Intracellular application of polyamine and polyamine amide inhibits the quisqualate-sensitive ionotropic glutamate receptor of locust (Schistocerca gregaria) muscle

The effects of intracellularly-applied philanthotoxin-343 (PhTX-343) on single channel currents gated by quisqualate-sensitive glutamate receptors (qGluR) of locust leg muscle have been studied. PhTX-343 initially increased qGluR channel open probability, mainly by virtue of an increase in mean channel open time, but this was followed by a decrease in channel open probability, sometimes to zero, because of a decline in the frequency of channel openings and a decline in mean channel open time. These results suggest that antagonism of qGluR by PhTX-343 can arise, in part, through binding of the toxin to a site or sites on the intracellular domain of this receptor.     

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.     

PCR primers for polymorphic microsatellite loci in the desert locust,Schistocerca gregaria (Orthoptera: Acrididae)

Nine pairs of polymerase chain reaction (PCR) primers that amplify polymorphic microsatellite loci in the desert locust, Schistocerca gregaria (Forskal), were developed using a magnetic bead‐based enrichment protocol. A sample of 48 locusts collected during the 1993 and 1995 upsurge periods in Eritrea, East Africa, were genotyped. The number of alleles per locus ranged from six to 20; the average was 12.67. Allelic distributions were significantly different between samples from different localities.     

The olfactory co-receptor Orco from the migratory locust (Locusta migratoria) and the desert locust (Schistocerca gregaria): identification and expression pattern

In locusts, olfaction plays a crucial role for initiating and controlling behaviours, including food seeking and aggregation with conspecifics, which underlie the agricultural pest capacity of the animals. In this context, the molecular basis of olfaction in these insects is of particular interest. Here, we have identified genes of two orthopteran species, Locusta migratoria and Schistocera gregaria, which encode the olfactory receptor co-receptor (Orco). It was found that the sequences of LmigOrco and SgreOrco share a high degree of identity to each other and also to Orco proteins from different insect orders. The Orco-expressing cells in the antenna of S. gregaria and L. migratoria were visualized by in situ hybridization. Orco expression could be assigned to clusters of cells in sensilla basiconica and few cells in sensilla trichodea, most likely representing olfactory sensory neurons. No Orco-positive cells were detected in sensilla coeloconica and sensilla chaetica. Orco expression was found already in all nymphal stages and was verified in some other tissues which are equipped with chemosensory hairs (mouthparts, tarsi, wings). Together, the results support the notion for a decisive role of Orco in locust olfaction.     

Inhibiton and gamma-aminobutyric acid-induced conductance on locust (Schistocerca gregaria) extensor tibiae muscle fibres

• 1.1. Increases in membrane conductance (g_m) were induced by GABA in distal bundles 32, 33 and 34 of extensor tibiae muscles of the locust (Schistocerca gregaria).
• 2.2. Bath application of GABA (10⁻⁵−5 × 10⁻³ M) induced reductions in muscle fibre space constant (λ).
• 3.3. GABA (5 × 10⁻³ M) induced additional membrane conductance of 2.21 ± 0.03 × 10⁻⁶ S/mm, 0.38 ± 0.03 × 10⁻⁶ S/mm and 0.29 ± 0.06 × 10⁻⁶ S/mm on muscle bundles 34, 33 and 32 respectively. The greater sensitivity of muscle fibres in bundle 34 to GABA is due at least in part to a larger number of GABA receptors on bundle 34 muscle fibres.
• 4.4. The decrement of electrotonic potentials in the presence of GABA were measured over distances of both half fibre length and whole fibre length. Good agreement was obtained between changes in space constant produced by GABA using half fibre length and whole fibre length data.
• 5.5. By taking into account changes in space constant induced by GABA it was possible to demonstrate that presynaptic GABA receptors were involved in the inhibition of slow excitatory postsynaptic potentials by GABA.
• 6.6. “Slow” excitatory postsynaptic potentials recorded under current clamp were inhibited in a dose-dependent manner by GABA. This inhibition was not dependent on muscle-fibre GABA sensitivity and could not be completely accounted for by GABA-induced changes in the cable properties of the muscle fibres.

