Corpus allatum activity in vitro during ovarian maturation in the desert locust, Schistocerca gregaria.

1. Radiochemical in vitro assays show that there are large and rapid changes in the spontaneous rate of juvenile hormone synthesis and release during the course of sexual maturation in the locust. 2. Parallel observations on glands incubated with farnesenic acid show that the rate-limiting step is always prior to the stage of esterification of farnesenic acid to the final intermediate, methyl farnesoate. 3. Corresponding changes in oocyte morphometrics do not reveal any clear correlation between endocrine activity of the corpus allatum and either the induction or maintenance of rapid vitellogenesis. 4. Peaks of synthetic activity in the corpus allatum correspond well with the onset of previtellogenic growth in the oocytes. 5. The data do not provide any evidence that 'corpus allatum insufficiency' is responsible for resorption of growing oocytes. 6. It is concluded that short-term in vitro radio-assays provide a valid method for estimating quantitatively the physiological activity of the corpus allatum.     

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.     

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.

     

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.     

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.     

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 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.     

Imaginal differentiation of the integument of the desert locust, Schistocerca gregaria Forsk. IV. Steps in morphogenesis of the glandular units

In the gregarious males of Schistocerca gregaria Forsk., imaginal moulting (mitosis, apolysis, new cuticle synthesis, ecdysis) is associated with the differentiation of numerous glandular units. These units, involved in a sexual, excitatory pheromone secretion are at that time composed only of a basal glandular cell and an apical duct cell. Each glandular unit originates from an isogenic group of cells of which the four elements (tetrade) are disposed on two levels. At each level a principal cell and an accessory one may be recognized. The lower accessory, or ciliary, cell shows, at the time of apolysis, both a strong cytoplasmic protrusion and a typical ciliary formation. This formation associated with a diplosome goes through the duct cell and ends up in the exuvial space. It makes a inner mould; arranged around it are epicuticular materials characteristic of the duct wall; then it disappears. The strong cytoplasmic protrusion also retracts thus allowing a glandular reservoir to form. A glandular cell may be recognized at an early stage owing to its R.E.R. development. The upper accessory cell strengthens the duct cell and secretes junctional cuticle between the duct and general cuticle. Accessory cells, after the imaginal moult do not degenerate but acquire epithelial cell characteristics. The duct has a dual origin : the receptive part is secreted by the ciliary cell and the vector part by the duct cell. The organization and stages of morphogenesis of the glandular unit are discussed and compared to those of other apterygote or pterygote insects.     

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.     

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.     

Proctolin: A possible releasing factor in the corpus cardiacum/corpus allatum of the locust

The corpus cardiacum (CC) and corpus allatum (CA) of the locust, Locusta migratoria, contain intense proctolin-like immunoreactivity (PLI) within processes and varicosities. In contrast, in the cockroach, Diploptera punctata, although a similar staining pattern occurs within the CC, PLI appears absent within the CA. The possible role of proctolin as a releasing factor for adipokinetic hormone (AKH) and juvenile hormone (JH) was investigated in the locust. Proctolin caused a dose-dependent increase in AKH I release (determined by RP-HPLC) from the locust CC over a range of doses with threshold above 10(-8)M and maximal release at about 10(-7)M proctolin. Isolated glandular lobes of the CC released greater amounts of AKH I following treatment with proctolin and in these studies AKH II was also released. Confirmation of AKH I release was obtained by injecting perfusate from incubated CCs into locusts and measuring hemolymph lipid concentration. Perfusate from CC incubated in proctolin contained material with similar biological activity to AKH. Proctolin was also found to significantly increase the synthesis and release of JH from locust CA, with the increase being greatest from CAs that had a relatively low basal rate of JH biosynthesis (<35 pmol h(-1) per CA). In contrast, proctolin did not alter the synthesis and release of JH from the cockroach CA. These results suggest that proctolin may act as a releasing factor for AKHs and JH in the locust but does not act as a releasing factor for JH in the cockroach.     

Neural influence on corpus allatum activity and egg maturation in starved virgin Periplaneta americana

ABSTRACT. Of sixty-seven adult female Periplaneta americana (L.) isolated when less than 8h old and kept without food at 25–30°C in LD 12:12, only six produced oothecae during 25–35 days. Growth of the basal oocytes was retarded, and maximal oocyte volume, only one-third of that in fed virgins, was achieved after about 12 days. By day 14, 60% of the basal oocytes were being resorbed in the starved females, and corpora lutea were usually all that remained beyond day 20. Oocyte growth was potentiated in starved, virgin females by severing either of the two nervi corporis allati 1 (NCA 1), and oothecae were then produced in 45–80% of cases. Sham-operated controls oviposited in fewer than 27% of the trials. Because oocyte maturation was prevented by extirpating both corpora allata (CA), but not when the glands were replaced, and because the juvenile hormone analogue, ZR 515, was highly effective in causing the starved cockroaches to produce oothecae, the starvation-induced reproductive failure probably reflects diminished hormone production by the CA. The most likely consequence of severing NCA 1 is de-repression of juvenile hormone production. The directness of the neural influence was shown by removing the one denervated CA, in which case stimulation of oogenesis was minimal even though the contralateral innervated gland was present. The incidence of ootheca production was not enhanced by transecting the NCA 2, which suggests that the CA of starved cockroaches are not inhibited via this pathway.     

The circadian clock genes affect reproductive capacity in the desert locust Schistocerca gregaria

The circadian clocks govern many metabolic and behavioral processes in an organism. In insects, these clocks and their molecular machinery have been found to influence reproduction in many different ways. Reproductive behavior including courtship, copulation and egg deposition, is under strong influence of the daily rhythm. At the molecular level, the individual clock components also have their role in normal progress of oogenesis and spermatogenesis. In this study on the desert locust Schistocerca gregaria, three circadian clock genes were identified and their expression profiles were determined. High expression was predominantly found in reproductive tissues. Similar daily expression profiles were found for period (per) and timeless (tim), while the clock (clk) mRNA level is higher 12 h before the first per and tim peak. A knockdown of either per or tim resulted in a significant decrease in the progeny produced by dsRNA treated females confirming the role of clock genes in reproduction and providing evidence that both PER and TIM are needed in the ovaries for egg development. Since the knockdown of clk is lethal for the desert locust, its function remains yet to be elucidated.     

The mechanism of C-20 hydroxylation of alpha-ecdysone in the desert locust, Schistocerca gregaria.

1. The C-20 hydroxylation of alpha-ecdysone to produce beta-ecdysone was investigated in the desert locust, Schistocerca gregaria. 2. alpha-Ecdysone C-20 hydroxylase activity was located primarily in the fat-body and Malpighian tubules. The properties of the hydroxylation system from Malpighian tubules investigated further. 3. The enzyme system was mitochondrial, had a pH optimum of 6.5, an apparent Km of 12.5 micron and required O2 and NADPH. 4. The activity of the hydroxylation system showed developmental variation within the fifth instar, the maximum activity corresponding to the maximum tire of endogenous moulting hormone. The significance of these results is assessed in relation to the control of the endogenous titre of beta-ecdysone. 5. The mechanism of the hydroxylation system was investigated by using known inhibitors of hydroxylation reactions such as CO, metyrapone and cyanide. 6. The CO difference spectrum of the reduced mitochondrial preparation indicated the presence of cytochrome P-450 in the preparation. 7. It concluded that the alpha-ecdysone C-20 hydroxylase system is a cytochrome P-450-deendent mono-oxygenase.