Physiological correlates of the availability of Glossina morsitans centralis Machado to different sampling methods

Abstract.

• 1 The feeding cycle for male tsetse flies and the pregnancy cycle for females are used as frameworks for investigating the field behaviour of Glossina morsitans centralis Machado in Zambia, and hence the sampling biases of different capture devices.
• 2 Flies were collected in the field using hand nets and an electric back pack on foot patrols, and hand nets, hand-catching and an electric screen on landrover patrols. They were analysed for wing-fray, vein-length, chloroform-extractable fat and haematin. In addition, samples of laboratory-bred females killed daily during their second pregnancy cycle were analysed for the last two parameters.
• 3 The daily flying time of males is estimated from the fat—haematin curve to be about 32 min/day, which is identical to previous estimates for G. morsitans from Tanzania.
• 4 From the varying numbers and fat content of male flies caught by the different sampling methods during the course of the feeding cycle it is concluded that both haematin levels and fat reserves influence fly behaviour.
• 5 Comparison of the frequency distribution of wild-caught and laboratory-bred females along the corrected residual dry weight axis of the pregnancy cycle suggests that the results of combined electric-trap and hand-net sampling reflect the actual frequency distribution in the wild population at least for the first 7 days of the pregnancy cycle; but females in the last 2 days of their pregnancy cycle are apparently unavailable to sampling devices, perhaps because of their reduced flight activity.
• 6 The very variable percentage female catch (10.9–43.4%) returned by the different sampling methods is discussed in the light of the detailed analysis of the differential availability of male and female flies to each capture device.

     

Glossina morsitans morsitansandGlossina palpalis palpalis:Dosage Compensation Raises Questions about the Milligan Model for Control of Trypanosome Development

Gooding, R. H., and McIntyre, G. S. 1998.Glossina morsitans morsitansandGlossina palpalis palpalis: Dosage compensation raises questions about the Milligan model for control of trypanosome development.Experimental Parasitology90, 244–249. Evidence that dosage compensation occurs in tsetse flies was obtained by comparing the activities of X chromosome-linked enzymes, arginine phosphokinase and glucose-6-phosphate dehydrogenase inGlossina m. morsitansand hexokinase and phosphoglucomutase inGlossina p. palpalis, with the activity of an autosome-linked enzyme, malate dehydrogenase, in each species. The shortcomings of the X chromosome model for the control ofTrypanozoonmaturation in tsetse are discussed in light of these findings and previously published reports on the lack of fitness effects of matureTrypanozooninfections in tsetse and on published results on antitrypanosomal factors in male and female tsetse flies.     

Prospects for the Development of Odour Baits to Control the Tsetse Flies Glossina tachinoides and G. palpalis s.l.

Field studies were done of the responses of Glossina palpalis palpalis in Côte d''Ivoire, and G. p. gambiensis and G. tachinoides in Burkina Faso, to odours from humans, cattle and pigs. Responses were measured either by baiting (1.) biconical traps or (2.) electrocuting black targets with natural host odours. The catch of G. tachinoides from traps was significantly enhanced (∼5×) by odour from cattle but not humans. In contrast, catches from electric targets showed inconsistent results. For G. p. gambiensis both human and cattle odour increased (>2×) the trap catch significantly but not the catch from electric targets. For G. p. palpalis, odours from pigs and humans increased (∼5×) the numbers of tsetse attracted to the vicinity of the odour source but had little effect on landing or trap-entry. For G. tachinoides a blend of POCA (P = 3-n-propylphenol; O = 1-octen-3-ol; C = 4-methylphenol; A = acetone) alone or synthetic cattle odour (acetone, 1-octen-3-ol, 4-methylphenol and 3-n-propylphenol with carbon dioxide) consistently caught more tsetse than natural cattle odour. For G. p. gambiensis, POCA consistently increased catches from both traps and targets. For G. p. palpalis, doses of carbon dioxide similar to those produced by a host resulted in similar increases in attraction. Baiting traps with super-normal (∼500 mg/h) doses of acetone also consistently produced significant but slight (∼1.6×) increases in catches of male flies. The results suggest that odour-baited traps and insecticide-treated targets could assist the AU-Pan African Tsetse and Trypanosomiasis Eradication Campaign (PATTEC) in its current efforts to monitor and control Palpalis group tsetse in West Africa. For all three species, only ∼50% of the flies attracted to the vicinity of the trap were actually caught by it, suggesting that better traps might be developed by an analysis of the visual responses and identification of any semiochemicals involved in short-range interaction.     

