Actinomycin-D and chiasma frequency in Schistocerca gregaria (Forskål)

The response of chiasma frequency to a high dose of Actinomycin-D (60 g/insect) was studied in male imagines of Schistocerca gregaria. Two stocks of locust were employed, one possessing a reduced chiasma frequency as a result of inbreeding. The high dose of AD caused rapid insect mortality, which limited the period of sampling to only 36 hours after injection. The chiasma frequencies of L and M bivalents were increased over the whole period of sampling in the inbred stock, and accurate estimates of meiotic timing place the period of sensitivity to the drug in late zygotene or pachytene. The other more heterozygous stock showed no response to AD, and in neither stock were the chiasma frequencies of the S bivalents affected. The possible mechanisms of the drug's action are briefly discussed.     

The Anatomy of the Tarsi of Schistocerca gregaria Forskål

Summary The tarsus of S. gregaria is divided into three units (here called segments) and an arolium set between a pair of claws. The first segment bears three pairs of pulvilli in the fore and middle legs, and one pair and two single pulvilli in the hind legs. Segment two bears a pair of pulvilli, segment three one long pulvillus and the arolium a similar pad on the undersurface. The outer layers of the arolium pad differ from those of the pulvilli in possibly lacking an epicuticle and in having a layer of cuticle which, unlike the corresponding layer in the pulvilli, does not stain with protein stains. The claws and dorsal surfaces bear trichoid sensilla, basiconic sensilla and campaniform sensilla. Smaller basiconic sensilla and canal sensilla occur on the proximal part of the pulvilli, and basiconic sensilla on the arolium undersurface. Internally the cuticle is modified in the arolium and pulvilli so that rods of probably chitin and resilin are formed. This would impart flexibility to the undersurfaces whilst retaining some degree of rigidity which might prevent damage to the small and delicate sense organs on the pulvilli. The tip of the arolium is specialised for adhesion, and there are two large neurones internally which could conceivably monitor attachment or detachment of the tip. There are chordotonal organs in segment three, and several other large neurones throughout the tarsus, some of which are associated with the slings of tissue holding the apodeme in a ventral position. Gland cells occurring in the dorsal epidermis of the adult mature male are also briefly described.     

The origin and nature of the ecdysial membrane in Schistocerca gregaria (Forskål)

The few innermost laminae of the fully formed larval endocuticle of Schistocerca gregaria show remarkable resistance to the action of the moulting fluid as well as to concentrated mineral acids. These laminae become subsequently isolated during moulting through the dissolution by the moulting fluid of the less resistant outer laminae of the endocuticle. They give rise to a discrete ecdysial membrane which persists throughout the premoult period and is ultimately cast with the inner lining of the larval exuvium. In Schistocerca an ecdysial membrane is formed at the larval adult moult as well as at all the preceding larval moults.     

The control of chiasma distribution in the locust,Schistocerca gregaria (Forskål)

Chiasma distribution at diplotene in Schistocerca gregaria males can be taken to indicate the positions at which crossing over occurred prior to diplotene since chiasma terminalisation is entirely absent. Analysis of chiasma frequency and position leads to a model for the mechanism controlling distribution which has three main components. — i) The bivalents vary in length between cells due to unknown factors and increase in bivalent length leads to an increase in chiasma frequency. — ii) Within bivalents chiasma initiation is sequential from telomere to centromere with the first chiasma usually forming close to the telomere. — iii) Interference operates with the same polarity and determines a distance within which crossing over is precluded.     

Some aspects of intermediary metabolism in the desert locust (Schistocerca gregaria Forskål)

The incorporation and distribution of radioactivity from [¹⁴C] glucose, [2-¹⁴C] acetate, and [1:4-¹⁴C₂] succinate into the soluble metabolic intermediates of homogenates of the fat-body, head, and leg muscle of Schistocerca gregaria Forskål have been studied. The tissue homogenates were found to utilize the labelled substrates, but the patterns of incorporation of the radio-activity from each substrate varied with the tissue.     

