Many plants support insect communities in structures that retain water. The containers formed by water retained in leaf axils of many bromeliads (“tank- plants”), gingers, and teasels, for example, or in rot- holes of trees, appear incidental to the plants. Others, namely the pitcher plants, have a complex architec- ture, designed to lure and trap insects, which are digested in the container liquid (Fig. 11.12).
The pitcher plants are a convergent grouping of the American Sarraceniaceae, Old World Nepenthaceae, and Australian endemic Cephalotaceae. They gener- ally live in nutrient-poor soils. Odor, color, and nectar entice insects, predominantly ants, into modified leaves – the “pitchers”. Guard hairs and slippery walls prevent exit and thus the prey cannot escape and drowns in the pitcher liquid, which contains digestive enzymes secreted by the plant.
Fig. 11.11 A tuber of the epiphytic myrmecophyte Myrmecodia beccarii(Rubiaceae), cut open to show the chambers inhabited by ants. Ants live in smooth-walled chambers and deposit their refuse in warted tunnels, from which nutrients are absorbed by the plant.
(After Monteith 1990.)
Fig. 11.12 A pitcher of Nepenthes(Nepenthaceae) cut open to show fly inquilines in the fluid: (clockwise from the top left) two mosquito larvae, a mosquito pupa, two chironomid midge larvae, a small maggot, and a large rat-tailed maggot.
Text continues on p. 294.
Box 11.5 Orthoptera (grasshoppers, locusts, katydids, and crickets)
The Orthoptera is a worldwide order of more than 20,000 species in some 13 to 30 families (the classification is unstable), comprising two suborders: Caelifera (grass- hoppers and locusts) and Ensifera (katydids and crick- ets). Orthopterans have hemimetabolous development, and are typically elongate cylindrical, medium-sized to large (up to 12 cm long), with enlarged hind legs for jumping. They are hypognathous and mandibulate, and have well-developed compound eyes; ocelli may be present or absent. The antennae are multisegmented.
The prothorax is large, with a shield-like pronotum curv- ing 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 lon- gitudinal 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 1– 4 segments.
The abdomen has 8 –9 annular visible segments, with two or three terminal segments reduced. Females have a well-developed appendicular ovipositor (Fig. 2.23b,c;
Box 5.2). The cerci each consist of a single segment.
Courtship may be elaborate and often involves com- munication by sound production and reception (sec- tions 4.1.3 & 4.1.4). 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. In all winged species, nymphal wing pad orientation changes between molts (as illustrated here for a locust); in early instars the wing pad rudiments are laterally positioned with the costal margin ventral, until prior to the penul- timate nymphal instar (actually the third last molt) they rotate about their base so that the costal margin is dor- sal and the morphological ventral surface is external;
the hind wing then overlaps the fore wing (as in the fifth- instar nymph illustrated here). During the molt to the adult, the wings resume their normal position with the costal margin ventral. This wing pad “rotation”, other- wise 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 (section 6.10.5; Fig. 6.13). Ensifera are more often night-active, camouflaged or mimetic, and are predators, omnivores, or phytophages.
Phylogenetic relationships are considered in section 7.4.2 and relationships of the order are depicted in Fig. 7.2.
The Phasmatodea is a worldwide, predominantly trop- ical order of more than 3000 species that is lacking a phylogenetically based classification. They have hemimetabolous development, and are elongate cylin- drical and stick-like or flattened and often leaf-like in form, up to >30 cm in body length (the longest species has a total length, including legs, of about 50 cm and is from Borneo). They have mandibulate mouthparts. The compound eyes are anterolaterally placed and relat- ively small, and ocelli occur only in winged species, often only in males. The antennae range from short to long, with 8 –100 segments. The prothorax is small, and the mesothorax and metathorax are elongate if winged, shorter if apterous. The wings, when present, are func- tional in males but are often reduced in females; many species are apterous in both sexes. The fore wings form leathery tegmina, whereas the hind wings are broad, with a network of numerous cross-veins and the ante- rior margin toughened as a remigium that protects the folded wing. The legs are elongate, slender, gressorial, with five-segmented tarsi; they can be shed in defense (section 14.3) and may be regenerated at a nymphal molt. The abdomen is 11-segmented, with segment 11
often forming a concealed supra-anal plate in males or a more obvious segment in females; the male genitalia are concealed and asymmetrical. The cerci are variably lengthened and consist of a single segment.
