Seasonal feeding activity of the tree-hole tick, Ixodes arboricola.

Bird-specific ticks do not infest humans and livestock, but these ticks often share their avian hosts with generalist ticks that do. Therefore, their feeding activity may have an impact on the transmission of pathogens outside bird-tick transmission cycles. Here we examined the seasonal feeding activity of the tree-hole tick (Ixodes arboricola) in relation to the activity of its hole-breeding hosts (Parus major and Cyanistes caeruleus). We analysed data on ticks derived from birds, on the abundance of engorged ticks inside nest boxes, and on bird nests that were experimentally exposed to ticks. We observed a non-random pattern of feeding associated with the tick instar and host age. The majority of adult ticks fed on nestlings, while nymphs and larvae fed on both free-flying birds and nestlings. Due to their fast development, some ticks were able to feed twice within the same breeding season. The highest infestation rates in free-flying birds were found during the pre-breeding period and during autumn and winter when birds roost inside cavities. Except during winter, feeding of I. arboricola overlapped in time with the generalist Ixodes ricinus, implying that tick-borne microorganisms that are maintained by I. arboricola and birds could be bridged by I. ricinus to other hosts.

[Considerations with respect to the use of corticosteroids in dentoalveolar surgical treatments]. / Beschouwingen over het gebruik van corticosteroïden in de dentoalveolaire chirurgie.

Corticosteroids are used incidentally in dentoalveolar surgical treatments to reduce possible postsurgical problems. Natural corticosteroids are produced in the adrenal cortex. Synthetic corticosteroids are known to have anti-inflammatory effects when they are administered in doses exceeding the normal physiological amounts which the body produces. Several contraindications and side effects are known. Administration of corticosteroids for dentoalveolar surgical treatments shows a reduction of edema and pain. When using corticosteroids, the risk of infections is not known to be higher than usual and the risk of adverse effects is minimal. According to the literature, there is no clear recommendation to use corticosteroids as a standard for dentoalveolar surgical treatments.

Empirical assessment of a threshold model for sylvatic plague.

Plague surveillance programmes established in Kazakhstan, Central Asia, during the previous century, have generated large plague archives that have been used to parameterize an abundance threshold model for sylvatic plague in great gerbil (Rhombomys opimus) populations. Here, we assess the model using additional data from the same archives. Throughout the focus, population levels above the threshold were a necessary condition for an epizootic to occur. However, there were large numbers of occasions when an epizootic was not observed even though great gerbils were, and had been, abundant. We examine six hypotheses that could explain the resulting false positive predictions, namely (i) including end-of-outbreak data erroneously lowers the estimated threshold, (ii) too few gerbils were tested, (iii) plague becomes locally extinct, (iv) the abundance of fleas was too low, (v) the climate was unfavourable, and (vi) a high proportion of gerbils were resistant. Of these, separate thresholds, fleas and climate received some support but accounted for few false positives and can be disregarded as serious omissions from the model. Small sample size and local extinction received strong support and can account for most of the false positives. Host resistance received no support here but should be subject to more direct experimental testing.

Reversible frequency-dependent switches in male mate choice.

Current sexual-selection theories predict that mating should occur preferentially with the highest-quality partner, and assume that for distinguishing among potential mates the choosy sex applies an internal representation of the characteristics of the desired mate, i.e. a template. Binary choice experiments were performed to test male mate choice between two different female colour morphs in the damselfly Ischnura elegans. Choice experiments were conducted before and after an habituation period, during which males were exposed to only one female colour morph. Given the choice between the two female morphs, males did exhibit a choice for the most recently experienced female morph. This is the first evidence for a reversible switch in mate choice in a frequency-dependent way. In contrast with previous studies on mate choice, template formation in male I. elegans seems not to be based on quality. Switching mate choice in a frequency-dependent manner, choosing the most common morph, probably allows males to minimize their search efforts and to maximize fitness.

