in the non-fed, female brown dog tick, Rhipicephalus sanguineus (Latreille), is induced by tick excreta and enhanced by low relative humidity.

We report that Rhipicephalus sanguineus (Ixodida: Ixodidae) faeces and its main component, guanine, act as assembly pheromones in short-range Petri plate bioassays. Arrestment activity in response to guanine was lower than that in response to natural excreta, indicating the presence of other active ingredients in natural excreta. The selective removal of appendages was used to establish the important roles played by the palps and the front pair of legs in the detection of the pheromone. Reaction to chemically pure guanine at varying concentrations occurred without a dose response; thus only the presence of guanine, not a critical amount, is required to induce assembly. Higher speed and intensity of clustering occurred at 33% relative humidity (RH). We conclude that female adults of R. sanguineus are more prone to assemble under dry conditions that match the arid microhabitats preferred by this species and that this tendency allows this tick to reside in human dwellings and dog kennels that maintain standards of comfort at 30-50% RH. Cleaning or removing tick excreta-covered surfaces on which ticks aggregate from within and around human dwellings may prove useful as a means of interfering with the establishment of off-host clusters of R. sanguineus.

Role of permanent host association with the Madagascar hissing-cockroach, Gromphadorhina portentosa, on the developmental water requirements of the mite, Gromphadorholaelaps schaeferi.

We provide the first complete description of the water requirements for the hissing-cockroach mite, Gromphadorholaelaps schaeferi, focusing on characteristics that result from the restriction of all stages to the Madagascar hissing-cockroach (Gromphadorhina portentosa). Particularly, we determine how G. schaeferi spends its entire life on the same individual cockroach. This mite is not parasitic, rather they feed on cockroach saliva and other moist organic debris that accumulates between the cockroach's legs. Water balance characteristics of this mite show that it is extremely hydrophilic and that it must maintain a high percentage body water content to function properly despite being very porous (high net transpiration rate) and sensitive to water loss, tolerating only 20% loss of their water content before death. This hydrophilic trend starts with the larva and is retained into adulthood. Developmentally, a shift occurs during postlarval development from an emphasis on water gain (low critical equilibrium activity for water vapor absorption from drier air) in the protonymph to an emphasis on water retention (reduced net transpiration rate for water conservation) in the adult. The minute-sized larva is prevented from replenishing water stores by water vapor absorption or feeding because it lacks functional mouthparts, thus dries up rapidly. To avoid dehydration and survive, the larval stage utilizes a quick shoot-through molt to the protonymph that can feed and grow. Our conclusion is that the hissing-cockroach creates an ideal, stable moisture-rich microhabitat that satisfies the high water demand for G. schaeferi during all stages, fixing this mite to a single cockroach as an ecological niche.