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1.
ABSTRACT. Movement of host odour was modelled in natural tsetse habitats with smoke and ultra-light 7-cm-long wind vanes; the speed and direction of the air movements were analysed from video recordings thereof. Wind of <1 ms-1 did not move in straight lines, since large packets of air (>10 m across) often changed direction together. The rate of this change of direction (meander) correlated negatively with windspeed. In open woodland with a shrubby understorey (in which windspeed was reduced by a factor of >5 from that above the canopy, to ax 0.3 m s-1), this wind meander fell by 2d? s-1 change of direction for each 0.1 m s-1 increase in windspeed (r2=0.96). Over open ground without shrub cover, the meander fell by 0.5d? s-1 per 0.1 m s-1 increase in windspeed (r2=0.85). In both situations, such meandering virtually ceased in winds of > 1 m s-1. In woodland, the relationship between the direction of air movement near the surface of bare earth (one potential tsetse landing site) and that c. 0.5 m above ground level (flight height) was often weak (r2=0.2-0.4), but this problem would be reduced if the fly averaged the ground-level wind for at least 30 s. Odour (smoke) travelling from a source 15 m ‘upwind’ over open ground arrived at a notional tsetse fly for 80% of the time from a direction within 10d? of the true source direction. In typical tsetse woodland, however, the ‘odour’ arrived from all directions (including >90d? away from the source), with only a 30% bias towards the true source direction (±10d?). Evidently, tsetse must navigate up odour plumes by means that get round these difficulties-simple, moth-type upwind anemotaxis alone seems unlikely to be adequate.  相似文献   
2.
  总被引:1,自引:0,他引:1  
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).  相似文献   
3.
ABSTRACT. The sesquiterpenoid euplotin C is a secondary metabolite produced by the ciliated protist Euplotes crassus and provides a mechanism for damping populations of potential competitors. Indeed, E. crassus is virtually resistant to its own product while different non-producer species representing an unbiased sample of the marine, interstitial, ciliate diversity are sensitive. For instance, euplotin C exerts a marked disruption of different homeostatic mechanisms in Euplotes vannus . We demonstrate by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay that euplotin C quickly decreases viability and mitochondrial function of E. vannus with a very high efficacy and at micromolar potency. In addition, euplotin C induces apoptosis in E. vannus as 4,6-diamino-2-phenylindole and terminal transferase dUTP nick end labeling staining show the rapid condensation and fragmentation of nuclear material in cells treated with euplotin C. These effects occur without detectable permeabilisation or rupture of cell membranes and with no major changes in the overall morphology, although some traits, such as vacuolisation and disorganized microtubules, can be observed by transmission electron microscopy. In particular, E. vannus show profound changes of the mitochondrial ultrastructure. Finally, we also show that caspase activity in E. vannus is increased by euplotin C. These data elucidate the pro-apoptotic role of euplotin C and suggest a mechanism for its impact on natural selection.  相似文献   
4.
Abstract. A behavioural test was used to determine the light sensitivity of the nocturnal mosquito Anopheles gambiae Giles s.s. to low intensities of 'white' light (tungsten filament), 'red' light (white light filtered by a darkroom safelight filter) and 'infra-red' light) of two types (white light filtered by a λ>700 nm filter, and light-emitting diodes with λ>900 nm). Mosquitoes were placed in a 20 cm diameter flight-tunnel and their 'optomotor' response to a pattern of stripes moving across their visual field (at 14.5 cm s-1) was recorded with infra-red-sensitive video. In free-flight, with ample light, the mosquitoes controlled their flight speed and direction in relation to the stripe movement, so that the stripes always appeared to move across their visual field from front to back. They did this by flying either with the moving stripes fast enough to overtake them (19.5 ± 0.7 cm s-1), or against them more slowly (10.3 ± 0.7 cm s-1)- The net ground speed of the mosquitoes was thus c. 4–5 cm s-1. This response was significant down to 10-5 W m-2 in 'white' light, and 10-3 W m-2 in 'red' light. At light intensities below threshold and in infra-red light, however, they appeared to fly at random with respect to the stripe movement. The assumption commonly made, that mosquitoes do not 'see' in red light, may thus have to be revised.  相似文献   
5.
