Adipokinetic hormone content of the corpora cardiaca in gregarious and solitary migratory locusts

Abstract. The adipokinetic hormone (AKH-I and AKH-II) content of the corpora cardiaca from adult males of crowded (gregarious) and isolated (solitary) Locusta migratoria migratorioides (Reiche & Fairmaire) was quantified by reverse-phase high-performance liquid chromatography.Significantly less total hormone was found in the corpora cardiaca of crowded locusts than in those glands of isolated locusts at the age of 12–19 days after fledging.The ratio of AKH-I/AKH-II was higher in crowded than in isolated locusts at this age.From the age of 12–19 days to that of 25–30 days, AKH content increased significantly in the corpora cardiaca of crowded locusts, but no such increase was found in the glands of isolated locusts, and at 25–30 days there were no significant differences in the AKH content of the glands from crowded and isolated locusts.     

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.     

Separation and characteristics of antidiuretic factors from the corpora cardiaca of the migratory locust

Summary

Corpora cardiaca (CC) of the migratory locust contain two antidiuretic (AD) factors increasing the fluid reabsorption of isolated recta over a 5-h period.

They are contained in storage lobes (SL) and glandular lobes (GL) of the CC. They differ in size and can be separated from each other in different ways (extraction, dialysis, electrophoresis).

The AD factor contained in GL of the CC is stable at 4°C and quickly destroyed at 100°C. It stimulates the fluid reabsorption in a dose-dependent manner. Its release into the haemolymph seems to be controlled by octopamine, which is probably synthesized in the lateral neurosecretory areas of the brain.     

Rapid in vitro activation of corpora allata by extracted locust brain allatotropic factor

Brains of young (newly emerged) adult female locusts (Locusta migratoria migratorioides) and of mature (> 9 days old) locusts contain an extractable allatotropic factor, soluble in 100% methanol and in distilled water. This factor stimulates juvenile hormone III (JH III) synthesis and release from corpora allata (CA) that have been excised from donor locusts and then incubated with (radiolabeled methyl)-methionine in vitro in its presence. In addition to JH III, which is the major product synthesized by the CA, other hexanesoluble, radiolabeled compounds–-more polar than JH III–-are also released when CA are incubated in vitro. The activation of CA by the allatotropic factor is rapid and quickly declines when the factor is removed from the medium. Corpora allata excised from young females are marginally active and can be activated by brain allatotropic factor to less of an extent than CA of mature locusts. The content of allatotropic factor in brains of mature locusts is higher than that ascertained in brains of young females. Allatotropic factor is also present in the corpora cardiaca.     

A comparative study on the isolation of adipokinetic and hypertrehalosaemic factors from insect corpora cardiaca

ABSTRACT. Extracts of corpora cardiaca from two cockroaches, Nauphoeta cinerea Olivier and Leucophaea maderae F., from a cricket, Gryllus bimaculatus De Geer, from the Colorado potato beetle, Leptinotarsa decemlineata Say, and from the sphinx moth, Sphinx ligustri L. were assayed for adipokinetic and hypertrehalosaemic activity, in acceptor locusts ( Locusta migratoria L.) and cockroaches ( Periplaneta americana L.) respectively. Both bioassays give positive results with all corpus cardiacum material tested except that from the sphinx moth; in this insect haemolymph lipid concentrations (but not those of the total carbohydrate) are, however, increased after injection of an extract of corpora cardiaca from the same species. A similar result is obtained when specimens of G. bimaculatus are injected with an extract of corpora cardiaca from G. bimaculatus. Biological activities of corpus cardiacum extracts from all species investigated can be resolved on reversed-phase high-performance liquid chromatography. Gland extracts from the two cockroach species each show a single absorbance peak which has hypertrehalosaemic activity, but with a (common) retention time distinct from all previously described arthropod neuropeptides. The corpora cardiaca of G. bimaculatus contain also a novel adipokinetic factor with a retention time distinct from previously characterized arthropod hormones, as well as from the new cockroach factor described in this study. The two hypertrehalosaemic factors from the corpora cardiaca of the potato beetle coelute with the hypertrehalosaemic hormones I and II of the American cockroach. The active (adipokinetic) compound from glands of S. ligustri appears to coelute with locust adipokinetic hormone I.     