Optimization of adult performance determines host choice in a grass miner.

Models and empirical studies on host selection in plant-insect, algae-amphipod, host-parasite and prey-predator systems assume that oviposition preference is determined by the quality of the oviposition site for offspring development. According to the oviposition-preference-offspring-performance hypothesis, oviposition-preference hierarchy should correspond to host suitability for offspring development because females maximize their fitness by optimizing offspring performance. We show, we believe for the first time, that adult feeding site and related adult performance may explain most of the variation in adult feeding and oviposition site selection of an oligophagous grass miner, Chromatomyia nigra (Diptera). This study advances our understanding of the complex interactions between plants and herbivores because it shows that host-preference patterns are not only shaped by the optimization of offspring performance, as previously assumed, but also by the optimization of adult performance.

Plant stress and larval performance of a dipterous gall former.

According to the plant vigour hypothesis, galling insects should respond positively and perform better on vigorous plants or plant parts, the opposite of the predictions of the plant stress hypothesis. I carried out field experiments to analyse the effects of sustained abiotic stress on the interactions between the common reed (Phragmites australis) and a gall-forming fly (Lipara lucens). The reed shoot diameter (a measure of plant vigour) is strongly affected by environmental conditions, where dry and/or nutrient-poor habitats produce thinner (stressed) shoots. L. lucens gall density is negatively correlated with shoot diameter. In a survival experiment with a wide range of shoot diameters, larval mortality was also highly correlated with shoot quality. Gall formation was higher on thinner, stressed shoots. An analysis of the gall tissues revealed that galls induced by L. lucens contain a high amount of a nutrient-rich feeding tissue. The impact of L. lucens is higher on thinner shoots. The results of this study showed that L. lucens performs better on stressed hosts, which contradicts the plant vigour hypothesis for galling insects. The low nutrient availability in the stressed shoots can be compensated by the production of galls with a nutrient-rich feeding tissue.

Long term effects of a 50 Hz electric field on the life-expectancy of mice.

The objective of our study was to determine the effect of an electric field (EF) on the life-span of mice. Male and female mice were paired and separated into two experimental groups: EF exposed and controls. The exposed mice were subjected to a 50 Hz, 10 kV/m electric field for 20 h/day. Offspring from both groups were identified as generation one and allowed to live for 18 months. Offspring from generation one were identified as generation two and allowed to die naturally. The age at which death occurred in both groups was recorded and post mortem examinations were performed. The obtained results were statistically analyzed by means of the chi-squared test. A statistically significant higher incidence of deaths before 18 months occurred in the first generation of the exposed group. The second generation of the exposed group showed a higher incidence of death at an earlier age. No increased incidence of malignant tumors nor any single specific cause of death was disclosed in the exposed animals. The results of this study indicate that continuous long-term exposure to a 10 kV/m electric field may shorten life-expectancy.

[West syndrome: clinical and electroencephalographic follow up of 70 patients and response to its treatment with adrenocorticotropic hormone, prednisone, vigabatrin, nitrazepam and valproate]. / Síndrome de West: evolução clínica e eletrencefalográfica de 70 pacientes e resposta ao tratamento com hormônio adrenocorticotrófico, prednisona, vigabatrina, nitrazepam e ácido valpróico.

In a retrospective study we assessed the outcome of the criptogenic and symptomatic forms of West syndrome and evaluated the efficacy of adrenocorticotropic hormone, vigabatrin, prednisone, valproate and nitrazepam in the spasms control. Seventy patients were follwed up by 2 years. Twelve (17%) were criptogenics and 58 (83%) symptomatics. In criptogenic group significantly more patients were in regular school classes and with normal motor development, better control of seizure, less tendency to evoluate to Lennox Gastaut syndrome and 83. 3% had control of spasms (72.4% of patients from symptomatic group had control of spasms). Adrenocorticotropic hormone and vigabatrin were the most efective drugs, with 68.75% and 60% of spasms control, respectivelly, when used as first line of therapy and 75% and 50%, respectivelly, as second line of therapy.

