Glutamatergic transmission between antagonistic motor neurones in the locust

The pharmacology of the direct central connections between the fast extensor and flexor motor neurones of a locust (Schistocerca gregaria) hind leg was studied. A spike in the fast extensor produces an EPSP in the flexor motor neurones. Glutamate depolarized the flexor motor neurones when injected into the neuropil. Quisqualate, but not by kainate or NMDA, also depolarized the flexor motor neurones. The fast extensor was also depolarized by glutamate, and also by kainate, but not by quisqualate, AMPA or NMDA. The glutamate response in the flexor motor neurones and the EPSP evoked by a spike in FETi both had similar reversal potentials. The FETi-evoked EPSP was blocked by bath application of the glutamate antagonist glutamic acid diethyl ester. The responses of extrasynaptic somata receptors to glutamate were compared to the neuropil responses. Glutamate usually hyperpolarized the somata of FETi and the flexor motor neurones. The response of a flexor motor neurone to glutamate was abolished at potentials less negative than -90 mV. The results provide evidence for glutamate transmission at central synapses in the locust, and show that presumed synaptic receptors in the neuropil differ to the extrasynaptic soma response     

Adipokinetic hormone content of the corpora cardiaca in gregarious and solitary migratory locusts

Abstract. The adipokinetic hormone (AKH-I and AKH-II) content of the corpora cardiaca from adult males of crowded (gregarious) and isolated (solitary) Locusta migratoria migratorioides (Reiche & Fairmaire) was quantified by reverse-phase high-performance liquid chromatography.Significantly less total hormone was found in the corpora cardiaca of crowded locusts than in those glands of isolated locusts at the age of 12–19 days after fledging.The ratio of AKH-I/AKH-II was higher in crowded than in isolated locusts at this age.From the age of 12–19 days to that of 25–30 days, AKH content increased significantly in the corpora cardiaca of crowded locusts, but no such increase was found in the glands of isolated locusts, and at 25–30 days there were no significant differences in the AKH content of the glands from crowded and isolated locusts.     

Relative motion parallax and target localisation in the locust,Schistocerca gregaria

Summary This paper addresses two questions. 1. Does Schistocerca gregaria detect edges which are defined solely by velocity-contrast, that is by the difference in the image speeds generated by an object and its background when the locust moves? 2. Is the locust's ability to measure the distance of a target by motion parallax independent of the relative motion between target and back-ground?A locust walking on a circular platform was surrounded by a stationary cylinder which was lined with an irregular texture. Against this background, the insect viewed 3 stationary, equidistant targets. One target was black, one grey and the last was textured like the cylinder. Peers and jumps were aimed preferentially at the textured and black targets showing that targets can be detected by virtue of their velocity-contrast with the background. When textured targets were wide, jumps were seen to be aimed at the targets' edge.To assess whether velocity-contrast between target and background distorts distance-estimates, we used jump-velocity as a measure of apparent distance and examined how it varied with different arrangements of target and background. When a textured background is close to a target or the target is very wide, velocity contrast is small. The locust's jump-velocity is then 10% greater than when velocity-contrast is increased by making the background distant or the target narrow. This suggests that the locust is efficient at separating signals encoding absolute motion from those encoding relative motion.     

Reflex modulation in locusts walking on a treadwheel intracellular recordings from motoneurons

Summary In locusts (Locusta migratoria) walking on a treadwheel, afferents of tarsal hair sensilla were stimulated via chronically implanted hook electrodes (Fig. 1). Stimuli applied to the middle leg tarsus elicited avoidance reflexes (Fig. 2). In quiescent animals, the leg was lifted off the ground and the femur adducted. In walking locusts, the response was phase-dependent. During the stance phase, no reaction was observed except occasional, premature triggering of swing movements; stimuli applied near the end of the swing phase were able to elicit an additional, short leg protraction.Central nervous correlates of phase-dependent reflex modulation were observed by recording intracellularly from motoneuron somata in walking animals. As a rule, motoneurons recruited during the swing phase showed excitatory stimulus-related responses around the end of the swing movement, correlated to the triggering of additional leg protractions (Figs. 3, 4, 5). Motoneurons active during the stance phase were often inhibited by tarsal stimulation, some showed only weak responses (Figs. 8, 9, 10). Common inhibitory motoneuron 1 was excited by tarsal stimulation during all phases of the leg movement (Figs. 6, 7). In one type of flexor tibiae motoneuron, a complex response pattern was observed, involving the inversion of stimulus-related synaptic potentials from excitatory, recorded during rest, to inhibitory, observed during long-lasting stance phases (Figs. 11, 12).The results demonstrate how reflex modulation is represented on the level of synaptic input to motoneurons. They further suggest independent gain control in parallel, antagonistic pathways converging onto the same motoneuron as a mechanism for reflex reversal during locomotion.Abbreviations CI ₁ common inhibitory motoneuron (1) - EMG electromyogram - Feti fast extensor muscle of the tibia     

