Order Diptera: Nematocera

• Phylum Arthropoda
• Class Insecta
• Order Diptera

Order Diptera Features

• One pair of wings, with the posterior pair modified into sensory structures called halteres
• Mouthparts are suctorial or adapted for biting and piercing
• Exhibits distinctive metamorphosis from egg to larva to pupa to adult
• Most species lay eggs, but some are viviparous, laying larvae

Division Nematocera Features

• Small insects
• Antennae longer than thorax, containing 8+ segments and no arista
• Seldom more than 2-3 mm long
• Slender bodies
• Larvae and/or pupae are aquatic within this division
• Females are obligate parasites, needing blood for reproduction
• Intermittent parasites, often not host-specific

Nematocera Classification

• Family Ceratopogonidae: includes biting midges, also called "sand-flies" in Australia
• Family Simuliidae: includes black flies
• Family Psychodidae: includes sandflies
• Family Culicidae: includes mosquitoes
• Family Chironomidae: includes non-biting midges

Effects on the Host

• Irritation from bites causes stamping, tail-switching, altered feeding behavior, and reduced milk production
• Blood loss occurs
• Acts as vectors for: viruses such as ephemeral fever, blue-tongue, and myxomatosis; bacteria (minor role); protozoa like Plasmodium, Leucocytozoan, and Leishmania; and nematodes like Dirofilaria and Onchocerca
• Poses significant economic problems for cattle in Northern Australia

Family Ceratopogonidae: Genus Culicoides

• Females have pilose antennae, while males have plumose antennae
• Spotted wings
• Larvae develop in aquatic environments like mud, decaying leaf mold, and sand
• Vectors of viral diseases like bluetongue, ephemeral fever, and African horse sickness
• Intermediate hosts to filarioid nematodes, such as Onchocerca gibsoni
• Biting can be a nuisance to animals and humans
• Several hundred Culicoides species reside in Australia

Major Species Groups in Australia

• "Maritime" species (C. immaculatus, C. marmoratus) breed in saline waters like mangrove swamps, feed on mammals or birds, and are a nuisance to humans
• "Native" species breed in fresh water, typically feed on marsupials but now also feed on livestock (e.g., C. marksi)
• Recent arrivals from Southeast Asia breed in cow dung, and feed primarily on livestock (e.g., C. brevitarsis, C. actoni, C. wadai)

Culicoides marksi

• Breeds in pools of water
• Most abundant during the wet season in northern Australia
• Most common midge to bite cattle in northern Australia
• Feeds on legs and along the ventral midline
• vector of Onchocerca gibsoni

Culicoides brevitarsis

• Hypersensitivity to bites of C. brevitarsis causes Queensland Itch in horses.
• Lesions appear mainly around the butt of the tail, over the rump, along the back line, poll, and ears
• Breeds exclusively in dung
• Crepuscular feeder; horses uneasy in late afternoon
• Must differentiate Queensland Itch from other allergic dermatitides, such as larval-tick hypersensitivity, trombiculid mites, aggregation of Onchocerca microfilariae, Oxyuris equi lesions, lice, and some mange mites
• Vectors viruses and transmits blue tongue

Culicoides wadai

• Part of same group as C. brevitarsis
• Limited to Northern Australia
• Very efficient vector of bluetongue
• Given two consecutive wet years, it is capable of spreading into major sheep-raising districts

Family Simuliidae: Genus Simulium

• Black flies

• Small, dark flies resembling Culicoides

• Antennae are plain

• Thorax is more humped

• Wings are not spotted or hairy

• Causes worse effects compared to Culicoides

• Austrosimulium pestilens and A. bancrofti are the most serious species in Australia

• The life cycle of A. pestilens is adapted to flood conditions; eggs survive in deep sand and hatch into larvae, then pupae, and develop into adults in approximately 10 days. These adults live in trees along waterways and emerge in dense swarms to take a blood meal before breeding

