Some advances in the trapping of tsetse (Glossina spp.) and other flies

Abstract. 1. Shortcomings in the methodology of testing mechanical traps for tsetse and other flies have been partically overcome by relating all trap efficiencies to that of electric trapping devices which have been shown, independently, to capture over 95% of tsetse colliding with them.
2. In Rhodesia the classical 'animal' type traps only caught a small percentage of tsetse which approached them. The addition of ox odour increased the number of tsetse visiting the trap but did not affect trap efficiency.
3. Changes in trap design have resulted in increases in trapping efficiency of up to 4–5-fold over classical designs.
4. The addition of large quantities of ox odour increased the efficiency of the most successful trap described here, as well as the absolute number of flies taken. When the odour of livestock of total mass 11.5 tonnes was used, over 2000 tsetse could be trapped in a 3 h period.
5. None of the traps described here was particularly suitable for tabanids but some were used to trap large numbers of biting muscids.
6. The implications for new methods of tsetse control are discussed.     

Relative efficiency of pitfall trapping and hand-collecting from plots for sampling of millipedes

Millipedes were sampled by hand-collecting from plots and by pitfall trapping at three forest sites in central Tasmania. Seven days of pitfall trapping each month over one year was less efficient than four weeks of hand-collecting in autumn, yielding fewer species and fewer specimens per working day in the field. Hand-collecting is likely to provide more accurate data on species diversity and relative abundance for a range of litter invertebrates.     

Spatio-temporal distribution of tsetse and other biting flies in the Mouhoun River basin, Burkina Faso

In the Mouhoun River basin, Burkina Faso, the main vectors of African animal trypanosomoses are Glossina palpalis gambiensis Vanderplank and Glossina tachinoides Westwood (Diptera: Glossinidae), both of which are riverine tsetse species. The aim of our study was to understand the impact of landscape anthropogenic changes on the seasonal dynamics of vectors and associated trypanosomosis risk. Three sites were selected on the basis of the level of disturbance of tsetse habitats and predominant tsetse species: disturbed (Boromo, for G. tachinoides) and half-disturbed (Douroula for G. tachinoides and Kadomba for G. p. gambiensis). At each of these sites, seasonal variations in the apparent densities of tsetse and mechanical vectors and tsetse infection rates were monitored over 17 months. Tsetse densities differed significantly between sites and seasons. Of 5613 captured tsetse, 1897 were dissected; 34 of these were found to be infected with trypanosomes. The most frequent infection was Trypanosoma vivax (1.4%), followed by Trypanosoma congolense (0.3%) and Trypanosoma brucei (0.05%). The mean physiological age of 703 tsetse females was investigated to better characterize the transmission risk. Despite the environmental changes, it appeared that tsetse lived long enough to transmit trypanosomes, especially in half-disturbed landscapes. A total of 3021 other biting flies from 15 species (mainly Tabanidae and Stomoxyinae) were also caught: their densities also differed significantly among sites and seasons. Their relative importance regarding trypanosome transmission is discussed; the trypanosomosis risk in cattle was similar at all sites despite very low tsetse densities (but high mechanical vector densities) in one of them.     

Extending the loop design for two-channel microarray experiments

The loop design of Kerr and Churchill is a clever application of incomplete blocks of size 2 to two-channel microarray experiments. In this paper, we extend the loop design to include more replicates, biological and technical replication, multi-factor experiments, and blocking. Loop and extended loop designs are shown to be more efficient than the reference design for any given number of arrays. We also show that adding new treatments to a loop design requires the same number of additional arrays as adding treatments to a reference design, with a greater gain in power. Given the flexibility of extended loop designs and their power, we propose that these should be the designs of choice for most experiments using two-channel microarrays.     

