Order Siphonaptera: Fleas

Life cycle

Eggs

• Laid on host but unattached; fall into nest. 
• Eggs smooth, but with aeropyles – tiny holes in eggshell to allow gas exchange. 
• Ovately rounded.

Larvae

• Feed on host-related debris on ground, usually in nest or lair.
• Primarily scavengers; blood excreted by adult fleas an essential part of larval diet in many species

Pupae

• Pupate in silken cocoon on ground; under high humidity may not spin cocoon
• Sometimes incorporate sand or other material into cocoon.

Adults

Ectoparasitic blood feeders: mostly on mammals, some on birds.

Detection of host differs in different species:

• • visual (detect shadows)
  • warmth
  • carbon dioxide and odours
  • vibrations

Transmission of Disease

Plague

Latin, plaga = a wound. Pl. plagues

Plague is a rodent-flea-rodent disease caused by the bacterium Yersinia pestis (formerly Pasturella pestis) – five forms 

• bubonic plague
• pneumonic plague
• pestis minor
• septicemic plague
• andean plague

Plague is endemic to southern Asia but spread elsewhere in 165 AD, 542 AD, 14th century and 17th Century. It is primarily a disease of rodents and exists as sylvatic zoonosis in colonial burrowing rodents; bacteriaemia of rodents varies in degree and duration.

Plague killed 25% of human population in Europe during Middle Ages due to over-crowded and unsanitary urban conditions which led to an increased black rat (Rattus rattus) population. Plague is transmitted by the rat flea (and probably other fleas). The bacteria reproduce in the gut of the rat flea and cause a plug in the alimentary canal.  The flea can’t successfully feed so regurgitates back into its host, spreading the pathogen to other hosts. Because the flea cannot feed, it grows hungrier and initiates more feeding attempts and movements between hosts, thus spreads plague very quickly.

Note:

Compared to their small size, fleas are capable of prodigious jumps. Not surprisingly scientists have been curious about how they manage to do this. Fleas have no wings and the metathorax is highly modified as it is associated with the large jumping legs. The energy for the jump is stored in the cuticle. Inside the thorax there is a system of cuticular ridges called the pleural arch. This structure has a pad of resilin that stores energy for the jump. The resilin pad is compressed by slow muscle action and a series of cuticular pegs and notches engage storing energy with the flea in a crouched position. A releaser muscle is activated and the stored energy is released, catapulting the insect into the air.