Identification of gonadotropic and antigonadotropic factors from the nervous part of the corpora cardiaca in the African locust

Summary

The nervous part of the locust corpora cardiaca (NCC) was extracted using 70% methanol and subjected to fast protein liquid chromatography (FPLC). Twenty fractions were collected and injected into females from the end of the IIIrd larval instar to day-12 of the adult life to screen the effects on metamorphosis, body pigmentation, and oocyte growth. The rate of juvenile hormone (JH) biosynthesis by the corpora allata of injected animals was evaluated in vitro. One fraction was found to stimulate ovarian maturation, and 3 to delay oocyte growth. None of them disturbed (i) either metamorphosis and body color (which are JH dependent), or (ii) rate of JH biosynthesis. Of the 3 fractions which inhibited ovarian maturation, 2 of them were identified as the neuroparsins A and B. The results clearly illustrate that antagonist factors from the brain are involved in the regulation of ovarian maturation in the locust.     

Hormonal control of lipid synthesis in the fat body of the adult female tsetse fly, Glossina morsitans

Aqueous extracts of brain, thoracic ganglion or corpora cardiaca of female Glossina morsitans were shown to contain a substance which inhibited the synthesis of lipid from l[U-¹⁴C] leucine by fat cells incubated in vitro. The highest concentration of this substance was found in the corpora cardiaca; approximately 1 × 10^?6 gland pairs μl^?1 were required for maximum inhibition. At concentrations greater than 1 × 10^?4 gland pairs μl^?1 the lipid synthesis inhibiting factor (hereafter referred to as the LSIF) was inactivated by the presence of a substance which could be removed by gel filtration. The concentration of LSIF in the corpora cardiaca and midbrain varied throughout the reproductive cycle of the female. Net release of LSIF from the midbrain occurred between the 2nd and 7th day of the 9-day reproductive cycle. Net release from the corpora cardiaca began on day 5 and continued until the end of the interlarval period on day 9. Results are consistent with the hypothesis that LSIF is synthesised mainly in the medial neurosecretory cells of the midbrain whereas the corpora cardiaca are the site of storage and release into the haemolymph. LSIF was present in midbrain and corpora cardiaca extracts from male G. morsitans but at lower concentrations than in females. No variation in LSIF concentration could be correlated with the feeding cycle. LSIF activity was not detected in fresh haemolymph but was found at high concentration in boiled haemolymph, suggesting the presence of an inhibitor which was inactivated at high temperature. Preliminary investigations into the nature of LSIF have shown it to be inactivated by proteolytic enzymes and to be recoverable in a single peak from a Sephadex G15 column.Results support the view that LSIF is a peptide hormone which, in conjunction with an inhibitor, controls the lipid synthetic ability of the fat cells of the adult female tsetse fly throughout the reproductive cycle.     

Neuroparsin: A new energetic neurohormone in the African locust

The effects of neuroparsins on hemolymph trehalose and lipid levels and on total glycogen content were analyzed in Locusta migratoria. Saline and methanol extracts of the two lobes of the corpora cardiaca were assayed. Neuroparsins (A and B) were demonstrated to be hypertrehalosemic and hyperlipemic proteins of the neural lobe. Both of these metabolic activities of neuroparsins were somewhat less potent than those of adipokinetic hormone (AKH). Neuroparsin activity could be distinguished from AKH by blockage with an antiserum specific to neuroparsin. The hypertrehalosemic response induced by neuroparsins, in contrast to that of AKH, appeared to occur without a decrease of total glycogen content. The differential modes of action of AKH and neuroparsins could contribute to the fine modulation of carbohydrate metabolism in Locusta migratoria.     