The response of tsetse flies to artificial baits in relation to age, nutritional and reproductive state

In various vegetation types in Zimbabwe, the catches of Glossina pallidipes Austen and G. morsitans morsitans Westw. (Diptera: Glossinidae) at a target baited with odour (acetone, 1-octen-3-ol and two phenols) were positively correlated with catches of the same species at an unbaited net. No correlation existed between target catches and hand net catches of tsetse flies sitting on the vegetation. G. pallidipes females caught at a target and at an unbaited net were older than those caught from vegetation. Of the female G. pallidipes caught at the target, 46% were in the first 3 days of pregnancy. Of those caught at the unbaited net, significantly fewer, 21%, were in this stage. G. pallidipes males caught from vegetation contained more fat (3.07±0.333 mg) than those caught at the unbaited net (2.06±0.339 mg) or at the target (2.19±0.218 mg). It is inferred that target catches consisted predominantly of tsetse which were already in flight when they sensed the stimuli from the target, and that target catches were biased towards female G. pallidipes in the first 3 days of pregnancy.     

The nutritional state of male tsetse flies,Glossina pallidipes,at the time of feeding

Abstract. The feeding intervals of tsetse flies have been estimated from the nutritional state of flies caught in traps. However, such estimates have been disputed on the grounds that traps catch a biased, hungry sample of the flies which are seeking hosts and will feed. In this paper we present data on the nutritional state of tsetse flies caught approaching and feeding on oxen. Individual oxen were surrounded with an incomplete ring of electric nets which caught Glossina pallidipes Austen that were approaching, departing unfed and departing fed from an ox. Non-teneral males caught in this way were analysed for their fat and haematin contents. The feeding interval was estimated from a comparison of the frequency distributions of the pre- and post-feed haematin contents of the flies which fed. The former was not measured directly, and was deduced from the frequency distributions of the haematin contents of the male flies caught approaching and departing unfed from the oxen, since it is assumed that the departing unfed and fed flies together form a sample of the approaching flies. There was no difference between the frequency distributions of haematin contents of flies caught approaching and departing unfed, and therefore the pre-feed haematin contents of the males which fed should have the same frequency distribution. Comparison of this distribution with that of the post-feed haematin contents of the males which fed indicated that the majority of male G.pallidipes were returning to feed after digesting on average 1.4 log haematin units of the previous bloodmeal. From data published elsewhere, this corresponds to a mean feeding interval of 42-60h. There was a strong, linear, negative relationship between the fat contents of males and their probability of taking a bloodmeal, suggesting that fat content is important in determining the feeding behaviour of tsetse flies.     

Detection of activity cycles of tsetse from capture–recapture data

ABSTRACT.

• 1 Activity cycles of female tsetse (Glossina palpalis palpalis Robineau-Desvoidy) in the field are contrasted with those of males, using mark-release-recapture data from continuous biconical trap samples over a period of 80 days in two villages in Ivory Coast.
• 2 Variability in recapture rates was examined using the techniques of autocorrelation and spectral analysis. In order to do this a two-dimensional diffusion model incorporating both mortality and emigration was first fitted to corrected recapture rate data to produce a trend line, deviations from which were subjected to the analysis.
• 3 The autocorrelations for the data for males suggest considerable variability in activity, presumably associated with feeding, around a mean period of about 4 days in one village and seven in the other.
• 4 Data for females show a strong regular periodicity of about 9–10 days, reflecting the pregnancy cycle, and shorter, more variable periodicities probably corresponding to feeding.

     

Effect of host odours on trap catch composition of Glossina pallidipes in Kenya

The effect of odour attractants on the composition of samples of Glossina pallidipes Austen was investigated by comparing the age and nutritional status of flies caught in unbaited biconical traps with those caught in traps baited with cow urine and acetone. For both male and female flies, baited traps caught more flies with significantly higher fat content than did unbaited traps. Thus the samples from baited traps were more representative of the population as a whole: males showed a fuller range of the fat/haematin conditions known to occur in the field and proportionately more females were in later stages of the pregnancy cycle, than from unbaited traps.     

