Nematocera and Brachycera: Mosquitoes and Horseflies

Posted on Mar 1, 2025 in Naval Architecture and Marine Engineering

Nematocera (Suborder) and Their Medical Importance

The Nematocera include four families of significant health importance. These families share the common characteristic of having a lower lip present in a trunk transformed into a proboscis.

  • Family 1: Culicidae
  • Family 2: Phlebotomidae
  • Family 3 & 4: Not specified, but implied to be of medical importance.

Culicidae Family (Mosquitoes)

True mosquitoes are subdivided into two subfamilies:

  • Culicinae: Genera include Aedes, Culex, Culiseta, and others.
  • Anophelinae: Genus Anopheles.

Morphology

Mosquitoes are small, slender-bodied insects with long legs. They perch using only two pairs of legs, keeping the third pair raised. The proboscis is long, as long as the head and thorax combined. Sexual dimorphism is evident in the antennae and palps.

Life Cycle

Pregnant females require a blood meal for egg maturation. They lay eggs on water, either singly or in masses. The eggs hatch into larvae, which are macrocephalic (large head) with a globose thorax and segmented abdomen. The last abdominal segment has a respiratory siphon used for breathing at the water’s surface. There are four aquatic larval stages. The fourth stage larva transforms into a pupa. The pupa has a cephalothorax and a free abdomen. Two respiratory turbinates are located in the cephalothorax region. The adult emerges through orthogenesis (a straight line).

Culicinae and Anophelinae: Key Differences

  • Antennae:
    • Males: Feathery appearance with long hairs from each segment.
    • Females: Short hairs, giving a hairy appearance.
  • Anopheles:
    • Males: Club-shaped palpi.
    • Females: Palpi longer than the proboscis.
    • Eggs: Deposited singly with lateral floats.
    • Larvae: Positioned parallel to the water surface; lack a respiratory siphon (apiracilous).
    • Adults: Positioned obliquely to the substrate.
  • Culex:
    • Males: Sharp-ended palpi.
    • Females: Palpi much shorter than the proboscis.
    • Eggs: Deposited singly or in masses; lack floats.
    • Larvae: Positioned obliquely to the water surface due to the presence of a respiratory siphon.
    • Adults: Positioned parallel to the substrate.

Public Health Significance

Mosquitoes have public health significance due to direct and indirect actions.

  • Direct Action: Caused by the bite. Only the female is hematophagous (blood-feeding). Some species are zoophilic (preferring animal blood), while others are anthropophilic (preferring human blood). Feeding habits can be nocturnal or diurnal.
  • Indirect Action: Vectorial transmission of diseases. Mosquitoes are vectors for viruses (causing encephalitis, for example), protozoa (causing malaria), and filarial larvae (causing heartworm).

Symptoms of Mosquito Bites

Symptoms include solitary or scattered papules, itching, swelling, and redness, persisting for several hours or days. Sensitive individuals may experience intense local reactions like vesicles, urticaria, and fever.

Species of Medical Interest

  • Culex pipiens: Nocturnal, common. Females are hematophagous.
  • Aedes aegypti: Hematophagous vector of yellow fever. Painful bite.
  • Aedes mariae: Diurnal feeding, painful bite.
  • Anopheles atroparvus: Larvae develop in marshes and rice fields; vector of malaria in the Iberian Peninsula.

Treatment and Prevention

  • Treatment: Wash the bite area. For sensitized individuals, use antihistamine or analgesic ointment.
  • Preventive Measures:
    • Install mosquito nets on doors and windows.
    • Remove overwintering female shelters (e.g., bathrooms and air conditioning vents).
    • Avoid areas with cracks.
    • Eliminate larval and pupal sources: small water containers, protective netting for wells and tanks.
  • Control: Electric traps, personal repellents, introduction of predatory fish in ponds and unused swimming pools.

Brachycera (Order Diptera): Horseflies (Tabanidae)

Horseflies and cattle flies.

Morphology

They are large (up to 3 cm) with prominent, iridescent green compound eyes. They resemble flies, with stout bodies, broad wings, and short legs. The mouthparts have mandibles and maxillae.

  • Mandibles: Act like scissors, but the inner edges are serrated.
  • Maxillae: Lateral movement.

Antennae have three segments, with the last segment ringed. The distinct morphology of the third segment allows for differentiation of three genera (not specified).