Condition and fate of larvae from insecticide-treated female tsetse flies Glossina palpalis

Many larvae from wild-caught female Glossina palpalis palpalis R.-D. treated topically with dieldrin or sumicidin or sumithrin or permethrin failed to pupariate and many larvae from mothers treated with sumicidin or sumithrin or neopynamin formed small or malformed puparia which failed to eclode. Puparia produced soon after maternal handling often did not emerge and many produced by flies starved more than 3 days also did not emerge. Very many puparia from dieldrin-treated mothers failed to emerge and non-emergence was common for puparia from flies treated with endosulfan or sumithrin or deltamethrin. Non-emerging puparia were produced soon after pyrethroid-treatment, probably due to effects on larval integumentand muscles, but were produced later after organochlorine-treatment, due to ingestion of insecticide by larvae while in utero.

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Résumé Les expériences ont porté sur des femelles sauvages de Glossina palpalis palpalis R.D. capturées dans la nature. Les comparaisons ont porté sur l'état et les performances de lots de pupes provenant de mouches non-traitées et de larves mûres traitées localement avec de l'acétone (témoin) ou avec 14 insecticides différents.Toutes les larves témoin se sont nymphosées, mais le taux d'échec augmentait avec la diéldrine, la sumicidine, la sumithrine et la permethrine. Les pupes anormales (petites ou déformées) étaient plus nombreuses dans le lot témoin que dans le lot non-traité, et les fréquences étaient plus élevées que chez le témoin avec la sumidicine, la sumithrine et la néopynamine.Seulement 3 mouches sont issues de 107 pupes anormales; il n'y a eu aucune éclosion pour 28% des pupes du lot témoin contre 15% pour le lot non-traité. Pour le témoin le taux d'émergence était faible dans les pupes formées le premier jour (jour du traitement), par suite de la manipulation maternelle; il n'a pas augmenté jours 2 et 3, mais a diminué par la suite à cause du jeûne in utero. Les doses élevées de tous les insecticides réduisent plus les émergences que les doses faibles. Les organophosphates et le propoxur ne limitent pas les émergences, mais elles sont réduites par l'endosulfane, la sumithrine et la deltaméthrine, et très fortement par la diéldrine. Les pupes stériles ont été surtout formées dès le traitement aux pyréthroïdes (jour 1); et surtout plus tard (jours 2 et 3) lors des traitements aux organochlorés. L'ingestion par la larve in utero de grandes quantités d'insecticides pendant les 3 jours précédant la parturition était la principale cause de mortalité, et aussi de la forte tolérance aux organochlorés des femelles prégnantes. Les effets de pyréthroïdes sur l'activité musculaire réduisent aussi les émergences.Aucune mouche ne s'est alimentée après les traitements.

     

Rate of trypanosome killing by lectins in midguts of different species and strains of Glossina

The activity of lectins in different species of tsetse was compared in vivo by the time taken to remove all trypanosomes from the midgut following an infective feed and in vitro by agglutination tests. Teneral male Glossina pallidipes Austen, G. austeni Newstead and G. p. palpalis R-D. removed 50% of all Trypanosoma brucei rhodesiense Stephens & Fantham infections within 60 h. A 'refractory' line of G. m. morsitans Westwood took 170 h to kill 50% infections while a 'susceptible' line of the same species failed to kill 50%. Agglutination tests with midgut homogenates showed differences between fly stocks which accorded with differences in rate of trypanosome killing in vivo. Flies fed before an infective feed were able to remove trypanosomes from their midguts more quickly than flies infected as tenerals. Increasing the period of starvation before infection increased the susceptibility to trypanosome infection of non-teneral flies. Teneral flies showed little agglutinating activity in vitro, suggesting that lectin is produced in response to the bloodmeal. Feeding flies before infection also abolished the differences in rate of trypanosome killing found between teneral 'susceptible' and 'refractory' G. m. morsitans, suggesting that maternally inherited susceptibility to trypanosome infection is a phenomenon limited to teneral flies. Electron micrographs of midguts of G. m. morsitans suggest that procyclic trypanosomes are killed by cell lysis, presumably the result of membrane damage caused by lectin action.     

