Amino acid metabolism during flight in tsetse flies.

Experiments carried out using teneral Glossina pallidipes indicate that flight can continue for at least 4 to 7 min after the thoracic proline reserves have fallen to low levels, suggesting that some other energy source is available. Earlier work suggests that alanine formed during flight is transported from the thorax to the abdomen where proline is resynthesized. Injection experiments using ¹⁴C alanine confirm that the transport mechanism does occur, that it is enhanced by flight, and that alanine is more rapidly incorporated into glutamate and proline in the abdomen than in the thorax. An analysis of published work shows that there is evidence for the involvement of residual blood meal amino acids even in the early stages of flight and supports the suggestion that they are of importance in prolonging flight. A decline in amino nitrogen during the early stages of flight is consistent with the action of glutamate dehydrogenase at this time. The poor flight durations in teneral flies may be due both to the low proline levels and to the absence of the residual blood meal. Very high energy consumptions are noted and appear to be related to the abnormally large musculature necessary for the fly's haematophagous and viviparous habits.     

The flight performance of tsetse flies.

The four species of tsetse used are shown to be aerodynamically rather similar. The wingbeat frequency, aerodynamic lift, flight duration, and number of wingbeats per flight are seen to undergo large increases during adult maturation. Tsetse can produce unusually large aerodynamic lifts, although the flight performance declines very quickly during individual flights. The large lifts appear to be associated with the high percentage of muscle in the fly, and the rapid decline with the inability of the fly to replenish rapidly its proline reserves. Wing mutilation has been shown to increase the wingbeat frequency. The potentiation of the flight performance during maturation appears to be causally linked to increases in the thoracic muscle, cuticle, and proline levels. The results presented here are at variance with those of an earlier study on the physics of flight in tsetse.     

Some changes in the flight apparatus of tsetse flies, Glossina morsitans and G. pallidipes, during maturation.

The residual dry weight of the thoracic cuticle of tsetse has been found to increase durint maturation and this finding affects the estimates of mitochondrial and contractile protein made by Bursell. The thoracic proline reserve was also found to increase during maturation, following much the same time course as that of the increases in contractile protein. The results are discussed with reference to the relevant published work on other insects.     

Reciprocal regulation of fat content and flight activity in male tsetse flies (Glossina palpalis)

Abstract. To disentangle cause and effect in previously observed relationships between fat content and flight activity in male tsetse ( Glossina spp.), three groups of flies were fed at different intervals to raise their fat content to different levels before their flight activity was recorded. The greater the mean daily blood intake, the higher the fat content and the greater the subsequent spontaneous flight activity, thereby using up almost all of the fat reserves before the next blood meal. It is proposed that although male flies would benefit from maximum food intake to permit maximum flight associated with mate-seeking, they do not in fact feed as often as possible either in the field or the laboratory. This is explicable if energy acquisition is constrained by an additional mortality risk associated with feeding.     

Development of mitochondrial and contractile components of the flight muscle in adult tsetse flies, Glossina morsitans

Estimates have been made of the phospholipid, the water, and the cytochrome-c content of the dorsal longitudinal flight muscles of the tsetse fly, and of the total non-fatty dry weight of the thorax, at different stages of adult development. The results have served as a basis for the partitioning of the dry weight of flight muscle into its three main components—contractile protein, mitochondrial protein, and phospholipid. Development is shown to involve a twofold increase in the amount of contractile protein, and a threefold increase in the amount of mitochondrial protein. These changes are discussed in relation to associated changes in wingbeat frequency.     

The effect of wind-borne odours on the direction of flight in tsetse flies, Glossina spp.

ABSTRACT. The direction of flight in tsetse flies ( Glossina pallidipes Aust. and G. m. morsitans Westw.) taking off in the presence of certain wind-borne odours showed a significant upwind shift both in the field and in the laboratory. The average angular deviation between the resting orientation and flight direction was not materially affected by odour, but turns were steered in relation to wind direction if odour was present. Upwind flight in an odour plume was regularly preceded by a standing turn, the fly turning partly or completely into the wind before taking off in upwind flight. This suggests that wind direction was assessed, and flight direction determined, before the fly took off.     