In the often prolonged copulation the smaller male is astride the female, as illustrated here for the spurlegged stick-insect, Didymuria violescens(Phasmatidae). The eggs often resemble seeds (as shown here in the enlargement of the egg of D. violescens, after CSIRO 1970) and are deposited singly, glued on vegetation or dropped to the ground; there may be lengthy egg dia- pause. Nymphal phasmatids mostly resemble adults except in their lack of wing and genitalia development, the absence of ocelli, and the fewer antennal segments.
Phasmatodea are phytophagous and predominantly resemble (mimic) various vegetational features such as stems, sticks, and leaves. In conjunction with crypsis, phasmatids demonstrate an array of anti-predator de- fenses ranging from general slow movement, grotesque and often asymmetrical postures, to death feigning (sections 14.1 & 14.2).
Phylogenetic relationships are considered in section 7.4.2 and depicted in Fig. 7.2.
The Thysanoptera is a worldwide order of minute to small insects (from 0.5 mm to a maximum length of 15 mm), comprising about 5000 species in two suborders:
Terebrantia with seven families (including the speciose Thripidae); and Tubulifera with one family (the speciose Phlaeothripidae). Their development is intermediate between hemi- and holometabolous. The body is slen- der and elongate, and the head is elongate and usually hypognathous. The mouthparts (Fig. 2.13a) comprise the maxillary laciniae formed as grooved stylets, with the right mandible atrophied and the left mandible formed as a further stylet; the maxillary stylets form a feeding tube. The compound eyes range from small to large, and there are three ocelli in fully winged forms.
The antennae are four- to nine-segmented and anteri- orly directed. Thoracic development varies according to the presence of wings; fore and hind wings are simi- lar and narrow with a long setal fringe (as illustrated on the left for a terebrantian thrips, after Lewis 1973). At rest the wings are parallel in Terebrantia (middle figure) but overlap in Tubulifera (right figure); microptery and aptery occur. The legs are short and gressorial, some- times with the fore legs raptorial and the hind legs sal- tatory; the tarsi are one- or two-segmented, and the pretarsus has an apical protrusible adhesive arolium (bladder or vesicle). The abdomen is 11-segmented (though with only 10 segments visible). In males the genitalia are concealed and symmetrical. In females the cerci are absent; the ovipositor is serrate in Terebrantia, very reduced in Tubulifera.
Eggs are laid into plant tissue ( Terebrantia) or into crevices or exposed vegetation ( Tubulifera). The first- and second-instar nymphs resemble small adults except with regard to their wings and genitalia; how- ever, instars 3 – 4 ( Terebrantia) or 3 –5 ( Tubulifera) are resting or pupal stages, during which significant tissue reconstruction takes place. Female thrips are diploid, whereas males (if present) are haploid, produced from unfertilized eggs. Arrhenotokous parthenogenesis is common; thelytoky is rare (section 5.10.1).
The primitive feeding mode of thrips probably was fungal feeding, and about half of the species feed only on fungi, mostly hyphae. Most other thrips primarily are phytophages, feeding on flowers or leaves and includ- ing some gall inducers, and there are a few predators.
Plant-feeding thrips use their single mandibular stylet to pierce a hole through which the maxillary stylets are inserted. The contents of single cells are sucked out one at a time; pollen- or spore-feeding thrips similarly remove the contents of individual pollen grains or spores. Several cosmopolitan thrips species (e.g. west- ern flower thrips, Frankliniella occidentalis) act as vectors of viruses that damage plants. Thrips may aggregate in flowers, where they may act as pollinators.
Subsocial behavior, including parental care, is exhib- ited by a few thrips (section 12.1.1).
Phylogenetic relationships are considered in section 7.4.2 and depicted in Fig. 7.2.
