Who are nasopharyngeal gadfly and why are they dangerous?

Nasopharyngeal gadfly - a subfamily of insects (considered by some biologists as an independent family) Oestrinae. Sometimes they are called abdominal. These are synanthropic flies, that is, those who prefer to be near human settlements. They do great harm to livestock, because their larvae are parasites that live in the heads of livestock. The subfamily got its name due to the path of infection of the animal - through the respiratory system.

The most dangerous types of nasopharyngeal gadfly

All females of nasopharyngeal gadfly are viviparous. They squirrel with larvae in the nostrils (more rarely, the oral cavity) of animals. From there, parasites move into the sinuses, and then the frontal cavity in the heads of livestock, feeding on its living tissues. Often the larvae are localized on the mucous membrane of the eye, making their way into its inner chamber.

In total, there are 35 types of nasopharyngeal gadfly, divided into 9 genera. In the territory of the former Soviet Union, the greatest damage to livestock breeding is brought by:

1. Sheep gadfly (lat. Oestrus ovis) is the most famous and common representative of its subfamily. Its adult individual (imago) is a nondescript fly whose body reaches 1–1.2 cm. Coloring is variable: from brown to gray-yellow. Black spots can be seen on the back. The whole body is covered with short hairs. This type of gadfly has small transparent wings, separated by brown veins and slightly spaced apart. The head is large enough and looks like half a ball. The eyes are dark, with a pronounced greenish tint, gleam in the light. As the name suggests, sheep are preferred for breeding.
2. Russian gadfly (lat.Rhinoestrus purpureus), often affecting horses. Outwardly, the adult is very similar to the imago of a sheep gadfly, but the body has a brownish-purple color. The back is cast in a red tint, decorated with longitudinal stripes, a little shiny, and numerous dark dots. The body is egg-shaped, painted in purple-gray color with a silver tone with a checker pattern, does not have villi. Transparent wings adorn 3 black dots located almost at the very base. They are a distinctive feature of Rhinoestrus purpureus from other gadflies.
   
3. Cephenamyia trompe is a gadfly that affects reindeer. It is the causative agent of cefenomyosis, which is an inflammatory disease of the upper respiratory tract, often with purulent discharge.
4. Cephalopina titilator injects its larvae into the nostrils of the camels. It provokes the development of cephalopinosis.
5. Short-body gadfly (lat. Rhinoestrus latifrons) and small-thorn gadfly (lat. Rhinoestrus usbekistanicus), like the Russian gadfly, parasitize in the heads of horses, but are less common.

There are other types of nasopharyngeal gadflies, but the ones listed above are significant in agriculture. The parasites of this family that affect humans are found only in the tropics, although there are rare exceptions for the attack of a sheep gadfly on people.

Adult insects do not feed, their mouth organs are not developed.

Development cycle

Mating of females and males occurs in the warm season. After that, the female individual expects the development of larvae in her abdomen, with almost no movement.For this, the fly finds itself a reliable and warm shelter, for example, cracks in wooden buildings. This period lasts from 10 to 20 days.

When the nasopharyngeal gadfly feels that the time has come for the appearance of the offspring, an active search begins for the victim - the future carrier. If a suitable animal is found, then the female, flying close to the nostrils, introduces several larvae by spraying along with a special liquid, without which they will die. Some animals have developed a unique way of protection against parasites: for example, deer, having sensed something was wrong, begin to inhale dust or soil intensively, which helps partially dry the airways and kill some of the larvae. If this did not happen, then the parasites begin to intensively develop, feeding on the body fluids of the victim.

The female gadfly is able to inject larvae from a distance of 40 cm.

Moreover, the process of “resettlement” of offspring can take several days. The total number of larvae with which she manages to infect animals reaches 700. At a time, the fly introduces no more than 30 into the nostrils.

1st stage of larval development

The size of each larva at the first stage of development is from 1 mm to 12 mm. Her light body has a fusiform shape. On its entire surface there are many spikes, and the head is equipped with two large hooks covered with hard chitin. This allows a small larva to easily be held on the slippery mucous membrane of the animal's nasal cavity.

This stage ends with molting, after which a new stage in the development of larvae begins. It occurs in the nasal cavities, ethmoid bone. Particularly active specimens move into the frontal sinuses and occasionally the cavity of the horns.

2 stage

The larvae are still white, but are increasing in size. Their length is from 4 to 15 mm. On the back of the body with an increase, microscopic yellow spiracles are noticeable. Their diameter does not exceed an injection from a needle. The stage ends with molting. All larvae finally move to the forehead and horny processes to complete their transformation.

3 stage

At stage 3, the body length of the larvae is significantly longer - up to 2.5 cm. As it develops, the color changes. First, the body is white, then transverse dark stripes appear on the back. Only the lower part of the larva is covered with spikes. The diameter of the spiracle at this stage is about 1 mm. It can be indicated in black, brown or yellow.

After that, the larvae have to get out, for which they move into the nasal passages. When an animal sneezes with a stream of air, they find themselves on the ground and pupate. Finding a gadfly in the pupal stage takes 14–46 days.

The number of generations that appear within 1 year depends on the climate of the area. In the southern regions, the process is faster.

When are gadflies the most dangerous?

The time of increased activity of nasopharyngeal gadfly directly depends on the climate. The longer the warm days last, the longer the duration of such a period. In the midland, this usually occurs in the summer months. At the same time, an increase in activity occurs in hot weather, while on rainy days the gadfly seeks shelter from inclement weather.

Nasopharyngeal gadfly harm animals. Their larvae create tissue damage through which pathogenic microorganisms can enter the body. Animals become nervous, which negatively affects the amount of milk in dairy animals. The fight against nasopharyngeal gadfly includes preventive measures, regular inspection of the livestock and the use of special drugs.