Hormonal control of phase-related changes in the number of antennal sensilla in the desert locust, Schistocerca gregaria: possible involvement of [His7]-corazonin

The effect of [His(7)]-corazonin on the abundance of antennal sensilla in the desert locust, Schistocerca gregaria, was investigated to test the hypothesis that injection of this neuropeptide would mimic a crowding effect. Solitarious locusts (reared in isolation) were injected with [His(7)]-corazonin at the 3rd nymphal instar and the numbers of sensilla on the 2nd, 8th and 14th antennal segments in the adult stage were compared with those for oil-injected solitarious controls or un-injected gregarious locusts (reared in group). The numbers of sensilla on these antennal segments were all reduced significantly after [His(7)]-corazonin injection compared with those for oil-injected controls, but similar to the values for gregarious individuals. Among the four major types of olfactory sensilla, coeloconic, trichoid, basiconic type A and basiconic type B, [His(7)]-corazonin injection influenced the abundance of all but the last type. The effect of [His(7)]-corazonin injection varied with the time of injection; the earlier the injection the larger the effects on the abundance of total antennal sensilla on the 8th segment, although the way in which the injection affected the abundance varied with the sensillum type. A hypothesis explaining how crowding affects the abundance of antennal sensilla and other phase-related characteristics through changes in [His(7)]-corazonin concentrations was proposed.     

Effects of [His(7)]-corazonin on the phase state of isolated-reared (solitarious) desert locusts,Schistocerca gregaria

[His⁷]-corazonin is a neuropeptide produced in the pars lateralis of the brain. It is stored in the corpora cardiaca and probably released from there. The only well-documented effect in locusts is increased melanization of the cuticle. We investigated whether this hormone might also be causally related to changes in behavior and morphometrics that, like melanization, occur during crowding-induced gregarization. Solitary fourth-instar nymphs of Schistocerca gregaria (Forsk.) were injected thrice with 1 nmol [His⁷]-corazonin. After molting to the 5th stadium their behavioral phase state was measured in an arena assay and analyzed using multiple logistic regression analysis. The hormone was found not to induce behavioral phase changes. Upon reaching adulthood, morphometrics shifts occurred towards values typical for crowd-reared and regregarized animals. Our results thus indicate that [His⁷]-corazonin is not involved in behavioral gregarization but may participate in morphometrical phase change.     

Hatching rhythms in the desert locust, Schistocerca gregaria

ABSTRACT. The eggs of Schistocerca gregaria (Orthoptera, Acrididae) incubated under natural conditions hatch only within a few of hours on either side of dawn. This gated hatching is controlled by a circadian clock that is phase set by the diel fluctuations in the temperature of the soil surrounding the eggs. There is a circadian fluctuation in haemolymph sugar concentration which is initiated at least 4 days before hatching. However, eggs hatch arrhythmically unless given cycled temperature incubation for at least 10 days of a 12–13-day incubation. Increase in acetylcholine esterase content of the brain during the penultimate day suggests that increased hatching rhythmicity occurring at this time is the result of increased neural organization. Embryonic activity and respiration show no circadian rhythm but do provide confirmatory evidence of a quiescent phase prior to hatching. This quiescent phase is an integral part of gated hatching behaviour.     

The body temperature of the desert locust Schistocerca gregaria

Summary The internal equilibrium body temperatures of hoppers (nymphs) of Schistocerca gregaria were studied in the field. The data obtained are here compared with theoretical estimates of the thermal balance resulting from the factors assumed to be concerned in heat loss and heat gain.In the field, the equilibrium body temperature of quiescent hoppers shaded from direct sunshine was up to 3.2° higher than the air temperature when the latter was about 25° or less, but was lower than the air temperature when this was above about 31°. In sunlight, body-temperature excesses increased linearly with total radiation intensity between 0.15 and 1.25 cal/cm²/min. Differences in orientation to the sun gave rise to differences in equilibrium body temperature of as much as 6°. At relatively low radiation intensities (about 0.5 cal/cm²/min) the equilibrium body temperatures were found to vary with a power of the wind speed of about 0.35. There were no demonstrable significant differences in equilibrium body temperature or rate of change of body temperature between hoppers having opposite extremes of possible coloration.Except in hoppers shaded from sunlight and those exposed to low radiation intensities there was good agreement between the observed equilibrium temperatures and those expected on theoretical grounds. This provides evidence of the relative importance of the factors concerned in thermal balance.The relation between body temperature and behaviour is discussed.