Box 11.8 Hemiptera (bugs, cicadas, leafhoppers, spittle bugs, planthoppers, aphids, jumping plant lice, scale insects, whiteflies)
The Hemiptera is distributed worldwide, and is the most diverse of the non-endopterygote orders, with more than 90,000 species in about 140 families. Historically, it was divided into two suborders (sometimes treated as orders): Heteroptera (bugs) and “Homoptera” (cicadas, leafhoppers, spittle bugs, planthoppers, aphids, jump- ing plant lice (=psylloids), scale insects (=coccoids), and whiteflies). However, homopterans represent a grade of organization (a paraphyletic rather than a monophyletic group). Currently, five suborders can be recognized (Fig. 7.5): (i) Heteroptera, the “true” bugs;
(ii) Coleorrhyncha, the moss bugs (family Peloridiidae);
(iii) Cicadomorpha (cicadas, leafhoppers, and spittle bugs); (iv) Fulgoromorpha (planthoppers); and (v) Ster- norrhyncha (aphids, jumping plant lice, scale insects, and whiteflies). Sometimes the Cicadomorpha and Fulgoromorpha are collectively called the Auchenor- rhyncha, but this grouping may also be paraphyletic.
Four hemipterans are illustrated here in lateral view: (a) Cicadetta montana(Cicadidae), the only British cicada (after drawing by Jon Martin in Dolling 1991); (b) a green lantern bug, Pyrops sultan(Fulgoridae), from Borneo (after Edwards 1994); (c) the psyllid Psyllopsis fraxini (Psyllidae), which deforms leaflets of ash trees in Britain (after drawing by Jon Martin in Dolling 1991); and (d) an
apterous viviparous female of the aphid Macromyzus woodwardiae(Aphididae) (after Miyazaki 1987a).
Hemipteran compound eyes are often large, and ocelli may be present or absent. Antennae vary from short with few segments to filiform and multiseg- mented. The mouthparts comprise mandibles and max- illae modified as needle-like stylets, lying in a beak-like grooved labium (as shown for a pentatomid het- eropteran in (e) and (f )), collectively forming a rostrum or proboscis. The stylet bundle contains two canals, one delivering saliva, the other uptaking fluid (as shown in (f )); there are no palps. The thorax often consists of large pro- and mesothorax, but a small metathorax.
Both pairs of wings often have reduced venation; some hemipterans are apterous, and rarely there may be just one pair of wings (in male scale insects). The legs are frequently gressorial, sometimes raptorial, often with complex pretarsal adhesive structures. The abdomen is variable, and cerci are absent.
Most Heteroptera hold their head horizontally, with the rostrum anteriorly distinct from the prosternum (although the rostrum may be in body contact at coxal bases and on anterior abdomen). When at rest the wings are usually folded flat over the abdomen (Fig.
5.8). The fore wings usually are thickened basally and
membranous apically to form hemelytra (Fig. 2.22e).
Heteroptera mostly have abdominal scent glands.
Apterous heteropterans can be identified by the ros- trum arising from the anteroventral region of the head and the presence of a large gula. Non-heteropterans hold the head deflexed with the complete length of the rostrum appressed to the prosternum, directed pos- teriorly often between the coxal bases. They have mem- branous wings that rest roof-like over the abdomen;
apterous species are identified by the absence of a gula and the rostrum arising from the posteroventral head or near the prosternum. Mouthparts are absent in some aphids, and in some female and all male scale insects.
Nymphal Heteroptera (Fig. 6.2) resemble adults except in the lack of development of the wings and gen- italia. However, immature Sternorrhyncha show much variation in a range of complex life cycles. Many aphids exhibit parthenogenesis (section 5.10.1), usually altern- ating with seasonal sexual reproduction. The immature stages of Aleyrodoidea (whiteflies) and Coccoidea (scale insects) may differ greatly from adults, with larviform stages followed by a quiescent, non-feeding
“pupal” stage, in convergently acquired holometaboly.
