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 importance of the ontogenetic niche in resource-associated divergence: evidence from a generalist grasshopper

Geographic variation in resource use can produce locally adapted populations that exhibit genetic and phenotypic divergence. In the bird-winged grasshopper (Schistocerca emarginata = [lineata]), we investigate whether genetic data exist in accordance with geographic variation in resource (host) use and coloration. In Texas, juvenile grasshoppers feed almost exclusively on one of two host plants, Rubus trivialis (Rosaceae) or Ptelea trifoliata (Rutaceae), whereas adults of both forms are dietary generalists and consume many plants from unrelated families. Along with differences in juvenile feeding, differences in a density-dependent color polyphenism are concordant with genetic (mitochondrial DNA) variation among eight populations of the bird-winged grasshopper. Forms feeding on R. trivialis and those feeding on P. trifoliata represent monophyletic lineages according to phylogenetic analysis and maximum-likelihood tests of two alternative phylogeographic hypotheses for geographic variation in host use. Character-state optimization of host-plant acceptability on a phylogeny containing S. emarginata and outgroup taxa indicates that populations consuming R. trivialis gave rise to populations consuming P. trifoliata. Juvenile grasshoppers that consume P. trifoliata acquire deterrence against predation, suggesting that enemy-free space facilitated this host shift. In extant populations, adaptations stemming from alternative resource use during ontogeny present possible barriers to gene exchange. This study represents the first demonstration of resource-associated divergence in an otherwise generalist insect that exhibits temporal variation in resource use, characterized as developmental changes in host specialization. Our findings suggest that exploitation of different resources may have unexplored significance for generalist species that compartmentalize specialization to particular life stages.     

Characterization and daily variation of nitrate reductase in Gracilaria tenuistipitata (Rhodophyta)

The chemosensory protein CSP-sg4 of the desert locust Schistocerca gregaria binds reversibly N-phenyl-1-naphthylamine in fluorescent-binding assays, with a dissociation constant of 4 microM. Upon binding to the protein, the emission peaks of the fluorescent probe undergo a marked blue shift, accompanied by an order of magnitude increase of the maximum intensity. The assay has also allowed the measurement of the affinity of CSP to other aromatic and aliphatic compounds. The binding capacity of this protein is unaffected by thermal treatments up to 100 degrees C for 20 min. The ligand-binding characteristics of chemosensory proteins may help in clarifying the role of this recently discovered class of soluble proteins in chemoreception.     

The effect of manipulating ecdysteroid signaling on embryonic eye development in the locust<Emphasis Type="Italic"> Schistocerca americana</Emphasis>

Adult body plan differentiation in holometabolous insects depends on global induction and control by ecdysteroid hormones during the final phase of postembryogenesis. Studies in Drosophila melanogaster and Manduca sexta have shown that this pertains also to the development of the compound eye retina. It is unclear whether the hormonal control of postembryonic eye development in holometabolous insects represents evolutionary novelty or heritage from hemimetabolous insects, which develop compound eyes during embryogenesis. We therefore investigated the effect of manipulating ecdysteroid signaling in cultured embryonic eye primordia of the American desert locust Schistocerca americana, in which ecdysteroid level changes are known to induce three rounds of embryonic molt. Although at a considerably reduced rate compared to in vivo development, early differentiation and terminal maturation of the embryonic retina was observed in culture even if challenged with the ecdysteroid antagonist cucurbitacin B. Supplementing cultures with 20-hydroxyecdysone (20E) accelerated differentiation and maturation, and enhanced cell proliferation. Considering these results, and the relation between retina differentiation and ecdysteroid level changes during locust embryogenesis, we conclude that ecdysteroids are not an essential but possibly a modulatory component of embryonic retina development in S. americana. We furthermore found evidence that 20E initiated precocious epithelial morphogenesis of the posterior retinal margin indicating a more general role of ecdysteroids in insect embryogenesis.Electronic Supplementary Material Supplementary material is available in the online version of this article at Edited by C. Desplan     

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.     

Stimuli inducing gregarious colouration and behaviour in nymphs of Schistocerca gregaria

Solitarious nymphs of Schistocerca gregaria were reared under various conditions in both Jerusalem and Oxford to tease apart cues involved in behavioural and colour phase change. Treatments included rearing nymphs from the IInd or IIIrd until the final nymphal stadium in physical contact with similarly aged conspecific groups or with another locust species, Locusta migratoria migratorioides, as well as confining single nymphs in mesh cages, which were kept within crowds of S. gregaria or L. migratoria migratorioides, providing visual and olfactory but no physical contact with other locusts. In the Oxford experiments, an extra treatment was included which provided olfactory cues without visual or contact stimulation. Our results confirm that transformation from the solitarious to the gregarious phase of locusts is complex, and that different phase characteristics not only follow different time courses, but are also controlled by different suites of cues. As predicted from earlier studies, behavioural phase change was evoked by non-species-specific cues. Rearing in contact with either species was fully effective in inducing gregarious behaviour, as was the combination of the sight and smell of other locusts, but odour alone was ineffective. Colour phase change was shown to comprise two distinct elements that could be dissociated: black patterning and yellow background. The former of these could be induced as effectively by rearing S. gregaria nymphs in a crowd of L. migratoria migratorioides as by rearing with conspecifics. Sight and smell of other locusts also triggered black patterning and, unlike behavioural change, some black patterning was induced by odour cues alone. Hence, physical contact was not needed to induce gregarious black patterning. Yellow colouration, however, was only fully induced when locusts were reared in contact with conspecifics, implying the presence of a species-specific contact chemical cue.     

