LIFE CYCLE 3.1 MATINS. 3.3.5 Breathing by the larva For its air supply the larva depends on air entering the vulva of the female and then passing into its posterior spiracles or polypneustic lobes. Medical and Veterinary Entomology (Third Edition), https://doi.org/10.1016/B978-0-12-814043-7.00018-2. Copyright © 2020 Elsevier B.V. or its licensors or contributors. The unusual feature of the Glossina life history is that the larva spends practically all its time, and does all its feeding, within the body of the female fly (Figure 3.1 A). 3.1 Side view of larva of Glossina, A, in the uterus; B, mature larva after being dropped by the female. There is no feeding by the larva after it is dropped by the female. The larva sucks up this secretion and passes it straight to the midgut. The first instar grows to 1.8 mm (G.morsitans)before changing to the next stage by getting rid of its old skin. At the end of this period, the adult fly is ready to emerge. 3.3.2 Second instar larva This is a stage of rapid growth and development. After 7 - 9 days she produces a single egg which develops into a larva within her uterus. Copyright © 2019 Elsevier Inc. All rights reserved. At this stage the body is very soft and the wings are small and crumpled. This position may be held for an hour or two, before the male and female flies part company. Tsetse flies are larviparous—the larva hatches from an egg within the female—and the young develop singly within the female’s uterus, feeding on a nutrient fluid secreted by paired milk glands on her uterine wall. Inside the pupa two main processes take place: the food still remaining in the midgut is digested and assimilated. This maternal care and the deposition of individual puparia by different species in particular microhabitats present unique challenges to controlling the adults and offspring. The third instar lasts just over two days and the larva grows to a length of 6–7 mm (G. morsitans). The female tsetse settles down either on the ground or on the overhanging object. The larva burrows into the ground and out of sight. When the larva in the uterus is fully grown, the female Glossina flies around looking for a suitable area in which to drop it. Tsetse flies, with one exception, are all found in Africa. The body works its way out of the hole so made, and also gets through the surrounding soil by using the ptilinum. About nine days later, the mother produces a larva which burrows into the ground where it pupates. Older males are better able to mate successfully than very young ones. 3.6.2 Teneral fly (see 7.5) From the time the fly emerges to the taking of its first meal, the young fly is called a teneral fly. The egg is about 1.6 mm long (Glossina morsitans). Rarely, T. b. gambiense may be acquired congenitally if the mother is infected during pregnancy. Lower temperatures give a lower rate of breeding; higher temperatures increase the rate of breeding. 3.3.3 Third instar larva (Figure 3.1 B) This is also a stage of rapid growth and development. This is called an abortion. During mating, the male penis is inserted into the vulva, reaching into the uterus as far as the exit of the spermathecal ducts. They have been extensively studied because of their medical, veterinary, and economic importances, because the flies can be raised in a laboratory, and because they are relatively large, facilitating their analysis. The pupa is slightly shorter than the larva that produces it. Female tsetse mate just once. Most of the weight and volume of the third instar larva is due to the gut which contains large amounts of unassimilated food. Usually 12 to 15 days elapse before flies that have picked up the parasites become infective toward humans. The mating of tsetse flies probably takes place near to or on host animals. For centuries, tsetse have been one of the greatest factors affecting the course of economic and social development in Africa. Higher temperatures shorten the pupal period; lower temperatures lengthen the pupal period (to more than 50 days in some climates). To either side of the posterior spiracles are swellings, and between the spiracles is an area of small spines. The rest of the larva is white in colour. Here it is slowly digested and assimilated. The mother continues to produce a single … Male flies settle on the back of the female, and the claspers at the posterior end of the male abdomen grip the end of the female abdomen. There are three larval instars in Glossina up to the time when the fully grown larva is dropped by the female fly: the first, second and third instars. The female flies away. The aborted larva dies. The biology of tsetse is relatively well understood by entomologists. Once mated, a female can produce larvae for the rest of her life. The polypneustic lobes are at first white, becoming black later. The cycle in the fly takes approximately 3 weeks. Within an hour or two the larva becomes barrel-shaped, darkens and may then be called a pupa. