The degree of invasion and the number of horses infested with gastrophyllus larvae depends on the conditions in which the animals are kept. I.A. Porchensky noticed that during the war period the number of horses suffering from gastrophiles increased significantly due to the deterioration of zoohygienic conditions.
Morphology and biology of the pathogen. G. intestinalis is a large, yellowish-brown gadfly. The head is large and covered with hairs. On the sides of it are compound eyes, and on the crown of the head there are three more simple eyes. Mesoscutum dark, with light yellow or brownish hairs. The abdomen is covered with hairs, brownish-yellow above with dark spots. The egg is yellowish, transversely striated, up to 1.2 mm long.
The larva of the third stage is oval-cylindrical, up to 20 mm long. On the surface of the pseudocephalus, under the sensory organs, there are two groups of small pigmented spines. Mouth hooks with a notch in front of the knee-shaped bend. Body segments of the larva from 2-10 are covered with two rows of spines, larger in the first row. On the dorsal side, starting from the 7th abdominal segment, they are no longer there. Posterior spiracle in the form of rounded plates with three slits.
Among other types of gastric gadflies, it is the most numerous and harmful. The average lifespan of adults is 10-20 days, the fecundity of females is up to 1000 eggs. Immediately after hatching, she sits on elevated places, sunlit stones and plants, or flies without attacking horses. Her behavior changes after mating. The female starts looking for horses to lay her eggs. Summer was recorded in areas with a temperate climate in July - August, in the south for a longer time.
The larva of the first stage at hatching is 1.05-1.1 mm long, white, spindle-shaped. Head armament - two movable curved hooks and a median point. Between them is the mouth opening. Egg laying occurs in flight. The female attaches one egg each to the hairline of proscar pills in those places where he can get them with his teeth, in particular, on the front legs, shoulders and sides. The number of eggs laid per animal reaches 3-5 thousand.
The development of larvae in eggs lasts 7-16 days, but they do not hatch immediately. They can remain viable in the egg for 40 - 50 and even 90 days. In order for the larva to emerge from the egg, it is necessary to influence a number of factors: humidity, heat of 37-42 degrees C and the touch of a foreign object.
Such conditions are created when the teeth are combing the places where the eggs are attached. At the same time, the lid of the egg bounces off, and the larva crawls out. The reasons why a horse scratches the egg attachment sites have not been fully elucidated. The larvae of propecia pills stage that emerged from the eggs enter the horse's oral cavity, attach to the mucous membrane of the tongue and develop in it for 21–28 days, after which they molt and pass into the second stage.
The development of larvae of stages 2 and 3 occurs in the stomach. Only single instances of them are found in the duodenum and esophagus. They attach in the stomachwith its strong oral hooks to its left cardial part. In the spring of the next year, mature larvae of propecia leave the stomach and, together with excrement, come out. Pupation occurs in faeces or the surface layer of the earth. Depending on the temperature, the pupal phase lasts from 18 to 52 days, after which an adult gadfly hatches from it.
G. haemorrhoidalis - dark brown in color, medium size 9 - 11mm, wing length 7 - 9mm. The head is large, almost equal in width to the anterior part of the mesoscutum; the frons are the same width in males and females. Mesoscutum black or dark brown, covered with dense hairs. The wings are transparent, with pale brown veins, the legs are brown-yellow, covered with hairs. The abdomen is slender, elongated, dark brown or black with lighter stripes. The egg is 1.34 mm long, black, with an elongated oval lid and an attachment appendage set aside in the form of a handle, striated, like the egg itself, with transverse stripes.
Larva of the 1st stage consists of 13 segments, at hatching 0.58 mm long and 0.13 mm wide, white. The larva of the 2nd stage is 14 mm long, 3.25 mm wide, similar to the larva of the large gastric gadfly. Larva of the 3rd stage up to 18.5 mm long, oblong, small spines on the segments arranged in two rows. The last three segments are unarmed. Gadfly larvae parasitize in the digestive tract of a horse. The flight of gadflies in the temperate climate zone occurs in July - August, in more southern regions in May - October.