Reversible switches between male-male and male-female mating behaviour by male damselflies.

For many animal groups, both sexes have been reported to attempt to mate with members of their own sex. Such behaviour challenges theories of sexual selection, which predict optimization of reproductive success. We tested male mate choice between opposite- and same-sex members in the damselfly Ischnura elegans. Binary choice experiments were conducted following exposure periods in insectaries with only males or with both sexes present. We show that switches in choice between the opposite sex and the same sex can be induced and reversed again by changing the social context. We argue that the observed reversibility in male-male- and male-female-directed mating behaviour is maladaptive and a consequence of strong selection on a male's ability to alter choice between different female colour morphs.

Electric field exposure and evidence of stress in mice.

The effect of stress induced by an electric field on the adrenal gland cortex of mice was examined by means of corticosterone serum assay and evaluation of the lipid profile of the different zones of the cortex. Six generations of experimental mice were exposed to a 10 kV/m electric field from conception and corresponding control groups were sham exposed. Mice were sacrificed at 35 days (n = 10), as adults (n = 20) and at 18 months (old mice) (n = 10). Blinded lipid estimates were performed on histological preparations of the adrenals, serum corticosterone levels were determined, and the results were statistically analyzed. The mean lipid volume in the zona glomerulosa of the exposed adult male group was significantly higher than that of the control group (P = 0.004). The median daytime corticosterone level of the exposed male mice was also significantly higher than that in the controls (P = 0.02). The lipid profiles and corticosterone values in the other subgroups did not differ significantly. As chronic stress increases the lipid volume of all the zones of the adrenal cortex and stimulates the zona glomerulosa to corticosterone secretion, the data suggests that the electric field acted as a chronic stressor in the adult male mice.

The influence of long-term exposure of mice to randomly varied power frequency magnetic fields on their nocturnal melatonin secretion patterns.

Disruption of the normal melatonin rhythm has many implications in health and disease. Exposure to magnetic fields is alleged to suppress nocturnal melatonin production, which could implicate magnetic fields in the development of, for example, breast cancer. Magnetic fields of overhead powerlines allegedly pose a risk in the development of childhood leukemia, and the question arises whether changed pineal function could play a role here. In this study two strains of mice were exposed to a rms 50-Hz magnetic field which varied randomly between 0.5 and 77 microT with an average of 2.75 microT and compared to sham-exposed groups. The male mice were exposed for 24 h per day from conception until adult age. Nighttime plasma melatonin values were determined using radioimmunoassay (n=9 for each time point). Statistical comparison was done by nonparametric 95% confidence intervals for median differences to determine nocturnal elevated melatonin values. Although a shortcoming of the study was the small sample size, no statistically significant difference in the nocturnal median elevated melatonin values between exposed and sham-exposed groups could be demonstrated. Long-term and continuous exposure to simulated powerline magnetic fields did not result in a decreased nocturnal melatonin secretion in mice.

Male choice for female colour morphs in Ischnura elegans (Odonata, Coenagrionidae): testing the hypotheses.

The occurrence of different conspecific female colour morphs, with one of the morphs resembling the male, is supposed to have consequences for mate choice. There are two hypotheses linking mate choice and female colour polymorphism. First, males may mate predominantly with female morphs that differ from the male because they do not recognize androchrome females as females (male mimic hypothesis). Second, males may be more attracted to the most common morph in the population (habituation hypothesis). We tested these hypotheses in five populations of the same species, Ischnura elegans, with a range of androchrome frequencies. In each population we performed binary choice experiments in small cages. Males did not consistently prefer gynochrome females but mated predominantly with the most common morph in the population. Moreover, a reanalysis of the available damselfly data in the literature also supported the habituation hypothesis. Copyright 1999 The Association for the Study of Animal Behaviour.