The effect of X-irradiation on male meiosis in Schistocerca gregaria (Forskål)

Symmetrical exchanges between non-homologous chromosomes were recovered following irradiation of germ-line cells of S. gregaria at different developmental stages. No X-Autosome exchanges were observed. It was found that the frequencies with which autosomes of the three size groups L, M and S participated in exchange agreed with the frequencies expected based on effective exchange lengths of polarized interphase chromosomes. All of the observed symmetrical exchanges were between euchromatic segments of the chromosomes and though many of the exchange points were close to the centromere, no exchanges were found with break points actually in the centric heterochromatin. None of the heterozygous symmetrical exchanges were seen to have an observable influence on the chiasma conditions of the cell.     

The effect of X-irradiation on male meiosis in Schistocerca gregaria (Forskål)

The pattern of response of chiasma frequency to X-irradiation has been studied in germ line cells of male imagines of Schistocerca gregaria. A correlation has been established between the observed changes in chiasma frequency of the L and M type bivalents and the time in the meiotic cycle at which the treatment is given. Two radio-sensitive periods have been identified in meiosis itself. At one (meiotic DNA synthesis) X-irradiation produces a decrease in chiasma frequency while at the other (leptotene-early zygotene) the treatment leads to an increase in chiasma frequency. Small bivalents however do not respond to treatment and form a single chiasma under all conditions.     

The fine structure of the terminal sensilla on the maxillary palps of Schistocerca gregaria (Forskål) (Orthoptera,Acrididae)

Summary The fine structure of the terminal sensilla on the maxillary palps of Schistocerca gregaria has been investigated. Most organules include six neurons with dendrites extending to the tip of the cuticular peg, the opening of which is controlled so that the dendrites are not always exposed. The neurons are isolated from each other by a neurilemma cell and two other glial cells, while typical epidermal cells containing dense bundles of microtubules support the whole group of cells. At the poles of the neurons are specialised areas in which the cytoplasm is differentiated from that elsewhere. It contains a large number of mitochondria and small helical structures, while close to it are characteristic spheres of membranes, termed onion bodies, in various stages of development.It is suggested that the fluid bathing the distal parts of the dendrites and exuding from the tip of the peg has a number of specialised functions. It is probably concerned in forcing open the tip of the peg by hydrostatic pressure, it prevents the exposed tips of the dendrites from desiccating and it acts as a transmitter in which chemicals on the surfaces touched by the sensillum must dissolve before reaching the dendrites. This fluid may be produced by the neurilemma cell or by the neurons themselves. Closure of the pegs does not seem to produce any material reduction in the overall loss of water by the insect.Each neuron sends an axon to the brain; there is no peripheral fusion of axons. Possibly one neuron has a mechanoreceptor function, although no specialised terminal at the base of the peg has been observed. The concentration of mitochondria at either end of the neuron may be concerned in the production of action potentials, while the cavity of the peg and tormogen cell perhaps has a role in the conduction of the receptor potential to the perikaryon. Intercellular connections are such as to give mechanical stability to the cells of the organule and permit transport between the cells. Extracellular tubules extending from the wall of the peg into the cell complex may serve to anchor the peg during the moulting process.We are grateful to the Royal Society for a grant for the purchase of an ultramicrotome, to the Anti-Locust Research Centre for supplying the locusts, and to various colleagues for assistance and advice. We are also indebted to the Cambridge Instrument Company Ltd. for permission to publish Figs. 2 and 3.     

Polyphenols and their quinone derivatives in the cuticle of the desert locust,Schistocerca gregaria (Forskål)

• 1.(1) Severl ortho-dihydroxyphenols, both deaminated and undeaminated, are present in the abdominal cuticle of adult Schistocera both before and after it has naturally hardened. They are thought to be derived from the phenolic substance formed in the blood by the enzymatic oxidation of tyrosine.
• 2.(2) It is shown that degradation of ortho-dihydroxyphenols takes place in the cuticle, and is accompanied by decarboxylation.
• 3.(3) No para-dihydroxyphenols are present, however, their absence being due to the fact that the cuticle is incapble of hydroxylating the naturally occurring aromatic amino acids.
• 4.(4) It is shown, in conclusion, that the colourless and unresistant exocuticle of Schistocera, which differs markedly from that of darkly coloured insects i.e. Periplaneta (Kennaugh, 1958), is tanned only by ortho-quinones.
     