Reproductive abnormalities in tsetse flies in Zimbabwe

Between November 1988 and July 1995 five technicians carried out ovarian dissections on 16,013 Glossina morsitans morsitans Westwood and 123,848 G. pallidipes Austen captured at Rekomitjie Research Station, Zambezi Valley, Zimbabwe. The ovarian age and uterine content were recorded, as were the lengths (l₁, l₂ and l_u) of the largest and second largest oocyte, and of any uterine inclusion. Major abnormalities and abnormal spermathecal contents were found in <0.1% of all flies dissected. Apparent abortions rates varied significantly between dissectors and occurred at frequencies of 0.8–4.5% in G. m. morsitans and 0.3–2.8% in G. pallidipes. The lowest estimates give the best picture of the field situation. Abortion rates were higher in flies caught on electric nets than in trapped flies where the rate was only 0.15%, indicating that reproductive losses are negligible for most of the year at Rekomitjie. The rates did, however, increase to >2% when mean temperatures exceeded 27°C and flies were captured in artificial refuges. There was little effect of ovarian age on the abortion rate, but the frequency of empty uteri declined markedly with age – with a suggestion, however, that it might increase again in the oldest flies. A knowledge of the rates of reproductive loss is important for the construction of realistic models of the dynamics of tsetse populations.     

Substrate utilization and flight speed during tethered flight in the locust

Mature laboratory locusts normally exhibit a characteristic pattern of change in flight speed with time. They fly at high speed for the first few minutes, during which carbohydrate forms the major fuel, but then slow to a cruising speed when lipid is used almost exclusively. Locusts flown for 30 min, rested for 2hr, and then reflown, exhibit an identical pattern of flight, even though they oxidise only half the amount of carbohydrate used in the first flight. The injection of adipokinetic hormone before the first flight elicits a low initial flight speed for 10 to 15 min but then the locusts accelerate to a constant higher speed. The injection of hormone before the second flight, when blood lipid levels are already high, reduces the utilization of carbohydrate by the flight muscles dramatically but results in constant high-speed flight.     

Lipid utilization during sustained flight of moths

Tethered moths were flown to exhaustion. In Spodoptera frugiperda flown for at least 16 hr and in Heliothis zea flown for at least 24 hr, the lipid content was considerably reduced. Triglycerides accounted for almost all of this reduction. In general, exhaustion was reached before the depletion of triglycerides. Exhausted moths with a triglyceride content of less than 2 mg also showed a greatly reduced diglyceride level.     

Labellar microstructure in tsetse flies (Glossinidae)

Abstract. Stereo-electron micrographs of the labellar armature of eleven of the commoner species of Glossina indicate that the most generalized type of labellum occurs in G.palpalis , a species which feeds on a wide range of animals. The species of the fusca and morsitans groups show independently evolved adaptations to feeding on bovids and other mammals. G.brevipalpis has a generalized type of labellum with special adaptations to feeding on hippopotamus and suids and the labellum of G.longipennis is specialized for feeding on elephant and rhinoceros. The range of labellar structure within Glossina is not entirely consistent with the traditional classification of the genus into fusca, palpalis and morsitans species-groups.     

Importance of proline and other amino acids during honeybee flight

Summary. The levels of proline and other amino acids in the haemolymph and other body parts of honeybee foragers were investigated by HPLC analysis. The concentrations of proline in the blood of glucose-fed or -injected bees finishing their exhaustive tethered flights on a roundabout were significantly reduced compared to bees that were fed and rested for one hour. This indicates some utilization of proline during flight metabolism. The levels of essential amino acids and of the sum of all amino acids except proline remained roughly constant, indicating that the decrease of proline did not result from a changed haemolymph volume. ¹⁴C-labelled proline was injected into bees either shortly before starting their flight or before a resting period of equal duration in an incubator at the same temperature. Bees that rested had incorporated more proline into thorax body protein, and less of the labelled substance was unrecovered (missing) and considered to be respired or less probably defecated. If the entire amount of missing ¹⁴C-proline is regarded as exhaled, the oxidative breakdown of proline reached higher levels after flight than in rested bees. This is another hint that proline is utilized during flight. Usually the exhaled amount did not exceed 10 μg proline in half an hour of flight. Although our data indicate involvement of proline in flight metabolism, the amount metabolized is low compared to the utilization of carbohydrates. Received December 5, 1998, Accepted February 1, 1999     

Activity patterns in pregnant tsetse flies, Glossina morsitans

ABSTRACT. Actograph measurements of the spontaneous flight activity of isolated female Glossina morsitans morsitans Westw. were made through their first two pregnancy cycles in constant conditions under LD 12:12. Activity fell from a mean of c. 20 units/day to near zero during the 24 h preceding the day on which larvipositionoccurred. Activity on the day of larviposition rose significantly, to c. 35 units/day, then fell back to the baseline 20 units on subsequent days. The circadian pattern of activity was changed markedly by larviposition: 48 h before it, activity in the morning peak of the usual V-shaped diel pattern was twice normal; over 70% of the flies then fed, and the evening arm of their V disappeared; 24 h before larviposition, most flies were totally inactive, the few that did fly performing only 1 or 2 units/day, and only in the first and last hours of the photophase; on the day of larviposition, the morning peak of the V was reduced by c. 70%, and activity peaked instead during the post-noon 2–3 h, before and during the act of parturition. Almost all larvipositions occurred between noon and lights-out. It is suggested that the c. 48 h of pre-larviposition quiescence may play a role in the fact that pregnant G. morsitans females often survive non-residual aerosol insecticide campaigns.     

