'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).     

The Secondary Metabolite Euplotin C Induces Apoptosis-Like Death in the Marine Ciliated Protist Euplotes vannus

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.     

The glandular hairs of Valeriana officinalis subsp. collina. I. Some unusual features in their development and differentiation

The ontogeny, morphology, histochemistry and nuclear structure of glandular hairs in Valeriana officinalis L. subsp. collina (Wallr.) Nyman were investigated. An interesting characteristic of these glandular hairs is their remarkable variability, not only in morphology, but in their chromatin activity, and the reactions of the secretions to histochemical tests.     

Identification of candidate volatiles that affect the behavioural response of the malaria mosquito Anopheles gambiae sensu stricto to an active kairomone blend: laboratory and semi‐field assays

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.     

Comparison of Molecular Cytogenetic and Genetic Analyses in Accessions of the Two Biotypes of Vicia benghalensis L.

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     

The optics of tsetse fly eyes in relation to their behaviour and ecology

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=1.08^o) and angular receptive field of individual ommatidia (Δp) of not less than 1.14^o. 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=3.7^o) and small angular receptive field (Δp = c. 1.6^o). 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 = 24^o, for females = 18^o). 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.     

Re‐evaluation of the conodont Iapetognathus and implications for the base of the Ordovician System GSSP

Terfelt, F, Bagnoli, G. & Stouge, S. 2011: Re‐evaluation of the conodont Iapetognathus and implications for the base of the Ordovician System GSSP. Lethaia, Vol. 45, pp. 227–237. In 2000, the International Union of Geological Sciences (IUGS) ratified the decision from the International Working Group on the Cambrian–Ordovician Boundary (COBWG) to place the Global boundary Stratotype Section and Point (GSSP) for the base of the Ordovician System in the Green Point section, Newfoundland, Canada, at a point coinciding with the first appearance of the conodont Iapetognathus fluctivagus. However, a restudy of the conodont successions from Green Point shows that this species is not present at the boundary interval, and as a consequence the section does not fulfil the biostratigraphical requirements of a GSSP. The GSSP horizon as now defined is based on a level part‐way through the range of I. preaengensis– a species with lower first appearance datum (FAD). The true FAD of I. fluctivagus is above the FAD of planktonic graptolites and well above the FAD of I. preaengensis. As a consequence of these problems, a restudy of the GSSP section and the other sections in the Cow Head Group is necessary. A redefinition of the GSSP horizon is suggested. The following four alternative horizons have potential as new horizons for the GSSP level: the FAD of Cordylodus intermedius; the FAD of Cordylodus andresi; the FAD of Eoconodontus notchpeakensis; and the FAD of the agnostoid Lotagnostus americanus. □Boundary, Cambrian, conodont, Global boundary Stratotype Section Point, Iapetognathus, Ordovician.     

Soil surface complexity has a larger effect on food exploitation by ants than a change from grassland to shrubland

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.     

Vestiges of an ancestral host plant: preference and performance in the butterfly Polygonia faunus and its sister species P. c‐album

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.     

Swarming behaviour of the mosquito Culex pipiens quinquefasciatus: a quantitative analysis

ABSTRACT. Analysis of video recordings of Culex pipiens quinquefasciatus Say swarms showed that the overall swarming patterns of males and virgin females are similar, even though the short-term characteristics of their flight, such as speed and turning angle, differ. This suggests they have the same response to the visual cue of the swarm 'marker'. The swarming pattern of an individual consists of elliptical loops which, in the short-term, define an area smaller than the swarm as a whole. The foci of these ellipses drift gradually with respect to the marker; individuals do not seem to have preferred positions within the swarm, but drift at random. Male mosquitoes identify and locate females by the sound of their wing-beats. Diffuse sound at the wing-beat frequency of female C.p. quinquefasciatus (500–600 Hz) caused males within the swarm to slow down significantly. Their turning behaviour remained unchanged, so the ellipses decreased in size. The swarm as a whole collapsed into a smaller volume, centred over the marker. Apparently, the response of males to sound consists of at least two parts: initially they alter their flight speed, and then alter their turning behaviour once they have located the source of the sound.