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.     

Karyakartia egyptensis n. sp. (Digenea: Lepocreadiidae) from the Jarbua terapon, Terapon jarbua (Forsskål) (Perciformes: Terapontidae), from the Red Sea and emendation of Karyakartia

Karyakartia egyptensis n. sp. (Digenea: Lepocreadiidae: Lepocreadiinae) is described from the intestine of the Jarbua terapon, Terapon jarbua (Forssk?l), collected from the Red Sea off the coast of Hurghada, Egypt. Karyakartia egyptensis n. sp. differs from K. pambanense in that the former species possesses larger spiniform structures around the perimeter of the mouth (48-54 microm as compared with 25-30 microm), a uroproct rather than ceca that end blindly or form a cyclocoel, and a somewhat smaller egg (60-68 microm as compared with 70-73 microm).     

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.     

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.     

Some observations on the juvenile hormone effect of farnesol in Rhodnius prolixus Stål (Hemiptera)

Pure farnesol applied to the surface of the cuticle in Rhodnius prolixus will reproduce all the effects of the juvenile hormone. It causes retention of larval characters in the moulting fifth-stage larva, it brings about a partial reversal of metamorphosis in the moulting adult, and it induces yolk formation in the decapitated adult female. This last observation provides further evidence for the probable identity of the yolk-forming hormone and the juvenile hormone.Farnesol (like the active extract from cecropia) exerts no effect on the progressive differentiation of wing lobes and genitalia in the larval stages of Rhodnius. This differentiation within the larva is controlled by the moulting hormone and is quite distinct from the metamorphosis controlled by the juvenile hormone.     

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 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.     

Observations on two species ofSystoechus (Diptera: Bombyliidae) preying on the desert locust,Schistocerca gregaria (Forskål), in Eastern Africa

Résumé Les larves de deux espèces deSystoechus (somali oldroyd etaurifacies greathead), attaquent les œufs du criquet pèlerin (Schistocerca gregaria Forsk?l) en Afrique orientale. La morphologie des larves et des pupes de ces deux espèces et de deux autres a été étudiée en détail. Les larves sont presque identiques; seulement quelques faibles différences ont été observées dans la forme des sclérites céphaliques. Les pupes, d'autre part, présentent des caractères plus distincts. La distribution duSystoechus parmi les lieux d'oviposition duSchistocerca et parmi les oothèques d'une même station est très irrégulière. Chaque larve demande 8–10 œufs (c'est-à-dire un huitième d'une oothèque) pour le développement complet. On trouve souvent plus d'une larve dans l'oothèque, mais il n'en résulte pas la destruction de tous les œufs. Le développement larvaire et le stade de pupe durent chacun à peu près une semaine, mais la larve développée passe dans le sol une période de repos dont la durée varie de plusieurs mois à plusieurs années. Les pluies déclenchent la formation des pupes; toutes les larves ne se transforment pas à la première pluie; en conséquence, l'éclosion des adultes est très échelonnée.      

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.     

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.     

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.     

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.     

Influence of eyestalk removal on the histochemical distribution of oxidative enzymes in the cheliped muscle of Scylla serrata (Forskål)

Histochemical studies on the oxidative enzymes, NAD- and NADP-dependent isocitrate (IDH) and malate (MDH) dehydrogenases, succinic dehydrogenase (SDH), and cytochrome oxidase of the cheliped muscle of Scylla serrata (Forskål) indicated that their concentrations are relatively lower than those of vertebrate muscle. The site of action of various oxidative enzymes is found to be common in the component fibres varying in diameter. The sarcolemma generally exhibited stronger positive reactions for the enzymes than the sarcoplasm.The bilateral removal of eyestalks had a stimulatory effect on the activity of oxidative enzymes. Initially increased activity of SDH, IDH and MDH (NAD-linked) and cytochrome oxidase 2–4 h after eyestalk removal was found to be maintained after 24 h; a noticeable increase in the NADP-linked MDH was also apparent by this time.The eyestalk extract when injected into de-stalked animals, caused a decrease in the levels of SDH, NAD-linked IDH and MDH, and cytochrome oxidase. Biochemical estimations of SDH clearly indicate that bilateral eyestalk extirpation results in remarkably enhanced enzyme activity; conversely, the administration of eyestalk extract brings about a sharp decline in the enzyme concentration. Thus, it seems that the eyestalks may contain a factor regulating oxidative metabolism.     

Characterization of Two Substocks of Penaeus kerathurus (Forskål, 1775) Using the Life-History Parameters

Russian Journal of Marine Biology - The growth parameters were determined separately for the two sexes of Penaeus kerathurus, as well as for the two (northeastern and southern) substocks of the...     

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 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.     

Regeneration of the tibia and somatotopy of regenerated hair sensilla in Schistocerca gregaria (Forskål)

After injury many arthropods are able to regenerate lost body parts and their innervation. Here, regeneration was studied in the desert locust Schistocerca gregaria after amputation of the midleg tibia and tarsus in the first larval instar. A regenerate was formed first in the third larval instar and it increased in size with each larval moult. The regenerate was always unsegmented and remained much shorter than the intact leg parts. The growth rate was initially rather high and decreased thereafter to that of intact parts. The amputation also influenced the growth rate of proximal leg parts (femur and trochanter) resulting in shortened leg segments. The regenerate carried many sense organs like trichoid sensilla and canal sensilla. The primary mechanosensory neurons of the trichoid sensilla projected somatotopically into the mesothoracic ganglion. A comparison of these projections from intact leg segments and regenerates showed a regrow into the target neuropil areas and a restoration of the somatotopy. Intact sensilla on the injured leg and regenerated sensilla expanded their central projections lateral-medially.