Reproductive rates of tsetse flies in the field in Zimbabwe

Abstract. Tsetse flies Glossina morsitans morsitans Westwood and G. pallidipes Austen were marked and released within 12 h of emergence at Rekomitjie Research Station, Zambezi Valley, Zimbabwe, and on Redcliff Island, Lake Kariba. Ovarian dissections were performed on recaptured flies and on wild collected samples. At Rekomitjie >90% of female G. m. morsitans were inseminated by age 4 days and G. pallidipes by 7 days. For both species at both sites the length of the largest oocyte, for flies in ovarian category zero, increased approximately linearly for about the first 6 days and was ovulated at c. 6–8 days. The largest oocyte grew significantly more slowly in later cycles. For G. m. morsitans , but not for G. pallidipes , the rate increased with temperature; the rates were always higher than observed in the laboratory. At Rekomitjie, for both species and at a mean screen temperature of 22C, the first larva was produced at c. 18 days and subsequent larvae at 11–day intervals; the intervals decreased with temperature by c. 0.5 days/C. On Redcliff Island the intervals for both species were 2 days shorter than at Rekomitjie at any given screen temperature and were sometimes as short as 7 days. The length of the larva in utero increased exponentially during pregnancy.     

Olfactory sensitivity in tsetse flies: a daily rhythm

The diurnal tsetse Glossina morsitans morsitans bites especially in early morning and late afternoon; around midday feeding is at a low. In laboratory apparatus that measures the amount of locomotion under constant conditions over the photophase, the flies display a similar patterning of activity levels. The profile of daily rhythms for G. morsitans reported in the literature includes a number of motor and sensory motor systems that fluctuate cophasically. Lacking is a study on the patterning of the senses' response levels. In this paper we present the first instance of a daily modulation in the sense of smell. We stimulated the antennae with concentration series of host-derived odours and measured the spiking rate of cells at different times during the photophase. The concentration-response curves suggest that the sensitivity of antennal olfactory cells flows in parallel with the other daily rhythms. This was also reflected in electroantennograms (EAGs). The electroantennography was extended to G. fuscipes fuscipes, whose level of spontaneous locomotor activity--instead of following a U- shaped pattern--rises gradually over the photophase. Again, the EAGs appeared to parallel the species' locomotor activity. What we believe happens is that the organism tones down the sensitivity of its odour receptors during periods of anticipated inactivity for reasons of economy.      

Starvation and desiccation in tsetse flies (Glossina)

Collections of tsetse flies were made from different regions and at different seasons, and their fat and water contents determined. The results showed that of the two potential causes of death, starvation is far more important than desiccation.

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Zusammenfassung In verschiedenen Gegenden und zu verschiedenen Jahreszeiten wurden Tsetsefliegen gesammelt und ihr Fett- und Wassergehalt bestimmt. Durch Extrapolation der Regressionen an Fett- und Wasserreserven konnten Schätzungen der nach Erschöpfung der Fettreserven übrigbleibenden Wasserreserven ermittelt werden, wie auch umgekehrt der übrigbleibenden Fettreserven nach Erschöpfung der Wasserreserven. Die Ergebnisse zeigten, dass von diesen zwei möglichen Todesursachen der Hunger viel wichtiger ist als das Vertrocknen. Dieses Ergebnis wurde durch eine Prüfung der Verteilung des Fett- und Wassergehalts bestätigt. Sie zeigte, dass sich eine beträchtliche Anzahl der Fliegen in der kritischen Zone des Fettgehalts oder sehr nahe daran befand, während nur ein geringer Bruchteil von ihnen einen Wassergehalt aufwies, der sich der kritischen Zone näherte.

     

Inhibition of the DNA amplification of trypanosomes present in tsetse flies midguts: implications for the identification of trypanosome species in wild tsetse flies

The present study was carried out in order to investigate if there was really a failure of PCR in identifying parasitologically positive tsetse flies in the field. Tsetse flies (Glossina palpalis gambiensis and Glossina morsitans morsitans) were therefore experimentally infected with two different species of Trypanosoma (Trypanosoma brucei gambiense or Trypanosoma congolense). A total of 152 tsetse flies were dissected, and organs of each fly (midgut, proboscis or salivary glands) were examined. The positive organs were then analysed using PCR. Results showed that, regardless of the trypanosome species, PCR failed to amplify 40% of the parasitologically positive midguts. This failure, which does not occur with diluted samples, is likely to be caused by an inhibition of the amplification reaction. This finding has important implications for the detection and the identification of trypanosome species in wild tsetse flies.