Comparisons of deterrency and toxicity of selected secondary plant compounds to an oligophagous and a polyphagous acridid

A comparison was made of the relationship between deterrence and toxicity of eight secondary compounds to two acridids. The grass specialist Locusta migratoria was compared with the polyphagous Schistocerca gregaria. L. migratoria was deterred by all compounds presented at natural concentrations to which S. gregaria showed a variety of behavioral responses. Overall, L. migratoria was significantly more susceptible to toxic effects of the chemicals when injected into the hemolymph than was S. gregaria and was more sensitive behaviourally to them. There was a significant correlation in both species between deterrency and toxicity of injected compounds, but little evidence of a relationship between deterrency and oral toxicity.

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Résumé La comparaison a porté sur les relations entre répulsion et toxicité de huit substances secondaires chez deux acridiens: Locusta migratoria, spécialiste de graminées, et Schistocerca gregaria, polyphage. L. migratoria est repoussé par toutes les substances proposées, aux concentrations naturelles, pour lesquelles S. gregaria a présenté des comportements trés divers. Mais surtout, L. migratoria a été significativement plus sensible que S. gregaria aux effets toxiques de ces substances quand elles sont injectées dans son haemolymphe; S. gregaria a réagi à ces substances plus par des modifications de son comportement. Il y a une corrélation significative pour les deux espèces, entre la répulsion et la toxicité des substances injectées.

     

The possible role of two species of Orthoptera in the dissemination of a plant pathogenic fungus

The ability of the locusts, Locusta migratoria and Schistocerca gregaria, to disseminate Colletotrichum graminicola, the fungal pathogen of maize anthracnose, were studied. The insects were fed with the diseased plants and spores were recovered in viable condition from the faeces. The spores recovered were able to grow on artificial media and were still infectious to the host plant.     

Co-localization of the adipokinetic hormones I and II in the same glandular cells and in the same secretory granules of corpus cardiacum of Locusta migratoria and Schistocerca gregaria

Summary The immunocytochemical reactivity of the glandular cells of the corpus cardiacum (CCG-cells) of Locusta migratoria and Schistocerca gregaria was investigated at the electron-microscopic level, using the protein A-gold method, with three antisera against fragments of the adipokinetic hormones AKH I and AKH II. This combination of antisera permitted discrimination between anti-AKH I and anti-AKH II immunoreactivity. Fixation in a mixture of 2% glutaraldehyde and 2% formaldehyde, in combination with low-temperature embedding in Lowicryl K₄M, produced the highest and most consistent selective immunogold labelling of the secretory and ergastoplasmic granules. All secretory granules in all CCG-cells investigated possessed a distinct anti-AKH I-immunopositive reaction, whereas most secretory granules showed a weaker anti-AKH II immunoreaction. Ergastoplasmic granules reacted similar to the secretory granules. The average immunolabelling of the secretory granules was higher in the processes than in the cell bodies of the CCG-cells. The results in Schistocerca gregaria were essentially similar to those in Locusta migratoria. It is concluded that (i) the individual CCG-cells synthesize AKH I as well as AKH II; (ii) these hormones coexist in the same ergastoplasmic and secretory granules; and (iii) these granules contain a higher content of AKH I than AKH II.     

A non-doubling DNA series in somatic tissues of the locusts Schistocerca gregaria (Forskål) and Locusta migratoria (Linn.)

Locusta migratoria has only 70% of the germ line DNA value of the related species Schistocerca gregaria in spite of a uniform karyotype. This difference is maintained in the nuclei of the testis wall, ovariole tip, mid-gut diverticulum, Malpighian tubule and fat. The distribution of nuclear DNA contents is tissue specific but the peaks in the distributions do not conform with members of a doubling series. It is suggested that both phenomena may be connected with the mechanism of tissue differentiation in insects, the latter by differential replication of those chromosome regions which are active in particular tissues.     