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. After a few urinates the wings begin to expand to reach their proper size. 3.2 Pupal stage and emergence; A, pupa; B, young fly emerging from the pupa, with ptilinum inflated in front of head. The fly is then termed a non-teneral fly. We use cookies to help provide and enhance our service and tailor content and ads. The underside of the abdomen appears whitish and semi-transparent, the ptilinum can sometimes be everted when the sides of the head are squeezed between the fingers, and the body has a soft feel to it. It breaks out of the chorion (see 2.5.2.2) using a sharp egg tooth. Fig. The pupal stage usually lasts about four to five weeks, according to temperature. The second instar lasts two days, and the larva grows to a length of 4.5 mm (G. morsitans). The ptilinum cannot easily be everted. Male tsetse fly adults may live two to three weeks, while females can live for one to four months. As with other flies, the larva in Glossinapasses through several stages or instars, as it grows. At a temperature of about 25°C a female fly will produce a mature larva every 9–10 days, except for the first one which may take 18–20 days from the time of emergence of the fly from the puparium (see 8.5.2 and Figure 8.6). Tsetse flies are obligately hematophagous and are in a group of flies with the unusual characteristic of having the female retain the larval offspring until it is fully grown and just about ready to pupate. 3.6.3 Non-teneral fly (see 7.5) After the first blood meal has been taken, the underside of the abdomen appears more creamy yellow, and when held up to the light the dark shape of the last meal can be seen. 3.3.1 First instar larva This is the stage that emerges from the egg. Tsetse females generally live for about 20–40 days but may have a maximum life span of 3–4 months. Sleeping sickness is not found wherever tsetse are known to occur because several species do not readily feed on humans, but nagana is found everywhere that tsetse are distributed. Abortions can be caused by the mother fly not obtaining sufficient food, and may also occur when the fly is carelessly handled, or when it comes into contact with insecticide. At the end of mating, the male releases his grip on the female and flies away. The egg may also be aborted for the same reasons. The hard case on the outside of the pupa is called the puparium. This position may be held for an hour or two, before the male and female flies part company. 2 of 2 - YouTube Females usually mate only once in their lives but some may mate more than once; males can mate several times. The flies become infected while feeding on the blood of infected people or other infected mammals. four days, while development of the first instar larva takes place inside. By continuing you agree to the use of cookies. In the next few hours sperm make their way up from the spermatophore into the spermathecal ducts and the spermathecae. The fully grown larva has a pair of large black swellings at the posterior end. 3.3.4 Feeding by the larva (Figure 3.1 A) Apart from the food already in the egg, all the food of the three larval instars comes from the milk gland of the mother fly. Life cycle image and information courtesy of DPDx. Sleeping sickness has hampered human productivity, and nagana has prevented the widespread use of domestic animals as sources of food, transport, labor, or fertilizer. This will usually be a place where there is a patch of loose sandy soil, sheltered by an overhanging rock, branch or twig. Tsetse are found over an estimated area of at least 10 million square kilometers on land governed by 36 different countries, which makes coordination and the institution of public health initiatives difficult. The thorax feels firmer and harder, because of the greater development of muscles in it. The pupa is a dark brown rounded object; at the posterior end are the polypneustic lobes the shape of which helps to distinguish the tsetse pupa from the pupae of other flies. These are the polypneustic lobes, which carry many small holes through which the larva breathes. The first instar lasts for about 1 day. The life cycle of the tsetse fly (1987) Pt. Females are mated young, before or at about the time of taking the first blood meal. The milky secretion of this gland is poured out of the duct of the gland, at the head end of the larva. the organs of the adult fly begin to form. The egg is fertilized immediately it enters the uterus by sperm from the spermathecae coming into contact with and penetrating the anterior part of the egg. Sperm remain active in the spermathecae for the rest of the female's life. 3.6.1 Emergence of the adult fly (Figure 3.2 B) When ready to emerge the young adult fly expands its ptilinum (see 1.3.4) to burst open the end of the puparium. Too high or too low a temperature will cause the death of the pupa. Fig. The mating of tsetse flies probably takes place near to or on host animals. Male flies settle on the back of the female, and the claspers at the posterior end of the male abdomen grip the end of the female abdomen. The fertilized egg remains lying in the uterus for about The males typically mate only once or twice during their lives and apparently survive in the wild for 2–3 weeks (Glasgow, 1963; Potts, 1973). The larva has a mouth at the anterior end, and two posterior spiracles. The larva then works itself backward cut of the vulva of the female, helped by pushing movements of the female's legs, and drops to the ground. In this way the young fly struggles to the top of the soil and out into the open air. The vast majority of human cases result from the transfer of T. brucei trypanosomes by tsetse flies as they suck human blood. 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