Pheromone perception in the tsetse fly Glossina morsitans morsitans

The perception of cuticular female sex pheromone (15, 19, 23-trimethylheptatriacontane=morsilure) in Glossina m. morsitans was studied electrophysiologically and behaviourally. Electrophysiological studies indicated no sensitivity of the tibial sensilla or the contact chemoreceptive hairs on the legs of males to the pheromone. However, electroantennograms were recorded during stimulation of antennae from male flies with the odour of morsilure, which indicated that the pheromone is detected by the insect via olfactory receptors on the antennae. This was further confirmed by behavioural experiments in which the antennal movements of intact males stimulated with the odour of both synthetic pheromone and female decoys were studied. Behavioural responsiveness to morsilure increased with increasing starvation and was not due to a general sensitivity to paraffins. These studies indicate that tsetse flies may be able to recognize conspecifics at close range using their sense of olfaction.

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Résumé La perception de la phéromone sexuelle des femelles de Glossina m.morsitans, la morsilure (15, 19, 23-triméthylheptatriacontane) a été examinée par électrophysiologie et par le comportement. L'électrophysiologie n'a pas révélé de sensibilité des sensilles tibiales, ni des poils chimioréceptives de contact sur les pattes des mâles à la phéromone. Cependant, les électroantennogrammes recueillis pendant la stimulation des antennes des mâles par l'odeur de morsilure, ont montré que la phéromone est décelée par l'insecte grâce aux récepteurs olfactifs des antennes. Ceci a été confirmé ultérieurement par des expériences de comportement au cours desquelles ont été examinés les mouvements antennaires de mâles intacts stimulés par l'odeur de phéromone synthétique et de femelles.La réponse comportementale à la morsilure a augmenté avec le jeûne, elle n'était pas due à une sensibilité générale aux paraffines.Ces études montrent que les mouches tsé-tsé peuvent être capables de reconnaître leurs congénères à faible distance grâce à l'olfaction.

     

A Low-cost Contamination Device for Infecting Adult Tsetse Flies, Glossina spp., with the Entomopathogenic Fungus Metarhizium anisopliae in the Field

A low-cost device for infecting adult tsetse fly, Glossina fuscipes fuscipes , with the entomopathogenic fungus Metarhizium anisopliae was designed and tested in the field. Tsetse flies that are attracted to the trap entered the contamination device and ultimately became infected with the fungus. Traps exposed to the sun attracted more flies than did the ones placed in the shade. The time spent by single flies in the contamination device varied between 5- 189 s, and the subsequent number of conidia collected varied between 1.6 ×10 5 conidia and 40.5 ×10 5 conidia per fly, and largely depended on the behavior of individual flies. Dry conidia of M. anisopliae in the device retained their viability for 31 days in the field, and efficacy against G. fuscipes was not affected.     

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.     

Estimating tsetse fertility: daily averaging versus periodic larviposition

When computing mean daily fertility in adult female tsetse, the common practice of taking the reciprocal of the interlarval period (called averaged fertility) was compared with the method of taking the sum of the products of daily fertility and adult survivorship divided by the sum of daily survivorships (called periodic fertility). The latter method yielded a consistently higher measure of fertility (approximately 10% for tsetse) than the former method. A conversion factor was calculated to convert averaged fertility to periodic fertility. A feasibility criterion was determined for the viability of a tsetse population. Fertility and survivorship data from tsetse populations on Antelope Is. and Redcliff Is., both in Zimbabwe, were used to illustrate the feasibility criterion, as well as the limitations imposed by survivorship and fertility on the viability of tsetse populations. The 10% difference in fertility between the two methods of calculation makes the computation of population feasibility with some parameter combinations sometimes result in a wrong answer. It also underestimates both sterile male release rates required to eradicate a pest population, as well as the speed of resurgence if an eradication attempt fails.     

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.     

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.     