Reproductive disorders in Glossina palpalis palpalis (Diptera: Glossinidae) in forested areas of Ivory Coast

Study of reproductive disorders were carried out through the dissection of 11,012 tsetse flies caught over a period of one year in forested different habitats of Glossina palpalis palpalis of Daloa in Ivory Coast. The proportion of females with reproductive disorders was very low and estimated at 0.79%. Out of 87 tsetse files with reproductive disorders, 93.10% were abortions, 5.77% were ovular blockage and 1.13% was uterine pupaison. Reproductive disorders were recorded from all age groups: 0.78% in young parous (out of 6,398 tsetse flies examined) and 0.80% in old parous (out of 4,614 tsetse flies dissequed). Our results show that reproductive disorders occur at any stage of the female pregnancy cycle. Amplifying these reproductive disorders using chemical compounds is proposed as a way of improving the efficacy of insecticide-impregnated targets (pour-on, traps and screens) of tsetse control in rain-forest areas.     

Bloodmeal evacuation from the midgut of Glossina pallidipes in relation to tsetse foraging activity and trappabiIity

Abstract.

• 1 Foraging for bloodmeals is the most frequently recurrent and probably the most targetable of all activities that render tsetse vulnerable to interception with static trapping devices.
• 2 Surgical monitoring of the rnidgut every 24 h during three successive days of food deprivation, showed that a full bloodmeal, irrespective of its size or source, vacated the rnidgut of both sexes of Glossina pallidipes Austen in eight progressive stages.
• 3 Probing responsiveness in both sexes increased exponentially during the first four stages of their midgut evacuation, reaching a peak between stages 3 and 5. Thereafter it decreased, also exponentially.
• 4 Most G.pallidipes caught by NG2G traps baited with cow urine and acetone had midguts in the last three stages (6–8) of bloodmeal evacuation. The same was true of the majority of those that failed to feed on a calf shortly after entrapment.
• 5 The implications of the foregoing for tsetse foraging activity and trappability as well as for the potency of cattle urine and acetone as odour-bait for tsetse are discussed.

     

The interaction of dispersal and control methods for the riverine tsetse fly Glossina palpalis gambiensis (Diptera: Glossinidae): a modelling study

We used a spatial model of a riverine tsetse fly species Glossina palpalis gambiensis life cycle to investigate the interaction between their dispersal and three control methods and to document these interactions using sensitivity analyses. The model is currently limited to gallery forest habitat inhabited by Glossina palpalis gambiensis in the dry season in the sub-humid zone of West Africa. The control methods modelled were traps and targets (TT), insecticide-treated livestock (ITL), and the sterile insect technique (SIT). Both distance dispersed (up to 800 m) and percent of flies dispersing each day (up to 60 %) increased the efficiency of control by TT. Most of this increase occurred for low values of both distance dispersed and percent dispersing, but the increase continued up to the limits tried. The daily movement of cattle assisted the control program and when movement was considerable (up to 600 m daily) the effects were greater than the effects of tsetse dispersal. Random dispersal decreased aggregation and equilibrium population size, and thus also increased the efficiency of SIT. Dispersal that was mostly oriented towards clumps was of much less value for SIT but acted on TT and ITL similarly to random dispersal.     

Age‐specific changes in sperm levels among female tsetse (Glossina spp.) with a model for the time course of insemination

The age, insemination and ovulation status of tsetse flies Glossina pallidipes Austen (n = 154369) and Glossina morsitans morsitans Westwood (n = 19659), captured over 11 years in Zimbabwe, are assessed by ovarian dissection. Instantaneous rates of insemination increase exponentially with age in both species; 90% insemination levels are reached after 5 days post‐emergence in G. m. morsitans and 7 days in G. pallidipes, varying little with season. More than 95% of both species have ovulated by the age of 8 days and 99% by 12 days. Older flies that have not ovulated are > 100‐fold more likely to be caught in October and November than in other months. A 500‐fold decrease in trap catches did not result in any detectible decrease in the probability of females being inseminated. The proportion of partially filled spermathecae rises for approximately 6 days then declines, consistent with some flies having mated more than once. For flies caught on electric nets, with wings undamaged during capture, wing‐fray data are used to extend ovarian age estimates up to 11 ovulations. Among these flies, the volume of sperm in the spermathecae declines little in flies that have ovulated up to seven times; thereafter, it declines by approximately 1% per ovulation. The time course of insemination and the mating frequency of females are important considerations in modelling tsetse fly populations, as well as for the dynamics of interventions involving the release of genetically‐modified insects, which should not be seriously compromised by the limited levels of polyandry currently observed.     