A miniaturized assay to quantify effects of chemicals or physical stimuli upon locust activity

Solitary and gregarious locusts differ in many traits, such as body color, morphometrics and behavior. With respect to behavior, solitary animals shun each other, while gregarious animals seek each other＇s company, hence their crowding behavior. General activity, depending on the temperature, occurs throughout the day but is much lower in solitary locusts. Solitary locusts occasionally fly by night while gregarious locusts fly regularly during daytime （swarming）. In search of new assays to identify substances that control or modify aspects of （phase） behavior, we designed a simple activity assay, meant to complement existing behavioral measurement tools. The general activity is reflected in the number of wall hits, that is, the number of contacts between the locust and the vertical walls of a small arena. Using this single parameter we were able to quantify differences in total activity of both nymphs and adults of isolation-reared （solitary）, regrouped- and crowdreared （gregarious） locusts under different conditions. Furthermore, we demonstrate that there are inter- and intra-phase dependent differences in activities of 5th instar nymphs afar injections of the three different adipokinetic hormones.     

Phase-related body-color polyphenism in hatchlings of the desert locust, Schistocerca gregaria: re-examination of the maternal and crowding effects

The mechanism controlling the body color of hatchlings was studied for the desert locust, Schistocerca gregaria. A pheromonal factor secreted by gregarious female adults into the foam plugs of egg pods has been suggested to cause darkening in their progeny. We re-examined the role of this maternal factor by washing or separating eggs at deposition. Eggs produced by crowd-reared female adults were washed with saline or separated individually without being washed immediately after deposition and the body color of the hatchlings from them was compared with that from the eggs unwashed and kept in the egg pod until hatching. Most hatchlings were dark and no significant difference was found in the proportions of dark- and light-colored hatchlings between the treatments and controls. Likewise, eggs separated before the foam plug deposition produced dark-colored hatchlings as in the un-separated controls. These results demonstrated that neither washing nor separation of eggs at deposition affected the hatchling body coloration. The variation in hatchling body color was correlated closely to the body weight at hatching, indicating that hatchling body color had been determined maternally. Green hatchlings reared under crowded conditions remained green until the second stadium at which black patterns were induced. It was concluded that body color at hatching has been determined maternally and crowding during the first nymphal stadium influences nymphal body color but its effect is not manifested until the second stadium. The present study casts doubts on the presence of a recently suggested pheromonal factor on the color of the hatchlings.     

External sensilla of the locust abdomen provide the central nervous system with an interganglionic network

External mechanoreceptors and contact chemoreceptors on the cuticle of the sixth abdominal segment of locusts have divergent primary projections of their sensory neurons that form arbours in the segmental and anterior abdominal ganglia. Homologous interganglionic projections from adjacent segments converge in the neuropile of each abdominal ganglion. Of the contributing types of sensilla, three were previously unknown for locust pregenital segments: tactile mechanosensory hairs with dual innervation, external proprioceptors of the hairplate type covered by intersegmental membranes and single campaniform sensilla that monitor cuticular strain in sternites and tergites. In general, interdependence of motor coordination in the abdominal segments is based on a neural network that relies heavily on intersegmental primary afferents that cooperate to identify the location, parameters and strength of external stimuli.     

The endocrine control of phase transition: some new aspects

Abstract. The present article summarizes some recent findings relating to the underlying mechanism of phase transition in locusts, from the nonswarming solitarious phase to the swarming gregarious phase. These phases differ in many traits, such as colouration, morphometrics and behaviour. The most comprehensive theory at present to explain the switch from the nonswarming to the swarming form is that the locusts are brought together by the heterogeneity of the environment. They gather at preferential structures and food plants and physical contact then stimulates individuals to gregarize. Phase change can also be transferred across generations by maternal pheromones. The endocrine regulation of phase polymorphism is still not fully understood. The role of ecdysteroids has been studied, so far with no final conclusion. It is remarkable that the prothoracic glands persist longer in isolated-reared adults, which implies that these glands continue to play a role, although they no longer release important amounts of ecdysteroids. Juvenile Hormone, without any doubt, induces certain solitarious characteristics, such as green colouration, but is not the primary causal factor. A real breakthrough was the discovery of [His⁷]-corazonin, made possible by using a novel assay system, the Okinawa albino mutant of Locusta migratoria , which was known to be deficient in this hormone. This peptide, which is produced in the brain and is most likely released via the corpora cardiaca, promotes the gregarious black pigmentation. It also plays a role in morphometrical phase change as well as in behavioural alterations. Corazonin is apparently quite an important peptide not only in locusts, but also in insects in general.