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Zusammenfassung Das innere Gleichgewicht der Körpertemperatur von vorzugsweise fünften Larvenstadien der Wüstenheuschrecke wurde unter Freilandbedingungen in Beziehung zu Lufttemperatur, relativer Luftfeuchtigkeit, Strahlungsintensität, Windgeschwindigkeit und Aktivität gemessen.Die verschiedenen Faktoren, die das Temperaturgleichgewicht der Heuschrecken beeinflussen, werden theoretisch behandelt. Die unter bestimmten Kombinationen der Umweltbedingungen zu erwartenden Gleichgewichts-Körpertemperaturen werden aus den theoretischen Werten für die verschiedenen beteiligten Faktoren errechnet und mit den unter entsprechenden Freilandbedingungen beobachteten Werten verglichen.Ohne Sonneneinstrahlung und unter relativ windstillen Bedingungen wurde bei ruhenden Larven des fünften Stadiums eine Gleichgewichts-Temperatur des Körpers gefunden, die bis zu 3,2° höher lag als die Lufttemperatur, wenn diese ca. 25° oder weniger betrug. Dieser Überschuß hatte eine abnehmende Tendenz bei Lufttemperaturen bis zu etwa 31° und über dieser Schwelle waren die Gleichgewichts-Temperaturen des Körpers im allgemeinen niedriger als die entsprechenden Lufttemperaturen. Theoretisch würde zu erwarten sein, daß unter diesen Umweltbedingungen das Temperaturgleichgewicht des Körpers in allen Niveaus annähernd der Lufttemperatur entspräche. Folglich scheint hier ein physiologischer Mechanismus zu bestehen, mit dessen Hilfe die Insekten in Abwesenheit von Sonnenschein und unter den Bedingungen schwacher Konvektion ihre Körperausgleichstemperaturen bei niedrigen Lufttemperaturen erhöhen, bei hohen senken können.Es war nicht möglich, im Freiland nachzuweisen, daß Unterschiede in der relativen Luftfeuchtigkeit irgendeinen signifikanten Einfluß auf die ausgeglichenen Körpertemperaturen in dem untersuchten Bereich (Sättigungsdefizit von 2 bis 27 mm) ausübten. Die erwarteten maximalen Differenzen der Gleichgewichts-Körpertemperaturen lagen in diesem Bereich des Sättigungsdefizits in einer Größenordnung von nur 0,5°.Unter relativ ruhigen Freilandbedingungen zeigten die Heuschrecken im Sonnenschein Körpertemperaturüberschüsse, die bei einer totalen Strahlungsintensität zwischen 0,15 und 1,25 cal/cm²/min annähernd linear anstiegen (von einem Mittel von 2–10° bei fünften Larvenstadien). Die in diesem Strahlungsintensitätsbereich gemessenen Übertemperaturen des Körpers stimmten einigermaßen gut mit Werten überein, die von anderen Untersuchern unter Laboratoriumsverhältnissen festgestellt wurden. Unter 0,40 cal/cm²/min waren die beobachteten Körpertemperaturüberschüsse im allgemeinen höher als theoretisch zu erwarten gewesen wäre. Die Körpertemperatur von Larven des ersten Stadiums nahm rascher zu als die von Larven des fünften, jedoch nur bis zu einem niedrigeren Niveau; auch das stimmte gut mit den theoretischen Vorstellungen und mit der Laborerfahrung überein. Die Einstellreaktion der Heuschrecken zur Sonne ergab beobachtete Unterschiede in der Gleichgewichts-Körpertemperatur bis zu 6° zwischen Larven des fünften Stadiums, die sich in Richtung der Sonnenstrahlen eingestellt hatten, und solchen, die im rechten Winkel zur Sonnenrichtung auf dem Boden standen; die erwarteten Unterschiede waren von der gleichen Größenordnung.Im Sonnenschein variierten die erwarteten Intensitätsproportionen zwischen der Ausgleichstemperatur und der Windgeschwindigkeit zwischen 0,5 und 0,6 mit dem Sättigungsdefizit. Bei Strahlungsintensitäten von etwa 1,10 cal/cm²/min stimmten die beobachteten Körpergleichgewichtstemperaturen engstens mit den erwarteten überein, aber bei geringeren Strahlungsintensitäten von etwa 0,50 cal/cm²/min variierten die Meßwerte mit einer Intensitätsproportion zur Windgeschwindigkeit von etwa 0,35. Darin zeigt sich möglicherweise, daß bei niederen Strahlungswerten die Körperausgleichstemperaturen zu höheren Werten tendieren als zu erwarten war.Das beobachtete Ansteigen der Körperausgleichstemperatur von ungefähr 1° bei dritten Larvenstadien und von 2–3° bei fünften Larvenstadien befindet sich in Übereinstimmung mit dem für entsprechende Umweltbedingungen errechneten.Zwischen Larven extrem entgegengesetzter Färbungstypen konnten keine Unterschiede in den Körperausgleichstemperaturen oder dem Ausmaß der Körpertemperaturänderung nachgewiesen werden.Mit Ausnahme der vor direkter Sonnenbestrahlung geschützten Heuschrecken unter relativ ruhigen Bedingungen und der Heuschrecken, die niederen Strahlungsintensitäten ausgesetzt waren, bestand eine gute allgemeine Übereinstimmung zwischen den beobachteten und den erwarteten Gleichgewichts-Körpertemperaturen. Es wurde deshalb geschlossen, daß die durchgeführten Bestimmungen Beweise für die relative Bedeutung der für den Temperaturhaushalt verantwortlichen Faktoren darstellen. Zur Erzeugung beträchtlicher Überschüsse der Körpertemperatur über die Lufttemperatur hat die Strahlung die größte Bedeutung. Für den Wärmeabfluß nach außen werden die durch Konvektion entstehenden Wärmeverluste, die insgesamt 94% oder mehr betragen, als bei weitem am wichtigsten angesehen.Einige mögliche Beziehungen zwischen Körpertemperatur und Verhalten werden besprochen.

