Morphology Adult

The body framework (Fig 2) consists of a hardened (sclerotized) exoskeleton made up of a head capsule with appendages; three fused thoracic segments, each with legs, and two pairs of wings, on the middle (mesothoracic) and third (metathoracic) segments; and an abdomen, which has 10 segments, is less sclerotized than the thorax, and is movable by intersegmental membranes. Complex genital structures of external origin arise from abdominal segments A8-10, and often there are accessory structures (pouches, glands, hair brushes) associated with sound reception, courtship, or other functions.

FIGURE 2 Schematic representation of the exoskeletal anatomy of a ditrysian moth, with prothoracic leg enlarged below. Head: an, antenna; eye, compound eye; oc, ocellus; l.p., labial palpus; ha, haustellum (proboscis); Thorax: pa, patagium; te, tegula; me, mesoscutum; w.b., wing base; co, coxa; tr, trochanter; fe, femur; ti, tibia; t.s., tibial spurs; ta, tarsomeres; cl, tarsal claws; ep, epiphysis. Abdomen: tergites and sternites 1-7 and spiracles shown.

FIGURE 2 Schematic representation of the exoskeletal anatomy of a ditrysian moth, with prothoracic leg enlarged below. Head: an, antenna; eye, compound eye; oc, ocellus; l.p., labial palpus; ha, haustellum (proboscis); Thorax: pa, patagium; te, tegula; me, mesoscutum; w.b., wing base; co, coxa; tr, trochanter; fe, femur; ti, tibia; t.s., tibial spurs; ta, tarsomeres; cl, tarsal claws; ep, epiphysis. Abdomen: tergites and sternites 1-7 and spiracles shown.

HEAD Structures include paired simple eyes (ocelli) and scaleless, raised spots (chaetosema), which are unique to Lepidoptera, although one or both are lost in many taxa (Figs. 2-4). There is enormous variation in the form of the antennae, often between the sexes of a species, being filiform or with the flagellar segments variously enlarged or branched. Antennae of butterflies are enlarged distally, forming apical clubs, while those of moths are not, although some moths have distally enlarged antennae that are tapered or hooked to the tip. The mouthparts of the most primitive moth families retain functional mandibles as in their mecopteroid ancestors, but in the majority of moths the mandibles are lost, and the maxillary galeae are elongate and joined to form a tubular

FIGURE 3 Descaled lepidopteran head, frontal aspect. ch, chaetosema; oc, ocellus; a.s., antennal socket; sc, scape; fr, frons; pi, pilifer; m.p., maxillary palpus; l.p., labial palpus; ha, haustellum, consisting of fused galeae.
FIGURE 4 Head of ethmiid moth, showing the strongly upcurved labial palpus that is characteristic of most Gelechioidea. Scale bar = 1.0 mm.

proboscis (haustellum) with musculature that enables it to be coiled under the head when not being used to suck nectar from flowers or other fluids into the digestive tract by a pumping action. The maxillary palpi consist of one to five segments and in primitive moths are conspicuous, often folded. The labial palpi are more prominent in most Lepidoptera and vary in curvature and length, but they are not folded.

THORAX The pro-, meso-, and metathorax are fused, each consisting of a series of nonmovable sclerites (Fig. 2). In primitive groups the meso- and metathorax and their wings are similar in size, but in derived families the mesothorax is larger and has more powerful musculature, and the forewing has more rigid vein structure, especially on the leading edge. In the largest superfamily, Noctuoidea, the metathorax is modified posteriorly into a pair of tympanal organs. The tibia of the foreleg has an articulated epiphysis on the inner surface, a uniquely derived feature in Lepidoptera, usually with a comb of stout setae, that is used to clean the antennae and proboscis by drawing them through the gap between the comb and the tibia. The wings are tiny and soft at eclosion from the pupa, then rapidly expand by circulation of blood pumped into the flaccid veins, causing them to extend, stretching the wing membranes to full size, after which they rapidly harden, with the membranes pressed closely together, and the system of tubular veins provides structure. Homologies of the six vein systems are discernible across all families of Lepidoptera, and the configuration of veins has been used extensively in classification. In the most primitive moths the fore wing (FW) and

FIGURE 5 Wing venation of a homoneurous moth (Eriocraniidae). Vein systems: Sc, subcostal; R, radial; M, medial; Cu, cubital; A, anal.

hind wing (HW) are similar in shape and wing venation (homoneurous) (Fig. 5), while the more derived groups have lost parts of the vein systems and have fewer remaining in the HW than in the FW (heteroneurous) (Fig. 6). There are various wing-coupling mechanisms by which the FW and HW are linked to facilitate flight. Primitive homoneurous moths have an enlarged lobe at the base of the FW (jugum) that folds under the HW when the insect is at rest but extends over the HW in flight, which does not couple the wings efficiently. Most moths have the HW frenulum that hooks under the FW retinaculum, the development of which varies among taxa and between the sexes of many species.

In a few groups (e.g., Psychidae, Lymantriidae) females of many species are flightless, having very reduced wings (brachypterous), or are apterous and may not even shed the

FIGURE 6 Wing venation of a heteroneurous moth (Tortricidae). Abbreviations as in Fig. 5.

pupal skin. Brachyptery has evolved many times independently, such as in high montane and winter-active species of various families in Europe, North America, and Australia. Both sexes are flightless in species of several families on remote southern oceanic islands and in one species of Scythrididae that occurs only on windswept coastal sand dunes in California.

ABDOMEN The abdomen has segments A7-10 or A8-10 modified to form external parts of the genitalia; the sternum of A1 in homoneurous families is small and is lost in other Lepidoptera. Articulation of the thorax and abdomen in derived families is accomplished by musculature attached to sclerotized struts (apodemes) that project from abdominal sternite 2. There are paired tympanal organs at the base of the abdomen in Pyraloidea and Geometroidea. Various male glandular organs associated with courtship occur on the abdomen in several families. Usually these are developed as expandable hair brushes or tufts, or as thin-walled, eversible sacs (coremata), from the intersegmental membrane at the base of the genitalia or on other segments.

The genitalia of Lepidoptera are highly complex and provide the basis for taxonomic species discrimination in most families and often generic or family-defining characteristics. In the male (Fig. 7) the valvae, which are thought to provide clasping stability during mating, usually are large, more or less covering the other structures in respose, and usually are densely setate on the inner surface, scaled exteriorly, and the most

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