Functional Morphology of Secretion by the Large Wax Glands (Sensilla Sagittiformia) Involved in Tick Defense

Abstract

Ticks are protected against ants by release of an allomonal defense secretion from the large wax glands (or type 2 glands) that line their bodies. To explore how the large wax glands operate, before and after microscopic observations of these glands (nonsecreted versus secreted test groups), mass determinations were made for Rhipicephalus sanguineus that had been exhausted of secretion by repeated leg pinching to simulate attack by a predator. Prior to secretion, the glandular organ is fully intact histologically and matches the sensillum sagittiforme, a key taxonomic structure described in the 1940s. The large wax gland is innervated and responds to pressure stimulation as a proprioceptor that stimulates the secretory response. Histological observations after secretion has occurred show that the entire glandular contents and associated cells are jettisoned out of the gland like a syringe. The glandular cellular components are subsequently rebuilt by underlying hypodermal cells within a few days so that secretion can take place again. Presumably, the active allomonal ingredients (hydrocarbons) are released when these derived epidermal cells reach and burst onto the cuticular surface. Our conclusion is that the large wax glands are holocrine and feature intermittent regeneration.

Dermal secretion physiology in Metastriata ticks; thermoregulation in the lone star tick Amblyomma americanum

“…Ticks have thick sclerotized cuticle covered with wax 13 preventing evaporative water loss. However, an important route of water loss through the integument may be secretion through dermal glands which accounts for 2.3-2.5% of the body weight in the case of R. sanguineus 23 and 4% in A. americanum (in this study). In metastriate ticks, the dermal secretion occurs through a large number of a subset of dermal glands opened to dorsal and ventral surface, which has been demonstrated to be triggered through mechanical stimulation 3,24 .…”

“…The secretion is proposed to contain defensive compounds against predators and pathogens. Such toxic compounds, like antimicrobials and squalene, can be externalized through pore openings on the cuticle surface 25,26 and may act as allomones against predatory ants like the case of squalene 23 . An earlier study identi ed o-nitrophenol and methyl salicylate in the type II glands of fed male ticks of A. variegatum and A. hebraeum, which are thought to have aggregation pheromonal activities 28,29 .…”

“…Two types of dermal glands and pores have been described in R. sanguineus 32 , namely type I and type II.…”

Integrative Alternative Tactics for Ixodid Control

“…Although ants, particularly the red imported fire ant, Solenopsis invicta Buren, have been associated with reduced ixodid populations [ 267 , 270 , 275 , 276 , 277 , 278 , 279 , 280 ], evidence for direct effects on ixodids has largely been circumstantial. While some ixodid species might be attacked by ants, metastriate ixodids (identified by a flap covering the sexual orifice) in the genera Amblyomma , Dermacentor , and Rhipicephalus (it is unclear as to whether cattle fever ticks, Rhipicephalus (Boophilus) spp., are included) [ 281 ], have dermal wax glands that secrete protective allomones [ 282 , 283 , 284 ]. The allomones occur in larval, nymphal, and adult metastriate ixodids; blood-engorged adults, however, might be more vulnerable to ants than nonfed adults and other life stages [ 282 , 283 , 284 ].…”

“…While some ixodid species might be attacked by ants, metastriate ixodids (identified by a flap covering the sexual orifice) in the genera Amblyomma , Dermacentor , and Rhipicephalus (it is unclear as to whether cattle fever ticks, Rhipicephalus (Boophilus) spp., are included) [ 281 ], have dermal wax glands that secrete protective allomones [ 282 , 283 , 284 ]. The allomones occur in larval, nymphal, and adult metastriate ixodids; blood-engorged adults, however, might be more vulnerable to ants than nonfed adults and other life stages [ 282 , 283 , 284 ]. Barré et al [ 285 ], however, observed that 8% of engorged tropical bont ticks, Amblyomma variegatum (F.), were attacked by tropical fire ants, Solenopsis geminata (F.).…”