The development of a multipurpose trap (the Nzi) for tsetse and other biting flies

New trap designs for tsetse (Glossinidae), stable flies (Muscidae: Stomoxyinae), and horse flies (Tabanidae) were tested in Kenya to develop a multipurpose trap for biting flies. Many configurations and colour/fabric combinations were compared to a simplified, blue-black triangular trap to identify features of design and materials that result in equitable catches. New designs were tested against conventional traps, with a focus on Glossina pallidipes Austen and G. longipennis Corti, Stomoxys niger Macquart, and Atylotus agrestis (Wiedemann). A simple design based on minimal blue and black rectangular panels, for attraction and contrast, with a trap body consisting of an innovative configuration of netting, proved best. This 'Nzi' trap (Swahili for fly) caught as many or significantly more tsetse and biting flies than any conventional trap. The Nzi trap represents a major improvement for Stomoxyinae, including the cosmopolitan species S. calcitrans (Linnaeus), with up to eight times the catch for key African Stomoxys spp. relative to the best trap for this group (the Vavoua). Catches of many genera of Tabanidae, including species almost never caught in traps (Philoliche Wiedemann), are excellent, and are similar to those of larger traps designed for this purpose (the Canopy). Improvements in capturing biting flies were achieved without compromising efficiency for the savannah tsetse species G. pallidipes. Catches of fusca tsetse (G. longipennis and G. brevipalpis Newstead) were higher or were the same as catches in good traps for these species (NG2G, Siamese). Altogether, the objective of developing a simple, economical trap with harmonized efficiency was achieved.     

Nutritional levels of female tsetse Glossina pallidipes from artificial refuges

Female tsetse flies, Glossina pallidipes Austen, caught in artificial refuges were subjected to ovarian dissection and analysed for levels of fat, residual dry weight (RDW) and haematin. There were rather small proportions of flies in ovarian categories 0 and 1, in part due to large losses in the immature and teneral stages at the hottest time of year. The distribution of the female catch among pregnancy days was close to uniform. The wet and dry weights (WW and DW) and RDW of eggs, larvae and pupae increased by 0.821, 0.303 and 0.204 mg respectively, with each mm3 increase in volume. Water accounted for 71.7% of the fat-free WW, and fat for 32.7% of the DW. Between birth and ovulation, fat increased from 2 to 4 mg and RDW from 7 to 11 mg; thoracic RDW increased by 2.5mg and changed little thereafter. Fat levels increased 3.5mg by day 6 of pregnancy, but only 0.5 mg thereafter. Over the same periods RDW corrected to zero haematin (CRDW) increased by 1 and 8 mg respectively. Full-term fat and CRDW levels were 8.2 and 19.4 mg respectively. Cumulative haematin frequencies formed a smooth curve with a slope that increased continuously. The raw data were well fitted by a model where feeding rates increased exponentially and capture probability was independent of haematin content. The mean feeding interval was 60 h; feeding probabilities of >0.9/day were only found in flies that had failed to feed for>72 h. In early pregnancy, fat levels declined with haematin for flies that had fed>36 h previously; by days 5-7 fat levels were maintained at a constant high level for 60 h post-feeding. Fat-haematin graphs for female tsetse cannot be used to estimate rates of fat utilization. Traps sample tsetse with below-average fat and RDW in early and late pregnancy respectively. Refuge samples are less biased than those from traps; they give a better picture of the dynamics of pregnancy in normal flies and facilitate the explanation of existing anomalies.     

