Nonsalivary Entangling Secretions

The posterior abdominal tergites and cerci of cockroaches in a variety of genera are covered with a viscous secretion that can act as an entangling glue for small predators. Species in genera as diverse as Blatta and Pseudoderopeltis produce proteinaceous secretions on the abdominal tergites that would be readily encountered by predators pursuing these cockroaches. After seizing the cockroaches, predatory centipedes, beetles, and ants rapidly release their prey while cleaning their mouthparts. The fleeing cockroaches generally have more than ample time to effect their escape.

Aphid species in many genera also utilize an entangling secretion as a primary means of defense. In this case the exudate is discharged in response to a confrontation, often hardening to a waxy plaque on an adversary within 30 s. This defensive behavior, which appears to be widespread in the Aphididae, uses tubular secretory organs, the cornicles, on the fifth and sixth abdominal tergites. The secretions, which are dominated by triglycerides, have been characterized in a range of genera, including Aphis, Myzus, Acyrthosiphon, and Therecaphis. The cornicular secretions are clearly more effective against generalized predators (e.g., ants) than they are against specialized predators (coccinellids, nabids). The secretions also contains alarm pheromones, E-fi-faxnesene and germacrene A, which release dispersive behavior that may cause aphids to drop off plants.

A variety of glands have been evolved by ants as sources of viscous defensive secretions. Many species in the subfamily Dolichoderinae discharge a pygidial (anal) gland secretion that is dominated by cyclopentanoid monoterpenes such as iridodial, compounds that rapidly polymerize on exposure to air. The viscous polymer effectively entangles small predators such as ants. Myrmicine species in the genus Pheidole also use the pygidial glands as a source of an entangling glue and in addition, an alarm pheromone. In contrast, a myrmicine species in the genus Crematogaster secretes a potent viscous deterrent from the hypertrophied metapleural glands. On the other hand, minor workers of a Camponotus sp. (Formicinae) produce a secretory "glue" in the capacious mandibular glands that extend through the entire body. Mechanical disturbance of the workers results in contraction of the gaster and eventual altruistic rupture, liberating the mandibular gland contents, which are very sticky and readily immobilize attacking ants.

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