The primitive feeding mode is piercing and sucking plant tissue (Fig. 11.4), and many species induce galls on their host plants (section 11.2.4; Box 11.2). All hemipterans have large salivary glands and an alimen- tary canal modified for absorption of liquids, with a filter chamber to remove water (Box 3.3). Many hemipterans rely exclusively on living plant sap (from phloem or xylem and sometimes parenchyma). Elimination of large quantities of honeydew by phloem-feeding Sternorrhyncha provides the basis for mutualistic rela- tionships with ants. Many hemipterans exude waxes (Fig. 2.5), which form powdery (see Plate 5.1, facing p. 14) or plate-like protective covers. Non-phytophagous Heteroptera comprise many predators, some scav- engers, a few hematophages (blood-feeders), and some necrophages (consumers of dead prey), with the last trophic group including successful colonizers of aquatic environments (Box 10.6) and some of the few insects to live on the oceans (section 10.8).
Phylogenetic relationships are considered in section 7.4.2 and depicted in Fig. 7.5.
have a large and mobile head, and large compound eyes; three ocelli are present in winged species, but absent in apterous ones. The antennae are usually 13-segmented and filiform. The mouthparts have asym- metrical chewing mandibles, rod-shaped maxillary laciniae, and reduced labial palps. The thorax varies according to the presence of wings. The pronotum is small, whereas the meso- and metanotum are larger.
The legs are gressorial and slender. The wings are often reduced or absent (as shown here for the booklouse Liposcelis entomophilus(Liposcelidae), after Smithers 1982). When present the wings are membranous, with reduced venation, with the hind wing coupled to the larger fore wing in flight and at rest, when the wings are held roof-like over the abdomen (as shown here for the psocid Amphigerontia contaminata(Psocidae), after Badonnel 1951). The abdomen has 10 visible segments, with the 11th represented by a dorsal epiproct and paired lateral paraprocts. Cerci are always absent.
Courtship often involves a nuptial dance, followed by spermatozoa transfer via a spermatophore. Eggs are laid in groups or singly onto vegetation or under bark, in sites where nymphs subsequently develop.
Parthenogenesis is common, and may be obligatory or facultative. Viviparity is known in at least one genus.
Adults and nymphs feed on fungi (hyphae and spores), lichens, algae, insect eggs, or are scavengers on dead organic matter. Some species are solitary;
others may be communal, forming small groups of adults and nymphs beneath webs.
Phylogenetic relationships are considered in section 7.4.2 and depicted in Fig. 7.5.
Box 11.9 Psocoptera (booklice, barklice, or psocids)
The Psocoptera is a worldwide order of common but cryptic minute to small insects (1–10 mm long), with over 3000 species in 36 families. Development is hemimetabolous with five or six nymphal instars. They
This apparently inhospitable environment provides the home for a few specialist insects that live above the fluid, and many more living as larvae within. The adults of these insects can move in and out of the pitch- ers with impunity. Mosquito and midge larvae are the most common inhabitants, but other fly larvae of more than 12 families have been reported worldwide, and odonates, spiders, and even a stem-mining ant occur in south-east Asian pitchers. Many of these insect inquilines live in a mutualistic relationship with the
plant, digesting trapped prey and microorganisms and excreting nutrients in a readily available form to the plant. Another unusual pitcher plant associate is a Camponotusant that nests in the hollow tendrils of the pitcher plant Nepenthes bicalcaratain Borneo.
The ants feed on large, trapped prey or mosquito larvae, which they haul from the pitchers, and thereby benefit the plant by preventing the accumulation of excess prey, which can lead to putrefaction of pitcher contents.