• Eggs may survive in damp sand for 2-1/2 years

• Overseas, simuliids act as intermediate hosts of the nematode Onchocerca gutturosa and the protozoan Leucocytozon anatis

Family Psychodidae

• True "sandflies"
• The principal genus in Australia is Phlebotomus (Sergentomyia)
• Confirmed vectors of Leishmania overseas, suspected of transmitting to kangaroos
• Australian species feed on reptiles

Family Culicidae

• Contains mosquitoes
• Important vectors of diseases like malaria, Murray Valley encephalitis, yellow fever, and equine encephalitis; seasonal conditions affect transmission dynamics
• Intermediate hosts of some filarial parasites of humans and Dirofilaria immitis of dogs
• The main vector in the transmission of myxomatosis
• Control of sandflies and mosquitoes is achieved with persistent insecticides and repellents

Division Brachycera: Family Tabanidae

• Antennae are variable, short, either with 8 short segments or with 2 short basal segments and a large, often ringed 3rd segment

• Large robust flies with powerful wings

• Called March flies or horse flies

• Biting mouthparts

• Females feed on blood; heavy infestations can lead to a loss of 100-300 ml daily

• Causes severe wheals on soft-skinned animals, resulting in painful, irritating bites

• Cattle and horses become restless, leading to a reduction in milk yield in cattle

• Mechanically transmits trypanosomes and anthrax

• Vectors of some filarioid nematodes

• More common in coastal country as well as timbered mountain areas

• Control is difficult

• Breeds in water; larval stages last several months

• Adults are active during summer months

Division Cyclorrapha Features

• Antennae are very short, comprised of 3 segments, with the apical segment being non-annulate
• Arista is present

Family Oestridae

• Commonly referred to as "bot flies" (origin: bot = sausage)
• Large flies with rudimentary mouthparts
• Don't feed, can't bite or sting
• Some lay eggs while others are viviparous
• Larvae are parasitic
• Oral hooks are present in larvae
• Larvae moult twice, then fully grown leave the host to pupate on the ground

Genus Gasterophilus

• Meaning "stomach loving"
• Large hairy flies, measuring 1-1.5 cm long
• Lay eggs on the hair of horses
• Larvae are parasitic in the horse stomach (bots)
• 5 species exist; 3 are present in Australia
• Called bot flies

Gasterophilus Species

• G. intestinalis: common bot fly
• G. nasalis: throat bot
• G. haemorrhoidalis: nose bot

Gasterophilus intestinalis

• Lays eggs mostly on the lower foreleg, mane, shoulder, and flanks, but can lay anywhere
• Eggs are bright yellow, 1-2 per hair
• These eggs are attached by 1/3 of their length

Gasterophilus nasalis

• Lays eggs between mandibles
• Eggs are small, pale, and attached along the whole length.

Gasterophilus haemorrhoidalis

• Eggs are inserted into the skin at the base of the hair at the lips
• Eggs are black and challenging to see

Life Cycle and Pathogenesis of Gasterophilus

• Adults exist only a few days in late summer and autumn
• They are prolific egg layers, averaging between 150-750 eggs per fly
• Eggs hatch spontaneously except for G. intestinalis eggs, which require friction and moisture provided by licking
• All larvae burrow into the tongue, cheeks, and gums, then move to the stomach
• Larvae of G. haemorrhoidalis appear reddish
• They may attach in the pharynx, or found in the pyloric end of the fundus, as well as the rectum on the way out
• Larvae anchor using mouth hooks and cause thickening on the tissues
• Abscessation may occur
• Perforation rarely occurs
• Larvae of G. intestinalis are red, may attach to the pharynx, and then attach on squamous mucosa in the cardiac area
• Larvae of G. nasalis are yellowish and predominantly located in the pylorus and duodenum
• Oedema of the pharynx can lead to respiratory problems.
• Larvae in the rectum may cause irritation
• Larvae remain in the horse for up to 12 months, then pass to the ground to pupate

Differentiation of Larvae

• G. nasalis: has one row of spines on each segment
• G. intestinalis: has mouth hooks with a saddle-like depression and 2 rows of spines

Treatment for Gasterophilus

• Ivermectin and Moxidectin (macrocyclic lactone)

Gasterophilus Control Methods

• Treat in late winter while all larvae are in the stomach and flies are not active.
• Eggs can be removed by grooming or washing, though this is of limited value

Genus Oestrus

• Oestrus is the Greek term for a gad-fly and alternatively means "frenzy"

Oestrus Features

• Viviparous; lays live larvae in nasal passages of sheep
• Occasionally lay larvae in the eye of humans.

