Structure and function of the urnulae inBalaustiumsp. (Parasitengona: erythraeidae) featuring secretion of a defensive allomone and alarm pheromone

Abstract

2006) Structure and function of the urnulae in Balaustium sp. (Parasitengona: erythraeidae) featuring secretion of a defensive allomone and alarm pheromoneABSTRACT -In studying predator-avoidance tactics of adult Balaustium sp. mites, a characteristic red fluid was observed leaking from a single pair of tubercles (umulae) that project from the dorsal idiosoma, just behind the eyes. Until now, the urnulae had no known function, but served a useful taxonomic purpose. When threatened, mites were observed actively secreting umulae-derived fluid that was spread over their body surface by means of numerous setae. Subsequent application of the fluid to mealworm beetle larvae (Tenebrio molitor) resulted in sudden diminished ant attacks, suggesting that this secretion serves a defensive role as an allomone. True to semiochemical parsimony, this secretion also prompted an excited dispersal response among conspecific mites, indicating that it also functions as an alarm pheromone, perhaps as an injury cue. More pronounced predator defense and alarm activities are displayed by mite body fluids, indicating that the activity of the emission from the umulae parallels that ofhemolymph. Based on positive staining with ammoniacal silver nitrate, their capacity to secrete, and additional morphological and histological investigations carried out, the role of the urnulae is clearly glandular. Of interest is that the defensive mechanism appears to operate by a novel form of reflex bleeding reminiscent of aposematic beetles.

Use of an alarm pheromone against ants for gaining access to aphid/scale prey by the red velvet miteBalaustiumsp. (Erythraeidae) in a honeydew-rich environment

“…putmani secretions, body fluid extracts and neryl formate. Control: untreated and acetone-treated mealworm larvae; nonsecretion: mites frozen before immersion into acetone, thus preventing urnulae secretion (Yoder et al, 2006b); secretion: live mites immersed into acetone, resulting in urnulae secretion, (Yoder et al, 2006b); whole-body extracts: mites crushed in acetone to provide whole-mite extracts. In each test, three mealworms were exposed to 15 worker ants for 24h, and each was replicated 15 times.…”

“…The mechanism of ant-avoidance used for gaining access to aphid/scale insect prey applies only to Balaustium deutonymphs and adults in that the alarm pheromone is not present in the larval stage because they lack the glands (urnulae) that produce this secretion (Southcott, 1961;Newell, 1963;Gabrys, 2000;Halliday, 2001;Yoder et al, 2006b). Thus, Balaustium larvae are seemingly not protected in this way against the ants.…”

“…A standard mealworm (Tenebrio molitor) predation assay (Yoder and Brunet, 1997;Yoder et al, 2006b) was used to test the response of ants to mite-based secretions and to the main component of this secretion (neryl formate; Sigma). Worker ants (cornfield ants, Lasius alienus, and black carpenter ants, Camponotus pennsylvanicus) were collected near Columbus, OH, USA.…”

“…Control mealworms consisted of untreated individuals and those treated with acetone (HPLC grade; Sigma). Acetone extracts from ground whole-body mites, secretion-only (mites immersed into acetone and removed after urnulae secretion) and from those that did not secrete (mites were frozen before immersion into acetone to prevent urnulae secretion; no secretion was observed) were prepared according to Yoder et al (Yoder et al, 2006b). Neryl formate was tested at the concentrations of 0.1 moll -1 , 0.01 moll -1 and 0.001 moll -1 dissolved in acetone.…”

“…are voracious predators of a range of soft-bodied arthropods and their eggs, including scale insects, phytophagous mites and adult aphids (Putman, 1970), which makes the observation that they are arrested on surfaces covered with honeydew rather than an actual prey item distinctive (these mites do arrest on prey because they are feeding on them). They thrive in semi-arid to arid biotopes (Wohltmann,a secretion that protects the mite from heat injury and excessive desiccation by providing additional water-proofing , while also functioning as an alarm and a defense from predators (Yoder et al, 2006b). One of the main components of the urnulae secretion is the terpene neryl formate (Yoder et al, 2007b).…”