    
InVicia benghalensis two different biotypes, named A and B,had been observed which differed for several cytological, geneticaland biochemical characters. In the present study 27 accessionsof this species belonging to the two biotypes were investigatedusing different molecular analyses, supported by an attemptto produce hybrids between selected accessions. RAPD fingerprintingof the 27 accessions demonstrated that accessions belongingto biotype A show a high degree of genetic similarity, whilethe opposite is true for the accessions of biotype B. The totalgenomic DNA from one reference accession was used as a probeto Southern blots of the DNA extracted from all the accessionsin use. This analysis demonstrated that cross hybridizationamong the DNA of the two biotypes occurs only to a limited extent.The chromosomal localization of 18S-5.8S-25S and 5S rRNA geneclusters was determined byin situ hybridization. The resultsindicate that the two biotypes differ in the position of oneof the 5S rRNA gene clusters. This indicates a major chromosomalrearrangement. Cell synchronization experiments on two referenceaccessions suggested that the two biotypes might differ in theduration of the single phases of the cell cycle. Finally, incrossing experiments three pods were obtained which developedfor only a few days and proved to bear no viable seeds. Theseresults confirm the existence of two divergent gene-pools anddemonstrate the reproductive barrier between the two biotypes,thus suggesting the possibility of a specific ranking. Vicia benghalensis L.; genetic differentiation; in situ hybridization; Southern hybridization; crosses; RAPDs; cell synchronization  相似文献   
6.
    
1. In the study of the evolution of insect–host plant interactions, important information is provided by host ranking correspondences among female preference, offspring preference, and offspring performance. Here, we contrast such patterns in two polyphagous sister species in the butterfly family Nymphalidae, the Nearctic Polygonia faunus, and the Palearctic P. c‐album. 2. These two species have similar host ranges, but according to the literature P. faunus does not use the ancestral host plant clade – the ‘urticalean rosids’. Comparisons of the species can thus test the effects of a change in insect–plant associations over a long time scale. Cage experiments confirmed that P. faunus females avoid laying eggs on Urtica dioica (the preferred host of P. c‐album), instead preferring Salix, Betula, and Ribes. 3. However, newly hatched larvae of both species readily accept and grow well on U. dioica, supporting the general theory that evolutionary changes in host range are initiated through shifts in female host preferences, whereas larvae are more conservative and also can retain the capacity to perform well on ancestral hosts over long time spans. 4. Similar rankings of host plants among female preference, offspring preference, and offspring performance were observed in P. c‐album but not in P. faunus. This is probably a result of vestiges of larval adaptations to the lost ancestral host taxon in the latter species. 5. Female and larval preferences seem to be largely free to evolve independently, and consequently larval preferences warrant more attention.  相似文献   
7.
    
Anopheles gambiae Giles sensu stricto (Diptera: Culicidae) is the most important vector of human malaria in sub‐Saharan Africa, affecting the lives of millions of people. Existing tools such as insecticide‐treated nets and indoor‐residual sprays are not only effective, but also have limitations as a result of the development of resistance to insecticides and behavioural adaptations in biting time. Therefore, novel mosquito‐control tools are needed. Odour‐releasing traps have a potential for both trapping and surveillance purposes. Based on the outcome of ex vivo gene expression assays and in vivo electrophysiological assays on hundreds of volatile organic compounds, 29 ‘candidate behaviourally‐disruptive organic compounds' (cBDOCs) are selected, belonging to 10 chemical categories, to be assayed in the laboratory using dual‐choice olfactometers for the ability to modify the ‘attractiveness’ (i.e. significantly more insects being caught in the associated trap) of a basic volatile blend consisting of ammonia, lactic acid and tetradecanoic acid but without additional carbon dioxide. Compounds that either reduce or increase trap catches by the basic blend in the olfactometer experiments are tested under African conditions in choice experiments in a semi‐field facility in Kenya. The release rates of cBDOCs are determined gravimetrically to allow the calculation of aerial concentrations at the trap outlet. Aerial concentrations in the sub‐p.p.m. range are reported for the first time to influence mosquito behaviour. The results of the olfactometer and semi‐field assays generally correspond. Under semi‐field conditions, three compounds, 3‐heptanol (0.025 p.p.m.), 2‐methylpropanal (0.05 p.p.m.) and 4,5‐dimethylthiazole (0.73 p.p.m.), significantly increase trap catches relative to the basic blend consisting of ammonia, lactic acid, tetradecanoic acid and carbon dioxide. 2‐Acetylthiophene, 2‐nonanone and 2‐phenylethanol decrease the number of mosquitoes caught at all concentrations tested under semi‐field conditions. These compounds hold promise as attractants and spatial repellents to be applied in mosquito control programmes.  相似文献   
8.
