No description available.

No description available.

No description available.

Some aspects of the ability of locusts and grasshoppers (Acrididae) to compensate for nutritional shortfalls were studied, with a special emphasis on the factors which constrain this ability. Chapter 1 investigates the effects over the short-term (12 h) of the plant-produced allelochemical tannic acid on the ability of Locusta migratoria (L.) and Schistocerca gregaria (Forskal) to compensate for dilution of dietary proteins and carbohydrates by increasing consumption. Tannic acid had no effect on compensatory feeding by L. migratoria, and stimulated feeding by S. gregaria. Chapter 2 extends this study over the longer-term (fifth instar) for L. migratoria. Over this period, tannic acid restricted intake and reduced growth of those insects fed lowprotein diets, indicating an inhibitory effect on compensatory feeding for protein. In addition, the levels of dietary proteins influenced regulation for carbohydrate intake and, to a lesser extent, vice-versa. A detailed discussion is presented of the ways that some dietary components can influence the intake of others, and how failure to take this into account can lead to poor experimental design and interpretation. Chapter 3 investigates some mechanisms involved in dietary selection by the grasshopper Schistocerca americana (Drury). It was found that S. americana conditioned on distinctly flavoured protein-inadequate diets then tested on nutritionally similar diets with the familiar or a novel flavour, tend to eat more of the novel-flavoured diets. This suggests that conditioned neophilia, possibly in conjunction with aversion learning, may be a factor facilitating dietary selection in acridids. Chapter 4 investigates the patterns of feeding and dietary selection behaviour of the polyphagous grasshopper Taeniopoda eques (Burmeister) in its natural desert habitat. Despite the overwhelming thermoregulatory requirements and unpredictable variability inherent in ecological complexity, these insects nonetheless maintained a pattern of feeding comparable to that observed under controlled laboratory conditions. The patterns of dietary selection behaviour were concordant with some of the mechanisms observed to operate in the laboratory. Chapter 5 addresses an important inadequacy in the methodology currently used to investigate some aspects of nutritional compensation. A computer-generated data set is used to illustrate how the analysis of the currently popular ratio-based nutritional indices may be flawed, and how this may be overcome using as an alternative the analysis of covariance.

xii, 197 leaves : ill. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1972) from the Dept. of Entomology, University of Adelaide

Thesis (Ph.D. 1972) from the Dept. of Entomology, University of Adelaide.

The investigation reported here is concerned with the study of certain visual responses in the Desert Locust Schistocerca gregaria. (Forsis). It is a behaviour study. The aim is to form some idea of the kind of information which the Insect is obtaining by means of compound eyes and the way in which this is manipulated. II Form perception. a. In spontaneous choice experiments it is shown that nymphs of the Desert Locust are attracted to black objects on a white background and to the contour lines of these objects. The degree of contrast between the object and the background is important. On a white background the darker the object the more attractive it is. III. Peering. a. It is shown that the swaying of the front part of the body and the head from side to side, called peering, is a visual response. An apparatus is described for measuring the angle through which the head moves laterally with respect to the original position of the longitudinal axis of the body. IV. Antenna waving. a. Two main types of antenna movement are distinguished - flicking and beating. The former is a movement of one antenna usually occurring as the insect passes an object. The latter is the alternate movement of both antennae as the insect is approaching head-on and close to an object. b. Flicking: The antenna to be flicked is the one on the same side as the object and the response occurs when the edge of the object is seen by the more lateral part of the eye. In conjunction with the flicking, the antenna in question is often pointed at the object edge. c. Beating: This takes place at a short distance from an object (less than one inch), the distance being independent of the angle sub-tended by the object. V. Responses to movement. a. Fright response to the movement of a large object across the visual field. The response varies in intensity. At low intensity the insect tenses; at higher intensity the insect jerks; at the highest intensity observed the insect moves (backs or moves sideways) away from the object. The response decreases with increased distance. b. Optomotor response; The insects show an optomotor response to moving stripes. They follow the movement of the stripes. The stimulus is effective even when it only occupies a small part of the visual field and the insects respond to stripes moving from front to rear of the eye and from rear to front. Moving stripes stimulating the anterior part of the eye appear to have less effect in releasing the optomotor response than when stimulating the lateral parts of the eye. The insects walk toward a steady movement of stripes in front of them. If the stripe movement is intermittent the insects show the fright response. VI. Discussion. The results of all the experiments are discussed and a system proposed whereby the insect responds to the stimulation of the visual receptors produced by the movement of the images of contours over the retina. The properties of the system are discussed well as the behaviour which would be expected as the results of these. A comparison is then made with the behaviour observed in the present investigation. One possible way in which such a system could be elaborated is briefly considered. VII. Conclusion. The conclusion is reached that, although the work has dealt with only few of the visual responses of these insects, sufficient information has been obtained to show that the insects possess a highly developed visual sense, that their compound eyes are quite efficient navigating instruments and that visual responses play a large part in the total behaviour repertoire, The analyses of the stimuli involved in each response studied gives some insight into the nature of this insect's visual environment.