Substrate utilization and flight speed during tethered flight in the locust

Mature laboratory locusts normally exhibit a characteristic pattern of change in flight speed with time. They fly at high speed for the first few minutes, during which carbohydrate forms the major fuel, but then slow to a cruising speed when lipid is used almost exclusively. Locusts flown for 30 min, rested for 2hr, and then reflown, exhibit an identical pattern of flight, even though they oxidise only half the amount of carbohydrate used in the first flight. The injection of adipokinetic hormone before the first flight elicits a low initial flight speed for 10 to 15 min but then the locusts accelerate to a constant higher speed. The injection of hormone before the second flight, when blood lipid levels are already high, reduces the utilization of carbohydrate by the flight muscles dramatically but results in constant high-speed flight.     

Purification and sequence determination of a yellow protein from sexually mature males of the desert locust, Schistocerca gregaria

A yellow protein from abdominal cuticle of the desert locust, Schistocerca gregaria, has been purified and its amino acid sequence determined. The yellow color comes from bound carotene, the protein is only deposited in the epidermis and cuticle of male locusts during their sexual maturation, and the deposition is dependent upon a sufficiently high titer of juvenile hormone. The sequence of the protein is atypical for a cuticular protein, but it has some similarity to a putative juvenile hormone binding protein from Manduca sexta. It is suggested that the protein is involved in the transport of carotenes from internal tissues to epidermis and cuticle of the locust.     

The distribution of GABA-like immunoreactivity in the thoracic nervous system of the locust Schistocerca gregaria

Summary An antiserum raised against gamma aminobuyric acid (GABA) was used to stain the thoracic nervous system of the locust. It stained both neuronal somata and processes within the neuropile. Among the stained somata, those of the three pairs of common inhibitory motor neurones could be identified in each of the three thoracic ganglia. In the pro- and mesothoracic ganglia five discrete groups of somata are stained, four ventral and one dorsal. In the metathoracic neuromere, an additional second dorsal group can be identified. In the abdominal neuromeres of the metathoracic ganglion both dorsal and ventral somata are stained but the latter cannot be divided into discrete populations. In each ganglion, dorsal commissures (DC) IV and V are composed of stained neurites, DCVII, the supramedian commissure, the perpendicular tract, and all the longitudinal tracts contain both stained and unstained neurites. DCI, II, III and VI, the T and I tracts are unstained. An abundance of GABA-like immunoreactive processes is found throughout the neuropile except for the anterior ventral association centre where stained processes are sparser. Some of the stained cell groups contain neurones that have been studied physiologically. The function of these neurones is discussed.Beit Memorial Fellow     

The dark-colour-inducing neurohormone of locusts in relation to an albino mutant of Schistocerca gregaria

In the albino mutant of an Okinawa strain of Locusta migratoria (L.) (Orthoptera: Acrididae), albinism is caused by the absence of the dark‐colour‐inducing neurohormone (DCIN), which is present in the corpora cardiaca (CC) of normally coloured phenotypes. This study tests whether the absence of DCIN is responsible for albinism in an albino mutant of another locust, Schistocerca gregaria (Forsk.) (Orthoptera: Acrididae). This seemed feasible because a single Mendelian unit controls albinism in both species. However, implantation of CC, or injection of an extract of CC, from albino donors of S. gregaria, induce dark coloration in crowded nymph recipients of the Okinawa albino mutant of L. migratoria, as effectively as do implanted CC, or injections of extract of CC, from normal phenotype donors of S. gregaria. Therefore, DCIN is present in the albino mutant of S. gregaria, and consequently, the albinism in this mutant is not caused by its absence. Implantation of CC, or injection of extracts of CC, from albino donors of S. gregaria to conspecific albino nymphs does not induce darkening. Only extremely high doses of synthetic DCIN injected into albino nymphs of S. gregaria are effective, inducing some darkening. The dose to induce such darkening in albino nymphs of S. gregaria is 50 nmol, ≈ 5 × 10⁶ times higher than that (10 femtomol) needed to induce equivalent darkening in nymphs of the Okinawa albinos of L. migratoria. The results are discussed and some possible explanations of the observed effects outlined.     