Differential susceptibility of two locust pests to the microsporidium Paranosema (Antonospora) locustae at suboptimal rearing temperature

Paranosema (Antonospora) locustae (Canning) is a microsporidium with an extensive host range including >100 reported insect hosts from the order Orthoptera. The susceptibility of two species of locusts (Orthoptera: Acrididae) – the migratory locust, Locusta migratoria subsp. migratorioides (Fairmaire & Reiche), and the desert locust, Schistocerca gregaria Forsskål – to P. locustae was compared under laboratory conditions at a decreased temperature of 27 °C to enhance susceptibility to infection. Locusta migratoria was found highly vulnerable as infection percentages exceeded 70% at 10⁴, 10⁵, and 10⁶ spores per insect, and mortality increased with increasing dosage. Conversely, P. locustae spores were not found in S. gregaria throughout the experiment. Only at 10⁷ spores per insect, as many as 20% of S. gregaria were infected. This suggests that the desert locust is resistant to P. locustae infection, as opposed to the migratory locust. The laboratory models of these parasite–host systems may be useful for elucidating mechanisms of insect immunity to microsporidia.     

The primary structure of an endocuticular protein from two locust species,Locusta migratoria and Schistocerca gregaria,determined by a combination of mass spectrometry and automatic Edman degradation

The complete primary structures of two variants of a protein, Abd-5, isolated from the endocuticles of the migratory locust Locusta migratoria and the desert locust Schistocerca gregaria, have been determined. The proteins from the two species are N-terminally blocked with pyroglutamic acid. Their sequences differed only in two positions. Comparison of the sequences to those of other cuticular proteins shows that moderate homologies exist to 11 other cuticular proteins from insects representing four different orders. Amino acid residues in certain positions appear to be strictly conserved.     

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.     

Adaptive difference in daily timing of hatch in two locust species,Schistocerca gregaria and Locusta migratoria: The effects of thermocycles and phase polyphenism

This study examined the effects of temperature and phase polyphenism on egg hatching time in the desert locust, Schistocerca gregaria, and the migratory locust, Locusta migratoria. The two species exhibited differences and similarities in hatching behavior when exposed to different temperature conditions. In 12-h thermocycles of various temperatures, the S. gregaria eggs hatched during the cryoperiod (low temperature period), whereas L. migratoria eggs hatched during the thermoperiod (high temperature period). The eggs of both species hatched during the species-specific period of the thermoperiod in response to a temperature difference as small as 1 °C. Furthermore, the locusts adjusted hatching time to a new thermal environment that occurred shortly before the expected hatching time. In both species, the hatching of the eggs was synchronized to a specific time of the day, and two hatching peaks separated by approximately 1 day were observed at a constant temperature after the eggs were transferred from thermocycles 3 days before hatching. Eggs laid by gregarious females hatched earlier than those laid by solitarious females in S. gregaria but this difference was not observed in L. migratoria.     

The effects of elevated temperature on chiasma formation in Locusts migratoria

Individuals from an inbred laboratory stock of Locusta migratoria were subjected to 40° C heat treatments. These involved both constant 40° C treatment and shorter periods of 5, 4, 3, or 2 days at the high temperature followed by a return to the lower temperature of 30° C. Chiasma frequency analyses revealed that a total of four different effects could be produced by the heat treatments at different stages of cell division: two of the effects involved increases and two involved decreases. Similar, though not identical, effects have also been obtained in the locus Schistocerca gregaria. The similarities and differences in the responses shown by these two species are compared and contrasted.Mrs. M.E. Williams     

Differential regulation of a homologous peptidergic neuron in grasshoppers: evolution of a neural circuit

The vasopressin-like immunoreactive (VPLI) neurons of grasshoppers have paired cell bodies in the suboesophageal ganglion and both anterior and posterior running axons. In non-oedipodine grasshopper species (e.g. Schistocerca gregaria), most of their arborisations are distributed in dorsal and lateral neuropil, while in oedipodine species (e.g. Locusta migratoria), the neurons have additional extensive axonal projections in both the optic lobes and proximal portions of the ganglionic peripheral nerves. This study demonstrates that these morphological differences correlate with their physiology. In L. migratoria, VPLI neuron activity is regulated primarily via a spontaneously active interneuron which descends from the brain. This descending interneuron is inhibited by a light-activated brain extraocular photoreceptor. Regulation of VPLI neuron activity by an extraocular photoreceptor is also seen in the other oedipodine grasshopper investigated. In the four non-oedipodines examined (from two subfamilies), we find no extraocular photoreceptor regulation of VPLI neuron activity. Despite this, VPLI neuron in S.␣gregaria does appear to be driven by a descending interneuron homologous to that in L. migratoria. The descending interneuron in both species receives similar mechanosensory input and excites the VPLI neuron via cholinergic synapses. Histamine injection into the medial protocerebrum of both species causes strong inhibition of the descending interneuron. The evolution of the neural circuitry, by which an extraocular photoreceptor comes to regulate the descending interneuron in oedipodine species, is discussed. Accepted: 6 January 1998     

