Arthropoda: Modification of mouth parts in insects | Zoology Optional Notes for UPSC PDF Download

Mouth Parts in Insects

• This type of mouthparts is considered the most primitive and serves as the basis for other mouthpart types.
• Components of this type include the labrum (upper lip), mandibles, first maxillae, second maxillae (forming the lower lip), hypopharynx, and epipharynx.
• The labrum is a rectangular flap-like structure situated in the median area.
• Mandibles are paired, equipped with toothed edges on their inner surfaces, and function to masticate food.
• The first maxillae are paired structures behind the mandibles, each with a five-jointed maxillary palp for tactile function.
• The second maxillae are fused to form the lower lip, aiding in pushing masticated food into the mouth.
• The hypopharynx is a single median tongue-like structure at its base, where the common salivary duct opens.
• The epipharynx is a small, membranous piece located beneath the labrum and contains taste buds.
• Insects with these mouthparts include cockroaches, grasshoppers, crickets, silverfish, termites, earwigs, beetles, some hymenopterans, and caterpillars of Lepidoptera.

• These mouthparts are adapted for collecting nectar, pollen, and wax molding, as found in honeybees, wasps, and other related insects.
• Components of these mouthparts include the labrum, epipharynx, mandibles, first pair of maxillae, and second pair of maxillae.
• Mandibles are short, smooth, and spatulated, primarily used for molding wax and constructing honeycombs.
• The labium (second pair of maxillae) has reduced paraglossae, and the glossae are elongated to form a retractile tongue at the tip, called a labellum or honey spoon.
• The labial palps are elongated.
• The glossa is used for gathering honey, and it also serves as an organ of touch and taste.
• The first pair of maxillae is situated at the sides of the labium and possesses small maxillary palps. They play a role in collecting nectar from flower nectaries.

• This type of mouthparts is adapted for piercing tissues to feed on blood and plant juices.
• Insects with these mouthparts include mosquitoes (Diptera) and bugs (Hemiptera).
• These mouthparts consist of components such as the labium, labrum, epipharynx, mandibles, maxillae (first pair), and hypopharynx.
• Mosquitoes have a long, straight, fleshy tube called a proboscis, formed from the modified labium, used for piercing and sucking. It features labella at the tip, formed from the labial palps.
• The labrum and epipharynx are fused and cover the dorsal side of the proboscis, forming a food channel.
• Stylets, needle-like structures, are created from the mandibles and maxillae, which are placed in the labial groove.
• In bugs, the labium is three-jointed and forms a proboscis.
• The mandibles and maxillae are modified to form stylets, with saw-like or blade-like tips.
• In bedbugs, the labrum is flap-like and covers the labial groove at the base.

These diverse mouthparts reflect the remarkable adaptability of insects to different feeding habits and ecological niches.

Head and Mouth Parts of Honey Bee

• The head of the honeybee features a pair of large compound eyes, which provide the bee with the ability to see and navigate its environment.
• It also possesses a pair of jointed antennae that serve as sensory organs, detecting environmental cues and helping the bee in various activities.
• Positioned in the center of the head is a median ocellus, which is a simple eye that can detect light intensity and aid in maintaining the bee's orientation.

• The mouthparts are adapted for a specific type of feeding known as chewing and lapping.
• The components of the mouthparts include:
  • A basal transverse plate-like structure known as the labrum-epipharynx.
  • A pair of short, clubbed, and spatulate mandibles situated on either side of the labrum-epipharynx. These mandibles are used for chewing.
  • A small triangular structure referred to as the mentum.
  • A large rectangular structure known as the prementum, located below the labrum-epipharynx.
  • A pair of short and rudimentary maxillary palps.
  • A pair of long galea, which are part of the maxillae. These structures are involved in lapping.
  • A pair of long and jointed labial palps.
  • A median tubular proboscis formed by the labium. The proboscis consists of the following parts:
    • A basal paraglossa.
    • A median glossa.
    • A lenticular-like terminal labellum or flabellum, often referred to as a "honey-spoon." The labellum is used for collecting nectar from flowers.

• The mouthparts of the honeybee are adapted for collecting nectar from flowers.
• The mandibles are used for chewing plant tissues when needed.
• The maxillae and labial palps form a tube that encloses the glossa, which can be extended to gather nectar. The labellum aids in this process.

These specialized mouthparts reflect the honeybee's feeding habits and its role in pollination as it collects nectar from flowers.