The flight and landing of tsetse (Glossina) in response to components of host odour in the field

ABSTRACT. Studies were conducted in Zimbabwe of the responses of Glossina morsitans morsitans Westwood and Glossina pallidipes Austen to various host odours using either arrangements of electrocuting nets or visual observations. Tsetse flying upwind in a plume of carbon dioxide, acetone and octenol turned downwind upon flying into a plume of acetone or octenol, but did not turn upon flying into a plume of carbon dioxide. They also turned in response to a transient decline in odour concentration. Tsetse landed on the ground in the vicinity of a source of natural odour or artificial odour containing carbon dioxide but not at sources of acetone or octenol only. The proportion of female G.pallidipes caught at a source of natural odour (37%) was significantly different from that caught at a source of synthetic odour (17%). Resting tsetse stimulated by natural odour took off sooner than non-stimulated flies and had a strong upwind bias in the direction of take off. Tsetse stimulated with artificial odour did not take off sooner than non-stimulated flies. It is suggested that there is an unidentified components) of ox odour that activates resting tsetse.     

'Anemotactic' flight paths of tsetse flies in relation to host odour: a preliminary video study in nature of the response to loss of odour

ABSTRACT. Free-flying, wild Glossina pallidipes Aust. and G. morsitans Westw. were video-recorded in the field in Zimbabwe as they flew out of air permeated with host odour (camera 2.5 m up, looking down at the ground). Analysis of the flight tracks supports the proposal of Bursell (1984) that tsetse flies attracted to an invisible source of host odour respond weakly if at all to wind direction while in flight: on losing contact with the odour the flies made a sharp turn that was uncorrelated with wind direction. The size of the turn varied considerably, with a marked discontinuity in the log-survivorship curve at 120° (a fly which had turned through at least 120° was 5 times as likely to stop the turn as a fly which had turned <120°). Over half the flies made turns of >90° (and <2 m diameter) within the 2×2.5 m field of view of the camera. It is suggested that these turns initially served to arrest the upwind progress of the fly, with the size of the turn determining the degree to which the fly backtracked towards where it last detected odour or continues cross-wind. Mean flight speed was c. 5 ms^-1 (min. 2.5, max. probably 7ms^-1).     

Trypanosoma theileri: In vitro cultivation in tsetse fly and vertebrate cell culture systems

Epimastigote forms of Trypanosoma theileri were grown at 25°C in insect cell culture media and in Glossina tissue cultures for more than 6 months. Doubling times of 10–14 h during exponential growth were observed. In cell cultures which had been derived from pupal tsetse flies growth rates were higher than in cell free media; in a larval cell line, however, growth of T. theileri was inhibited. Ecdysteroids and juvenile hormone I reduced multiplication of T. theileri in cell free media. When T. theileri was incubated in different sera only fetal calf serum (FCS) supported growth. Epimastigote forms transformed into trypomastigote bloodforms when cultured at 37°C in FCS, vertebrate cell cultures, and Eagle's medium, but not in insect media or Glossina cell cultures. Oxygen uptake of epimastigotes could be inhibited by rotenone antimycin A and cyanide; trypomastigotes were not affected by these inhibitors.     

Wandering behaviour and pupariation in tsetse larvae

Abstract .Following parturition, the third instar larva of Glossina morsitans morsitans West begins a wandering period in which it crawls to the site of pupariation. The duration of wandering can be drastically shortened by pinching or by denying the larva physical contact with the substrate. Contact with water increases the wandering period. Duration of subsequent activities appears to be rigidly fixed. At the end of the wandering period, the larva quickly progresses through a stereotypic sequence of behaviours that include immobilization and excretion of a liquid from the anus, retraction of the anterior segments, cuticular shrinkage, and tanning. Muscular activity and mechanical changes in the cuticle are reflected in changes of haemocoelic pressure. Muscular contractions produce pressure pulses that gradually increase in frequency and intensity, reaching a peak during retraction of the anterior segments. Changes in the mechanical properties of the cuticle cause a more gradual elevation of baseline pressure as the cuticle shrinks and loses its plasticity. As tanning begins, muscular activity ceases and haemocoelic pressure gradually decreases. In spite of its unusual early development within the confines of the female's uterus, the free-living larva shows the full behavioural repertoire observed in other cyclor-rhaphous Diptera at pupariation.     