The role of the frontal ganglion and corpora cardiaca/corpora allata complex in post-feeding weight loss in adult Heliothis zea

Abstract A post-feeding diuretic response has been observed in adult Heliothis zea (Boddie) (Lepidoptera: Noctuidae). 2-day-old starved adults which were allowed to feed to repletion on a 10% (w/v) sucrose solution lost 49.1% (females) and 85.8% (males) of the weight of the ingested meal during the first hour following feeding. Ligation between head and thorax or frontal ganglionectomy, when performed immediately following feeding, each resulted in a significant and permanent reduction in this normal weight-loss. Injection of homogenates of the corpora cardiaca/corpora allata (CC/CA) complex into non-ligated insects immediately after feeding also reduced significantly the post-feeding weight-loss, but this inhibition was transient and disappeared after 1 h. Dissection and weighing of the crop from either ligated, frontal ganglionectomized, or CC/CA-injected insects confirmed the crop as the predominant site of fluid retention in each case. We suggest that a soluble antidiuretic factor from the CC/CA acts in conjunction with the frontal ganglion to control the rate of crop emptying and subsequent diuresis by regulating the volume of ingested fluid that is passed into the haemolymph from the crop/midgut.     

The catabolism of glucose in Tenebrio molitor: The effects of corpora cardiaca

During the development of the mealworm Tenebrio molitor, the effects of corpora cardiaca (CC) extracts on glucose catabolism were tested. In control insects and in insects receiving CC extracts, the activity of the pentose cycle and the glycolytic-citric acid cycle, were evaluated in vivo by a radiorespirometric method using [1-¹⁴C] glucose and [6-¹⁴C] glucose as substrates. The CC extracts strongly divert glucose from the pentose phosphate pathway, which is very active in Tenebrio molitor. Glucose oxidation is reduced by the CC extracts in pupae and adults but is increased in last instar larvae. It seems that the effects of CC extracts vary depending upon the state of carbohydrate reserves.     

FMRFamide-like immunoreactivity in the metathoracic ganglion of the locust (Schistocerca gregaria)

Summary The distribution of FMRFamide-like immunoreactivity in the metathoracic ganglion of the locust, Schistocerca gregaria, has been investigated in serial semithin transverse sections with the use of the peroxidase-antiperoxidase (PAP) technique. The topographical distribution of approximately 120 immunopositive neurons was established. Antiserum against bovine pancreatic polypeptide (BPP) stains the same ganglionic cells as FMRFamide-antiserum, yet this staining is largely blocked after preabsorption to FMRFamide. A comparison of these results with those from other studies suggests that there may be more than one type of endogenous RFamide-like peptide.     

Maternal effects on phase characteristics in the desert locust, Schistocerca gregaria: a review of current understanding

Desert locusts demonstrate pronounced density-dependent polyphenism: a complex suite of traits shifts over the lifetime of an individual in response to crowding or isolation. These changes also accumulate across generations through a maternal effect. Female desert locusts alter the developmental trajectory of their offspring in response to their own experience of crowding. The mother possesses a memory of both the recency and extent of crowding and shifts the phase state of her hatchlings accordingly. Extensive experimental work has shown that offspring behaviour is controlled by a low molecular weight, polar compound (or compounds) released from the mother's accessory glands. The chemical identity of this agent is not yet known.     