     

The influence of environmental microstructure on the behavioural phase state and distribution of the desert locust Schistocerca gregaria

Abstract. In previous studies we used logistic regression analysis to quantify the change in behavioural phase state of Schistocerca gregaria (Forskål) nymphs subjected to variations in population density. Such work involved restricting insects in small containers either alone or in a crowd. In the present paper we have shown that the fine-scale distribution of food plants, perches and favourable microclimatic sites influences the spatial distribution of locusts, both in the laboratory and under semi-field conditions. When multiple resource sites were provided, solitarious locusts tended to disperse and behavioural gregarization was inhibited. However, provision of only a single site promoted congregation, overcoming the tendency of solitarious insects to avoid each other, and led to behavioural gregarization. The time-course and extent of this response was fully consistent with our earlier experiments using enforced crowding. We suggest that such quantitative, experimental studies of the effects of environmental microstructure on behaviour may yield fundamental insights into the dynamics of plague formation in the desert locust.     

Pharmacological study of the second messengers that control rectal ion and fluid transport in the desert locust (Schistocerca gregaria)

The involvement of second messengers in modulating Schistocerca gregaria rectal ion and fluid transport was investigated using two in vitro bioassay systems: everted rectal sacs and rectal flat sheets. Various agents known to block or activate specific signal transduction pathways were employed in these bioassays. Cyclic AMP stimulated rectal fluid reabsorption (J_v) and Cl⁻ transport (I_sc) to the same extent as aqueous extracts of corpus cardiacum storage lobes. Cyclic GMP also partially (50%) stimulated both rectal J_v and I_sc. Exogenous Ca²⁺ was not required for the maintenance of rectal transport, indeed Ca²⁺ free conditions increased the amount of stimulatable J_v. There was some evidence indicating intracellular Ca²⁺ may play a minor role in controlling rectal transport. The phospholipase C mediated signal transduction pathway was not involved with the stimulation of rectal transport, and appeared to have an inhibitory role. Neuroparsins, antidiuretic neuropeptides from Locusta migratoria, showed no activity upon either S. gregaria rectal ion or fluid transport. The findings of this study show that the two closely related insects possess discrete antidiuretic factors which stimulate rectal transport via different signal transduction pathways. © 1996 Wiley-Liss, Inc.     

Pharmacology of GABA receptors on skeletal muscle fibres of the locust (Schistocerca gregaria)

GABA and the trans isomer of 4-aminocrotonic acid are equally potent at inducing increases in Cl- conductance when applied to distal extensor tibia muscle fibres of the locust (Schistocerca gregaria). beta-Alanine, norvaline, glycine and norleucine induced conductance increases of less than 5% of GABA responses. C9 and meso-di-GABA did not alter input conductance in a manner consistent with actions on a GABA receptor Cl- channel complex. Picrotoxin and anisatin were equally potent GABA antagonists, however bicuculline and penicillin G did not reduce GABA-induced changes in input conductance. Pentobarbitone, in addition to inducing an increase in K+ conductance, potentiated GABA-induced increases in Cl- permeability.     

Isolation and characterization of nine polymorphic microsatellite loci from the desert locust,Schistocerca gregaria

Because of the scarcity of polymorphic genetic markers, only a few genetic studies on the population structure of the desert locust, Schistocerca gregaria, have been carried out. We isolated and characterized nine polymorphic dinucleotide microsatellite loci. These markers were evaluated using individuals from Niger and Senegal. Seven of these microsatellite markers are also applicable to the nongregarious subspecies Schistocerca gregaria flaviventris. Cross‐species applicability was limited to one of the loci in the sister species S. americana and in the locust Locusta migratoria.     