Asymmetrical competition between Neotropical dung beetles and its consequences for assemblage structure

Abstract.  1. This study combines the results of laboratory experiments using representative assemblage components and pitfall trapping over a large geographical area to examine the hypothesis that ongoing interspecific competition structures Neotropical dung beetle assemblages.
2. From Guatemala to Panama assemblages of large to medium-sized, fast-tunnelling dung beetles include a single large, nocturnal dichotomiine species, Dichotomius annae (Kohlmann & Solís, 1997). In competition experiments, this species out-competed the medium-sized coprine species, Copris lugubris Boheman and Phanaeus demon Laporte-Castelnau, for dung and nesting space, in spite of earlier colonisation by the diurnal species, P. demon .
3. Differences in the abundance of D. annae at Central American sites did not affect total fast-tunnelling dung beetle assemblage richness over the rainy season. However, D. annae rank order was directly related to the probability of interspecific encounters (Hurlbert's Δ ₁) among species. These trends were also observed when species lists from published and unpublished studies of other large allopatric dichotomiine species, with a more northerly distribution, were included in the analyses.
4. The results obtained suggest that where large dichotomiine species are abundant, their efficient pre-emption of a considerable proportion of available resources drives all, or most, other fast-tunnelling species to a lower population density, thereby decreasing assemblage diversity.     

Estimating tsetse population parameters: application of a mathematical model with density-dependence

A density-dependent model is used to describe the dynamics of an open population of tsetse flies (Diptera: Glossinidae). Immigration (or emigration) takes place when the total population is below (or above) a biologically determined threshold value. The population is also subjected to birth and death rates, as well as to the risk of being trapped (continuously or intermittently). During trapping the population decreases toward a 'low' equilibrium population and when trapping ceases the population starts recovering and increases toward a 'high' equilibrium. The model is fitted using data collected on trapped flies in four experiments. The first one was conducted with 'intermittent trapping' (i.e. several trapping-recovery cycles) on Glossina fuscipes fuscipes Newstead in the Central African Republic (Bangui area). In the other experiments, trapping data on Glossina palpalis palpalis (Robineau-Desvoidy) was collected in 'aggregate' form over several days at a time. Two of these were in Congo-Brazzaville (Bouenza area) and one in the Ivory Coast (Vavoua focus). Estimates are derived for the low and high equilibrium values as well as the trapping rate. The estimated effect of sustained trapping is to reduce the population to low equilibrium values that are 85-87% lower than the levels without trapping. The effects of the natural intrinsic growth and of the migration flows cannot be estimated separately because in the model they are mathematically indistinguishable.     

Modelling the effect of feeding-related mortality on the feeding strategy of tsetse (Diptera: Glossinidae)

Abstract. Free-living haematophagous insects risk death through host grooming responses or through increased susceptibility to predation whenever they take a bloodmeal. In this paper we investigate the effects of these risks on the feeding strategy of tsetse. A model is presented that allows for death of tsetse by starvation if they do not succeed in feeding within a fixed time (set at 6 days in the first instance) and for mortality specifically associated with feeding. In addition there is background mortality that applies to all flies at all times.
The model is used to compute the individual life-time fertility (number of female puparia per female) as a function of the probability of obtaining a meal (indicated by field data to be very high, usually > 0.85 per day) and the day on which flies start to search for a meal. We suggest that the feeding strategy that would be selected for is that which allows the maximum reproductive output. The model shows that this strategy involves making no attempts to feed for 3–4 days after the previous meal and then attempting to feed with the greatest possible probability until a meal is obtained. The predicted feeding interval, obtained independently of any trapping data, agrees closely with all previous estimates from field studies using a variety of methods. Preliminary results from a laboratory experiment reveal an increased risk of predation of recently fed as compared with hungry tsetse. The lower the actual feeding mortality the more frequently will flies be able to feed should conditions so demand. It is adaptive, however, for tsetse to delay attempting to feed for as long as they can, which is made possible by the near certainty of locating and feeding on a host within 1 day, using their sophisticated sensory systems.     

