Abstract

The owl-fl y or Ascalaphus ( Libelloides macaronius; Neuroptera ) is an insect with a UV-sensitive superposition eye. Although optical superposition is mainly a feature of dusk/dark active animals, this is a predator living and hunting in bright sunlight. In such conditions the process of light adaptation is believed to be very important, yet it has so far only been partially explored in the owl-fl y. Here we present physiological evidence for the migration of the screening pigment, which functions as a light control mechanism. The process of light adaptation was studied optically by dynamic imaging and optical refl ection spectroscopy of the eye-glow. We established that the eye-glow is reduced uniformly upon illumination and that its diameter doesn’t get smaller, which is indicative of pigment migration in the primary pigment cells. The change in spectral absorbance of the dorso-frontal eye is very similar to the absorbance spectrum of the primary pigment cell screening pigment. We found that the change in the light screening due to adaptation is rather small – no more than 10 fold for a 10000 fold change in light intensity. We also found that the rate of adaptation is light-sensitive. We propose that a signifi cant part of this light sensitivity is due to indirect heating of the eye and to the very steep temperature dependency of the rate of adaptation between 30 and 35°C.

Keywords

Ascalaphus, Libelloides macaronius , owl-fl y, light adaptation, pigment migration, eye glow, light intensity dependence, temperature dependence

Abstract

Firebugs ( Pyrrhocoris apterus) pass through the winter in adult state. They undergo a series of physiological changes in order to increase their capacity to survive at low ambient temperatures. Nevertheless, even during winter their body temperature can rise up to 28 °C for a few hours on a sunny day, which is comparable to summer conditions. To establish the impact of cold acclimatization on the function of mechanoreceptors, the resting activity of T1 type trichobothria warmed up to 20 °C is compared in cold and warm acclimatized animals, as well in animals acclimated to laboratory conditions. In cold acclimatized animals the mean resting activity is 3300 imp/min (SE 90, n=13), in warm acclimatized 3400 imp/min (SE 60, n=15), and in animals acclimated to laboratory conditions 3700 imp/min (SE 130, n=17). The similar trend is observed in the variability of inter-impulse time intervals. The mean coeffi cient of the interval variation is in both cold and warm acclimatized animals 0.28 (cold SE 0.013, n=13; warm SE 0.010, n=15), and in animals acclimated to laboratory conditions 0.33 (SE 0.012, n=17). These data show negligible differences between the three groups. We can conclude that the resting activity of type T1 trichobothrium remains limited to a narrow range, regardless of the phase of the acclimatization process.

Keywords

Pyrrhocoris apterus , mechanoreception, trichobothrium, resting activity, thermal acclimatization.

Abstract

The owlfly Libelloides macaronius (Insecta: Neuroptera: Ascalaphidae) is an airborne predator, hunting for flying insects during the daytime in the summer. Its success relies entirely on the quality of image supplied by the bipartite superposition eyes, sensitive almost exclusively to UV. The speed of visual performance in the owlfly was investigated at temperatures between 10 °C and 45 °C by means of electroretinography and intracellular recordings. The laboratory experiments were supplemented with activity and temperature measurements in the field. All parameters of the electrical response of the eye were dramatically affected by temperature. At body temperatures below 26 °C the owlfly remains landed, and the photoresponse becomes sluggish. Vision speeds up monotonically with the temperature, exhibiting large values of Q ₁₀ (up to 10), and a clear optimum at 40 °C. The flicker fusion frequency reaches a maximum of 230 Hz at 40 °C, and the receptor potential latency attains a minimal value of 4 ms at 38 °C. Compared to the values measured in Calliphora (flicker fusion frequency > 400 Hz, latency < 3 ms), the speed of vision in the owlfly is almost half of what is possible to encounter in an insect eye. The physiological working range of Libelloides eyes is above 30°C, indicating that the animal is optimised to high body temperatures, resulting from the heat-generating muscle work while hunting in a hot habitat.

Keywords

Libelloides macaronius , owl-fly, Ascalaphus , photoreceptor, ERG, flicker fusion frequency, latency, temperature dependence

Abstract

Reliable characterisation of the hazardous properties of effl uents is an important step in water quality management. A “ chemical-specifi c” approach, based on measurements of individual chemicals or chemical groups, has been shown to have limitations particularly in complex mixtures of chemicals such as effl uents. This study shows the importance of direct toxicity assessment of wastewater samples using a toxicity test. Data obtained by direct testing were compared to the toxicity predicted using key toxic compounds data. Toxicity of wastewater samples from tannery and chemical industries as well as key toxic chemicals were assessed using the water fl ea Daphnia magna . The toxicity predicted from the levels and toxicities of wastewater components was found to be unreliable due to under- or over-estimation of the experimentally determined toxicity. For this reason, direct toxicity measurement is more appropriate for the effective and reliable assessment of effl uent quality.

Keywords

toxicity, Daphnia magna , direct toxicity assessment, chemical industry, tannery wastewater, toxic unit

Abstract

Between years 2005 and 2006 was conducted a research based on extended questionnaire about implementation of computer-based laboratory into Science teaching. One of the specifi c goals was to fi nd out preliminary data about status of laboratory exercises in teaching biology. Our interest was in sources of teachers’ manuals, which style of laboratory work prevails, how often teachers include laboratory work in their teaching, the way in which exercises are performed and teacher’s attitudes toward such work. Answers from 70 teachers (about 40% of Slovene secondary school biology teachers) were received. Based on the answers of the questionnaire we can conclude that teachers have generally positive attitudes toward laboratory work, and they include into teaching most of the prescribed laboratory exercises. Not so positive are the fi ndings that a large part of the exercises is

presented to the students as demonstrations, and expository style is preferred. Into the future efforts should be done to transfer expository labs into inquiry and problem-based laboratory work. If the situation stayed unchanged the function of laboratory work will be only in function of presentation and clarifi cation of concepts. The infl uence of such work in the domain of so called higher educational goals would be minimal or nonexistent. If the intention is to improve Biology teaching then the prescribed curriculum should be changed in the way that more time is given to few topics. On the other hand teachers need more in-service trainings in didactics of problem-based teaching.

Keywords

Biology, education, laboratory work, secondary schools, teachers’ attitudes