     

SERINE proteinase like activity in apolipophorin III from the hemolymph of desert locust, Schistocerca gregaria

Apolipophorin III (apoLp-III) has been known as a lipid transport protein of insects. Recent studies indicated the involvement of apoLp-III in immune reactions and in the control of cell destruction, but no enzymatic activity has so far been detected. In the present study, a protease from the hemolymph of Schistocerca gregaria was purified to homogeneity and its enzymatic activity was examined. Identity as chymotrypsin-like proteinase was established by its high affinity toward bulky aromatic substrates and its catalytic specificity for amide or ester bonds on the synthetic substrates, Suc-Ala-Ala-Pro-Xaa-AMC (where Xaa was Phe, Tyr, Trp, and Lys, and AMC is 7-amino-4-methyl-coumarin) and thiolbenzyl ester substrate Suc-Ala-Ala-Pro-Phe-SBzl. The sensitivity for serine protease and chymotrypsin-specific covalent inhibitors, PMSF, TPCK, and noncovalent inhibitors SGCI, showed that it is a chymotrypsin-like proteinase. It showed its maximum activity at pH 8.0 and 55°C for the hydrolysis of Suc-Ala-Ala-Pro-Tyr-AMC. According to similarities in the amino terminal sequence, molar mass (19 kDa) and retention on reversed-phase analytical high-performance liquid chromatography (HPLC) column, this protein is S. gregaria homologue of Locusta migratoria apoLp-III. Our data suggest that apoLp-III also has an inherent proteolytic activity. Results indicated that S. gregaria apoLp-III is a good catalyst and could be used as a biotechnological tool in food processing and in agricultural biotechnology.     

