Field experiments on a new method for determining age in tsetse flies (Diptera: Glossinidae)

ABSTRACT.

• 1 Data are presented which suggests that the accurate determination of the age of tsetse flies (Glossina morsitans morsitans Westwood and G. pallidipes Austen) in the field can be achieved by measuring the fluorescence content of the head capsule.
• 2 The way in which this can be achieved and further work which would improve the accuracy of the technique are discussed.

     

Performance of the tsetse, Glossina morsitans morsitans reared under various feeding regimens in Zambia

Groups of Glossina morsitans morsitans Westwood fed at emergence and thereafter daily, every second or third day respectively, up to the end of their first pregnancy cycle, survived well (73–79%) and produced virtually the same number of puparia/ (0.83–0.85) in the same puparial weight class (23–24 mg). However, adult survival (29%), number of puparia/ (0.30) and puparial weight (19 mg) were much lower in the group consistently fed every 4th day after the initial meal at emergence. It is proposed that tsetse colonies could be fed on Mondays, Wednesdays and Fridays without jeopardising adult survival, puparial production/ and the size (weight) of puparia produced.

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Performances en Zambie de la mouche Tsé-Tsé (Glossina morsitans morsitans) élevée en utilisant différents régimes alimentaires

Résumé Afin d'estimer si une alimentation quotidienne de G. morsitans morsitans présente un avantage sur une alimentation moins fréquente, nous avons enrigestré la survie des adultes, la production et le poids des pupes chez des individus nourris à l'émergence et, ensuite, tous les jours ou tous les 2, 3 ou 4 jours. Les femelles alimentées quotidiennement, ou tous les 2 ou 3 jours, ont produit le même nombre de pupes (0,83–0,85), avec des poids de même ordre (23–24 mg), et avec une aussi bonne survie (73 à 79%). Alimentées tous les 4 jours, elles ont produit 0,30 pupe/femelle, pesant 19 mg/pupe et avec une plus faible survie (29%). Ces résultats montrent qu'il est inutile de nourrir les mouches chaque jour au lieu de tous les 2 ou 3 jours. Cependant une alimentation à des intervalles supérieurs à 3 jours, a eu des conséquences clairement défavorables. Ainsi, peuvent être considérablement réduits et le travail et le coût des élevages, sans porter préjudice à la production, en alimentant les mouches 3 fois par semaine, par ex. les lundis, mercredis et vendredis.

     

Effect of host packed cell volume on the bloodmeal size of male tsetse flies, Glossina pallidipes

aematin contents of engorged, male tsetse flies, Glossina pallidipes Austen, were compared with the packed cell volumes of oxen on which they had fed. Haematin contents icnreased with packed cell volume up to packed cell volumes of approximately 30%. Haematin contents appeared to level off or decline with further increase in packed cell volume. These results support a model of blood-feeding in tsetse flies in which the rate of blood consumption decreases as packed cell volume increases, because of increase in blood viscosity, and tsetse are unable to compensate for the decrease in consumption rate by feeding for a longer time. After allowing for the effects of packed cell volume, bloodmeal sizes of tsetse increased with ox body temperature.     

A comparison of susceptibility to stocks of Trypanosoma simiae of Glossina pallidipes originating from allopatric populations in Kenya

Abstract. A colony of Glossina pallidipes which originated from Nguruman, Rift Valley Province, Kenya, was significantly more susceptible than a colony of the same species which originated from Shimba Hills, Coast Province, Kenya, to infection with a stock of Trypanosoma simiae CP 11 isolated from wild G. austeni in Coast Province, Kenya, irrespective of whether pigs or goats were used as infecting hosts. Male G. pallidipes from both the colonies were more susceptible than females to this T. simiae stock. Similarly, a G. pallidipes colony of Nguruman origin was significantly more susceptible than the colony of Shimba Hills origin to infection with another stock of T. simiae CP 813 isolated from wild G. pallidipes in Coast Province, Kenya, again irrespective of whether pigs or goats were used as infecting hosts. The susceptibility of the sexes of G. pallidipes from both the colonies to T. simiae CP 813 did not differ significantly when pigs were used as infecting hosts, but male G. pallidipes from both the colonies were significantly more susceptible than female tsetse to this T. simiae stock when goats were used as infecting hosts. Nevertheless, if the observed differences in susceptibility of the two G. pallidipes colonies reflect transmission of trypanosomes by the two allopatric populations of tsetse in the field, then the epidemiology of simiae- trypanosomiasis probably differs between these two areas of Kenya.     

The optics of tsetse fly eyes in relation to their behaviour and ecology

Abstract The visual acuity of two species of tsetse flies, Glossina morsitans morsitans Westw. and Glossina pallidipes Aust., was investigated. Male G. morsitans eyes have an acute zone in the forward region, with large hexagonal lenses (mean minimum diameter, D=33, SE±0.7 μm), relatively small interommatidial angle (Δ(φ=1.08^o) and angular receptive field of individual ommatidia (Δp) of not less than 1.14^o. A narrow band of square lenses, with intermediate diameter and Δφ, merges with smaller hexagonal lenses in the periphery (24±0.7 μm), with relatively large interommatidial angle (Δφ=3.7^o) and small angular receptive field (Δp = c. 1.6^o). G.pallidipes eyes are similar, except that the lenses in the acute zone are larger than those of G.morsitans , in proportion to their larger body size. Female eyes are not significantly different from male eyes, except that they have a narrower region of binocular overlap (maximum for males = 24^o, for females = 18^o). The eye parameter (p=DΔφ) in the acute zone of male G.morsitans = 0.62, and in the peripheral zone = 1.56. These relatively high values are consistent with fast flight, visual detection of drift due to low wind speeds, mating chases and discrimination of cryptic host animals at high light intensities. The extended region of binocular overlap in males may serve as an early warning system of the approach of potential females. From our estimates, tsetse flies ought to be able to detect small objects against the sky c. 30 min before sunrise and after sunset, and to use their peripheral vision perhaps 15 min earlier and later than this.     

