Aerial distribution, flight behaviour and eggload: their inter-relationship during dispersal by the sweetpotato whitefly

1. The aerial distribution of Bemisia tabaci Gennadius (the sweetpotato whitefly) was studied during the early ascent phase of flight, to test the degree to which dispersal patterns reflect the flight behaviour of individuals.
2. Marked whiteflies were trapped at four heights between 0 and 7·2 m above fallow ground, and at six distances between 0 and 100 m from the insect source. Insects were trapped during a 2–3 h period after the initiation of flight activity during the summers of 1995 and 1996.
3. Analysis of trap catch data revealed a clear negative exponential relationship between height and aerial distribution, and a slightly weaker negative power relationship between distance and aerial distribution. Marked insects were caught in the uppermost traps adjacent to the source, indicating that a portion of the population had a strong capacity for ascent out of the flight boundary layer.
4. Eggload decreased with the height, but not the distance, at which whiteflies were trapped. Mean eggload close to the ground was significantly greater than that for those trapped at 4·8 and 7·2 m, supporting the hypothesis that there is a trade-off between flight and oogenesis in weak-flying insects.
5. Air temperatures during the trapping periods were positively correlated with the proportion of male and female B. tabaci caught in the highest traps, but not in the most distant traps.
6. The significance of these results for accurate prediction of whitefly dispersal is discussed, and the importance of individual's behaviour in determining dispersal patterns of small insects is emphasized.     

Cyclic AMP-dependent control of the rat hepatic glutathione disulfide-sulfhydryl ratio.

The disulfide-sulfhydryl ratio of rat hepatic tissue has been found to vary diurnally lowest in the early morning and highest in the early evening (Isaacs, J. (1976) Fed. Proc. 35, 1472, and Isaacs, J. and Binkley, F. (1977) Biochim. Biophys. Acta 497, 192-204). Intraperitoneal injections of dibutyryl cyclic AMP induces an increase in hepatic glutathione protein mixed disulfides (GSSProt) combined with a corresponding decrease in reduced glutathione (GSH) and protein sulfhydryl (ProtSH). Also, dibutyryl cyclic AMP caused hepatic catalase activity to decrease and to increase hepatic production of peroxide molecules. A decrease in catalase activity directs more of the increased peroxide into the glutathione peroxidase pathway. This leads to increased amounts of oxidized glutathione (GSSG) which ultimately results in increased levels of GSSProt. Therefore cyclic AMP may mediate its effect on the disulfide-sulfhydryl ratio via control over catalase and peroxide generation. Support for this idea is provided by the close temporal correlation between the diurnal variations in cyclic AMP, hepatic catalase, peroxide generation and GSSProt-GSH levels.     

Expression of a novel FGF in the Xenopus embryo. A new candidate inducing factor for mesoderm formation and anteroposterior specification.

We have cloned and sequenced a new member of the fibroblast growth factor family from Xenopus laevis embryo cDNA. It is most closely related to both mammalian kFGF (FGF-4) and FGF-6 but as it is not clear whether it is a true homologue of either of these genes we provisionally refer to it as XeFGF (Xenopus embryonic FGF). Two sequences were obtained, differing by 11% in derived amino acid sequence, which probably represent pseudotetraploid variants. Both the sequence and the behaviour of in vitro translated protein indicates that, unlike bFGF (FGF-2), XeFGF is a secreted molecule. Recombinant XeFGF protein has mesoderm-inducing activity with a specific activity similar to bFGF. XeFGF mRNA is expressed maternally and zygotically with a peak during the gastrula stage. Both probe protection and in situ hybridization showed that the zygotic expression is concentrated in the posterior of the body axis and later in the tailbud. Later domains of expression were found near the midbrain/hindbrain boundary and at low levels in the myotomes. Because of its biological properties and expression pattern, XeFGF is a good candidate for an inducing factor with possible roles both in mesoderm induction at the blastula stage and in the formation of the anteroposterior axis at the gastrula stage.     

How dangerous are falls in old people at home?

From a survey in six general practices information was obtained on 125 people aged 65 and over who fell in their own homes. Three fractured their femurs and 15 had other fractures; most of the rest suffered only trivial injuries. Twenty lay on the floor for more than one hour; none were known to have suffered hypothermia. One-quarter of these patients died within one year of the fall, five times as many as in an age- and sex-matched control group; while of those who lay on the floor for more than one hour, half died within six months of the fall. Factors associated with mortality from falls were impaired mobility, abnormal balance, and a disturbed pattern of gait. Falls at home in old age are often indicative of the presence of severe ill health.     

Effects of Prescribed Burning and Mechanical Bush Clearing on Ungulate Space Use in an African Savannah

Savannah ecosystems exhibit constant transitions between states dominated by trees and states dominated by a combination of trees and grasses. Transitions between these states are driven by interactions between fire and herbivory. Bush encroachment (i.e. an increase in the density of woody vegetation) is often caused by anthropogenic disturbance such as climate change, invasive plants, fire control, and livestock practices. As bush encroachment alters the dynamics between fire and herbivory, it may have significant impact on savannah ecosystems. Two of the most common measures to mitigate bush encroachment are prescribed burning and bush clearing by mechanical treatments. We studied the effects of these two mitigation measures on ungulate space use in Lapalala Wilderness, a private conservation area within the Waterberg Biosphere Reserve, northern South Africa. Burning and bush clearing affected both the overall abundance and the species composition of ungulates at particular patches, but these effects were influenced by habitat and the type of bush clearing treatment. Contrary to our expectations, most species occurred less frequently in burnt patches, and also less frequently in patches that had been bush cleared. Our results suggest that combined effects of fire and bush clearing may have positive effects on grazers and negative effects on browsers. Although our sampling design did not allow us to fully resolve interactive effects of burning and bush clearing treatments across habitats, our study highlights the fact that there are complex ecological consequences of habitat alterations in savannah ecosystems.