The time-course of behavioural phase change in nymphs of the desert locust, Schistocerca gregaria

Abstract. The time-course of behavioural phase change was investigated in nymphs of Schistocerca gregaria , using logistic regression analysis of behaviour recorded in a standard assay. Gregarization occurred very rapidly. Solitary-reared nymphs became markedly gregarious in behaviour within 1-4h of being placed in a crowd. These insects re-solitarized equally quickly if removed from the crowd. Crowd-reared locusts also solitarized within l-4h, but this effect was not complete. Results indicate that, while behavioural gregarization is maximal within a few hours of crowding, solitarization is a two-stage process, changing rapidly at first, then more slowly as a function of the period of previous crowding.     

Relative motion parallax and target localisation in the locust,Schistocerca gregaria

Summary This paper addresses two questions. 1. Does Schistocerca gregaria detect edges which are defined solely by velocity-contrast, that is by the difference in the image speeds generated by an object and its background when the locust moves? 2. Is the locust's ability to measure the distance of a target by motion parallax independent of the relative motion between target and back-ground?A locust walking on a circular platform was surrounded by a stationary cylinder which was lined with an irregular texture. Against this background, the insect viewed 3 stationary, equidistant targets. One target was black, one grey and the last was textured like the cylinder. Peers and jumps were aimed preferentially at the textured and black targets showing that targets can be detected by virtue of their velocity-contrast with the background. When textured targets were wide, jumps were seen to be aimed at the targets' edge.To assess whether velocity-contrast between target and background distorts distance-estimates, we used jump-velocity as a measure of apparent distance and examined how it varied with different arrangements of target and background. When a textured background is close to a target or the target is very wide, velocity contrast is small. The locust's jump-velocity is then 10% greater than when velocity-contrast is increased by making the background distant or the target narrow. This suggests that the locust is efficient at separating signals encoding absolute motion from those encoding relative motion.     

Behaviour in vitro of separated fractions of haemocytes of the locust Schistocerca gregaria

Summary The haemocytes of locusts (Schistocerca gregaria) have been partially separated, by centrifugation on discontinuous Percoll gradients, into 3 subpopulations of plasmatocytes of which the most dense (band 5) displays more than 95% morphological homogeneity. The cells of band 5 are very granular, adhere and spread on glass, and contain nearly all the phenoloxidase activity of the total haemocyte population, as shown by 1,3-glucan (laminarin)-stimulation of both haemocyte lysate supernatant and monolayers of living cells. Cells from band 5 show negligible endocytosis of fluorescent latex beads, whereas those of band 4, which are less granular, plasmatocyte-like cells, are actively endocytic in vitro. The majority of the haemocytes are found in band 3, which is a mixture of coagulocytes and agranular plasmatocytes, with negligible phenoloxidase activity. The in vitro locomotory behaviour of adherent cells from bands 3 and 5 was compared, and addition of laminarin-activated haemocyte lysate supernatant, in which the prophenoloxidase activation sequence had been initiated, stimulated chemokinesis in cells of band 5 but not band 3. The separated fractions thus show marked behavioural and biochemical differences.     

The effect of wilting on palatability of plants to Schistocerca gregaria,the desert locust

Summary Previous work has shown that host choice by acridids (grasshoppers and locusts) is sensitive to alterations in host quality. In particular, reduced plant water content has been found to increase palatability of certain plant species. To determine if this phenomenon is general, and to gain preliminary information on causes, turgid and wilted plant material of forty-one species was tested using nymphs of the desert locust, Schistocerca gregaria. Twelve plant species (29%) had increased and five (12%) had decreased palatability (as measured by meal size) when wilted. Among fifteen families tested, the increases occurred in six, the decreases in three. The greatest change occurred in Taraxacum officinale; further tests on this plant revealed the increase to be continuous, rising with decreasing water content. The behavioral observations combined with the pattern of the results across plant species suggest that changes are due to alterations in specific deterrents or stimulants, rather than to decreased water content or increased concentrations of amino acids and/or sugars. The implications of these results for understanding drought-associated population outbreaks are discussed.