Yellowing,morphology and behaviour in sexually mature gynandromorphs of the desert locust Schistocerca gregaria

The morphology, colouration and sexual behaviour of two gynandromorph adults of the desert locust Schistocerca gregaria Forskål are described. In each of these specimens, the left half of the external genitalia has male characteristics and the right half has female characteristics. Yellowing of the epidermis occurs to different degrees in normal sexually mature male and female adult S. gregaria under crowded conditions. Two hypotheses are known to explain this phenomenon. One suggests involvement of a sex‐hormone/receptor complex, whereas the other proposes different sensitivities of the epidermis to the same hormonal environment. To examine which hypothesis is more likely, one gynandromorph adult is kept under crowded conditions and the other is maintained under isolated conditions. In the former, the left half of the body turns bright yellow, as in a sexually mature crowded male, and the right half is brownish with little yellowing, as in a sexually mature crowded female of the same age. The bilaterally divided body colouration may support the second hypothesis. In the second gynandromorph, which is isolated after adult emergence, the body colour remains brownish. Upon sexual maturity, this individual is kept together with normal male or female adults for behavioural observations. It attempts to mount a female but is approached and mounted by males.     

Spatial distribution of populations of solitarious adult desert locust (Schistocerca gregaria Forsk.) on the coastal plain of Sudan

Abstract 1 Densities of solitarious adult desert locusts were measured on regular grids of up to 126 sample sites in the southern part of the coastal plain of Sudan during the winters of 1999/2000 and 2000/2001. Geostatistical procedures were used to characterize spatial dependence of locust density, to evaluate the possibility of estimating locust densities at unvisited sites, based on information obtained at surveyed sites, and to create density maps. 2 Sample variograms indicate that population densities were spatially correlated over ranges from 5 to 24 km. The range of spatial correlation decreased as dry conditions towards the end of the rainy season concentrated the locusts in contracting areas of sufficient humidity and availability of green vegetation. The rather small ranges of spatial correlation indicate that sampling needs to be conducted at a refined scale (< 24 km between sample points) to avoid missing hot spots of desert locust. 3 Locust densities were highly correlated with cover abundance of the wild plant Heliotropium arbainense and cultivated millet, Pennisetum typhoidum. The association of locusts with these host plants can be used to target sampling and enhance detection chance. 4 The relationship between sampling intensity and kriging variance was explored. Implications for monitoring of desert locust are discussed.     

The sense organs on the mouth parts of the Desert locust (Schistocerca gregaria)

The "hairs" and various types of sensilla present on the mouth parts of Schistocerca gregaria are described. The distribution of the sensilla on the clypeo-labrum, labium and theHmaxillae has been plotted in detail, and the general distribution of all types of sensilla on each of the mouth parts is described.
A comparison is made between the distribution of certain sensilla on the clypeo-labrum in first instars and adults.
The probable role of the sensilla in feeding is discussed.     

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.     

Yellowing and YPT gene expression in the desert locust,Schistocerca gregaria: Effects of developmental stages and fasting

The yellow protein of the takeout family (YPT) controls the development of yellow body color in the desert locust. This study focused on two aspects related to YPT in the locust. We first examined the expression pattern of YPT during nymphal stages because yellowing was not obvious during the early instars. YPT expression levels were extremely low in the second and third instars compared with the last two nymphal instars. Warm rearing temperature and juvenile hormone (JH) injection, which stimulated YPT expression in the late instars, had little effect in the second instar, suggesting that YPT expression during the early instars was suppressed and could not be stimulated by either of these factors. We also investigated delayed yellowing in fasting male adults, under the hypothesis that fasting decreased the JH titers and delayed the onset of YPT expression. Yellowing was delayed in fasting adults compared with well‐fed adults and YPT expression was stimulated by JH injections at Day 15. However, we failed to obtain evidence that fasting significantly influenced the expression levels of YPT and the JH early‐inducible gene Krüppel homolog 1 at Days 15 and 20 post‐adult emergence. Results suggest that a YPT‐independent mechanism possibly induces delayed yellowing in fasting males.     

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.     