The effects of azadirachtin on the testes of the desert locust,Schistocerca gregaria (Forskål)

Testes removed from Schistocerca gregaria, injected with 5 or 7&mgr;g azadirachting(-1) body wt on day 0-2 of the Vth instar and killed by decapitation 20days after treatment, showed significant reductions between the widths, lengths and volumes of the treated groups, compared to control insects. Under cytological examination these testes, from insects exhibiting classical signs of azadirachtin poisoning, showed arrested spermatogenic meiosis at Metaphase I.     

The fine structure of the salivary glands of the desert locust Schistocerca gregaria Forskål

Summary This paper describes the structure of the salivary glands of Schistocerca gregaria as seen under the electron microscope and the light microscope. The salivary glands consist of a number of acini located on both sides of the pro-, meso-, and metathoracic segments of the locust. Each acinus is drained by a duct which unites with others from the same side to form a lateral collecting duct. The ducts from the two sides join in the head capsule and open into a salivary cup on the labium. Each acinus consists of parietal cells, zymogenic cells, duct cells, tracheoblasts, sheath cells and pigment cells. The parietal and zymogenic cells are the main sites for the production of the salivary gland secretions, which pass through microvilli from the zymogenic cells to the lumen of the ducts within the acinus. Outside the acinus each duct is composed of highly specialized cells with infolded basement membranes extending about a third of the way across the cell. The cytoplasm between the membranes contains elongated mitochondria and glycogen granules. The apical border of the cell is thrown into microvilli which are closely aggregated under the cuticle lining the duct. These cells have all the features of cells previously described in vertebrates and invertebrates which are known to absorb water and/or ions. Absorption of water from the gut could allow the excretion of hypertonic saliva by the locust.     

Glandular pouches of the genital chamber of female Schistocerca gregaria (Forskål) (Orthoptera : Acrididae)

Females of the desert locust, Schistocerca gregaria, have a pair of conspicuous glandular pouches associated with the genital chamber and gonoducts. Each pouch consists of a cuticular sac with an epithelium comprising at least 3 types of cells, namely epidermal cells, vacuolated secretory cells, and duct cells. The vacuole of each secretory cell is connected to the cavity of the pouch by a long, convoluted, cuticular duct some 1 μm in diameter, which runs through the cuticle. Each duct has an accompanying duct cell closely situated. The cuticle is perforated also by numerous fine ducts that do not extend into the epithelium: these appear to be large pore canals. Plates of secretion with a wax-like appearance are found in some pouch cavities, often forming close replicas of the latter. All the major features mentioned above are found in females with undeveloped ovaries as well as those with mature oöcytes: the pouches show little alteration in structure with advancing maturity. The nature of the pouches is compared with that of other Acrididae, and their functions are discussed.     

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.     

The vermiform larva of Schistocerca gregaria (Forskål): Form and activity (Insecta,Orthoptera)

A detailed study of the vermiform larva of Schistocerca gregaria was made using film analysis in combination with morphological studies. The adaptations of the body are illustrated, and the use of these in digging up to the surface of the ground is described. The means of orientation were investigated, and unusual club-tipped hairs are suggested as important mechanoreceptors.Now Centre for Overseas Pest Research.     

