STUDY OF THE TYPES OF INSECT ANTENNAE, MOUTHPARTS AND LEGS

Aim: To study the various types of insect antennae, mouthparts and legs

1. Insect antenna
Insects possess a pair of antennae, the appendages of second head segment,
articulating with the head in front or in between the compound eyes. Antennae are well
developed in almost all adults and nymphs but, completely absent in the order Protura and
reduced in endopterygote larvae. These are sensory organs useful for perceiving smell,
hearing and also act as tactile organs. In some, they may be useful for holding the food or
mating and for communication.

Typically, antenna is divisible into three regions i.e., scape, pedicel and flagellum.
Scape-first elongated segment. Pedicel - second segment and usually small in size and in
many insects
possess special auditory organ called Johnston's organ. (Absent in Diplura and Collembola).
Flagellum - terminal part of the antennae from third segment to apex having number of
segments (flagellomeres). Size and shape of antennae varies in different insects; the character
is useful in scientific classification of insects and also as secondary sexual character to
identify the sex of the insect in some species.

Types of (Modification) Antennae

 Filiform (thread like) – Ex: Grasshopper. Segments are more or less uniform
throughout from base to apex and never end with bristle.
 Setaceous (Whip Like) – Ex: Cockroach. Segments gradually decreases from base to
apex presenting a whip or bristle like structure.
 Moniliform (Beaded) – Ex: Termites. Segments are round or oval with well-
developed constrictions between segments, appearing like a string of beads.
 Pectinate (Comb like) – Ex: Female arctiid moth. Segments possess lateral processes
on one side giving comb like appearance.
 Bipectinate (Double comb) – Ex: Male lymantriid moth and mulberry silk worm
moth. Segments bear lateral processes on either side.
 Serrate (Saw like) – Ex: Pulse beetle. Segments are triangular with projecting points
on one side giving saw like appearance.
 Clavate (Clubbed) – Ex: Butterflies. Segments gradually increase in diameter near the
tip ending in a club like apical part.
 Clavate with hook (Clubbed antennae with hook) – Ex: Skipper butterflies. Segments
gradually increase in diameter from near the tip and the last one ends with a small
hook like structure.
 Capitate (Clubbed with knob) – Ex: Red flour beetle. Segments gradually increase in
diameter near the apex and the terminal 3 to 5 segments suddenly enlarge to form a
knob like structure.
 Geniculate (Elbowed) – Ex: Ants, Honey bees. The first segment (scape) is greatly
elongated and flagellum always makes an angle with it.
 Lamellate (Plate like) – Ex: Rhinoceros beetle, dung rollers, chaffer beetles. The
terminal segments expand to one side into lateral oval lobes.
  Flabellate (Plate like) – Ex: Stylopids. The terminal segments expand on one side
into lateral lobes. The sides of the lobes are parallel.
 Plumose (Brush like with dense hairs) – Ex: Male mosquito. Whorls of hairs arise
from each joint of the segment. Each whorl contains a number of hairs.
 Pilose (Brush like with sparse hairs) – Ex: Female mosquito. Looks like plumose but
each whorl contains a smaller number of hairs.
 Aristate (Antennae with arista) – Ex: Housefly. Antennae are small, microscopic,
three segmented. Third segment enlarged and bears a bristle called arista on its dorsal
side.
 Stylate (Antennae with style) – Ex: Robberfly. Antennae small 3 to 4 segmented.
Terminal segment elongate into bristle like structure called style.

2. Insect legs
Legs are the locomotory appendages of the thorax in insects. Generally, three pairs of
legs are present in all adults and nymphs. This character is so constant that the name
hexapoda is directly derived from this. The number is variable in larvae of endopterygote
insects from zero to eleven pairs. In larvae, legs may be seen attached to both thorax and
abdomen. (Thoracic legs are true legs while abdominal legs are prolegs). Insects being
arthopods possess jointed legs. A typical thoracic leg consists of five parts; coxa, trochanter,
femur, tibia and tarsus. Coxa articulates with the thorax by single or double articulations.
Trochanter is small and articulates with coxa but rigidly fixed to the femur. Femur is usually
strong and articulates with tibia. Tibia is also equally longer as femur or even more and
articulates with tarsus. Tarsus is generally subdivided from 2 to 5 segments and each
subdivision is called as tarsomere. All tarsomers unite with each other without any
articulation. However, the tarsus as a whole articulates with the tibia. Last tarsomere possess
certain additional structures which are collectively called as pre-tarsus. Structure of the pre-
tarsus varies but generally consists of a pair of claws and an arolium in the center and in some
with an empodium. Normally legs are useful for walking. However, they are modified in
different insects to suit different functions depending upon the habit and habitat of insects.