Innate phase behavior in the desert locust,Schistocerca gregaria

Abstract Detailed aspects of the transition from the solitarious to the gregarious phase in the framework of locust ecology are undoubtedly most important for understanding locust phase polyphenism. Nevertheless, due to obvious difficulties in studying the solitarious phase in nature, such information is limited and mostly available from research carried out under laboratory conditions. In the current study, we examined the dispersal patterns of newly hatched locust nymphs in a laboratory setup that simulated seminatural conditions. This was carried out with no previous manipulation of the nymphs other than controlling their parental density. We comparatively tested the spatial distribution of newly hatched nymphs on perches located at different ranges within an emergence arena, and the expected Poisson (random) distribution. Hatchlings were found to disperse among the perches in a pattern significantly different from that expected by random. Irrespective of their parents’ phase, the observed distributions of all nymphs were clearly clumped, similar or close to those expected for gregarious locusts. It seems that rather than emerging with a parentally derived and predetermined phase, hatchlings have an independent default or innate behavioral state, which reflects at least tolerance if not attraction to conspecifics. The typical phase behavior may later become dominant under the appropriate environmental conditions. These results imply novel perspectives on locust phase transformation, which contribute to our understanding of the formation of locust crowds under field conditions. These should be considered in any rationale for developing a preventative management strategy of locust populations.     

The dynamics of yolk deposition in the desert locust Schistocerca gregaria

Injection of the protein dye Fast Green or the fluid-phase probe fluorescein dextran into the haemolymph of vitellogenic female desert locusts (Schistocerca gregaria) resulted in their incorporation into oocytes. We used Fast Green to study the physical dynamics of yolk deposition during vitellogenesis. Timed maternal injections of Fast Green reveal that yolk deposition and oocyte growth are inextricably linked during vitellogenesis, and that little or no yolk movement occurs within oocytes prior to embryogenesis. The yolk granules laid down early during vitellogenesis lie at the centre of the egg, with yolk granules deposited later packed around these, such that they lie progressively closer to the eventual egg surface. In contrast, during early embryogenesis yolk granules migrate in a manner that closely resembles the movement of early cleavage nuclei. We find fluorescein dextran to be a clear, robust and developmentally inert marker for the timing of maternal injections relative to vitellogenesis in S. gregaria, and we propose its use in parental RNAi or morpholino knockdown experiments. With such experiments in mind, we show that fluorescein-labelled DNA oligonucleotides are internalized within oocytes during vitellogenesis. However, neither Fast Green, fluorescein dextran nor fluorescein-labelled DNA oligonucleotides are detectably transferred from yolk granules to embryonic cells during embryogenesis, and our initial attempts at parental RNAi using maternal injections of dsRNA targeted to late vitellogenesis have proved unsuccessful.     

Sulfakinins reduce food intake in the desert locust, Schistocerca gregaria

In vertebrates, the peptides cholecystokinin (CCK), neuropeptide Y, galanin, and bombesin are known to be involved in the control of food intake. We report here that insect sulfakinins, peptides which display substantial sequence similarities with the vertebrate gastrin/CCK peptide family, significantly inhibit food uptake in fifth instar nymphs of the locust, Schistocerca gregaria. Upon injection of Lom-sulfakinin, a neuropeptide present in the corpus cardiacum of locusts, food intake was significantly reduced in a dose-dependent manner within a fixed 20 min time period. The induced effect ranged from 13% inhibition (10 pmol of injected peptide) to over 50% inhibition at 1 nmol. Other naturally occurring sulfakinins from different insect species also elicited this satiety effect. Analogous to the satiety effect of CCK in vertebrates, the sulfate group is required for activity. No effect on the palptip resistance was found after injection with sulfakinin. Therefore it seems unlikly that sulfakinins reduce food intake by decreasing the sensitivity of the taste receptors.     

Ecdysone 20-mono-oxygenase in the desert locust, Schistocerca gregaria.

