Variety Of Salivary Defensive Functions Salivary Venoms

The spitting cobra, Naja nigricollis, has an insect parallel, both in terms of the general chemistry of the saliva and the ability to accurately "fire" the venom at a moving target. For example, Platymeris rhadamanthus is a black and orange assassin bug (Reduviidae) that is very conspicuous because of its aposematic (warning) coloration. This insect can eject its saliva for a distance up to 30 cm, and if this enzyme-rich solution (proteases, hyaluronidase, phospholipase) strikes the nose or eye membranes of a vertebrate, intense pain, edema, and considerable vasodilation may follow. The saliva of P rhadamanthus is admirably suited to deter vertebrate predators, including birds and reptiles. This salivary venom has clearly been evolved for predation on invertebrates, and rather than a specific site of action, it is reported to attack many organs simultaneously. Its speed of paralytic action is very pronounced: an American cockroach (Periplaneta americana) can be totally immobilized in about 4 s.

Entspannungsschwimmen (Chemically Induced Aquatic Propulsion)

The proteinaceous saliva of the hemipteran Velia capraii has been adapted to promote escape from potential predators in aquatic environments. This aquatic true bug will discharge its saliva onto the water surface, a reaction that results in lowering the surface tension of the water behind the bug. Under these circumstances, V capraii is rapidly propelled across the water surface, putting considerable distance between itself and the source of the disturbance. Discharge of saliva posteriorly from the rostrum may project the bug 10 to 25 cm on the contracting water surface on which it is riding.

Allomonal Pheromones

Male bumble bees (Bombus spp.) scent-mark territorial sites with cephalic products that are very odoriferous. The secretions, which originate in the cephalic lobes of the salivary glands, are dominated by terpenes, some of which are well-known defensive compounds. This appears to be an excellent example of semiochemical parsimony, with the males utilizing the compounds both as territorial pheromones and as defensive allomones.

Salivary "Glues"

Termite workers in both primitive and highly evolved genera secrete defensive exudates that are rapidly converted to rubberlike or resinous products that can rapidly entangle small predators such as ants. This conversion frequently reflects the polymerization of salivary proteins that have reacted with p-benzoquinone, a highly reactive salivary defensive product. Similar systems for generating entangling salivas have been detected in a diversity of termite genera, including Mastotermes, Microtermes, Hypotermes, and Odontotermes.

Termites in other genera discharge cephalic exudates that are fortified with toxic terpenes. Species of Nasutitermes and Tenuirostritermes secrete mixtures of compounds that rapidly form a resin that entangles ants and other small predators. The presence of monoterpene hydrocarbons is probably responsible for killing ants and, in addition, may function as an alarm pheromone for recruiting termite soldiers.

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