The Inadequate Environment

Dynamics of the pregnancy cycle in the tsetse Glossina morsitans.

A successful technique for feeding colonies of Glossina morsitans morsitans Westw. and G. austeni Newst. in the absence of living hosts is described. Insects are fed through membranes made of silicone rubber or of agar and Parafilm, overlying blood pools poured onto grooved glass plates. The diet employed is fresh pig blood, collected at slaughter, and aseptic procedures are adopted at every stage of diet preparation and presentation. The reproductive performance of these in vitro-fed colonies in terms of adult survival, fecundity, and offspring size, is the same as that of colonies fed on living hosts, when compared over a long period of time. The fact that the technique is successful when used with a diet of pig blood, but is not successful when used with cow blood prepared in the same way, suggests that the technique per se is adequate to elicit a normal feeding response from these tsetse species. The nature of the nutritional superiority of pig blood is not understood.

Large-scale rearing of tsetse flies (Glossina spp.) in the absence of a living host.

Tsetse flies, sole members of the genus Glossina, family Glossinidae (77, 79), are the well-known vectors of trypanosome diseases, including both human African sleep­ ing sickness and the cattle disease nagana (6). Tsetse flies are biological peculiarities; not only are they obligate blood feeders, but they reproduce by adenotrophic viviparity [giving birth to live offspring, nourished within the mother by secretion from highly modified accessory glands, and born at an advanced stage of develop­ ment (see 25, 36)]. The female produces a single offspring at regular intervals. It passes three larval instars within the mother and derives all its nourishment from her during this time. After parturition (larviposition) the larva does not feed and usually pupariates within 1-2 hr. Approximately 30 days later, the adult fly emerges. Thus all the nutrients required for developplent to the adult stage are maternally derived, and accordingly at parturition the larva usually weighs at least as much as the mother ( 103). In addition, at regular intervals the mother takes blood meals that weigh up to several times the weight of the unfed fly ( 103). Thus the female fly undergoes large changes in volume and weight during each pregnancy cycle; short­ term changes are associated with feeding and long-term changes are associated with the growth of the larva ( 103). However, these changes impose limitations in terms of feeding and flying, which become more severe as pregnancy progresses. The female fly leads a precarious existence and both nutrition and reproduction must be precisely regulated to ensure reproductive success. The interaction between repro­ ductive events and the transfer of nutrients from mother to larva are therefore of importance to our understanding of the physiology of Glossina, and these areas will be of particular concern in the present paper.

Reproductive Physiology of Glossina

Tropical Animal Health and Production

The large-scale rearing of Glossina austeni Newst. in the laboratory: IV.—The final technique

By manually applying cages to the ears of ordinary rabbits and coaxing the tsetse flies to feed, we have for the first time approached the full reproductive potential of G. austeni and reared an insect which does not seem to be physically inferior to that found in nature. The tedious coaxing process has been overcome by strapping cages to the ears of lop-eared rabbits, but at a small loss in pupal weight. Our preliminary findings suggest that a method has been found which should enable a research worker to keep his own small colony of tsetse and achieve an excellent survival rate for trypanosome transmission experiments.

A promising method for rearing Glossina austeni (newst.) on a small scale, based on the use of rabbits' ears for feeding

The rearing of Glossina austeni Newst. with lop-eared rabbits as hosts. I. Efficacy of the method.

The Large-Scale Rearing of Glossina austeni (Newst.) in the Laboratory. I. The Use of Pregnant and Non-Pregnant Goats as Hosts.

To permit detailed study of individual tsetse, either as insects or as the vectors of trypanosomiasis, a method has been devised which resulted in excellent survival and reproduction when tested on females or Glossina austeni Newst. Each mated female was maintained in asmall cage comprising a stainless steel frame covered with non-absorbent black Terylene netting through which the larvae and faeces fell into a tray. Each cage was applied daily to the ear of a rabbit, and records were kept of the number of feeds, time taken to feed, numbers of larvae produced, lengths of interlarvel periods and weights of pupae. The following conclusions are tentative as they are based on detailed studies of only eight females. Five of these produced larvae regularly at 8½- to 9-day intervals. Ninety-six interlarval periods were investigated. Although the mean interval between meals was two days, the flies tended to fast before larviposition and to engorge repeatedly afterwards. Among nearly regular breeders, failure to larviposit did not seem to interrupt the normal feeding rhythum: the reproductive rhythum later re-integrated with the feeding ehythum. A tendency to deviate from the normal feeding pattern either by too frequent feeding after larviposition or by prologation of the fasting period before larviposition, may possible be related to pemature death, but flies which tend to feed on the day before larviposition centainly risk death from pupation in utero —a condition found in 5 per cent. of dead rabbit-fed flies; the complex of pressures which lead to this condition is described. Limited data suggest that females which live to a great age enter a post-productive period when about 6½ month old; the feeding pattern breaks down completely, the fly fasting for periods of up to 11 days, or even longer in the immediate pre-death period. The maximum output of reasonably sized pupae is probably about 20 for G. austeni . Pupal weight increased until the parent flies were about 90 days old, but there was much individual variation; thereafter the weight remained high, but among very old dlies it fell towards the end of reproductive life. Certain individuals tended to produce heavy pupae, a characteristic probable associated with the size of the fly and the total weight of blood taken up in each interlarval period—not with the frequency of feeding; a very infrequent feeder may, however, produce underweight pupae at irregular intervals.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0007485300050057

A method of maintaining Glossina austeni newst. singly, and a study of the feeding habits of the female in relation to larviposition and pupal weight.

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