Stress-accentuation of the LSD-induced disaggregation of brain polysomes

The application of three types of stress; restraint, food deprivation or epinephrine injection markedly accentuated the disaggregation of rabbit brain polysomes to monosomes induced by LSD (25 μg/kg) whereas no shift of polysomes to monosomes was found with any of the stress treatments alone. LSD when administered intravenously at a very low dose of 1 μg/kg and combined with the restraint procedure produced a massive brain polysome shift. LSD alone at this dosage did not induce a disaggregation of polysomes. Elevations in plasma corticosteroid levels relative to control were found following LSD administration with or without the stressing procedures. LSD and certain elements of environment and physiological arousal appear to have a synergistic effect on disrupting the protein synthesis apparatus of brain.     

Trapping tsetse flies on water

Riverine tsetse flies such as Glossina palpalis gambiensis and G. tachinoides are the vectors of human and animal trypanosomoses in West Africa. Despite intimate links between tsetse and water, to our knowledge there has never been any attempt to design trapping devices that would catch tsetse on water. In mangrove (Guinea) one challenging issue is the tide, because height above the ground for a trap is a key factor affecting tsetse catches. The trap was mounted on the remains of an old wooden dugout, and attached with rope to nearby branches, thereby allowing it to rise and fall with the tide. Catches showed a very high density of 93.9 flies/"water-trap"/day, which was significantly higher (p < 0.05) than all the catches from other habitats where the classical trap had been used. In savannah, on the Comoe river of South Burkina Faso, the biconical trap was mounted on a small wooden raft anchored to a stone, and catches were compared with the classical biconical trap put on the shores. G. p. gambiensis and G. tachinoides densities were not significantly different from those from the classical biconical one. The adaptations described here have allowed to efficiently catch tsetse on the water, which to our knowledge is reported here for the first time. This represents a great progress and opens new opportunities to undertake studies on the vectors of trypanosomoses in mangrove areas of Guinea, which are currently the areas showing the highest prevalences of sleeping sickness in West Africa. It also has huge potential for tsetse control using insecticide impregnated traps in savannah areas where traps become less efficient in rainy season. The Guinean National control programme has already expressed its willingness to use such modified traps in its control campaigns in Guinea, as has the national PATTEC programme in Burkina Faso during rainy season.     

PSII photochemistry and antioxidant responses of a chickpea variety exposed to drought

The effect of drought on the chickpea variety ILC 3279 was investigated at the vegetative stage. After 20 days from sowing, the plants subjected to drought stress for 3, 5 and 7 days imposed by withholding water were permitted to recover by rewatering for 2 days after 3, 5 and 7 days of drought. Shoot elongation, leaf production, fresh and dry biomass reduced while MDA and proline accumulation increased with extended duration of stress. The plants stressed for 3 days exhibited a rapid drop in their relative and absolute water contents. The quantum efficiency of PSII open centres in the dark-adapted and light-saturated state, excitation energy trapping of PSII and electron transport rate decreased significantly from the 5th day to the end of the drought treatments. Plants drought-stressed for 7 days brought about a marked increase in non-photochemical energy dissipation and a marked decline in photochemical quenching. After rewatering all chlorophyll a fluorescence characteristics except for F(M) completely recovered and reached the control values. Under 5 and 7 days of drought, the anthocyanin content increased gradually while the total chlorophyll content of leaves declined compared to the controls. The total carotenoid content remained unchanged during the experiments. The antioxidant enzyme response to drought treatments was quite variable. The total SOD activity upregulated with increasing duration of stress. On the other hand, the total APX activity was significantly higher only on the 7th day while the total POD activity increased from the 5th day. Differences in the total GR activity of treated groups were not statistically significant compared to their controls throughout the treatments. The present results indicate that the chickpea variety ILC 3279 withstands severe drought with its upregulated protective mechanisms at the vegetative stage.     

