Phasmatodea (also known as Phasmida) comprises 3000 species worldwide with only 15 species known in Europe. Stick-insects are found in nearly all temperate and tropical ecosystems. Species are mostly nocturnal and phytophagous. Phasmatodea bears several common morphological characters that clearly defi ne the order: an emarginated labrum, a pair of exocrine glands located inside the prothorax, and a thorax fused with the first abdominal sternum. Phasmids undergo an incomplete metamorphosis (four to eight instars), with the young nymphs resembling miniature, albeit wingless, adults.
Phasmida are terrestrial, nocturnal, phytophagous insects found in nearly all temperate and tropical ecosystems (Günther, 1953). Scientists have described over 3,000 species (Bragg, 1995), yet this figure is uncertain since some taxon names are synonyms, and many new species have not been formally described.
Walking Sticks Overview
Order Phasmida is also known as Order Phasmatodea. Walking sticks (or stick insects) use camouflage for protection. Their morphology resembles sticks or leaves. They young are usually green in color and the adults are usually brown. Adults are usually seen from midsummer to late fall. They can also release a foul odor that may ward off predators. They are able to regenerate or partially regenerate lost limbs and have compound eyes. They can be anywhere from 2.5 centimeters to a little over a foot in length. They live in tropical areas all over the world, including South America, Australia, Southeast Asia, and the United States. All species in the United States (except one in Florida) are wingless. More than 3, 000 species are currently described. Walking sticks feed on the leaves of shrubs and trees. Females can lay eggs without a male and the eggs will all be exact female copies of the mother. The nymphs molt several times before becoming an adult. Walking sticks can be seen in the fossil record as far back as the Eocene.
Phasmida are variable in appearance, ranging from relatively generalized forms, to some that are wonderful mimics of sticks and/or leaves. They display varying degrees of brachyptery, and can be winged or wingless. The tarsi have three articles in Timema Scudder and five in other Phasmida. Cerci are composed of one article, except for adult males of Timema which have a lobe on the right cercus.
Sexual dimorphism is usually extreme: the males are smaller and more gracile than the females. Reproduction is typically sexual, but parthenogenesis occurs frequently. The egg capsule is distinctively shaped, possessing a lid called the operculum and a micropylar plate (Sellick, 1997). Eggs are large and oftentimes highly sculptured resembling plant seeds. They are laid singly, and are dropped, flicked, buried, glued to a surface, or riveted to a leaf. Some species that drop the eggs rely on ants to disperse them in a process analogous to myrmecochory (Windsor et al., 1996). The entire life cycle from egg to adult can take from several months to several years depending on the species.
Egg capsule of Extatosoma popa. The nymph escapes by popping off the operculum. Photograph copyright © 2001, Erich Tilgner.
Phasmida possess several unique anatomical features that distinguish them from other Neoptera and indicate they are a monophyletic group (see Tilgner et al., 1999; 2002). For example:
- The labrum is emarginated.
- All possess a pair of exocrine glands inside the prothorax (in a few species, these glands can discharge an irritating, tear gas-like spray used for defense).
- The intestine has unique filament bearing glands.
- Thorax fused with abdominal sternum I
- The dorso-ventral muscles of the abdomen are numerous, short, and arranged in parallel.
- Males of many species possess a unique sclerite termed the vomer. This structure is located above the genitalia and permits the male to clasp the female.
Evolution and Systematics
Discussion of Phylogenetic Relationships
Timema is hypothesized to be the sister group to the remainder of Phasmida (Kristensen, 1975, Bradler 1999, Tilgner et al. 1999, Tilgner 2002), termed Euphasmida by Bradler (1999). Timema lack the autapomorphies of Euphasmida and possess traits found in other more distantly related Neoptera (Tilgner et al. 1999).
Molecular Biology and Genetics
Statistics of barcoding coverage
Specimens with Sequences:822
Specimens with Barcodes:388
Species With Barcodes:127
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