Flies

Question 1

How do parasitic arthropods of the genus Demodex demonstrate extreme deviation in body form, and where do they typically reside?

Answer 1

Demodex mites have evolved into tiny, cigar-shaped organisms. This extreme deviation allows them to comfortably fit and reside within the hair follicles and sebaceous glands of the skin of their hosts, optimizing their parasitic lifestyle.

Question 2

What is the primary reason the provided text devotes more attention to lice, fleas, ticks, and mites than to mosquitoes, despite mosquitoes’ significant role as disease vectors?

Answer 2

The text prioritizes lice, fleas, ticks, and mites because their control and management are more directly within the daily responsibilities and interests of most veterinarians. Mosquito control, while important for disease transmission, is typically the domain of medical entomologists.

Question 3

Distinguish between simple metamorphosis and complex metamorphosis in insects, providing an example of an insect group for each type.

Answer 3

In simple metamorphosis (hemimetabolous), juvenile instars (nymphs) resemble smaller versions of the adult, growing through successive molts (e.g., cockroaches, bugs, lice). In complex metamorphosis (holometabolous), juvenile stages (larvae) are worm-like and undergo a complete restructuring during a pupal stage before emerging as an adult (eclosion) (e.g., flies, beetles, fleas).

Question 4

Explain the veterinary significance of caddisflies.

Answer 4

Caddisflies are veterinary significant because they serve as biological vectors of Neorickettsia risticii, the causative agent of Potomac horse fever. Horses contract the disease by ingesting caddisflies that contain trematode metacercariae infected with N. risticii.

Question 5

What are halteres, and what is their function in Diptera?

Answer 5

Halteres are small, club-shaped balancing organs found in Diptera (true flies). They are evolutionarily modified metathoracic wings and are crucial for the fly’s stability and maneuverability during flight.

Question 6

Describe the unique feeding mechanism of female blackflies and contrast it with that of mosquitoes.

Answer 6

Female blackflies are “pool feeders”; they lacerate host tissues with blade-like stylets until a pool of blood forms, from which they then imbibe. In contrast, mosquitoes are “vessel feeders”; they pierce directly into a blood vessel and feed from its lumen.

Question 7

How do the life histories and typical feeding behaviors of Musca domestica (common housefly) and Musca autumnalis (face fly) differ?

Answer 7

Musca domestica (housefly) lays eggs on a wide variety of decaying organic materials and filth, often found indoors, and transmits pathogens mechanically via vomit and feces. Musca autumnalis (face fly) prefers to lay eggs in fresh cattle dung and remains outdoors, primarily feeding on ocular and nasal discharges of livestock.

Question 8

Why is the sterile insect technique (SIT) considered a major ethical dilemma in the context of tsetse fly eradication in Africa?

Answer 8

Tsetse fly eradication using SIT raises an ethical dilemma because the removal of these vectors and the trypanosomes they carry could lead to negative long-term environmental impacts. This is due to the potential for increased colonization by non-indigenous species competing with long-protected indigenous African wildlife.

Question 9

Explain the host-parasite reaction that can occur when cattle are treated for Hypoderma (cattle grub) infection, and what causes it.

Answer 9

The host-parasite reaction during Hypoderma treatment is caused by a toxin liberated from the dead Hypoderma larvae when killed by systemic insecticides during their migration phase. This can lead to clinical signs like bloat, salivation, ataxia, or posterior paralysis, particularly if larvae are in the esophagus or spinal canal.

Question 10

Describe the unique way Dermatobia hominis (human botfly) ensures its eggs reach a warm-blooded host.

Answer 10

Dermatobia hominis females employ a unique strategy called phoresy; they capture another blood-feeding fly (e.g., mosquito or stable fly) and glue their eggs to its abdomen. When the “slave fly” lands on a warm-blooded animal to feed, the Dermatobia larvae hatch instantly and penetrate the host’s skin.

Question 11

Arthropods: Definition and key characteristics.

Answer 11

A diverse phylum including insects, spiders, and crustaceans, typically exhibiting body segmentation and jointed legs, though variations exist (e.g., mites lack obvious segmentation, many insect larvae lack legs).

Question 12

What is a common diagnostic pitfall in veterinary practice regarding arthropods?

Answer 12

The mere presence of arthropods in a sample does not always indicate parasitism; for instance, fly maggots in fecal specimens are often post-defecation invaders, never parasitic in the host.

Question 13

What is the composition and function of the insect exoskeleton?

Answer 13

The insect exoskeleton is a chitinous cuticle secreted by the hypodermis. It serves as a body covering, a place for muscle attachment, and allows for movement and expansion. It is shed during molting (ecdysis) to permit growth.

Question 14

What is the function of the epicuticle in insects?

Answer 14

The epicuticle is the outermost, thin, lipoidal layer of the insect cuticle that functions as a vital water barrier, being impermeable to water but freely permeable to lipids and lipid-soluble substances.

Question 15

Define instar.

Answer 15

An instar is any of the life stages of an insect or other arthropod between molts.

Question 16

What is Myiasis?

Answer 16

Myiasis is a pathologic condition caused by the invasion of living tissues by fly larvae (fly maggots or bots).

Question 17

Distinguish between oviparous and ovoviviparous flies.