Detecting dispersal of Nuphar lutea in river corridors using microsatellite markers

1. River corridors are well-known for their role in plant dispersal. The buoyancy of seeds, the possibility of dispersal by vegetative fragments, and the frequency and efficiency of dispersal among different river catchments determine linear distribution patterns. Little is known about the relative importance of these factors to observed patterns of genetic variation.
2. One hundred and fifty-six Nuphar lutea individuals from forty-four sampling sites in the river catchments of the Cidlina River, the Mrlina River and the Labe River (Czech Republic) were studied using ten microsatellite markers. Interpretation of patterns in genetic variation allowed several conclusions about dispersal mechanisms.
3. Vegetative long-distance dispersal is probably very limited in this species. Only one multilocus genotype was found in more than one sampling site. The distance between the sites was about 75 km.
4. To explain the distribution of Bayesian based clusters of related multilocus genotypes, both along-river and inter-river long-distance dispersals have to be invoked.
5. A marginally significant tendency for higher genetic diversity in the lower part of the river Cidlina was detected. Continuous downstream dispersal of seeds by water currents could be a valid explanation.
6. Significant positive autocorrelation was found among individuals at within-river distances of up to 25 km. Repeated dispersal of seeds over distances in the range of tens of kilometers is common.     

Efficacy of Electrocuting Devices to Catch Tsetse Flies (Glossinidae) and Other Diptera

Background

The behaviour of insect vectors has an important bearing on the epidemiology of the diseases they transmit, and on the opportunities for vector control. Two sorts of electrocuting device have been particularly useful for studying the behaviour of tsetse flies (Glossina spp), the vectors of the trypanosomes that cause sleeping sickness in humans and nagana in livestock. Such devices consist of grids on netting (E-net) to catch tsetse in flight, or on cloth (E-cloth) to catch alighting flies. Catches are most meaningful when the devices catch as many as possible of the flies potentially available to them, and when the proportion caught is known. There have been conflicting indications for the catching efficiency, depending on whether the assessments were made by the naked eye or assisted by video recordings.

Methodology/Principal Findings

Using grids of 0.5m² in Zimbabwe, we developed catch methods of studying the efficiency of E-nets and E-cloth for tsetse, using improved transformers to supply the grids with electrical pulses of ~40kV. At energies per pulse of 35–215mJ, the efficiency was enhanced by reducing the pulse interval from 3200 to 1ms. Efficiency was low at 35mJ per pulse, but there seemed no benefit of increasing the energy beyond 70mJ. Catches at E-nets declined when the fine netting normally used became either coarser or much finer, and increased when the grid frame was moved from 2.5cm to 27.5cm from the grid. Data for muscoids and tabanids were roughly comparable to those for tsetse.

Conclusion/Significance

The catch method of studying efficiency is useful for supplementing and extending video methods. Specifications are suggested for E-nets and E-cloth that are ~95% efficient and suitable for estimating the absolute numbers of available flies. Grids that are less efficient, but more economical, are recommended for studies of relative numbers available to various baits.     

The diurnal activity, movement and trypanosome infection rates of Glossina fuscipes fuscipes （Diptera： Glossinidae） in Buvuma Island, Lake Victoria, Uganda

The diurnal activity patterns, trypanosome infection rates and movement of Glossinafuscipesfuscipes （Diptera： Glossinidae） were investigated in Buvuma Island, Lake Victoria, Uganda. Hourly trapping of tsetse flies was undertaken to determine their activity rhythm while a capture-mark-release-recapture method was conducted to assess the movement and dispersal of tsetse flies between lakeshore, hinterland and further inland sites along a transected area. Dissection of tsetse flies was also undertaken to determine the trypanosome infection rates in salivary glands, proboscis and mid-gut. Results indicated a bimodal diurnal activity profile for G. f fuscipes on the Island, both on the lakeshore and in the hinterland. Movement and dispersal of G. f fuscipes tsetse flies occurred between lakeshore, hinterland and further inland sites with a greater tendency of flies to move to the lakeshore. Trypanosome infection rates of 4.32% for Trypasoma vivax and 1.15% for 7. congolense were found in G. f. fuscipes.     