Seasonal distribution and abundance of tsetse flies (Glossina spp.) in the Faro and Deo Division of the Adamaoua Plateau in Cameroon

Ten years after the large-scale tsetse control campaigns in the important cattle rearing areas of the Faro and Deo Division of the Adamaoua Plateau in Cameroon, the seasonal distribution and abundance of tsetse flies (Glossina spp.) were determined. During a period of 12 consecutive months (January-December 2005), the tsetse population was monitored along four trap transects consisting of a total of 32 traps and two flyround transects traversing the study area, which comprised the tsetse-infested valley, a buffer zone and the supposedly tsetse-free plateau. Throughout the study period, a total of 2195 Glossina morsitans submorsitans and 23 Glossina tachinoides were captured in the traps and 1007 G. m. submorsitans (78.8% male flies) were captured along the flyround transects. All G. tachinoides and almost all G. m. submorsitans were captured in the valley. Five G. m. submorsitans were captured in traps located in the buffer zone, whereas no flies were captured in traps located on the plateau. The index of apparent abundance (IAA) of G. m. submorsitans was substantially higher in the areas close to game reserves. In the remaining part of the valley, where wildlife is scarce and cattle are present during transhumance (dry season), the IAA of tsetse was substantially lower. In this part of the valley, the abundance of tsetse seemed to be associated with the presence of cattle, with the highest IAA during transhumance when cattle are present and the lowest apparent abundance during the rainy season when cattle have moved to the plateau. It is concluded that the distribution of tsetse in a large part of the valley undergoes substantial seasonal changes depending on the presence or absence of cattle. The repercussions of those findings for the control of tsetse in the valley and the probability of reinvasion of the plateau are discussed.     

Use of vector control to protect people from sleeping sickness in the focus of Bonon (Côte d’Ivoire)

BackgroundGambian human African trypanosomiasis (gHAT) is a neglected tropical disease caused by Trypanosoma brucei gambiense transmitted by tsetse flies (Glossina). In Côte d’Ivoire, Bonon is the most important focus of gHAT, with 325 cases diagnosed from 2000 to 2015 and efforts against gHAT have relied largely on mass screening and treatment of human cases. We assessed whether the addition of tsetse control by deploying Tiny Targets offers benefit to sole reliance on the screen-and-treat strategy.Methodology and principal findingsIn 2015, we performed a census of the human population of the Bonon focus, followed by an exhaustive entomological survey at 278 sites. After a public sensitization campaign, ~2000 Tiny Targets were deployed across an area of 130 km² in February of 2016, deployment was repeated annually in the same month of 2017 and 2018. The intervention’s impact on tsetse was evaluated using a network of 30 traps which were operated for 48 hours at three-month intervals from March 2016 to December 2018. A second comprehensive entomological survey was performed in December 2018 with traps deployed at 274 of the sites used in 2015. Sub-samples of tsetse were dissected and examined microscopically for presence of trypanosomes. The census recorded 26,697 inhabitants residing in 331 settlements. Prior to the deployment of targets, the mean catch of tsetse from the 30 monitoring traps was 12.75 tsetse/trap (5.047–32.203, 95%CI), i.e. 6.4 tsetse/trap/day. Following the deployment of Tiny Targets, mean catches ranged between 0.06 (0.016–0.260, 95%CI) and 0.55 (0.166–1.794, 95%CI) tsetse/trap, i.e. 0.03–0.28 tsetse/trap/day. During the final extensive survey performed in December 2018, 52 tsetse were caught compared to 1,909 in 2015, with 11.6% (5/43) and 23.1% (101/437) infected with Trypanosoma respectively.ConclusionsThe annual deployment of Tiny Targets in the gHAT focus of Bonon reduced the density of Glossina palpalis palpalis by >95%. Tiny Targets offer a powerful addition to current strategies towards eliminating gHAT from Côte d’Ivoire.     

Standardising Visual Control Devices for Tsetse Flies: Central and West African Species Glossina palpalis palpalis

Background

Glossina palpalis palpalis (G. p. palpalis) is one of the principal vectors of sleeping sickness and nagana in Africa with a geographical range stretching from Liberia in West Africa to Angola in Central Africa. It inhabits tropical rain forest but has also adapted to urban settlements. We set out to standardize a long-lasting, practical and cost-effective visually attractive device that would induce the strongest landing response by G. p. palpalis for future use as an insecticide-impregnated tool in area-wide population suppression of this fly across its range.

