Mechanosensitive potassium channels in locust muscle membrane

Patch clamp recordings have been made from adult locust (Schistocerca gregaria) muscle membrane to study the mechanosensitivity of potassium channels (BK and IK) in cell-attached patches by transiently applying measured pressures to the contents of the patch pipettes. The aim of the investigations was to demonstrate a novel gating behaviour by pressure of the BK channel in contrast to the familiar behaviour of the IK channel. The open probability (p ₀) of the IK channel increased rapidly in response to a pressure step and monotonically during a pressure ramp. This gating was readily repeatable and rapidly reversible. The relationship between ln[p ₀/(1–p ₀)] and transmembrane pressure was linear. In comparison, p ₀ for the BK channel was also increased by pressure, but its gating was delayed, cumulative, and hysteretic. Received: 12 July 1998 / Revised version: 7 October 1998 / Accepted: 7 October 1998     

Purification, characterisation and titre of the haemolymph juvenile hormone binding proteins from Schistocerca gregaria and Gryllus bimaculatus

Juvenile hormone binding proteins (JHBPs) were extracted from the haemolymph of adult desert locusts, Schistocerca gregaria, and Mediterranean field crickets, Gryllus bimaculatus. The JHBPs were purified by polyethyleneglycol precipitation, filtration through molecular weight cut off filters and chromatography on a HiTrap heparin column. The juvenile hormone (JH) binding activity of the extracts was measured using a hydroxyapatite assay and the purification progress was monitored by native gel chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The haemolymph JHBPs of both insects are hexamers composed of seemingly identical subunits. The JHBP of the locust has a native Mr of 480 kDa with subunits of 77 kDa, whereas the JHBP of the cricket has a Mr of 510 kDa with subunits of 81 kDa. The locust JHBP binds JH III with moderate affinity (KD = 19 nM). Competition for binding of JH II and JH I was about 2 and 5 times less, respectively. The cricket JHBP also has a moderate affinity for JH III (KD = 28 nM), but surprisingly, competition for binding of JH II was equal to that of JH III and JH I competed about 3 times higher. No sequence information was obtained for the locust JHBP, but the N-terminal sequence of the cricket JHBP shows ca. 56% sequence homology with a hexamerin from Calliphora vicina. Antisera raised against the purified JHBPs were used to measure age- and sex-dependent changes in haemolymph JHBP titres and to confirm that the JHBPs of both species are immunologically different.     

Morphology of the central projections of physiologically characterised neurones from the locust metathoracic femoral chordotonal organ

Summary The metathoracic femoral chordotonal organ of the locust (Locusta migratoria) is an internal proprioceptor composed of mechanosensory neurones which respond to tibial position, velocity, or acceleration, or to combinations of these parameters. Discriminant function analyses confirmed the visual observation that neurones with different responses to tibial movements had different central branching patterns. Some aspects of the projections were consistent for all neurones (e.g., the path taken by the main neurite through the metathoracic ganglion), whereas other regions of branches were consistently reduced or missing in some response classes. Some position-and-acceleration receptors had no main branches off the main neurite, and must therefore make relatively restricted contact with motor neurones and interneurones. Phasic or tonic neurones which responded in ranges of tibial extension had branches which projected further medial in Dorsal Commissures III and IV than similar neurones which responded in ranges of tibial flexion. I compare my results to previous studies of mapping in the insect CNS.Abbreviations (ms) (mt)FCO (mesothoracic) (metathoracic) femoral chordotonal organ - ANOVA Analysis of Variance     

Oxygen consumption of flying locusts

ABSTRACT. Desert locusts ( Schistocerca gregaria Forskal.) were flown into an airstream from a wind tunnel while tethered to a balance. Rate of oxygen consumption and lift were recorded. The mean rate of oxygen consumption of male locusts in level flight at airspeeds between 2.5 and 3m/s was found to be 12.6ml/g/h.     

First Record of the Entomopathogenic Fungus Sorosporella sp. (Deuteromycotina: Hyphomycetes) in Locusta migratoria (Orthoptera: Acrididae) from Madagascar: Symptoms of Infection, Morphology and Infectivity