On the origin of the desert locust Schistocerca gregaria (Forskål) (Orthoptera: Acrididae: Cyrtacanthacridinae)

The locust genus Schistocerca (Stål) has a transatlantic disjunction, which has been controversial for more than a century. Among 50 species within the genus, only one species, the desert locust (S. gregaria Forskål), occurs in the Old World, and the rest occur in the New World. Earlier taxonomists suggested that the desert locust is a migrant from America, but this view was strongly challenged when a large swarm of the desert locust successfully crossed the Atlantic Ocean from West Africa to the West Indies in 1988. The currently accepted view, supported by this incident, is that the New World species are descendants of a gregaria-like ancestor, and the desert locust would be ancestral to the rest of the genus. However, there is surprisingly little evidence to support this view other than the 1988 swarm. I present the most comprehensive phylogenetic study that suggests that the desert locust originated from the New World, contrary to the accepted view. I also present a hypothesis about how the ancestral Schistocerca might have colonized the New World in the first place in light of phylogenetic relationships with other cyrtacanthacridine genera.     

The intermediate moult (First Ecdysis) of Schistocerca gregaria (Forskål) (Insecta,Orthoptera)

Ecdysis of the embryonic cuticle has been studied in detail. The initiation and mechanical processes involved in this ecdysis, and the associated differential size increases of cuticular parts have been given most attention. The roles of air swallowing and of thoracic contraction are most imoprtant for rupturing the old cuticle, while abdominal contractions assist the whole process. Some specialized cuticular structures are described.     

Isolation and properties of a glycerophosphate acylating fraction in the fat body of Schistocerca gregaria (Forsk?l).

An acyl-CoA-L-alpha-glycerophosphate acyltransferase system has been found in the fat body of the locust Schistocerca gregaria (Forsk?l). After homogenization and differential centrifugation the enzyme system has been localized in two distinct particulate fractions. In both fractions phosphatidic acid was the main reaction product. The 10 000 g -30 000 g particulate fraction was further studied. The enzyme system is very sensitive to pH and Mg2+ concentration. An apparent Km of 0.3-0.5 mM for glycerophosphate was measured. The substrate concentration curve for palmitoyl-CoA is influenced by the protein concentration in the assay medium. This effect would partly explain the non-lineariy of the acylation reactions with respect to enzyme concentration. These observations are correlated with physiological phenomena.     

Zur Regelung der Stellung des femur-Tibia-Gelenkes im Mesothorax der Wanderheuschrecke Schistocerca gregaria (Forskål)

The feedback loop controlling the position of the femur-tibia-joint in cut open. As input to the open loop system the femoral chordotonal organ is stimulated by sine, step and triangular functions. As output of the system the position of the freely moving tibia is used. The attributes of the system are similar to those of the femur-tibia-control-system of Carausius. The main differences are: In Schistocerca the gain is much lower. The upper corner frequencies are also lower. Therefore the system has a large phase-reserve (see Bode-plot, Fig. 6). The asymmetry of the system is not so high. The adaptation time after a step stimulus is longer. — The results are confirmed by experiments with the closed loop system (coupling an inert mass; return movements after passive bending of the joint). In a first approximation the system can be described by two independent subsystems consisting of a rectifier, a low pass and a high pass filter each.—The evolution of the system in Carausius is discussed.

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Mit Unterstützung der Deutschen Forschungsgemeinschaft (Ba 578/1)

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Der Artikel enthält einen Auszug aus der Dissertation von I. Ebner (Kaiserslautern, 1976)     

Antifeedant effects of in vitro culture extracts of the neem tree,Azadirachta indica against the desert locust (Schistocerca gregaria (Forskål))

Callus and micropropagated shoots were initiated from leaf explants of the neem tree, Azadirachta indica A. Juss. A variety of whole plant and in vitro cell cultures from neem seedlings of Ghanian origin were tested for insect antifeedant compounds using the desert locust (Schistocerca gregaria (Forskål)). Feeding suppression occurred when whole extracts of seed, leaf, callus, suspension and shoot cultures were tested in no-choice feeding bioassays. Controls of sucrose, carrot callus and the plant growth medium showed no feeding deterrence. Azadirachtin, the main known antifeedant in neem seed kernels, was quantified from a seed extract by HPLC but was not detected in any of the other extracts. Antifeedancy was determined during batch growth of a suspension culture which had been in culture for 5 months; results indicated that antifeedants were still being formed and that levels increased after maximum biomass was attained.