Methodology/Principal Findings

Trials were conducted in wet and dry seasons in the Ivory Coast, Cameroon, the Democratic Republic of Congo and Angola to measure the performance of traps (biconical, monoconical and pyramidal) and targets of different sizes and colours, with and without chemical baits, at different population densities and under different environmental conditions. Adhesive film was used as a practical enumerator at these remote locations to compare landing efficiencies of devices. Independent of season and country, both phthalogen blue-black and blue-black-blue 1 m² targets covered with adhesive film proved to be as good as traps in phthalogen blue or turquoise blue for capturing G. p. palpalis. Trap efficiency varied (8–51%). There was no difference between the performance of blue-black and blue-black-blue 1 m² targets. Baiting with chemicals augmented the overall performance of targets relative to traps. Landings on smaller phthalogen blue-black 0.25 m² square targets were not significantly different from either 1 m² blue-black-blue or blue-black square targets. Three times more flies were captured per unit area on the smaller device.

Conclusions/Significance

Blue-black 0.25 m² cloth targets show promise as simple cost effective devices for management of G. p. palpalis as they can be used for both control when impregnated with insecticide and for population sampling when covered with adhesive film.     

A dynamic population model for tsetse (Diptera: Glossinidae) area-wide integrated pest management

A spatial model of tsetse (Glossina palpalis ssp. and G. pallidipes) life cycle was created in FORTRAN, and four control measures [aerial spraying of non-residual insecticides, traps and targets, insecticide-treated livestock (ITL) and the sterile insect technique] were programmed into the model to assess how much of each of various combinations of these control tactics would be necessary to eradicate the population. The model included density-independent and -dependent mortality rates, temperature-dependent mortality, an age-dependent mortality, two mechanisms of dispersal and a component of aggregation. Sensitivity analyses assessed the importance of various life history features and indicated that female fertility and factors affecting survivorship had the greatest impact on the equilibrium of the female population. The female equilibrium was likewise reduced when dispersal and aggregation were acting together. Sensitivity analyses showed that basic female survivorship, age-dependent and temperature-dependent survivorship of adults, teneral-specific survivorship, daily female fertility, and mean temperature had the greatest effect on the four applied control measures. Time to eradication was reduced by initial knockdown of the population and due to the synergism of certain combinations of methods [e.g., traps-targets and sterile insect technique (SIT); ITL and SIT]. Competitive ability of the sterile males was an important parameter when sterile to wild male overflooding ratios were small. An aggregated wild population reduced the efficiency of the SIT, but increased it with increased dispersal. The model can be used interactively to facilitate decision making during the planning and implementation of operational area-wide integrated pest management programs against tsetse.     

Comparative efficacy of three suction traps for collecting phlebotomine sand flies (Diptera: Psychodidae) in open habitats

The efficacy of three suction traps for trapping phlebotomine sand flies (Diptera: Psychodidae) was compared. Traps were baited with Co₂ and used without any light source. CO₂‐baited CDC traps were evaluated either in their standard downdraft orientation or inverted (iCDC traps). Mosquito Magnet‐X (MMX) counterflow geometry traps were tested in the updraft orientation only. Both updraft traps (iCDC and MMX) were deployed with their opening ～10 cm from the ground while the opening of the downdraft (CDC) trap was ～40 cm above ground. Comparisons were conducted in two arid locations where different sand fly species prevail. In the Jordan Valley, 3,367 sand flies were caught, 2,370 of which were females. The predominant species was Phlebotomus (Phlebotomus) papatasi, Scopoli 1786 (>99%). The updraft‐type traps iCDC and MMX caught an average of 118 and 67.1 sand flies per trap night, respectively. The CDC trap caught 32.9 sand flies on average per night, significantly less than the iCDC traps. In the Judean desert, traps were arranged in a 3×3 Latin square design. A total of 565 sand flies were caught, 345 of which were females. The predominant species was P. (Paraphlebotomus) sergenti Parrot 1917 (87%). The updraft traps iCDC and MMX caught an average of 25.6 and 17.9 sand flies per trap per night, respectively. The CDC trap caught 7.8 sand flies on average per night, significantly less than the iCDC traps. The female to male ratio was 1.7 on average for all trap types. In conclusion, updraft traps deployed with their opening close to the ground are clearly more effective for trapping sand flies than downdraft CDC traps in open habitats.     

Monitoring oak processionary moth Thaumetopoea processionea L. using pheromone traps: the influence of pheromone lure source,trap design and height above the ground on capture rates

相似文献