Box 11.10 Coleoptera (beetles)
The Coleoptera is probably the largest order of insects, with some 350,000 described species in four suborders (Archostemata, Myxophaga, Adephaga, and the spe- ciose Polyphaga). Although the family-level classifica- tion is unstable, some 500 families and subfamilies are recognized. Adult beetles range from small to very large, but are usually heavily sclerotized, sometimes even armored, and often compact. Development is holometabolous. The mouthparts are mandibulate, and compound eyes range from well developed (sometimes even meeting medially) to absent; ocelli are usually absent. The antennae comprise 11 or frequently fewer segments (exceptionally with 20 segments in male Rhipiceridae). The prothorax is distinct, large, and extends laterally beyond the coxae; the mesothorax is
small (at least dorsally), and fused to the metathorax to form the wing-bearing pterothorax. The fore wings are modified as sclerotized, rigid elytra(Fig. 2.22d & Plate 1.2, facing p. 14), whose movement may assist in lift or may be restricted to opening and closing before and after flight; the elytra cover the hind wings and abdom- inal spiracles allowing control of water loss. The hind wings are longer than the elytra when extended for flight (as illustrated on the upper left for a soldier beetle, Cantharissp. (Cantharidae), after Brackenbury 1990), and have variably reduced venation, much of which is associated with complex pleating to allow the wings to be folded longitudinally and transversely beneath the elytra even if the latter are reduced in size, as in rove beetles (Staphylinidae) such as Staphylinus caesareus
(illustrated on the lower left, after Stanek 1969). The legs are very variably developed, with coxae that are some- times large and mobile; the tarsi are primitively five- segmented, although often with a reduced number of segments, and bear variously shaped claws and adhes- ive structures (Fig. 10.3). Sometimes the legs are fosso- rial (Fig. 9.2c) for digging in soil or wood, or modified for swimming (Figs. 10.3 & 10.8) or jumping. The abdomen is primitively nine-segmented in females, and 10- segmented in males, with at least one terminal segment retracted; the sterna are usually strongly sclerotized, often more so than the terga. Females have a substitu- tional ovipositor, whereas the male external genitalia are primitively trilobed (Fig. 2.24b). Cerci are absent.
Larvae exhibit a wide range of morphologies, but most can be recognized by the sclerotized head capsule with opposable mandibles and their usually five-segmented thoracic legs, and can be distinguished from similar lepidopteran larvae by the lack of ventral abdominal crochet-bearing prolegs and lack of a median labial silk gland. Similar symphytan wasp larvae have prolegs on abdominal segments 2–7. Beetle larvae vary in body shape and leg structure; some are apodous(lacking any thoracic legs; Fig. 6.6g), whereas legged larvae may be campodeiform(prognathous with long thoracic legs;
Fig. 6.6e), eruciform(grub-like with short legs), or scar- abaeiform(grub-like but long-legged; Fig. 6.6f ). Pupa- tion is often in a specially constructed cell or chamber (Fig. 9.1), rarely in a cocoon spun from silk from Malpi- ghian tubules, or exposed as in coccinellids (Fig. 6.7j).
Beetles occupy virtually every conceivable habitat, including freshwater (Box 10.6), a few marine and inter- tidal habitats, and, above all, every vegetational micro- habitat from external foliage (Fig. 11.1), flowers, buds, stems, bark, and roots, to internal sites such as in galls in any living plant tissue or in any kind of dead material in all its various states of decomposition. Saprophagy and fungivory are fairly common, and dung and carrion are exploited (sections 9.3 & 9.4, respectively). Few beetles are parasitic but carnivory is frequent, occurring in nearly all Adephaga and many Polyphaga, including Lampyridae (fireflies) and many Coccinellidae (ladybird beetles; vignette to Chapter 16, Fig. 5.9). Herbivorous Chrysomelidae and Curculionidae are widely intro- duced as biological control agents of weedy plants, and Coccinellidae have been used as biological control agents for aphid and coccoid pests of plants (Box 16.2).
Some beetles are significant pests of roots in pastures and crops (especially larval Scarabaeidae), of timber (especially Cerambycidae such as Phoracantha semi- punctata, illustrated on the upper right, after Duffy 1963), and of stored products (such as the granary wee- vil, Sitophilus granarius (Curculionidae), illustrated on the lower right). These last beetles tend to be adapted to dry conditions and thrive on stored grains, cereals, pulses, and dried animal material such as skins and leather.
Phylogenetic relationships are considered in section 7.4.2 and depicted in Fig. 7.2.
Box 11.11 Lepidoptera (butterflies and moths)