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=1.08o) and angular receptive field of individual ommatidia (Δp) of not less than 1.14o. 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=3.7o) and small angular receptive field (Δp = c. 1.6o). 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 = 24o, for females = 18o). 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.  相似文献   
9.
ABSTRACT. Actograph measurements of the spontaneous flight activity of isolated female Glossina morsitans morsitans Westw. were made through their first two pregnancy cycles in constant conditions under LD 12:12. Activity fell from a mean of c. 20 units/day to near zero during the 24 h preceding the day on which larvipositionoccurred. Activity on the day of larviposition rose significantly, to c. 35 units/day, then fell back to the baseline 20 units on subsequent days. The circadian pattern of activity was changed markedly by larviposition: 48 h before it, activity in the morning peak of the usual V-shaped diel pattern was twice normal; over 70% of the flies then fed, and the evening arm of their V disappeared; 24 h before larviposition, most flies were totally inactive, the few that did fly performing only 1 or 2 units/day, and only in the first and last hours of the photophase; on the day of larviposition, the morning peak of the V was reduced by c. 70%, and activity peaked instead during the post-noon 2–3 h, before and during the act of parturition. Almost all larvipositions occurred between noon and lights-out. It is suggested that the c. 48 h of pre-larviposition quiescence may play a role in the fact that pregnant G. morsitans females often survive non-residual aerosol insecticide campaigns.  相似文献   
10.
    
1. Changes in vegetation community composition, such as a transition from grassland to shrubland (woody encroachment), are associated with reductions in plant cover and increases in bare ground. Encroachment‐driven changes in surface cover at small spatial scales can alter ant community assemblages by changing their foraging behaviour and their ability to locate and monopolise resources. 2. Artificial arenas with three levels of complexity were used to examine changes in ant foraging efficiency, body size and ability to monopolise food. The three levels of complexity included a control (no substrate), low‐complexity treatment (woody debris) and high‐complexity treatment (leaf litter). 3. No difference was found in ant species composition within the complexity arenas between grassland and shrubland, but ant functional groups ‘generalised Myrmicinae’ and ‘subordinate Camponotini’ were more abundant in grassland arenas, whereas ‘opportunists’ were more abundant in shrubland arenas. Ants took twice as long to find baits in high‐complexity treatments, and 1.5 times as long in low‐complexity treatments, than in control treatments, which were bare arenas with no substrate. Ant body size declined with increasing surface complexity, suggesting that larger ants are discouraged from foraging in complex habitats. 4. There was also significantly greater monopolisation of the protein bait (tuna) in low‐ and high‐complexity treatments, but there were no differences between tuna and carbohydrate (honey) in the control treatment. Consistently, no differences were found in ant behaviour between grasslands and shrublands. 5. The present study shows that ants are more responsive to small‐scale alterations in soil surface complexity than to changes in vegetation community composition. Changes in soil surface complexity select for ants based on body size, which in turn influences their foraging success. Changes in vegetation complexity at small spatial scales are therefore likely to influence ant behaviour and abundance of some functional groups, potentially having an effect on the many ecosystem functions carried out by ants.  相似文献   
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