Midgut lectin activity and sugar specificity in teneral and fed tsetse

Abstract. . Midgut infection rates of Trypanosoma congolense in Glossina palpalis palpalis and of Trypanosoma brucei rhodesiense in Glossina pallidipes are potentiated by the addition of D+ glucosamine to the infective feed, but not to the levels of super-infection reported for G. m. morsitans. G. p. palpalis and G.pallidipes are shown to possess two trypanocidal molecules: a glucosyl lectin which can be inhibited by D+ glucosamine and a galactosyl molecule inhibited by D+ galactose. Addition of both D+ glucosamine and D+ galactose to the teneral infective feed promotes super-infection of the midguts of G.p.palpalis. The glucosyl lectin is specific for rabbit erythrocytes and is present in guts of fed G.m.morsitans and G.p.palpalis , titres of lectin activity do not increase substantially after the second bloodmeal. The galactosyl specific molecule does not show any erythrocyte specificity, although haemolytic activity is observed only in G.p.palpalis and not in G.m.morsitans. The presence of two trypanocidal molecules in some species of tsetse may account for the innate refractoriness of these flies to trypanosome infection.
As D+ glucosamine also inhibits the killing of procyclic trypanosomes taken as an infective feed, it is suggested that the midgut lectin is normally responsible for the agglutination of trypanosomes in the fly midgut by binding to the pro-cyclic surface coat, prior to establishment in the ecto-peritrophic space.     

Single cell recordings from tsetse (Glossina m.morsitans) antennae reveal olfactory, mechano - and cold receptors

Abstract. Action potentials from individual cells and receptor potentials were recorded from antennae (funiculi) of living tsetse flies, Glossina m.morsitans Westwood, using a 'surface-contact' recording technique. Stimuli were pressure of the electrode, changes in temperature and the vapours of l-octen-3–ol, acetone, 3–methylphenol, dichloromethane and CO₂. Two types of mechano-receptive cells were found. One type only fired action potentials when pressure was increased, the other type continued firing when pressure was maintained. Of the 182 cells tested for their sensitivity to temperature change and the odour stimuli, 19% did not respond to any of the stimuli, suggesting that we are still unaware of cues which may be of import to the flies, and 4% responded to temperature only, increasing and decreasing their activity with a decrement and increment in temperature, respectively. Of the 141 cells which were olfactory receptors, 52% responded to 1-octen-3–ol and 40% were exclusively sensitive to this substance. For 3–methylphenol these percentages were 23 and 18, for acetone 13 and 11, for dichloromethane 12 and 7, for CO₂ 13 and 13. No clustering of cell types in certain areas of the funiculi was found, nor was a difference apparent between the sexes. The majority of the olfactory cells responded by increasing their activities on odour stimulation. Inhibition was found in three cells only, in which spontaneous activity was suppressed on stimulation with 3–methylphenol. Spike responses were phasic-tonic and varied between two extremes: Cells showing relatively rapid cessation of spike activity after the end of stimulation, and cells which continued firing for several seconds or minutes after stimulation. Possible behavioural effects of the activities of the various cell types are discussed.     

Effect of temperature on the reproduction of Glossina pallidipes, with reference to G. m. morsitans

The reproductive biology of G. pallidipes Austen was studied at 28°, 25° and 22° C. Experiments showed that incubation of puparia at 28° C resulted in sterility of both males and females. Incubation at 22° C resulted in a reduced fecundity of the females due to egg retention; the fertility of the males was not affected.Comparative studies with G. m. morsitans Westw. showed that G. m. morsitans puparia are less affected by a temperature of 28° C than are G. pallidipes puparia.

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Effet de la température sur la reproduction de Glossina pallidipes, avec référence à G. m. morsitans

Résumé Les productivités de G. pallidipes Austen élevés au laboratoire pendant tout leur cycle à 22, 25 et 28° C, ont été comparées.A 28° C, la vie intrapupale est réduite à environ 23 jours, contre 30 jours environ à 25° C; la survie des adultes est plus brève qu'à 25° C et les mouches ne s'accouplent pas. Les ovaires présentent une rétention d'oeufs et seulement 1/3 des mâles contient des spermatozoïdes mobiles. A 22° C, le cycle est considérablement prolongé, la vie intrapupale durant environ 40 jours. Les femelles s'accouplaient environ 14 jours après l'émergence. Les ovaires présentaient une rétention d'oeufs, bien que moins souvent qu'à 28° C. Les mâles contenaient des spermatozoïdes mobiles.Des expériences avec changements de température à différents moments du cycle ont montré que la stérilité des mâles et des femelles est provoquée par l'incubation de pupes de G. pallidipes à 28° C. La mensuration des ovocytes montre à 28° C un effet nocif sur leur maturation. Des observations sur les testicules dans les pupes révèlent, par comparaison avec 25° C, que l'enroulement des testicules et des spermatozoïdes est retardé à 28° C, tandis que la pigmentation des testicules est retardée à 22° C. Les pupes de G. m. morsitans sont moins affectées à 28° C que celles de G. pallidipes.