Thysanurans

Thysanura, sensu lat.

Thysanurans are considered to comprise the most primitive order of true insects because of their complete winglessness, weak sclerotization, and presence of vesti-pal, jointed appendages on the underside of the abdomen. Immatures grow gradually into adults without appreciable change in form (i.e., no metamorphosis). They also bear three long, many-jointed tails extending from the tip of the abdomen, and the equal thoracic segments have rather large lateral lobelike expansions. They are generally small (most BL 10-15 mm). The body is covered with scales but may be bare except for numerous fine bristles.

There are two suborders, the silverfish (Zygentoma) and the bristletails (Microco-ryphia) (Remington 1954). These categories have been variously recognized and named by taxonomists, and some confusion remains on the best way to classify the group.

Members of both groups are widely distributed and mostly secretive, occurring in all sorts of general habitats such as in rotten wood, in rock crevices, and in humus and ground litter. Some have highly specialized habits, living in bird's nests, associating with social insects, or living in caves (Wygodzinsky 1967). Many have been transported throughout the world by human traffic. Free-living thysanurans, especially those requiring a warm environment, often become adapted to domiciles.

References

Remington, C. L. 1954. The suprageneric classification of the order Thysanura (Insecta). Entomol. Soc. Amer. Ann. 47: 277-286.

Wygodzinsky, P. 1967. On the geographical distribution of the South American Micro-coryphia and Thysanura (Insecta). In D. Deboutteville and E. Rapoport, eds., Biologie de L'Amérique Australe. 3: 505— 524. Ed. Cent. Nat. Recher. Sci., Paris.

Silverfish

Zygentoma ( = Lepismatoidea; formerly Thysanura, in part). Spanish: Pececitos de plata, pescaditos plateados (General). Portuguese: Traças dos livros (Brazil).

Silverfish (so called because of their shiny, slick appearance) are familiar cosmopolitan household pests. However, the classic domestic species, Lepisma saccharina, has been found in Latin America only sporadically in the cooler highlands of Brazil, Bolivia, and Argentina. They apparently do not tolerate humid, tropical conditions. Lepisma wasmanni is a soil-dwelling resident of the lomas of coastal Peru but seems to have been introduced from the Mediterranean region.

The long-tailed house silverfish (Ctenole-pisma longicaudata, fig. 4.10c) is the species most commonly encountered indoors in Latin America (Wygodzinsky 1967). It has a thick body covering of slick, slate-colored scales. It usually occurs in damp situations, but its precise range in the region is unknown. Stylifera gigantea is also common but seldom occurs indoors. There are many other species in various genera, but knowledge of their distribution and habits is rudimentary (Wygodzinsky 1967).

Members of this suborder are characterized by their cylindrical or somewhat flattened shape, thorax that is not arched, mouthparts that are directed forward, and small eyes that are set widely apart. The lateral lobes of the thorax are only slightly expanded. The group as a whole requires warmer environments than the bristletails, which prefer cooler, usually mountainous climates.

Three of the world's four families are found in Latin America (Paclt 1963, 1967; Wygodzinsky 1972). The Lepismatidae is the largest and most diverse and contains several domestic types as well as many native species. Several of the latter are associated symbiotically with social insects, as are the Nicoletiidae. Members of the latter family are subterranean, often inhabiting caves (Mexico and Cuba) and living in ant and termite nests. Cave forms lack eyes and integumentary pigment. The Maindro-niidae, with its single bizarre genus, Maindronia, has only been encountered under drying seaweed along arid Peruvian and Chilean coasts. These silverfish have a very elongate, pigmented, unsealed body.

References

Paclt, J. 1963. Thysanura Fam. Nicoletiidae.

Genera Insectorum 216: 1—58. Paclt, J. 1967. Thysanura Fam. Lepido-trichidae, Maindroniidae, Lepismatidae. Genera Insectorum 218: 1-86. Wygodzinsky, P. 1959. Thysanura and Ma-chilida of the Lesser Antilles and northern South America. Stud. Fauna Curasao Carib. Is. 36: 28-49. Wygodzinsky, P. 1967. On the geographical distribution of the South American Mi-crocoryphia and Thysanura (Insecta). In D. Deboutteville and E. Rapoport, eds., Biologie de L'Amerique Australe. 3: 505-524. Ed. Cent. Nat. Recher. Sci., Paris. Wygodzinsky, P. 1972. A review of the silverfish (Lepismatidae, Thysanura) of the United States and the Caribbean area. Amer. Mus. Nov. 2481: 1-26.

Bristletails

Microcoryphia (= Archaeognatha,

Machiloidea, Machilida). Rock jumpers.

While silverfish tend to be cylindrical or slightly flattened, bristletails are compressed laterally. The head is rotated downward so that the mouthparts project ven-trally, and the thorax is strongly arched. The eyes are well developed and contiguous, with many facets. The lobular sides of the thorax are large and appressed to the sides. Also, in contrast to silverfish, bns-

details are much less seen, completely wild insects, living secretly in all sorts of dry or moist hideaways, under stones and bark, in leaf litter, and among rocks at the seashore. They are terrestrial or littoral, nocturnal or crepuscular, and are highly active, running swiftly and, if threatened, jumping violently to escape capture.

The largest and most widespread Neotropical genus is Neomachillelus (fig. 4.10d), which inhabits spaces under tree bark and the soil surface. It is found over the entire area except for Patagonia (Wygodzinsky 1959). The southern temperate regions are inhabited by Machiloides and Machilinus. The latter tends toward arid zones. The genus Meinertellus is represented by several species in northeastern South America.

Reference

Wygodzinsky, P. 1959. Thysanura and Ma-chilida of the Lesser Antilles and northern South America. Stud. Fauna Curaçao Carib. Isl. 36: 28-49.

0 0

Post a comment