Passalus Beetles

Passalidae, Passalinae. Spanish: Pin-pin (Guatemala). Bessbugs, betsy bugs, patent-leather beetles.

In wooded areas, almost any damp, rotting log or stump may harbor a passalus beetle family or two. These are highly developed subsocial insects with adults and maturing larvae living together in groups (Schuster and Schuster 1985). Both stages produce a repertoire of sounds that apparently serve a number of purposes in their complex life histories. Prevalent signals express disturbance, aggression, and courtship (Schuster and Schuster 1971, Schuster 1983). Some fourteen different acoustic signals have been recognized, associated with eleven behavioral actions, the most known for any arthropod species (Schuster 1983).

The adults stridulate by rubbing rough places on the undersides of the elytra with the hind wings or spiny areas on the hind legs against the abdomen (Reyes-Castillo and Jarman 1983). The sounds are strong and perceptible to the human ear as high-pitched squeaks. Faint sounds are also emitted by the larvae, but with the hind legs, which are modified into pawlike stumps used to scrape over a file on the coxa of the midleg (Reyes-Castillo and Jarman 1980). These sounds are similar to those of their parents, yet their function remains unknown.

Adults feed on decaying wood and their own feces that has decomposed through microbial action. The larvae also eat the latter material and wood chewed into small pieces by the adults (Mason and Odum 1969, Gray 1946).

The beetles are easily recognized by their elongate, large prothorax, ridged elytra, shiny black color, and curved antennae tipped with a club composed of three to five flat plates (fig. 9.5f). Many also have a short horn on the top of the head and somewhat depressed elytra. They range in size from 1.2 to 10 centimeters in length. Some have hind wings reduced to thin straps used only for stridulation and useless for flight. Many species can fly, but this is seldom witnessed. Larvae (Costa and Ruy V. da Fonseca 1986) are pale, with a well-developed, pigmented head and slightly enlarged posterior (fig. g 5e). They are unique in the reduction of the hind legs to form a part of the stridulatory device.

The family is well developed throughout the Neotropics, except the southern Chilean temperate forests. It is divided ¡nto numerous genera, all in the New World subfamily Passalinae, containing 278 species (Schuster and Reyes-Castillo 1981, Reyes-Castillo 1979). The larvae are keyed to genera by Schuster and Reyes-Castillo (1981).

Most occur in moist forests, at high as well as low elevations, although some abound in dry woodlands and even in special niches such as the nest of desert ants and oil bird caves (Schuster 1978). Ptichopus are associated with leaf cutter ants (Atta), commonly living in detritus piles or in the chambers formed by these ants (Schuster 1984). The most common microhabitat is a rotting log in intermediate stages of decay. Hardwoods are the usual hosts, but some inhabit the broken-down wood of conifers and palms.

Like other beetles, passalids are infested with ectoparasitic and phoretic mites but in greater variety than any other family of insect hosts. Trichomycetes fungi are found in the gut of both larvae and adults and may be involved in cellulose digestion (Licht-wardt 1986: 231-232, 306).

References

Costa, C., and C. Ruy V. da Fonseca. 1986. Larvae of Neotropical Coleoptera. XIII. Passalidae, Passalinae. Rev. Brasil. Entomol. 30: 57-78.

Gray, I. E. 1946. Observations on the life history of the horned passalus. Amer. Midi. Nat. 35: 728-746. Uchtwardt, R. W. 1986. The Trichomycetes (Fungal associates of arthropods). Springer, Berlin.

#*ASon, w. H„ and E. P. Odum. 1969. The i effect of coprophagy on retention and f bioelimination of radionucleides by detritus-; feeding animals. In D. J. Nelson and E C.

Evans, eds., 2d Natl. Symp. Radioecol. (Ann Arbor) Proc. Pp. 721-724. Reyes-Castillo, P. 1979. Coleoptera, Passalidae: Morfología y división en grandes grupos: Géneros Americanos. Fol. Entomol. Mexicana 20-22:1-240. Reyes-Castillo, P., and M. Jarman. 1980. Some notes on larval stridulation in Neotropical Passalidae (Coleoptera: Lamellicornia). Coleop. Bull. 34: 263-270. Reyes-Castillo, P., and M. Jarman. 1983. Disturbance sounds of adult passalid beetles (Coleoptera: Passalidae) structural and functional aspects. Entomol. Soc. Amer. Ann. 76: 6-22.

Schuster, J. C. 1978. Biogeographical and ecological limits of New World Passalidae (Coleoptera). Coleop. Bull. 32: 21-28. Schuster, J. C. 1983. Acoustical signals of passalid beetles: Complex repertoires. Fla. Entomol. 66: 486-496. Schuster, J. C. 1984. Passalid beetle (Coleoptera: Passalidae) inhabitants of leaf-cutter ant (Hymenoptera: Formicidae) detritus. Fla. Entomol. 67: 175-176. Schuster, J. C., and P. Reyes-Castillo. 1981. New World genera of Passalidae (Coleoptera): A revision of larvae. Escuela Nac. Cien. Biol. Mexico An. 25: 79-116. Schuster, J. C., and L. B. Schuster. 1971. Un esbozo de señales auditivas y comportamiento de Passalidae (Coleoptera) del Nuevo Mundo. Rev. Peruana Entomol. 14: 249-252. Schuster, J. C., and L. B. Schuster. 1985. Social behavior in passalid beetles (Coleoptera: Passalidae): Cooperative brood care. Fla. Entomol. 68: 266-272.

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