Polytene chromosome maps in four species of tsetse flies Glossina austeni, G. pallidipes, G. morsitans morsitans and G. m. submorsitans (Diptera: Glossinidae): a comparative analysis

Photographic polytene chromosome maps from pupal trichogen cells of four tsetse species, Glossina austeni, G. pallidipes, G. morsitans morsitans and G. m. submorsitans were constructed and compared. The homology of chromosomal elements between the species was achieved by comparing banding patterns. The telomeric and subtelomeric chromosome regions were found to be identical in all species. The pericentromeric regions were found to be similar in the X chromosome and the left arm of L1 chromosome (L1L) but different in L2 chromosome and the right arm of L1 chromosome (L1R). The L2 chromosome differs by a pericentric inversion that is fixed in the three species, G. pallidipes, G. morsitans morsitans and G. m. submorsitans. Moreover, the two morsitans subspecies appeared to be homosequential and differ only by two paracentric inversions on XL and L2L arm. Although a degree of similarity was observed across the homologous chromosomes in the four species, the relative position of specific chromosome regions was different due to chromosome inversions established during their phylogeny. However, there are regions that show no apparent homology between the species, an observation that may be attributed to the considerable intra—chromosomal rearrangements that have occurred following the species divergence. The results of this comparative analysis support the current phylogenetic relationships of the genus Glossina.     

Olfactory responses to attractants and repellents in tsetse

The aims of this study were to investigate how antennal olfactory cells of tsetse (Diptera: Glossinidae) code odour quality and how they are able to discriminate between attractive and repellent odours. For Glossina pallidipes Austen, a survey is presented of the cells' responses to attractive (1-octen-3-ol, acetone, 3-methylphenol, carbon dioxide) and repellent stimuli (2-methoxyphenol, acetophenone, lactic acid, naphthalene). In addition, the responses of these cells to binary mixtures and the dose-response curves of 1-octen-3-ol, 3-methylphenol, 2-methoxyphenol and acetophenone are presented. A minority of the cells responded to one attractant or repellent only, whereas the vast majority were excited by more than one of the attractive and/or repellent stimuli. It is proposed that the peripheral olfactory cells of tsetse discriminate between different compounds via an across-fibre pattern coding, in which the cells that specifically code for attractants or repellents may play a substantial role in composing a unique excitation pattern that informs the central nervous system about the specificity of odours.     

Responses of Glossina austeni to sticky panels and odours

The responses of male tsetse Glossina austeni Newstead (Diptera: Glossinidae) towards blue and white sticky legged panels, baited with odour attractants, and towards modified panels were studied in the Jozani forest of Unguja Island, Zanzibar. Increasing the height of the body of a standard panel from 30 to 60 or 90 cm, increased the catch two-fold. Increasing the height of the legs (from 15 to 60 or 120 cm) or raising the device more than 5 cm above the ground reduced the catch significantly. The legs of the panels were the preferred landing sites of the flies, irrespective of the height of the body of the panel. Acetone (300 mg/h) combined with cow urine (60-130 mg/h) significantly increased the catches two- to threefold during the rainy season, but not during the dry season. Acetone had no effect during the dry season and its effect during the rainy season was less consistent. There was no effect of octenol (2.5-12.5 mg/h), used alone or in combination with acetone. Likewise, the catch did not increase through the addition of cow sebum, pig urine (60-860 mg/h), pig urine combined with acetone and octenol. The observed seasonal differences in the response of G. austeni towards odours are discussed in relation to host location strategies.