Chapter 1: A general account of insect orders
Collembola (springtails)
The springtails are non-insect hexapods, and include about 8000 described species in more than 30
families, but the true species diversity may be much higher.
Taxonomy:
The group is subdivided into four suborders, the Poduromorpha, Entomobryomorpha, Neelipleona, and
Symphypleona. Poduromorpha currently comprise 11 families (e.g., Hypogastruridae, Onychiuridae,
Neanuridae), Entomobryomorpha also 11 (e.g., Isotomidae, Entomobryidae, Tomoceridae),
Neelipleona only a single family (Neelidae), and Symphypleona nine (e.g., Sminthuridae,
Bourletiellidae).
Size, color and shape:
Small (usually 2–3 mm, but up to 12 mm) and soft-bodied, their body varies in shape from globular to
elongate, and is pale or often characteristically pigmented grey, blue, or black.
Eyes:
The eyes and/or ocelli are often poorly developed or absent; the antennae have four to six segments.
Behind the antennae usually there is a pair of post antennal organs, which are specialized sensory
structures (believed by some to be the remnant apex of the second antenna of crustaceans).
Digestive system:
The entognathous mouthparts comprise elongate maxillae and mandibles enclosed by pleural folds of
the head; maxillary and labial palps are absent. The legs each comprise four segments. The six-
segmented abdomen has a sucker-like ventral tube (the collophore), a retaining hook (the retinaculum),
and a furca (sometimes called furcula; forked jumping organ, usually three-segmented) on segments
1, 3, and 4, respectively, with the gonophore on segment 5 and the anus on segment 6; cerci are
absent.
Excretory system:
The ventral tube is the main site of water and salt exchange and thus is important to fluid balance, but
also can be used as an adhesive organ. The springing organ (furca), formed by fusion of a pair of
appendages, is longer in surface-dwelling species than those living within the soil. In general, jump
length is correlated with furca length, and some species can spring up to 10 cm.
Reproduction and Development:
Amongst hexapods, collembolan eggs uniquely are microlecithal (lacking large yolk reserves) and
holoblastic (with complete cleavage). The immature instars are similar to the adults, developing
epimorphically (with a constant segment number); maturity is attained after five molts, but molting
continues for life.
Habit and Habitat:
,Springtails are most abundant in moist soil and litter, where they are major consumers of decaying
vegetation, but also they occur in caves, in fungi, as commensals with ants and termites, on still water
surfaces, and in the intertidal zone. Most species feed on fungal hyphae or dead plant material, whereas
some species eat other small invertebrates. Many collembolan species can digest plant and fungal
tissues but it is unclear if the enzymes involved (cellulase, chitinase, and trehalase) are produced by
the springtails themselves or by microorganisms in their gut. Only a very few species are injurious to
living plants; for example, the “lucerne flea” Sminthurus viridis (Sminthuridae) damages the tissues of
crops such as lucerne and clover and can cause economic injury.
Economic importance:
Large species can cause damage by feeding on young leaves and negative impact on fungiculture is
also described. Due to their high population densities collembolans can play a very important role in
transforming organic matter into humus. They are also indicators of negative side effects of pesticides.
Orthoptera (grasshoppers, locusts, katydids, and crickets)
The Orthoptera is a worldwide order of more than 22,000 described species in up to 30 families (the
classification is unstable), comprising two suborders: Caelifera (grasshoppers and locusts) and
Ensifera (katydids and crickets).
Taxonomy:
Orthoptera is divided into the two suborders Ensifera and Caelifera. The former comprises six extant
superfamilies (Tettigonioidea, Stenopelmatoidea, Rhaphidophoroidea, Hagloidea, Grylloidea,
,Schizodactyloidea) and the latter eight (Acridoidea, Trigonopterygoidea, Pneumoroidea,
Pyrgomorphoidea, Tanaoceroidea, Eumastacoidea, Tetrigoidea, Tridactyloidea). Caelifera are strongly
supported by apomorphies (e.g., shortened antennae, strongly modified ovipositor) whereas Ensifera
are mainly characterized by plesiomorphic features, but are consistently supported as a monophylum
in phylogenetic studies. A characteristic which may have evolved twice within this suborder is the
protibial tympanal organ.