Diel variability in counts of reef fishes and its implications for monitoring

Studies of reef fish assemblages in space rarely consider the effects of temporal variability on spatial comparisons, and when they do, usually examine timescales of months to years. The nature of fish monitoring surveys is such that particular locations may be surveyed at one time of day, and surveys designed to establish the degree of spatial variability in assemblages may be confounded if the order of sampling within treatments is not randomised with respect to time of day. In this study, we tested the degree of temporal variability in temperate reef fish counts at the same sites in New Zealand and Italy, within and between days. Repeated counts separated by months returned quite different assemblages, whereas counts separated by days did not. Although overall assemblage structure did not generally differ significantly with time of day, at some locations there was evidence of changes in the relative density of certain species in the afternoon relative to the morning. Care must be taken not to introduce systematic bias to spatial comparisons due to behavioural variability in fishes at differing times of day.     

Quantifying the relative importance of niches and neutrality for coexistence in a model microbial system

1.  Ecologists have identified two types of processes promoting species coexistence: stabilizing mechanisms (niche differentiation and related processes) that increase negative intraspecific interactions relative to negative interspecific interactions, and equalizing mechanisms (neutrality) that minimize the differences in species' demographic parameters. It has been theoretically and empirically shown that the two types of mechanisms can operate simultaneously; however, their relative importance remains unstudied although this is a key question in the synthesis of niche and neutral theories.
2.  We experimentally quantified the relative importance of niche and neutral mechanisms in promoting phenotypic diversity in a model microbial system involving different phenotypes of the bacterium Pseudomonas fluorescens . Initially isogenic populations of the bacterium can diversify into a series of major and minor classes of phenotypes that can be treated as analogues of species. We estimated the relative population growth rate when rare of 32 phenotypes from six replicate microcosms. Each phenotype was assessed in a re-assembled microcosm in which the relative densities of all phenotypes remained the same except for the focal one which was reduced in frequency. A growth rate advantage when rare was considered evidence of non-neutral processes.
3.  Approximately one-third of the phenotypes had a growth rate advantage when rare while the remaining two-thirds showed neutral or near-neutral dynamics. Furthermore, there was overall little evidence that productivity increased with phenotypic diversity.
4.  Our results suggest that niche and neutral processes may simultaneously contribute to the maintenance of biodiversity, with the latter playing a more important role in our system, and that the operation of niche mechanisms does not necessarily lead to a positive biodiversity effect on ecosystem properties.     

Kinetics of liver trapping of infective larvae in murine toxocariasis

Mice sensitized by prior infection with Toxocara canis eggs trap many larvae of a challenge infection within the liver. In this study the distribution of challenge larvae in sensitized mice was examined to determine the earliest onset of liver trapping and to establish if the previously described phenomenon truly represented larval trapping. In all experiments, C57BL/6J mice were infected with a sensitization dose of 125 infective T. canis eggs on day 0 postinfection (PI) and challenged with 500 infective eggs on day 28 PI. In the initial experiments, larval numbers were determined within the intestinal contents, intestinal wall, mesenteric tissues, liver, lungs, skeletal muscle, and brain of each mouse on days 0.5, 1, 2, 3, 5, and 6 postchallenge (PC). Migration patterns were similar among the test and control groups except the peak of larval numbers in the liver, seen at 1 day PC in control mice, was delayed until 3 days PC in the test group. Larval trapping occurred within the liver of test mice at least by day 5 PC. In subsequent experiments, larval numbers were determined within the liver, skeletal muscle, brain of each mouse, and within the eyes of each mouse group at 4, 8, 12, and 16 wk PC. Larval numbers within the liver of test mice were similar both at 5 days PC and 16 wk PC, implying that larvae were trapped in this organ rather than delayed in their migration to other body sites. Liver trapping did not protect the eyes or brain of sensitized mice from larval migration, nor did it result in larval killing.     