The enzyme catalysing the hydroxylation of ecdysone to 20-hydroxyecdysone, ecdysone 20-mono-oxygenase (EC 1.14.99.22), was investigated in the Malpighian tubules of fifth-instar locusts, Schistocerca gregaria. Enzyme activity was optimal at 35 degrees C and pH 6.8-8.0. Under these conditions the mono-oxygenase exhibited an apparent Km for ecdysone of 7.1 X 10(-7) M, a maximal specific activity of 1.1 nmol/h per mg of protein and was competitively inhibited by 20-hydroxyecdysone with an apparent Ki of 6.3 X 10(-7) M. Enzyme activity was decreased in the presence of Ca2+, Mg2+, EDTA and non-ionic detergents. The Malpighian tubule ecdysone 20-mono-oxygenase was localized primarily in the subcellular fraction sedimenting at 7500 g and, on the basis of marker enzyme profiles, was assigned mainly to the mitochondria. NADPH was required for activity, although addition of NADH together with NADPH had a synergistic effect. NADP+-dependent isocitrate dehydrogenase (EC 1.1.1.42) and an energy-dependent NAD(P) transhydrogenase (EC 1.6.1.1.) appeared to be the major sources of reducing equivalents, with the contribution from the 'malic enzyme' (EC 1.1.1.40) being less important. The monooxygenase was characterized as a cytochrome P-450-containing mixed-function oxidase from the inhibition patterns with metyrapone, CO and cyanide; CO inhibition was reversible with monochromatic light at 450 nm. However, the ecdysone 20-mono-oxygenase shows much lower sensitivity to CO inhibition and to photodissociation of the CO-inhibited complex than do vertebrate cytochrome P-450-dependent hydroxylation systems. The concentration of cytochrome P-450 in the Malpighian tubule mitochondria was 30 pmol/mg of protein. The properties of the mono-oxygenase are discussed in relation to hydroxylation enzymes from other sources.     

Frequency-dependent selection in the grazing behaviour of the desert locust Schistocerca gregaria

ABSTRACT.

• 1 The locust displayed clear preferences in the ranking of five possible food plants: wheat > barley =Cypeius alternifolia > chives > lemon grass.
• 2 In two-species stands of constant numerical density, the locust grazed selectively on the less-favoured plant when it was relatively less abundant.
• 3 The behavioural mechanism of selective grazing was a change in the readiness to eat a plant as its relative frequency changed: i.e. the consumption/encounter ratio rose as relative density fell.
• 4 With the exception of Cyperus, which nutritionally is below chives, the preference ranking matched nutritional ranking as estimated by rearing-success on single plant species.
• 5 It is suggested that such negative frequency-dependent selection may be a common strategy for polyphagous herbivores as it permits a wide dietary intake without hazards from potentially toxic foods.

     

The optomotor yaw response of the desert locust, Schistocerca gregaria

Abstract The optomotor yaw response of the desert locust, Schistocerca gregaria (Forsk.), was investigated under open- and closed-loop conditions. When flying tethered in the centre of a vertically striped hollow sphere, the polarity of response of the locust was always the same as the stimulus. The response, therefore, appears suitable to stabilize body posture against passive rotations around the yaw-axis in free flight. Responses were induced by contrast frequencies up to 150 Hz with a maximum of amplitude at about 20 Hz. The characteristic curve, measured between 0.3 and 160 Hz, is widened up towards higher frequencies as compared with those of bees and flies.
Variability was the most striking feature in the locust's yaw response. The amplitude of modulation not only varied greatly between individuals but also changed with the same visual stimulus in the course of an experiment. We therefore suppose that the locust's turning behaviour is subject to gain control mechanisms and that spontaneous gain modulations are responsible for the observed variability in the stimulus-response conversion.     

The imaginal ecdysis of the desert locust, Schistocerca gregaria.

ABSTRACT. The imaginal ecdysis of the desert locust, Schistocerca gregaria (Frsk.), is described in detail. Ecdysis is considered to begin when the fifth instar nymph ceases to feed and to end when the adult takes its first meal. It is here divided into six stages: Stages 1 and 2 constitute the pre-emergence behaviour; Stages 3 and 4, emergence; Stage 5, the expansion of the new cuticle; and Stage 6, the post-expansional behaviour.     

The imaginal ecdysis of the desert locust, Schistocerca gregaria.

ABSTRACT. The newly-emerged adult locust stretches its soft new cuticle into its adult shape and size, and at the same time caters for its ventilatory demands, by means of a pattern of behaviour, the 'expansional motor programme'. This programme begins after emergence and persists until about an hour after wing-folding, during which time its period changes in a predictable manner. In the post-expansional period, abdominal dorsoventral movements occur that may serve to deflate the gut and to fill the air-sacs, and the mandibles are periodically ad ducted.     

Studies on the mid-gut of the desert locust, Schistocerca gregaria.

ABSTRACT. The gross morphology of the mid-gut musculature of the desert locust, Schistocerca gregaria is described. Some of the electrophysiological characteristics of the external longitudinal muscle fibres were examined. The membrane potentials have mean values of -24.7mV (SE ± 7.3). Spontaneous post-synaptic potentials were recorded, and the responses of the muscle fibres to electrical stimulation of their nerve supply studied.     