The consumption, digestion and utilization of food by Locusts

A comparative study was made of the consumption, digestion and utilization of cabbage by the 3rd-, 4th- and 5th-instar hoppers of Schistocerca gregaria and Locusta migratoria. The rate of consumption (C.I.) and the digestibility (except in 3rd instar) of cabbage by Locusta hoppers were greater than by Schistocerca hoppers. However, weight increase, growth rate (except in 4th instar), gross and net efficiency of food utilization were found to be significantly higher in Schistocerca hoppers than in Locusta hoppers. The total live weight gain of Schistocerca hoppers for a period of 18 days was about twice that in Locusta hoppers. Slower growth rate and lesser efficiency of food utilization by Locusta hoppers were considered to be due to nutrient imbalance of cabbage for Locusta.

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Zusammenfassung Es wurde eine vergleichende Untersuchung des Verbrauchs, der Verdauung und der Ausnutzung von Kohl durch das 3., 4. und 5. Larvenstadium von Schistocerca gregaria und Locusta migratoria durchgeführt. Die Verbrauchsrate (C.I.) und die Verdaulichkeit von Kohl war (mit Ausnahme des 3. Larvenstadiums) bei Locusta-Larven größer als bei Schistocerca-Larven. Jedoch erwiesen sich Gewichtszunahme, Wachstumsrate (mit Ausnahme des 4. Larvenstadiums), Brutto- und Netto-Wirkungsgrad der. Nahrungsverwertung bei Schistocerca-Larven als signifikant höher als bei denen von Locusta. Die gesamte Lebendgewichtszunahme von Schistocerca-Larven war über einen Zeitraum von 18 Tagen etwa zweimal so groß wie bei Locusta-Larven. Die langsamere Wachstumsrate und der geringere Wirkungsgrad der Nahrungsausnutzung durch die Locusta-Larven werden als Folge der nutritiven Unausgeglichenheit von Kohl für Locusta angesehen.

     

Changes in the auditory system of locusts (Locusta migratoria and Schistocerca gregaria) after deafferentation

Deafferentation experiments during postembryonic development show morphological and/or physiological changes of receptor fibers and of identified auditory interneurons in the CNS of the locusts Locusta migratoria and Schistocerca gregaria after unilateral ablation of one tympanic organ either in the larva or the adult animal.

Yolk formation in Locusta migratoria and Schistocerca gregaria: Related ligands and oocyte receptors

During vitellogenesis the transport of yolk precursor proteins, the vitellogenins (VTG), from the hemolymph into the oocyte is achieved by receptor-mediated endocytosis. Recently the receptor for the VTG of Locusta migratoria has been isolated. Now a new protocol has been developed for the purification of the VTG receptor of this locust from ovarian membranes. By CHAPS solubilization of the membranes followed by ion exchange and immunoaffinity chromatography, a 100-fold purification of the VTG receptor was achieved. The amino acid composition of the receptor protein has been determined. However, first attempts to sequence the receptor failed due to the N-terminal blocking of the molecule. With the same methods the VTG receptor of another locust, Schistocerca gregaria, has been isolated, purified, and characterized. This receptor has an apparent M_r of 186 kDa under nonreducing conditions. It recognizes L. migratoria VTG and vice versa. However, in cross-competition experiments in which the Schistocerca VTG competed with Locusta VTG for binding to the Locusta VTG receptor, the Schistocerca VTG was less efficient. Furthermore, the VTG receptor proteins of S. gregaria and L. migratoria are immunologically related as revealed by Western blotting with anti-Locusta VTG receptor antibodies. It appears that important structural elements required for efficient and specific endocytosis of VTG have been conserved. © 1994 Wiley-Liss, Inc.     