Combined effects of allelochemical-fed and scarce prey on the generalist insect predator Podisusmaculiventris

1. The simultaneous effects of allelochemicals ingested by herbivorous insect prey and prey scarcity on the performance of a generalist insect predator were examined.
2. Fifth-instar predatory stinkbugs ( Podisus maculiventris : Pentatomidae) were fed caterpillars ( Manduca sexta : Sphingidae) in three prey scarcity treatments: every day (unlimited amount), one caterpillar every third day, one caterpillar every fifth day. The caterpillars were fed either a plain diet or a diet containing rutin, chlorogenic acid and tomatine, which are three of the major allelochemicals in tomato leaves ( Lycopersicon esculentum : Solanaceae), the preferred food of these caterpillars.
3. Food consumed, efficiency of conversion of ingested food to biomass (ECI), biomass gained, stadium duration and relative growth rate (RGR) of predators were negatively affected by prey scarcity. The allelochemicals negatively affected food consumed and ECI.
4. There were prey scarcity by allelochemical interactions for ECI, biomass gained and RGR. For ECI, the allelochemicals had a greater negative impact on the predatory stinkbugs when prey were scarce. When prey diet contained allelochemicals, biomass gained and RGR declined more steeply with increased prey scarcity. There was an allelochemical by predator gender interaction for biomass gained. Allelochemicals had no effect on biomass gained by female stinkbugs, whereas biomass gained declined more steeply with increased prey scarcity for male stinkbugs fed caterpillars containing allelochemicals than for males fed control caterpillars.     

The use of discriminant analysis for the estimation of sampling biases for female tsetse

ABSTRACT.

• 1 In this paper we investigate whether the technique of discriminant analysis can be used to estimate sampling biases for female tsetse.
• 2 Discriminant analysis was first applied to laboratory samples of female tsetse, Glossina morshans morsitans Westwood, to test whether flies of known history could be assigned to the correct day of the pregnancy cycle on the basis of their fat, haematin and corrected residual dry weight.
• 3 Following the satisfactory results from the laboratory samples, the same technique was applied to field samples of G.m. centralis Machado captured by electric traps and hand nets in Zambia and of G.palpalis palpalis (Robineau-Desvoidy) captured in biconical traps at five sites in Ivory Coast. The results show that flies on day 1 of the pregnancy cycle were most likely to be caught, with a second peak of day-6 and day-7 flies, while very few day-8 or day-9 flies were caught.
• 4 These major peaks in fly trappability coincide with the known feeding habits of female tsetse, and indicate synchrony of feeding by many members of the population immediately after larviposition and again as the larva in utero moults from the second to third instar. G.palpalis is relatively more available at this later stage of its pregnancy cycle to the capture methods used than is G.morsitans. A third feed may be taken at a more variable point in the pregnancy cycle.
• 5 This method of estimating the sampling biases of female tsetse could allow an estimate of total population size, as long as the absolute sampling efficiency of flies on any one day of the pregnancy cycle could be established by, for example, mark-release-recapture experiments.

     

Effect of egg dosage and host genotype on liver trapping in murine larval toxocariasis

In this study we examined the effect of various initial sensitizing doses of infective Toxocara canis eggs and the effect of murine host genotype on the level of trapping of larvae in the liver after larval challenge. In the initial experiments, C57BL/6J mice were infected with a sensitization dose of 5, 25, 75, 125, or 250 infective T. canis eggs on day 0 postinfection (PI). On day 28 PI all mice were challenged with 500 infective eggs. On days 7, 14, and 21 postchallenge (PC) larval numbers within individual livers were determined. Trapping of larvae was observed in mice receiving a sensitization dose of 25 or more eggs. At 7 and 14 days PC the level of trapping increased with sensitization egg dose up to a dose of 125 eggs. At 21 days PC the level of trapping reached a plateau at a sensitization dose of 75 eggs. The peak level of larval trapping was observed on day 7 and day 14 PC following sensitization doses of 125 and 250 eggs, respectively. In the subsequent experiments, mice of various strains and H-2 haplotypes were inoculated with an initial sensitization dose of 125 eggs and a challenge dose of 500 eggs on day 0 and day 28 PI, respectively. Larval trapping within the liver was determined on day 14 PC. C57BL/6J mice trapped significantly more larvae than DBA/2J mice (P less than 0.01); all other strains trapped larvae at a lower, but statistically similar, level to the C57BL6/J mice.(ABSTRACT TRUNCATED AT 250 WORDS)