Standardized atlas of the brain of the desert locust, Schistocerca gregaria

In order to understand the connectivity of neuronal networks, their constituent neurons should ideally be studied in a common framework. Since morphological data from physiologically characterized and stained neurons usually arise from different individual brains, this can only be performed in a virtual standardized brain that compensates for interindividual variability. The desert locust, Schistocerca gregaria, is an insect species used widely for the analysis of olfactory and visual signal processing, endocrine functions, and neural networks controlling motor output. To provide a common multi-user platform for neural circuit analysis in the brain of this species, we have generated a standardized three-dimensional brain of this locust. Serial confocal images from whole-mount locust brains were used to reconstruct 34 neuropil areas in ten brains. For standardization, we compared two different methods: an iterative shape-averaging (ISA) procedure by using affine transformations followed by iterative nonrigid registrations, and the Virtual Insect Brain (VIB) protocol by using global and local rigid transformations followed by local nonrigid transformations. Both methods generated a standard brain, but for different applications. Whereas the VIB technique was designed to visualize anatomical variability between the input brains, the purpose of the ISA method was the opposite, i.e., to remove this variability. A novel individually labeled neuron, connecting the lobula to the midbrain and deutocerebrum, has been registered into the ISA atlas and demonstrates its usefulness and accuracy for future analysis of neural networks. The locust standard brain is accessible at http://www.3d-insectbrain.com .     

Solution structure of a chemosensory protein from the desert locust Schistocerca gregaria

Chemical stimuli, generally constituted by small volatile organic molecules, are extremely important for the survival of different insect species. In the course of evolution, insects have developed very sophisticated biochemical systems for the binding and the delivery of specific semiochemicals to their cognate membrane-bound receptors. Chemosensory proteins (CSPs) are a class of small soluble proteins present at high concentration in insect chemosensory organs; they are supposed to be involved in carrying the chemical messages from the environment to the chemosensory receptors. In this paper, we report on the solution structure of CSPsg4, a chemosensory protein from the desert locust Schistocerca gregaria, which is expressed in the antennae and other chemosensory organs. The 3D NMR structure revealed an overall fold consisting of six alpha-helices, spanning residues 13-18, 20-31, 40-54, 62-78, 80-90, and 97-103, connected by loops which in some cases show dihedral angles typical of beta-turns. As in the only other chemosensory protein whose structure has been solved so far, namely, CSP from the moth Mamestra brassicae, four helices are arranged to form a V-shaped motif; another helix runs across the two V's, and the last one is packed against the external face. Analysis of the tertiary structure evidenced multiple hydrophobic cavities which could be involved in ligand binding. In fact, incubation of the protein with a natural ligand, namely, oleamide, produced substantial changes to the NMR spectra, suggesting extensive conformational transitions upon ligand binding.     

Phase-related morphological changes induced by [His7]-corazonin in two species of locusts, Schistocerca gregaria and Locusta migratoria (Orthoptera: Acrididae)

The effects of a neurohormone, [His(7)]-corazonin, on phase-related morphological traits (F/C and E/F ratios; F = length of the hind femur, C = maximum width of the head; E = length of fore wing) were re-examined in the desert locust, Schistocerca gregaria Forsk?l. The F/C ratio was significantly different between adults with five and six nymphal instars, respectively, indicating that they need to be analysed separately. Injections of the synthesized peptide (1 nmol) into individually-reared (solitary) nymphs at the second and third instars caused a shift in classical morphometric ratio towards the value typical for crowded (gregarious) individuals in both sexes. The E/F ratio, which is smaller in solitary locusts than in gregarious ones, was also influenced significantly by injections of [His(7)]-corazonin into individually-reared locusts. The effect of [His(7)]-corazonin on E/F ratios was shown more clearly when the nymphs were injected at a higher dose (2 nmol) at the beginning of the third instar. Single injections of the peptide into individually-reared nymphs at different instars revealed that the earlier the injection the larger the 'gregarizing' effects of the peptide on F/C and E/F ratios. The same tendency was also detected in Locusta migratoria Linnaeus. These results supported the hypothesis that [His(7)]-corazonin plays an important role in the control of phase polymorphism in locusts.