A Comparative Study of the Chemical Defensive System of Tenebrionid Beetles. Defensive Behavior and Ancillary Features1,2

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Abstract
The behavior accompanying the release of the defensive secretion of 64 species of tenebrionid beetles was studied. The secretion was characteristically released by eversion of the reservoir, by exuding, or by spraying, with intermediates between these occasionally represented. Everting is considered primitive and is found among several genera of Tenebrionini, Bolitophagini, Strongyliini, and Lagriini with a few occurrences in other tribes. Spraying is restricted mostly to the subgenera Eleodes and Steneleodes of Eleodes but scattered occurrences are found in other subgenera of Eleodes as well as other genera within the family. Some species of Meracanthini and Amarygmini spray by rapidly everting the glands, a method quite distinct from all other spraying species. Species of Eleodes frequently exhibit headstanding behavior when disturbed and prior to giving off secretion, but headstanding has evolved in other groups as well and is frequently associated with species which spray. Certain species which lack defensive glands also headstand, and the evolution of headstanding is discussed in this light. Many species in all taxa have evolved the ability to wipe the secretion via the metalegs, from the abdominal tip onto the handler; species of Argoporis can transfer secretion between adjacent pairs of legs. Numerous species of Diapirini, Tenebrionini, Scaurini, Ulomini and Phaleriini fold the legs and antennae flat against the ventrum and remain motionless when disturbed; this habit is also represented in a few species of other groups. In some species of Diapirini and Ulomini, the epipleural margins of the elytra are formed into “gutters” which conduct secretion forward, and in some the elytra are entirely wet by secretion. In a species of Zadenos, elytral sulcae conduct the secretion. All species of Platynotini possess gular stridulatory apparati, and several stridulate when releasing secretion.

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