In Madagascar, a fungal disease was observed in the migratory locust, Locusta migratoria capito, which was caused by the deuteromycete Sorosporella sp. Multiplication of the fungus in locusts results in the formation of brick-red resting spores filling the body of the insect, and in a pale and fragile cuticle which breaks easily, releasing these spores. The conidia of the fungus (only observed in artificial cultures) are cylindrical in shape, measuring 11.0 2.8 mu m. The growth of the fungus was compared on several solid and liquid media, but was invariably slow. The best growth was obtained on a medium containing 3% ground rice, 3% malt extract, 0.3% peptone and 1.5% agar. Attempts were made to initiate artificial infections in L. migratoria migratorioides and Schistocerca gregaria from a laboratory stock. This was carried out by feeding resting spores or through contact with Sorosporella material from agar cultures. However, it rarely resulted in mortalities with typical symptoms. Inoculations by injection were more successful, and resulted in the formation of resting spores in the cadavers 12 to 21 days after inoculation. In Madagascar, Sorosporella sp. seems to be an important, and frequently occurring, locust pathogen. However, the natural mode of infection and the ecology of the fungus are still unclear. Une mycose causee par le champignon deuteromycete Sorosporella sp. a ete observee a Madagascar chez le criquet migrateur Locusta migratoria capito. La multiplication du champignon dans le corps des criquets entraine la formation de spores rouge-briques, qui emplissent celui-ci. Les individus infestes developpent en outre une cuticule pale et fragile, qui se brise facilement, laissant ainsi les spores se disseminer. Les conidies (observees uniquement en cultures artificielles) mesurent 11.0 2.8 mum. La croissance du champignon reste lente sur tous les milieux solides et liquides compares. La meilleure croissance a ete obtenue sur un milieu contenant 3% de riz, 3% d'extrait de malt, 0.3% de peptone et 1.5% d'agar. Des essais d'infection par ingestion de spores d'une part, par contact avec du materiel de culture sur agar d'autre part, ont etes effectues avec L. migratoria migratorioides et Schistocerca gregaria (mate riel d'elevage). Ces essais n'ont abouti que rarement a une mortalite avec des symptomes typiques. Des resultats plus positifs ont ete obtenus au moyen d'inoculations par injection. Ils se forment dans ce cas des spores dans les cadavres des criquets 12 a 21 jours apres l'inoculation. Sorosporella sp. semble etre un agent pathogene des criquets important et frequent a Madagascar. Le mode d'infection naturel, ainsi que l'ecologie de ce champignon restent cependant peu connus.     

Prevalence of a Nosema sp. (Microsporida: Nosematidae) in Natural Populations of Chorthippus brunneus (Orthoptera: Gomphocerinae) in Southern Spain

A microsporidium Nosema sp. was isolated from the grasshopper Chorthippus brunneus (Thunberg) collected in Spain. Infected individuals were found throughout most of the season when nymphs and adults of C. brunneus were present (March-June). Other acridoids collected in the same area were not found to be infected, indicating that this microsporidium is probably host specific. Attempts to artificially infect Dociostarus maroccanus (Thunberg) nymphs failed.     

Neurophysiological analysis of locust behaviour during ecdysis: The slow rhythm underlying expansion

The behaviour of Schistocerca during the expansional stage of the imaginal ecdysis was analysed using electromyograms. The behaviour of the abdomen consisted of a slow rhythm in which tonic compressions and rapid ventilation alternated. The same abdominal motor neurones were excited in the tonic compression and rapid expiratory strokes. The results suggest that different interneurones excited the motor neurones in these two phases. The excitation of muscles in the head and thorax was also correlated with the abdominal rhythm.     

Effects of Temperature, Humidity and Inoculation Method on Susceptibility of Schistocerca gregaria to Metarhizium flavoviride

The effects of temperature on conidial germination and susceptibility of adults of the desert locust , Schistocerca gregaria, to four isolates of Metarhizium flavoviride were determined . In addition , the effects of inoculation method (topical or spray) , spore carrier (oil or water) and ambient relative humidity (RH) on susceptibility of the locust to the most thermotolerant isolate (Mf324) were investigated . There were differences among the isolates in the effects of temperature on germination of conidia after a 24 - h incubation period . Over 90% of conidia of all isolates germinated after 24 h at 30 o C . In contrast , at 40 o C , none of the isolates germinated for up to 72 h . However , there were differences in germination between the isolates at 35 o C . Locust mortality and disease progression were significantly affected by temperature . At both 25 and 30 o C , all isolates induced 98 - 100% mortality within 8 days; however , there were differences between isolates at 35 o C . None of the isolates caused significant mortality at 40 o C . Humidity and inoculation method had no influence on levels of mortaility in fungus treated locusts . In contrast , carrier type significantly affected cumulative mortality . Topical oil treatment resulted in higher overall mycosis than the three other treatments . Control mortality on the other hand was strongly affected by inoculation method and to a lesser extent by humidity and carrier . In these conditions , application of oil by spray was generally toxic at all humidities whereas topical application of water was most toxic at near saturation . The results of these laboratory studies demonstrate the importance of strain selection , formulation and application method in the development of a microbial control agent against the desert locust . Low RH should not impede use of this fungus under dry conditions .     

The distribution of GABA-like immunoreactivity in the thoracic nervous system of the locust Schistocerca gregaria

Summary An antiserum raised against gamma aminobuyric acid (GABA) was used to stain the thoracic nervous system of the locust. It stained both neuronal somata and processes within the neuropile. Among the stained somata, those of the three pairs of common inhibitory motor neurones could be identified in each of the three thoracic ganglia. In the pro- and mesothoracic ganglia five discrete groups of somata are stained, four ventral and one dorsal. In the metathoracic neuromere, an additional second dorsal group can be identified. In the abdominal neuromeres of the metathoracic ganglion both dorsal and ventral somata are stained but the latter cannot be divided into discrete populations. In each ganglion, dorsal commissures (DC) IV and V are composed of stained neurites, DCVII, the supramedian commissure, the perpendicular tract, and all the longitudinal tracts contain both stained and unstained neurites. DCI, II, III and VI, the T and I tracts are unstained. An abundance of GABA-like immunoreactive processes is found throughout the neuropile except for the anterior ventral association centre where stained processes are sparser. Some of the stained cell groups contain neurones that have been studied physiologically. The function of these neurones is discussed.Beit Memorial Fellow