1. A technique has been developed to isolate the first basalar (BA1) motoneurone of the locust (Schistocerca gregaria) from its ganglionic environment. The isolated neurone soma remained viable (often for up to 9hrs), enabling its electrophysiological and pharmacological properties to be investigated. The findings of these studies were comparable with those from the BA1 motoneurone in situ, and with other insect neurones whether studied in vitro or in situ. 2. The application of selected agonists to the isolated BA1 motoneurone soma demonstrated the presence of nicotinic and muscarinic acetylcholine receptors, GABA receptors and dopamine (DA) receptors. The membrane depolarization evoked by nicotine was blocked by BTX, while the GABA- induced membrane hyperpolarization response was sensitive to picrotoxin. Muscarinic receptor and DA receptor activation both induced membrane depolarization which was evoked without a detectable change in membrane conductance. The ionic dependency of these agonist-induced responses is discussed. 3. When applied between pressure applications of GABA, DA could induce either membrane depolarization or hyperpolarization, both of which were associated with an increase in membrane conductance. Furthermore, the amplitude and/or duration of the GABA response was potentiated by DA. Possible mechanisms underlying these observations are proposed. 4. Using the Ca2+-sensitive fluorescence probe, fluo-3, and confocal laser scarming microscopy, the effects of the muscarinic agonist, McN A-343, and DA on [Ca2+]i in the isolated BA1 motoneurone were examined. McN evoked an increase in [Ca2+]i, whilst DA evoked a decrease in [Ca2+]i. Similar observations were made from isolated cockroach fast coxal depressor (Df) motoneurones. The cellular events underlying these observations are discussed. 5. A technique was established to maintain dissociated unidentified adult locust neurones in culture for up to two weeks; a similar protocol was used to maintain isolated BA1 motoneurones in culture. Electrophysiological recording techniques demonstrated that the neurones remained viable in culture.

1. Head movement in the locust Schistocerca gregaria is mediated by 14 pairs of muscles. The normal motor output to, and the innervation pattern and muscle fibre spectrum of many of these muscles have been examined by a variety of histological and experimental techniques. 2. The anatomy, histology and the fine structure of the neck muscalature and innervation have been examined by both light and electron microscopy. The axons to some muscles have been traced by serial sections from the ganglion of origin to the muscle concerned, and axon counts of each motor nerve have been made. 3. The inervation pattern of many muscles has been investigated by recording with two intracellular microelectrodes from different fibres of the same or different muscles during graded stimulation of the motor nerve or nerves. 4. Both the normal motor output to, and the innervation pattern and muscle fibre spectrum of, many muscles have been investigated in the intact insect by recording with two intracellular microelectrodes from different fibres of a muscle during optokinetic nystagmus elicited by rotation of a striped drum in the visual field. Each electrode is inserted through a small hole in the exoskeleton into a fibre of the muscle close to its fixed insertions on the prothorax. 5. The sensory innervation of the neck and prothoras has been examined, and some of the sense organs are described. A chordotonal organ is attached to each lateral longitudinal muscle of the neck, and the system is so arranged as to be ideally situated for monitoring lateral head movement. The sense organ is shown to serve such a proprioceptive function. Chordotonal organs attached to muscles have not been previously described in insects. 6. A number of structural differences are found between muscle fibres, and each muscle contains a variety of muscle fibre types classified on the basis of electrical responsiveness to innervation. In one muscle, a definite correlation is shown between the structural and physiological differences between different muscle fibres. In this muscle, the larger fibres are of phasic type and have shorter sarcomeres and smaller fibres are of tonic type and have longer sarcomeres. In general, however, the structural differences between fibres in different muscles are greater than the differences between fibres in the same muscle.

The in vitro, short-circuited locust rectum actively transports chloride. This electrogenic transport is energized by aerobic metabolism, based primarily upon proline oxidation. Isolated rectal mito-chondrialoxidize a variety of substrates, but the highest state 3 rate of 0₂ consumption occurs when proline is the stubstrate. An enzyme profile of the rectal tissue indicates that the rectum can oxidize amino acids and carbohydrates but has a limited capacity for lipid oxidation. Analysis of the two fluids which bathe the rectum in vivo, the hemolymph and the Malpighian tubule fluid, reveals that proline is present in bothethe hemolymph (12-15 mM) and tubule fluid (38-43 mM). Although glycine is also found in high concentration in the hemolymph (13-17 mM), far lower concentrations of this and other amino acids are found in the Malpighian tubule fluid. Glucose is also found in the hemolymph (2 mM) and Malpighian tubule fluid (4 mM). The high concentraion of proline in the tubule fluid indicated that this amino acid may be actively transported by tubules. This prediction was confirmed by experiments with in vitro tubules. This is the first evidence of aetive secretion of a metabolically useful compound by insect Malpighian tubules. Experiments involving the measurement of short-circuit current (Isc) across the locust rectum were also performed. The results of these experiments indicate that high levels (50 mM) of proline stimulate the Isc of substrate-depleted recta better than high levels of any other substrate tested. Physiological levels of proline also cause a large increase in the Isc of substrate-depleted recta, while physiological levels of glucose produce a much smaller stimulation. Over 90% of the Isc stimulation can be produced by adding proline (15 mM) solely to the lumen side of the tissue. Other studies were performed to estimate the metabolic cost of actively transporting chloride. The oxygen consumption of chloride-depleted recta were measured before and after reintroduction of chloride. From these data a Cl⁻/ATP ratio of 3-4 was obtained. Further calculations indicated that tissue proline oxidation is sufficient to energize active chloride transport. The results outlined here suggest that in vivo, the rectal lumen is bathed with a high concentration of proline which can be readily oxidized by the rectal mitochondria to support the work of actively transporting chloride. / Science, Faculty of / Zoology, Department of / Graduate