VPA 221: Veterinary Entomology and Acarology (1+1)

HEAD - INSECTA

Head

• Head is a rigid capsule formed by union of number of sclerites
• In some sutures between the sclerites are visible
• On the head is seen 
  • Eyes
  • Antennae
  • Mouth parts 

Eyes

Two types,

• Compound
• Simple 

Compound Eyes

• Are placed laterally on the head.
• They are seen above the cheek or the gena.
• They may be

  • HOLOPTIC - Compound eyes may meet at the mid line. e.g. Male mosquitoes, Male Tabanus
  • DICHOPTIC-  Compound eyes may be placed wide apart. e.g. Female mosquitoes, Female Tabanus

Dichoptic eye

• Each compound eye is made up of numerous facets or ommatidia
• Function
  • Perceives movement of objects
  • Also night/day vision

Simple Eyes or Ocelli

• Typically three in number forming an inverted triangle
• Placed dorsally on the vertex (area between compound eyes)
• Function
  • Perception of very near objects-coarse image light & dark

Antenna

• A pair of mobile jointed antenna are seen attached to head in front of and between the eyes
• Function
  • Olfactory sense
  • Tactile
  • Hearing (auditory)- Johnston’s organ-important for identification
  • The 1^st antennal segment is called the scape, the next is the  Pedicel while the remaining segments are called the Flagellum
• Based on the number of segments the Order Diptera is classified into three sub orders-
  • Nematocera
  • Brachycera 
  • Cyclorrhapha
    • Nematocera are dipterans  with 14-16 antennal segments
    • Brachycera have less than 6 segments usually 3 with annulations
    • Cyclorrhapha have three antennal segments (short/squat in house flies).
  • Antenna is also called Pilose or Plumose antenna based on the number of hairs on them
  • Pilose antenna has less hair on the segment, the hairs are short (eg. female mosquito), while plumose antenna is one which is very hairy. The hairs are long (eg. male mosquito)
  • Some antennae also bear a specialised bristle called Arista
  • Such antennae are called aristate antennae e.g. Musca domestica has a arista which is bilaterally plumed upto to the tip

Mouth parts

• Mouth parts are studied to know the host skin piercing and non-piercing nature of insects thereby how the pathogenic organisms are aquired and transmitted and what control measures may be best employed

Comprise of,

• Upper lip or Labrum which is the  upper boundary of mouth
• Lower lip or Labium which is the lower boundary of the mouth
• Between these are a pair of mandibles and maxillae
• On the underside of labrum is a small membraneous structure – Epipharynx which bears the organ of taste
• Usually epipharynx is attached to the  labrum to form Labrum epipharynx
• On the upper surface of labium is another membraneous structure - Hypopharynx which bears the opening of salivary duct
• Sensory structures include maxillary and labial palps
• Typical chewing mouth parts are not seen in all insects
• Modifications occur e.g. fine piercing stylets as in mosquitoes   expansion of labium into a greatly expanded structure for inbibing fluids e.g. Musca spp.
• Mouth parts are classified -
• lapping type (sieve mechanism) e.g. House fly
• Piercing and sucking type e.g. Bed bug, Tick, Mosquito
• Cutting and lapping type e.g.Tabanus