The pattern of feeding of first instar nymphs of Schistocerca americana

ABSTRACT The feeding behaviour of nymphs Schistocerca americana (Drury) was recorded throughout the light phases of the first stadium using a behavioural event recording program on a microcomputer. Most food was ingested on day 4 of the stadium, very little on day 1 and none on day 6, the final day of the stadium. Only 26–45% of the total food intake over the stadium occurred during the dark periods and more food was eaten in the last 4 h of each light period than earlier. Feeding occupied only about 5% of the total time. Variation in food intake was a consequence primarily of changes in the numbers of meals. After day 1, the average meal size did not change significantly. Meal length increased relatively slightly compared with meal size as a consequence of an increase in the proportion of time spent feeding in each meal as meal size increased. Meal size was correlated with the length of the previous interfeed suggesting a volumetric regulation. The distribution of pauses within meals was also consistent with the thesis that meal size is governed by the level of excitation in the central nervous system at the start of the meal.     

The relationship between diet and the size of the midgut caeca in grasshoppers (Insecta: Orthoptera: Acridoidea)

A survey of the size and form of the midgut caeca in relation to diet has been carried out on 173 species from 21 families and subfamilies of Acridoidea (grasshoppers). Although differences exist in the size of the anterior caecal arms relative to body length, these differences are not related to the type of food eaten. Assuming that the anterior arms have a key role in digestive and absorptive processes, this suggests that different foods make similar demands on these processes. The posterior caecal arms are smaller in graminivorous species than in species eating other types of plants as a whole or part of their diet. This is true across all the taxa, including those families and subfamilies that are predominantly forb-feeding. It is suggested that the posterior caecal arms have a special role in the detoxification of plant secondary compounds and that the requirement for this is reduced in graminivorous species because of the lower levels of toxic secondary compounds in grasses. A specialized pocket region is present in the posterior caecal arms of some forb-feeding species. Its occurrence across the taxa is spasmodic. It may be concerned with the removal of phenolic compounds.     

Tarsal chemoreception in the polyphagous grasshopper Schistocerca americana: behavioural assays, sensilla distributions and electrophysiology

ABSTRACT Behavioural and electrophysiological responses of Schistocerca americana (Drury) (Orthoptera: Acrididae) to chemical stimulation of the tarsi were investigated. Using restrained insects, differences in leg-waving behaviour were observed following stimulation by sucrose and nicotine hydrogen tartrate (NHT), compared to control stimulations by water. Furthermore, free-walking insects were able to detect NHT on leaf surfaces, resulting in leg-raising to avoid tarsal contact.
SEM studies showed the presence of numerous peg chemoreceptor sensilla on the ventral surface of the tarsus. Tip recordings from such pegs showed activity from up to three chemosensitive neurones, plus a mechanoreceptor neurone. Stimulation by NaCl and KC1 elicited similar responses from two or three neurones in all sensilla tested, with increased firing rates at higher concentrations. Sucrose caused an increase in firing rate in few sensilla. In such cases several neurones were stimulated, and there was no evidence of a specific neurone sensitive to sucrose. In contrast, NHT elicited rapid firing in a single neurone, which was not sensitive to NaCl. Stimulation by NHT also inhibited the activity of the NaCl-sensitive neurones.
Possible mechanisms for chemical discrimination in S. americana tarsi are compared with those previously proposed for grasshopper mouthpart sensilla, and the significance of a NHT-sensitive neurone in tarsal sensilla is discussed.     

Effects of two Triethylamines on the Carotenoids of Strelitzia reginae and of Hemerocallis flava

A method for the successful uptake of two triethylamines, 2-(4-chlorophenylthio)-triethylaminehydrochloride (CPTA) and 2-(4-ethylphenyloxo)-triethylamine(EPOT), by flowers of Hemerocallis flava (yellow day-lily) andby sepals of Strelitzia reginae is described. CPTA is more effectivethan EPOT in causing lycopene accumulation which appears tobe through a different mechanism in the two plants studied.Whereas inhibition of cyclase(s) may account for lycopene accumulationin H. flava, this is not so in S. reginae. The permeabilityof the cell wall to the triethylamines may be one of the reasonsfor the differences observed. Strelitzia reginae, Hemerocallis flava, day-lily, triethylamine, lycopene, carotenoids     

The British Society For Clinical Cytology Certificate of Competence In Cytology Screening: A Report of the First 3 Years'' Experience

In 1988 the Department of Health (DOH) recognized the cytology screener grade of laboratory staff. Cytology screeners have a 2 year training period after which they must sit a 'competence examination'. The British Society for Clinical Cytology offers an examination to meet the DOH specification. It consists of a written paper, a practical screening test, a spot test and a short viva voce. The screening test is paramount and candidates who miss a dyskaryotic smear cannot be successful. In the first 3 years there have been 22 examinations, 294 candidates and a pass rate of 76%. The majority of candidates were Cytology Screeners of 2-3 years experience but significant numbers of Medical Laboratory Scientific Officers (MLSOs) and senior MLSOs also chose to sit the examination.     

Individuality and modular organisms

The semantics of the problem of individuality are examined and the difficulty of reconciling individuality with levels of organization is emphasized. Clear distinctions between various types of phenotypic, morphological expression are difficult to make and the attempt is of decreasing explanatory value. It can be avoided, in part at least, by the use of the term modular to denote repeated, physiologically connected sub-units.     

The Control of Lipid Mobilization in Cucumis Cotyledons

An investigation has been carried out into the role of the axisand testa in the control of lipid mobilization during the germinationof cucumber seedlings. A very close correlation is observedbetween axis growth and lipid depletion. It is suggested thatthis depends upon the rate at which the axis can remove themajor product, sucrose, and not upon a hormonal mode of controlas has been previously suggested. Excised testaleas cotyledons show considerable lipid breakdownand can develop maximum levels of isocitrate lyase and ß-oxidationenzymes even though the axis is not present. The presence ofthe testa inhibits their development however. A novel indirectcontrol mechanism involving the automatic removal of the testa(a phenomenon common amongst most members of the Cucurbitaceae)is suggested.