Modification of legs
• Cursorial - Ex- Cockroach. Used for walking and running. All the legs uniformly
well-developed without any special modification.
 Saltatorial - Ex- Grasshoppers and gryllids. Used for Leaping and Jumping. Femur
and tibia elongated.
 Fossorial - Ex- Mole crickets and dung rollers. Used for Digging. Tibia and tarsus
short and broad with teeth like projections.
 Rapotorial - Ex- Mantids. Used for Preying. Femur spinose and possess a central
longitudinal groove. Tibia narrow, blade like spinose and fits into the groove of
femur.
 Natatorial - Ex- Water beetles. Used for swimming. Hind legs paddle like. Tibia and
tarsus short and broad having dense long marginal hairs.
 Scansorial - Ex- Head lice. Used for clinging tibia possess tibial thumb. Tarsus
single segmented and pre-tarsus with a single long curved claw.
 Prehensile - Ex- Dragonflies. Used for catching prey. Thoracic segments obliquely
arranged. Sternal plates pulled forward and tergal plates pushed backward, resulting
 that all the legs pushed forward and seen below the head, together form a basket like
structure useful for catching the prey even in flight.
 Antenna cleaning legs - Ex- Fore legs of Honey bee. Used for cleaning antennae.
Tibia possess a process and the first tarsal segment with a semicircular notch.
 Wax pick type- Ex- Honey bee. Used for picking wax plates. Tibia possess a spine
called wax pick for removing the wax plates from the ventral side of the abdomen.
 Pollen carrying or foragial - Ex- Hind legs of Honey bee. Used for collecting pollen
and cleaning the body. Inner surface of the tibia has a grove and is used as pollen
basket for temporary storage of pollen grains. First tarsal segment enlarged and
possess short stiff hairs all over the surface called pollen brush.
 Climbing leg – Ex – House fly. The terminal segment of the leg is pre-tarsus. The
pre-tarsus bears two claws and lying below the claws are two lobes called pulvilli and
an elongate spur called empodium. This helps insect to climb smooth or steep surface.
(i) Insect mouth parts

The basic and most primitive type of mouth parts is the biting and chewing type
present in grasshoppers, cockroaches and beetles. In order of appearance from anterior to
posterior side, a typical chewing mouth part consists of the followings-
i) A single labrum (Upper lip)
ii) A pair of mandibles (Jaws)
iii) A pair of maxillae (Second pair)
iv) A labium (Lower lip)
v) A single hypopharynx (Tongue like organ)

i) Labrum: A movable flap hanging down from the edge of clypeus. It covers the
mouth parts. Its inner side forms the front of the pre-oral cavity called the
epipharynx. It is an appendage of head segment -1.
ii) Mandibles: Hard, heavily sclerotized, paired appendages of head segment – 4,
having a set of teeth. It occurs just behind the labrum. It varies greatly in structure
depending upon the food taken.
iii) Maxillae: Paired appendages of head segment 5th lying just behind the mandibles.
Each maxilla bears a feeler like organ, the maxillary palp. The basal segment of
maxillae is the cardo, the second segment is the stipes. The five segmented palp is
borne on a lobe of the stipes called the palpifer. The stipes bears at its apex two
processes – an elongated jaw like structure called lacinia and the lobe like
structure, the galea.
iv) Labium: A single median appendage of head segment – 6 lying posterior to the
maxillae. It is evolved from a pair of maxillae like structure fused along the mid-
line. It is divided by a transverse sulcus into basal post-mentum, and a distal pre-
mentum. Post mentum comprised basal sub-mentum and distal mentum. The pre-
mentum bears a pair of 3-segmented labial palps borne on lateral lobe, the
palpiger. Apical lobes of pre-mentum constitute the ligula. Ligula consists of
mesal lobes glossa and lateral lobes paraglossa.
 v) Hypopharynx: It is a short tongue-like structure located immediately in front of or
above the labium and between the maxillae.

(ii) Types (Modification) of mouthparts

Insect mouth parts are chiefly of two general types viz., (i) Mandibulate – chewing
type and (ii) Haustellate – sucking type

1. Mandibulate
In mandibulate type of insects, they are capable of biting and chewing foods which is
not the case in haustellate type. The mandibles cut off and grind the solid food and the
maxillae and labium push it into the oesophagus. Ex: found in grasshoppers, lepidopterous
larvae, cockroaches, thysanurans etc.

2. Haustellate: It has several types –

i) Cutting and sponging type
 Mandibles modified to sharp blades
 Maxillae modified to long probing styles
 Labium to spongelike structures
 Epipharynx and hypopharynx fit together to form sucking tube
 The former two cuts and tear the integument of mammals and blood is sucked by
labium. Ex: Horseflies (Tabanidae)

i) Sponging type
 Mandibles and maxilla are non-functional
 Other parts form a proboscis with sponge like apex or labella
 Liquid food or food readily soluble in saliva are taken. Ex: Horse flies and
non-biting flies.

ii) Chewing and lapping type:

 Mandibles and labrum are chewing type
 Maxillae and labrum are developed into a series of flattened elongate
structures of which the glossa forms the extensible channelled organ to
probe deep into nectaries of blossoms. Ex: Honeybee

iii) Piercing-sucking type

 Labrum, mandibles and maxillae, sometimes hypopharynx is slender, long,
fit together to form a delicate hollow needle.
 Labium forms a stout sheath to hold the rigid needle.
 Entire structure is called a beak. It is a needlelike structure which is
pierced into the host tissue to suck sap. Ex: Hemipteran and Homopteran
bugs, mosquitoes.

iv) Rasping and sucking type

  Components of mouthparts modified to stylet like but together form a
rasping cone rather than a beak.
 Feeding is accomplished through rasping and sucking. Ex: Thrips

v) Siphoning/Tube type
 United galea of each maxilla forms a long proboscis which open into the
oesophagus.
 Liquid food and nectar are sucked in by this type of mouth parts. Ex: Adult
Lepidopterous insects (moths and butterflies).