Answer 17

Most flies are oviparous, meaning they lay eggs that hatch outside the mother’s body. Some, like Hippoboscids and tsetse flies, are ovoviviparous, meaning they deposit larvae that have already hatched, with larval development occurring inside the mother’s abdomen.

Question 18

What are the three main groups of flies (Order Diptera)?

Answer 18

The three main groups are Nematocera (gnats and mosquitoes), Brachycera (horseflies and deerflies), and Cyclorrhapha (houseflies, flesh flies, blowflies, botflies, tsetse flies, and keds).

Question 19

What is the primary characteristic that distinguishes Cyclorrhapha antennae?

Answer 19

Cyclorrhaphan antennae consist of three dissimilar segments, the third and largest of which bears a frond-like or bristle-like appendage called an arista near its proximal end.

Question 20

What is ‘Queensland itch’ and which flies cause it?

Answer 20

Queensland itch is an allergic dermatitis in horses caused by hypersensitivity to the bites of biting midges (Culicoides spp.), specifically Culicoides robertsi.

Question 21

How do Tabanidae (horseflies and deerflies) affect livestock, beyond disease transmission?

Answer 21

They cause annoyance and severe pain from bites due to their lacerating mouthparts, leading to blood pooling. This can result in host exhaustion, secondary bacterial infections, and attracts other flies to the wound.

Question 22

What is the significance of zebra stripes in relation to fly control?

Answer 22

Work suggests that zebra stripes prevent tabanid attacks, possibly because their use of polarized light for visual signals makes them significantly less attractive to these flies compared to uniformly colored horses.

Question 23

What are eyeworms (Thelazia spp.) and how are they transmitted?

Answer 23

Eyeworms (Thelazia spp.) are nematode worms that infect the conjunctival sacs of animals and humans. They are transmitted by non-bloodfeeding Drosophilidae (fruit flies) like Amiota variegata or Phortica variegata (Europe/Asia), and muscoid flies like Fannia or Musca autumnalis (US).

Question 24

What is a puparium?

Answer 24

A puparium is the hardened, barrel-shaped outer casing formed from the last larval cuticle, within which the pupa develops in Cyclorrhaphan flies.

Question 25

What is a ptilinum?

Answer 25

A **ptilinum** is a **bladder-like structure inflated with hemolymph**, used by adult Cyclorrhaphan flies to **force open the puparium** when emerging, then retracts into the head.

Question 26

How do *Musca domestica* (common housefly) and *Musca autumnalis* (face fly) mechanically transmit pathogens?

Answer 26

***Musca domestica*** transmits pathogens via **feces, vomit spots, sticky feet, and body hairs**. ***Musca autumnalis*** can mechanically transmit **infectious bovine keratoconjunctivitis (*Moraxella bovis*)**.

Question 27

How does a **Bruce walk-through horn fly trap** work?

Answer 27

It is a mechanical trap where **cattle walking through contact strips of canvas or carpeting, which dislodge horn flies** from their backs and sides, leading to a significant reduction in the fly population.

Question 28

Describe the appearance and habitat of Hippoboscidae (Keds).

Answer 28

They are **dorsoventrally flattened flies with piercing mouthparts** and antennae embedded in pits. Some are wingless (*Melophagus ovinus*), some retain wings (*Hippobosca*), and some shed wings after finding a host (*Lipoptena*). They are **obligate parasites, often spending their entire life cycle on the host**.

Question 29

Distinguish between primary and secondary myiasis.

Answer 29

**Primary myiasis** is when the insect **requires a living host for larval development** (e.g., *Cochliomyia hominivorax*). **Secondary myiasis** is caused by flies that usually feed on dead flesh but can develop in **debilitated, wounded, or soiled animals**.

Question 30

What is 'wool strike' in sheep, and what causes it?

Answer 30

**Wool strike** is a common and serious form of myiasis where **adult blowflies (*Calliphoridae*, e.g., *Lucilia cuprina*) are attracted to soiled or damp fleece** and lay eggs. The maggots feed on scales and exudate, and can invade living tissue, leading to weight loss, wool loss, and death. Predisposing factors include **fleece rot and dermatophilosis**.

Question 31

How was the American screwworm (*Cochliomyia hominivorax*) eradicated from the United States?

Answer 31

It was eradicated using the **Sterile Insect Technique (SIT)**, where **hordes of sexually competent but sterile males** (sterilized by gamma radiation) were released to mate with wild females, reducing the probability of successful fertilization to nil.

Question 32

What are the general characteristics of adult botflies (Oestridae)?

Answer 32

They are highly **host-specific and site-specific larval parasites**. The **adults have vestigial, non-functional mouthparts** and rely on energy stored during their larval stage for reproduction.

Question 33

What is 'gadding about' in cattle?

Answer 33

"**Gadding about**" is the **apprehensive and excited behavior of cattle** (galloping aimlessly with tails held high) in response to the approach of **heel flies (*Hypoderma*)**, even though these flies have no functional mouthparts for biting.

Question 34

What are 'warbles' in cattle?

Answer 34

**Warbles** are walnut-sized **lumps or swellings on the backs of cattle** in spring, caused by the larval stage (**cattle grub**) of *Hypoderma* botflies. Each warble has a small hole for the larva to breathe.

Question 35

What is the 'Mules' operation' and what is

Question 36

Do flies have functional mouthparts for biting?

Answer 36

No, flies have no functional mouthparts for biting.