Population structuring of the tsetse Glossina tachinoides resulting from landscape fragmentation in the Mouhoun River basin,Burkina Faso

The impact of landscape fragmentation resulting from human‐ and climate‐mediated factors on the structure of a population of Glossina tachinoides Westwood (Diptera: Glossinidae) in the Mouhoun River basin, Burkina Faso, was investigated. Allele frequencies at five microsatellite loci were compared in four populations. The average distance between samples was 72 km. The sampling points traversed an ecological cline in terms of rainfall and riverine forest ecotype, along a river loop that enlarged from upstream to downstream. Microsatellite DNA demonstrated no structuring among the groups studied (F_ST = 0.015, P = 0.07), which is contrary to findings pertaining to Glossina palpalis gambiensis Vanderplank in the same geographical area. The populations of G. tachinoides showed complete panmixia (F_IS = 0, P = 0.5 for the whole sample) and no genetic differentiation among populations or global positioning system trap locations. This is in line with the results of dispersal studies which indicated higher diffusion coefficients for G. tachinoides than for G. p. gambiensis. The impact of these findings is discussed within the framework of control campaigns currently promoted by the Pan African Tsetse and Trypanosomosis Eradication Campaign.     

Microsatellite diversities and gene flow in the tsetse fly,Glossina morsitans s.l

Tsetse flies occupy discontinuous habitats and gene flow among them needs to be investigated in anticipation of area-wide control programs. Genetic diversities were estimated at six microsatellite loci in seven Glossina morsitans submorsitans Newstead (Diptera: Glossinidae) populations and five microsatellite loci in six G. m. morsitans Westwood populations. Nei's unbiased diversities were 0.808 and 76 alleles in G. m. submorsitans and 0.727 and 55 alleles in G. m. morsitans. Diversities were less in three laboratory cultures. Matings were random within populations. Populations were highly differentiated genetically. Populations were strongly subdivided, as indicated by fixation indices (F(ST)) of 0.18 in G. m. morsitans and 0.17 in G. m. submorsitans. 35% of the genetic variance in G. m. submorsitans was attributed to differences between populations from The Gambia and Ethiopia. All available genetic evidence suggests that genetic drift is much greater than gene flow among G. morsitans s.l. populations.     

Amino acids as taste stimuli for tsetse flies

Abstract.This paper reports the responses of taste cells on the legs of the blood-feeding tsetse fly Glossina fuscipes fuscipes Newstead 1910 (Diptera: Glossinidae) to twenty protein amino acids and to their mixture as it is present in human sweat. It is investigated whether the mixture is sensed differently than the amino acids singly. The taste cells are most sensitive to phenylalanine (K≈ 1 μm ) and tyrosine; and they respond in a lesser degree to methionine, valine, isoleucine, cysteine, tryptophan, histidine, alanine, and threonine. The amino acids serine, proline, asparagine, arginine, glutamine, lysine, aspartic acid, glutamic acid, and glycine give little or no response even at 10 mm . As the succession of effectiveness of the amino acids appears to be the same for all cells, it is deduced that the flies are unable to discriminate the amino acids by comparing responses across sensory cells. A temporal coding of quality does not seem feasible either. Thus, the properties of the taste cells limit the sense to assessing the intensity of an amino acid stimulus and not its identity. Although several parameters in the response adaptation curves are concentration-dependent, it is suggested that the flies judge intensity of a stimulus only from the first 50 or so milliseconds. Although other studies and these indicate that a multiplicity of binding sites may be responsible for the reception of amino acids, the response to the mixture can be predicted from a no-interaction model, whereby each ligand's access to the binding sites is proportional to its mole fraction. It is argued that this may be the case for more of the naturally occurring mixtures which comprise structurally similar ligands. The responses to the mixture and to phenylalanine alone are equally susceptible to inhibition by sodium chloride. It is suggested that, although discrimination of hosts probably requires another sense, the sense of taste is an excellent tool to detect a host underfoot during the local search for a feeding site.     

Effect of species, age, and sex of tsetse on response to infection by Metarhizium anisopliae

Laboratory studies were carried out to determine the effect of sex and age on the susceptibility of tsetse, Glossina morsitans morsitans and G. m. centralis, to the entomopathogenic fungus, Metarhizium anisopliae. Both species of host flies were susceptible to fungal infection. Female flies were generally more susceptible than male flies. Three host ages (40, 20, and <1 day-old) were used; the youngest group was most resistant to fungal infection. Interactions between species, sex and age were significant on many occasions. Age usually accounted for the largest variability in mortality, followed by sex. All flies of age 40 days died between 7 and 8 days after infection whereas some of the younger flies, especially age 0, lived longer than 10 days. Log10 day probit (LDP) mortality regressions fitted well to most of the data sets. LDP slopes were significant and high, ranging between 4.3 and 12.8, indicating a generally high mortality rate of increase over days. The slopes differed significantly between species, sexes, and ages, but grouping by age was more intra homogeneous than by species or sex. The 50% lethal time mortalities (LT50) ranged between 4 and 7 days for age 0, 3 and 6 days for age 20, and about 5 days for age 40. Corresponding ranges of the LT95 were 8 to 20, 5 to 10, and 6 to 7 days for ages 0, 20 and 40, respectively. The significance of these results in the fungal disease transmission by tsetse is discussed.