The role of metabotropic glutamate receptor (mGluR) ligands in parkinsonian muscle rigidity

Summary. It has been shown that the primary striatal dopaminergic hypofunction which is at the origin of Parkinson's disease, results in a secondary hyperactivity of glutamatergic neurotransmission. In the search for a therapy of Parkinson's disease, ionotropic, mainly NMDA, receptor antagonists were found to have moderately beneficial, yet also some undesirable side-effects. Therefore the present study was aimed at determining whether some metabotropic glutamate receptor (mGluR) ligands may have antiparkinsonian effects in the haloperidol-induced muscle rigidity. To this end three mGluR ligands were used: the potent and selective mGluR I antagonist (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA), the mixed group II agonist/group I antagonist (S)-4-carboxy-3-hydroxyphenyl-glycine ((S)-4-C3HPG), and the potent group II agonist (+)-2-aminobicyclo[3.1.0.]hexane-2,6,-dicarboxylic acid (LY354740). Only LY354740 penetrated the brain from the periphery; for this reason other drugs were injected bilaterally into the rostral striatum or nucleus accumbens. The muscle tone was recorded by a mechanomyographic/electromyographic (MMG/EMG) method which measured the resistance of a rat's hind foot and the EMG reflex response of its muscles to passive movements. (S)-4C3HPG (5 and 15 μg/0.5 μl) and LY354740 (5 and 10 mg/kg i.p.) diminished the muscle rigidity induced by haloperidol (1 mg/kg i.p.). AIDA (0.5–15 μg/0.5 μl) injected into the striatum was only slightly effective in the highest dose used. However, when injected into the nucleus accumbens AIDA (15 μg/0.5 μl) significantly and strongly counteracted the haloperidol-induced muscle rigidity. Our results suggest that stimulation of group II striatal mGluRs seems to play a major role in diminution of parkinsonian-like muscle rigidity. However, it seems that the antagonism of group I mGluRs located in the nucleus accumbens may also be of importance to the antiparkinsonian effect. Received August 31, 1999 Accepted September 3, 1999     

Partial purification and some properties of pyruvate carboxylase from the flight muscle of the locust (Schistocerca gregaria)

A procedure is described for the partial purification of pyruvate carboxylase (pyruvate:CO2 ligase (ADP-forming), EC 6.4.1.1) from the flight muscle of the locust (Schistocerca gregaria). Characterisation of the kinetic properties of this enzyme indicates that it is activated by acetyl-CoA, is insensitive to inhibition by di- and tricarboxylic acids and exhibits an apparent Km for HCO3-(16 mM) which differs by an order of magnitude from that observed for other pyruvate carboxylases. It is suggested that activation of this locust flight muscle pyruvate carboxylase during the rest leads to flight transition may result from increases in the concentrations of pyruvate and HCO3- under these conditions.     

Synthesis and properties of photolabile (caged) phosphotriester derivatives of dinucleoside phosphates

Dinucleoside phosphates that harbor phosphate groups transiently blocked (caged) byo-nitrobenzyl oro-nitroveratryl residues were synthesized. It was shown that the conditions of the UV-induced deprotection largely depend on the nature of the protective group. The phosphotriesters obtained were resistant toward snake venom phosphodiesterase and nucleases of the cellular extract. The synthesis of the dinucleoside phosphates containing a photolabile group preceeded the incorporation of the modified blocks into extended oligonucleotides by the phosphoramidite method.     

The distribution of dopamine-like immunoreactivity in the thoracic and abdominal ganglia of the locust (Schistocerca gregaria)

Summary An indirect gold-labeling method utilizing the lectin from Limax flavus was employed to characterize the subcellular distribution of sialic acid in glycoconjugages of the salamander olfactory mucosa. The highest density of lectin binding sites was in secretory vesicles of sustentacular cells. Significantly lower densities of lectin binding sites were found in secretory granules of acinar cells of both Bowman's and respiratory glands. Lectin binding in acinar cells of Bowman's glands was confined primarily to electron-lucent regions and membranes of secretory granules. In the olfactory mucus, the density of lectin binding sites was greater in the region of mucus closest to the nasal cavity than in that closest to the epithelial surface. At the epithelial surface, the density of lectin binding sites associated with olfactory cilia was 2.4-fold greater than that associated with microvilli of sustentacular cells or non-ciliary plasma membranes of olfactory receptor neurons, and 7.9-fold greater than non-microvillar sustentacular cell plasma membranes. Lectin binding sites were primarily associated with the glycocalyx of olfactory receptor cilia. The cilia on cells in the respiratory epithelium contained few lectin binding sites. Thus, sialylated glycoconjugates secreted by sustentacular cells are preferentially localized in the glycocalyx of the cilia of olfactory receptor neurons.