Oestrus ovis Features

• Stout grey fly, 1 cm in length with black spots on abdomen
• Adults only live 1-4 weeks, can't bite, sting, or feed

Oestrus ovis Life Cycle and Pathogenesis

• The fly darts at sheep and, as the head is lifted, lays larvae in the nostril
• Makes sheep restless
• Lays approximately 500 larvae in its lifetime
• 1st instar is 1 mm long and attaches to nasal mucosa with its strong hooks
• Later moves to frontal sinuses to molt to the 2nd instar and then the mature 3rd instar (may take 1-10 months)
• Larvae don't appear to cause substantial harm, although sheep may have mucoid or purulent discharge
• Higher incidence of bacterial pneumonia in infected sheep
• Larvae crawl back into the nostril and are sneezed out
• Larvae are whitish, about 2 cm long,, with black bands on dorsal surface and rows of small spines on ventral surface
• Pupate on the ground in 3-8 weeks

Oestrus ovis Treatment

• MLs (ivermectin, abamectin, moxidectin), trematocide closantel

Genus Hypoderma

• (= beneath skin)

Hypoderma Features

• Warble flies or gad flies
• Large hairy flies, often mistaken for bees
• Not found in Australia
• Common in Europe, Asia, and North America (temperate regions)
• Two species: H. lineatum and H. bovis
• Larvae are mainly found in cattle, but can also be seen in horses, sheep, goats, and humans

Adult Hypodermis bovis

• H. lineatum*
• 1 cm long and black with bands of yellow or orange hair
• Thorax covered with yellowish hair except for four distinct longitudinal lines
• H. bovis*
• Approximately 1.5 cm long, black and yellow
• Tip of abdomen is lemon yellow

Hypoderma Life Cycle

• Flies are active in spring and early summer
• Flies don't feed and live for 5-6 days
• Eggs attach to hairs.
• H. bovis attaches 1 egg per hair; eggs laid further up the legs and on the rump.
• Eggs hatch in 3-6 days; larvae emerge and penetrate skin
• Migrate via epidural fat and then encyst in the back
• Larvae encyst for 5-8 weeks
• Eventually, larvae emerge, fall to the ground and pupate
• H. lineatum attaches eggs in rows, each hair having up to 20 eggs
• Eggs laid on short hairs at back of hoof
• Larvae migrate via subcutaneous tissues to the thorax and into the wall of the oesophagus, then to subcutaneous tissue over the loins. Small breathing holes cut in skin

Hypoderma Pathogenesis

• Loss of hide in the most valuable area
• Infected animals don't thrive as well
• Severe reaction within 72 hours if larvae are killed in oesophageal tissue or in the spinal canal
• In heavy infestations, up to 300 larvae in subcutaneous tissue on the back

Genus Dermatobia

• D. hominis
• Tropical warble fly
• Dark blue thorax and a short brilliant blue abdomen
• *Only found in tropical America
• Eggs are attached to the bodies of blood-sucking arthropods, which act as transport hosts, such as mosquitoes, biting flies, and ticks
• Eggs only hatch when on a suitable host
• Affects humans, cattle, dogs, cats, and sheep

Genus Tracheomyia

• Tracheomyia macropi
• Tracheal bot of kangaroo, only mildly pathogenic

Genus Cephalopina

• Cephalopina titillator
• Nasal bot of camels
• Common in camels in Australia
• Included because it has an amusing name