A novel granular cell type of locust Malpighian tubules: ultrastructural and immunocytochemical study

Summary A novel secretory cell type in the initial segment of the Malpighian tubules of the locusts Schistocerca gregaria and Locusta migratoria is described ultrastructurally and studied by means of immunocytochemical techniques. The cells show abundant rough endoplasmic reticulum with interspersed Golgi zones. The richness of the cell secretory machinery and the presence of apical dense plemorphic granules suggest a role in secretion of proteinaceous material to the tubule lumen. The surprising finding of ACTH (1–24)-, -MSH-, and 7B2-like immunoreactivity for this cell is discussed.     

Identification of pheromone-like compounds in male reproductive organs of the oriental locust Locusta migratoria

Despite the great economical interest of locusts in agriculture, knowledge on their chemoreception systems is still poor. Phenylacetonitrile is recognised as a pheromone of the desert locust Schistocerca gregaria, triggering gregarization, promoting aggregation and inhibiting courtship. However, in the other major locust species, Locusta migratoria, pheromones have not been reported. We have identified the two isomers of naphthylpropionitrile from the male reproductive organs of L. migratoria. Chemical synthesis has confirmed the identity of the two compounds. Both isomers show significant affinity to CSP91, a protein reported in the testis, but not to three other proteins of the same family (CSP180, CSP540 and CSP884) expressed in female accessory glands. The striking similarity of these compounds with phenylacetonitrile and the unusual nature of such chemicals strongly suggest that naphthylpropionitrile could be pheromones for L. migratoria, while their site of expression and binding activity indicate a role in communication between sexes.     

Recombination nodules and chiasma localization in two orthoptera

The distribution of recombination nodules (RNs) is reported from observations on two-dimensional spreads of Locusta migratoria and Chloealtis conspersa spermatocytes; C. conspersa is a known example of a species with terminally localized chiasmata, while L. migratoria has nonspecific positioning of chiasmata. Measurements of the distances from 102 RNs to the ends of the synaptonemal complexes (SCs) on which they were found show the RNs to be near-terminally localized in C. conspersa and to occur along the lengths of the SCs in L. migratoria. Thus, the localization of RNs appears to reflect the localization of chiasmata. These observations are interpreted as support for the proposed recombinant function of RNs.     

Intercellular junctions in the corpora cardiaca of locusts

Summary The intercellular junctions in the corpora cardiaca of the locusts Schistocerca gregaria and Locusta migratoria were investigated by transmission electron microscopy. In the glandular lobes, complexes consisting of scalariform junctions and associated mitochondria, comparable to those previously observed in ion transporting epithelia, are formed between gland cells, and more rarely between gland cells and the neurons innervating them. Their structure and abundance are apparently unaffected by the stage of development or by the various experimental conditions employed. In the neural lobe, scalariform junctions form between glial cells and show close association with the endoplasmic reticulum. Gap junctions are present among glandular, neural and glial elements, and are formed between cells of the same type and of different types. Contacts resembling punctate tight junctions are widely distributed in the gland, but would be unlikely to form a barrier to diffusion. Septate junctions are formed exclusively between glial cells.     

Knockdown of the corazonin gene reveals its critical role in the control of gregarious characteristics in the desert locust

The two plague locusts, Schistocerca gregaria and Locusta migratoria, exhibit density-dependent phase polyphenism. Nymphs occurring at low population densities (solitarious forms) are uniformly colored and match their body color to the background color of their habitat, whereas those occurring at high population densities (gregarious) develop black patterns. An injection of the neuropeptide, corazonin (Crz) has been shown to induce black patterns in locusts and affect the classical morphometric ratio, F/C (F, hind femur length; C, maximum head width). We herein identified and cloned the CRZ genes from S. gregaria (SgCRZ) and L. migratoria. A comparative analysis of prepro-Crz sequences among insects showed that the functional peptide was well conserved; its conservation was limited to the peptide region. Silencing of the identified SgCRZ gene in gregarious S. gregaria nymphs markedly lightened their body color and shifted the adult F/C ratio toward the value typical of solitarious forms. In addition, knockdown of the gene in solitarious nymphs strongly inhibited darkening even after a transfer to crowded conditions; however, these individuals developed black patterns after being injected with the Crz as a rescue treatment. SgCRZ was constitutively expressed in the brains of S. gregaria during nymphal development in both phases. This gene was highly expressed not only in the brain in both phases, but also in the corpora allata in the gregarious phase. This conspicuous phase-dependent difference in SgCRZ gene expression may indicate a functional role in the control of phase polyphenism in this locust.     

