Insects - Agricultural Entomology - page 5

Fig. 3 Examples of insect mouthparts: (a) piercing mouthparts of an hemipterous bug. including transverse
sections through the rostrum (above) and feeding stylet (= stylet bundle) (below): (b) lapping mouthparts of a
house fly; (c) sucking mouthparts of a butterfly.

agromyzid flies), the basal part of the tibia may
be distinctly coloured and is often called the
'knee". The tarsus is typically multisegmented
and terminates in a small pad (the arolium),
located between a pair of small tarsal claws.
Although insect legs have the same basic struc-
ture, they are often considerably modified. The
forelegs, for example, may be raptorial (modified
for grasping) as in mantises. or fossorial (modi-
fied for digging) as in mole crickets; the hindlegs
are often saltatory (modified for jumping), as in
grasshoppers and flea beetles. Fine details of leg
structure (e.g. in beetles, the number of tarsal
segments) are often useful for distinguishing
between groups of insects.
Adults of most insects also possess one or two
pairs of wings: a pair of forewings arising from
the mesothorax and a pair of hindwings arising
from the metathorax. The base of the wings may
be covered by scale-like lobes (the tegulae) or, as
in certain flies, protected by membranous folds
(the squamae). Wing-coupling arrangements
for four-winged insects vary considerably. For
example, in some instances (e.g. aphids and

hundred. The basal segment (the scape) is often
elongate and separated by an often distinct seg-
ment (called the pedicel) from the rest of the
antenna, which forms the flagellum (the seg-
ments of which are called flagellomeres). Vari-
ous types of antennae are recognizable (see. for
example, Fig. 4).
The muscle-filled insect thorax is composed
of three segments: prothorax. mesothorax and
metathorax. The prothorax is often very large (as
in cockroaches, crickets and many beetles) and
the dorsal section (called the pronotum) may be
shield-like and cover much or all of the head. In
some insects (e.g. flies), the mesothorax forms
the bulk of the thorax and the prothorax and
metathorax are much reduced. In many insects,
the hind part of one of the thoracic segments
forms a distinct dorsal scutellum and, sometimes,
a postscutellum (see Fig. 112).
Each thoracic segment bears a pair of jointed
legs. Each leg has four main components: coxa,
femur, tibia and tarsus; there is also a small seg-
ment, called the trochanter, lying between the
coxa and femur (Fig. 5). In some insects (e.g.