Structure and function of the arolium of Mantophasmatodea (Insecta)

Abstract

All species of the insect order Mantophasmatodea characteristically keep the 5th tarsomere and pretarsus (arolium plus two claws) turned upwards and off the substrate. The unusually large arolium was studied in two species of Mantophasmatodea using bright field light microscopy, reflection microscopy, fluorescence microscopy, TEM, SEM, and Cryo-SEM. It contains an epithelial gland, numerous tracheoles, and nerves. The gland consists of enlarged epithelial cells with large nuclei, mitochondria, RER, golgi complexes, microtubules, and numerous secretion vesicles. Evidence for exocytosis of the vesicles into the gland reservoir between the epithelial gland and the thick cuticle could be observed. Cryo-SEM revealed that the ventral side of the arolium and distal part of its dorsal side are covered with a liquid film. Fluid footprints of arolia of individuals walking on a glass plate also indicate the presence of secretory fluid on the arolium surface. Behavioral experiments using animals with ablated arolia showed that representatives of Mantophasmatodea do not need their arolia to detect and respond to vibratory communication signals nor to catch small to medium-sized prey. Individuals with ablated arolia were not able to move upside down on a smooth glass plate. We conclude that Mantophasmatodea use their arolia for attachment when additional adhesion force is required (e.g. windy conditions, handling large prey, mating). They can bring their arolia in contact with the surface in a very fast reflex (18.0 +/- 9.9 ms). The secretory fluid found on the surface is produced by the gland and transported to the outside, presumably through small pore channels, to enhance adhesion to the substrate.

Functional morphology of tarsal adhesive pads and attachment ability in ticksIxodes ricinus(Arachnida, Acari, Ixodidae)

“…Uplifted pretarsal structures, including the arolium, are also known in heelwalkers (Mantophasmatodea). They only use arolia when additional adhesion force is needed, in order to keep the adhesive surface away from debris and surface asperities that could contaminate or even damage the thin fragile surface of the arolium (Eberhard et al, 2009). Such a strategy must be also advantageous for ticks, considering their longevity and the less sclerotised acarid pretarsus .…”

“…Compared with that of female ticks, tenacity is 10 times higher in arolia of adult tortricid moths (0.2 µN µm −2 ; Al Bitar et al, 2009), 5 times higher in pulvilli of adult coreid bugs (0.1 µN µm −2 ; , but 3 times lower in adhesive pads in sawfly larvae (0.006 µN µm −2 ; . Similar to fast movements of arolia in Mantophasmatodea (Eberhard et al, 2009), tick forelegs pads can suddenly be brought in contact with and instantly adhere to the host surface, facilitating first access and attachment to the host. By rough calculation, a single expanded pad on a female tick's foreleg generates force roughly corresponding to 31 times female body weight.…”

Biodiversity, ecology, and behavior of the recently discovered insect order Mantophasmatodea

“…[4][5][6]). These descriptions were accompanied by a comprehensive description of the morphological features, such as genitalia of both sexes [4], the structure of sperm [7], eggs [8,9], head [10,11], circulatory organs [12], arolium and tarsus [13][14][15][16], and antennae [4,17,18], as well as studies on reproductive biology [19], communication [20][21][22], peptide hormones [23,24], physiology [25], and development [17,26,27]. In addition to molecular studies [4,[28][29][30][31], these studies provided the initial information for reconstructing the Mantophasmatodea phylogeny.…”

Two functional types of attachment pads on a single foot in the Namibia bush cricketAcanthoproctus diadematus(Orthoptera: Tettigoniidae)

“…In polyneopteran species, arolia and euplantulae have been described to be smooth, covered with protuberances or completely absent (figure 2) [2,[6][7][8][9][10][11]13,14,[20][21][22][23][24][25][26][27][28][29][30][32][33][34]36,37]. Different outgrowths of tarsal adhesive pads have been previously described: nubs, acanthae, microtrichia and setae.…”

“…Friction forces of nubby euplantulae increased when large normal forces were applied. Hence, the high [11, 14,28] (c); [10] [37] [13,14] [ 13,30] (d); [9,13,33,34,36] arolium/euplantulae absent (e) ventral surface of arolium or euplantulae, repectively, smooth structures vary depending on the species ventral surface of arolium or euplantulae, repectively, nubby (aspect ratio £ 4) ventral surface of arolium or euplantulae, repectively, setae-shaped (aspect ratio > 4) kind of structure cannot be entirely resolved from the images given in the papers ? ?…”