Immunological evidence for an allatostatin-like neuropeptide in the central nervous system of Schistocerca gregaria,Locusta migratoria and Neobellieria bullata

Methanolic brain extracts of Locusta migratoria inhibit in vitro juvenile hormone biosynthesis in both the locust L. migratoria and the cockroach Diploptera punctata. A polyclonal antibody against allatostatin-5 (AST-5) (dipstatin-2) of this cockroach was used to immunolocalize allatostatin-5-like peptides in the central nervous system of the locusts Schistocerca gregaria and L. migratoria and of the fleshfly Neobellieria bullata. In both locust species, immunoreactivity was found in many cells and axons of the brain-retrocerebral complex, the thoracic and the abdominal ganglia. Strongly immunoreactive cells were stained in the pars lateralis of the brain with axons (NCC II and NCA I) extending to and arborizing in the corpus cardiacum and the corpora allata. Although many neurosecretory cells of the pars intercerebralis project into the corpus cardiacum, only 12 of them were immunoreactive and the nervi corporis cardiaci I (NCC I) and fibers in the nervi corporis allati II (NCA II) connecting the corpora allata to the suboesophageal ganglion remained unstained. S. gregaria and L. migratoria seem to have an allatostatin-like neuropeptide present in axons of the NCC II and the NCA I leading to the corpus cardiacum and the corpora allata. All these data suggest that in locusts allatostatin-like neuropeptides might be involved in controlling the production of juvenile hormone by the corpora allata and, perhaps, some aspects of the functioning of the corpus cardiacum as well. However, when tested in a L. migratoria in-vitro juvenile hormone-biosynthesis assay, allatostatin-5 did not yield an inhibitory or stimulatory effect. There is abundant AST-5 immunoreactivity in cell bodies of the fleshfly N. bullata, but none in the CA-CC complexes. Apparently, factors that are immunologically related to AST-5 do occur in locusts and fleshflies but, the active protion of the peptide required to inhibit JH biosynthesis in locusts is probably different from that of AST-5.     

Volumetric feedback and the control of meal size in Schistocerca gregaria

The role and nature of volumetric feedbacks in the regulation of meal size was investigated for Schistocerca gregaria. Feedback from the anterior region of the crop was found to be important and denervation led to hyperphagia. Additional feedbacks were found from more posterior gut regions. Cannulating agar or paraffin into the mid- and hindgut caused a decrease in the size of a following meal. This effect was removed by cutting the ventral nerve cord anterior to the terminal abdominal ganglion. Increasing the blood volume by injections of isotonic saline into the haemocoel was also found to decrease subsequent meal size. This effect was not mediated via the gut or body wall stretch receptors and possible mechanisms are discussed. The results for S. gregaria are compared with those obtained previously from Locusta migratoria.

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Résumé L'étude de la nature et du rôle des feed backs volumétriques dans la régulation de la taille du repas a été effectuée chez S. gregaria. Un feed back, originaire de la région antérieure du jabot, s'est révélé important et la dénervation a provoqué l'hyperphagie. Des feed backs supplémentaires ont été décelés dans des régions plus postérieures du jabot. De l'agar ou de la paraffine canulés dans la jabot moyen et postérieur ont provoqué une diminution de la taille du repas suivant. Ces effets sont supprimés avec la section de la corde nerveuse centrale avant le ganglion abdominal terminal. L'augmentation du volume sanguin par des injections de solution saline isotonique a aussi diminué la taille du repas suivant. Cet effet n'est pas transmis via des récepteurs de tension du jabot ou de la paroi du corps; des mécanismes envisageables sont discutés. Ces résultats avec S. gregaria sont comparés à ceux obtenus antérieurement avec Locusta migratoria.