Size and shape:
Orthopterans have hemimetabolous development, and are typically elongate cylindrical, medium-sized
to large (up to 12 cm long), with enlarged hind legs for jumping.
Eyes:
They are hypognathous and mandibulate, and have well-developed compound eyes; ocelli may be
present or absent. The antennae are multisegmented.
Thorax:
The prothorax is large, with a shield-like pronotum curving over the pleura; the mesothorax is small,
and the metathorax large. The fore wings form narrow, leathery tegmina; the hind wings are broad, with
numerous longitudinal and cross-veins, folded beneath the tegmina by pleating. Aptery and brachyptery
are frequent. The legs are often elongate and slender, and the hind legs large, usually saltatorial; the
tarsi have one to four segments.
Reproduction and Development:
The abdomen has eight to nine annular visible segments, with two or three terminal segments reduced.
Females have a well-developed appendicular ovipositor. The cerci each consist of a single segment.
Courtship may be elaborate and often involves communication by sound production and reception. In
copulation the male is astride the female, with mating sometimes prolonged for many hours. Ensiferan
eggs are laid singly into plants or soil, whereas Caelifera use their ovipositor to bury batches of eggs in
soil chambers. Egg diapause is frequent. Nymphs resemble small adults except in the lack of
development of wings and genitalia, but apterous adults may be difficult to distinguish from nymphs.
Molting:
In all winged species, nymphal wing pad orientation changes between molts; in early instars the wing
pad rudiments are laterally positioned with the costal margin ventral, until prior to the penultimate
nymphal instar (actually the third last molt) they rotate about their base so that the costal margin is
dorsal and the morphological ventral surface is external; the hind wing then overlaps the fore wing.
During the molt to the adult, the wings resume their normal position with the costal margin ventral. This
wing pad “rotation”, otherwise known only in Odonata, is unique to the Orthoptera amongst the
orthopteroid orders.
Caelifera are predominantly day-active, fast-moving, visually acute, terrestrial herbivores, and include
some destructive insects such as migratory locusts. Ensifera are more often night-active, camouflaged
, or mimetic, and are predators, omnivores, or phytophages, and have long antennae (usually more than
30 segments).
Economic importance:
Larger species are traditionally used as seasonally available protein-rich food in different cultures.
Locusts are already mentioned in very old sources (e.g., the Bible) as the cause for disastrous famines.
The most harmful species belong to the caeliferan family Acridiidae. Approximately ten species are
known to cause damage to vegetation and crops on a large scale. Swarms of Schistocerca gregaria
can comprise approximately 50 billion of individuals and cover thousands of square miles (Grimaldi &
Engel 2005).
Blattodea: epifamily Termitoidae (former order Isoptera; termites)
The termites form a small autapomorphic clade of more than 2600 described species of
hemimetabolous neopterans, living socially with polymorphic caste systems of reproductives, workers,
and soldiers.
Taxonomy:
The phylogenetic relationships of the blattarian lineages are not well understood. A preliminary
classification mainly based on the comprehensive works of McKittrick (1964) and Klass (1995) was
recently proposed by Bohn (2005a). Eight families are distinguished but the very heterogeneous
“Ectobiidae” (=“Blattellidae”) (five subfamilies, ca. 1,800 spp.) were clearly identified as paraphyletic.
Blattidae comprise two subfamilies and ca. 650 species, Corydiidae (=Polyphagidae) five sub families
and ca. 230 species, and Blaberidae nine subfamilies and ca. 1,200 species.
Blaberidae are subdivided into three subunits by Bohn (2005), the blaberoid-complex (Zetoborinae,
Blaberinae, Panesthiinae), the panchloroid-complex (Pycnoscelinae, Diplopterinae, Panchlorinae,