A Rapid Purification of L-Glutamic Acid Decarboxylase from the Brain of the Locust Schistocerca gregaria

L-Glutamic acid decarboxylase (GAD; EC 4.1.1.15) was purified to apparent homogeneity from the brain of the locust Schistocerca gregaria using a combination of chromatofocusing (Mono P) and gel filtration (Superose 12) media. The homogeneity of the enzyme preparation was established by native polyacrylamide gel electrophoresis (PAGE) with silver staining. The molecular weight of the purified enzyme was estimated from native gradient gel electrophoresis and gel filtration chromatography to be 97,000 +/- 4,000 and 93,000 +/- 5,000, respectively. When analysed by sodium dodecyl sulphate-PAGE, the enzyme was found to be composed of two distinct subunits of Mr 51,000 +/- 1,000 and 44,000 +/- 1,500. Tryptic peptide maps of iodinated preparations of these two subunits showed considerable homology, suggesting that the native enzyme is a dimer of closely related subunits. The purified enzyme had a pH optimum of 7.0-7.4 in 100 mM potassium phosphate buffer and an apparent Km for glutamate of 5.0 mM. The enzyme was strongly inhibited by the carbonyl-trapping reagent aminooxyacetic acid with an I50 value of 0.2 microM.     

The effect of phase viscosity ratio on the rheology of liquid two phase gelatin-locust bean gum systems

The rheological behaviour of liquid two phase gelatin–locust bean gum (LBG) systems, comprising of (a) liquid LBG enriched continuous phase, and (b) flow-deformable gelatin-enriched dispersed particles seems to be determined, at the same phase composition, by phase viscosity ratio (μ). In the μ range from 0.03 to 0.21, viscosity dropped to values noticeably lower (13–40 times) than those of the corresponding LBG solution. Decrease in the viscosity of the mixtures was not observed at μ=0.5–0.6, corresponding that to the maximum energy scatter inside the droplets, in agreement with Mason’s conception of droplet deformation and disruption of liquid Newtonian emulsions.     

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 .     

Field Treatment of Desert Locust ( Schistocerca gregaria Forskal) Hoppers in Mauritania Using an Oil Formulation of the Entomopathogenic Fungus Metarhizium flavoviride

A field trial was conducted to test the efficacy of an oil formulation of the entomopathogenic fungus , Metarhizium flavoviride Gams & Rozsypal (Deuteromycotina: Hyphomycetes) , as a control agent for the desert locust , Schistocerca gregaria Forskal (Orthoptera: Acrididae) , in Mauritania . The treatment was applied to hopper bands in the field . In caged samples of the treated insects , 99% mortality was observed in 15 days . On average during application only 51% of the hoppers received spray droplets directly , the additional mortality being due to pick - up of spores from the spray residue . This mortality was assessed by exposing insects to a treated plot at intervals , and monitoring disease levels during subsequent incubation in cages . The spray residue remained highly infective for a period of 6 days after application . The number of nymphs in the hopper bands was estimated using a computer - based photographic image - processing technique . Unfortunately , most of the hopper bands dispersed into small groups , but a population reduction could be demonstrated for one hopper band . Maximal daily mortality in the field was observed 10 - 11 days after application , compared with 6 - 10 days in cages .     

蝗虫多型现象的神经内分泌调控

蝗虫有两种型,即散居型和群居型。蝗灾通常由群居型蝗虫所引发。多年来人们试图找到控制蝗虫由散居型向群居型转变的关键因子,以期控制蝗虫危害。该文主要从神经内分泌的角度概述了蝗虫多型性的生理机制,重点介绍了保幼激素、蜕皮激素和脑神经肽［His7］-corazonin在蝗虫多型性中的主要作用和机制。     

Composition of Acridid gut bacterial communities as revealed by 16S rRNA gene analysis

The gut bacterial community from four species of feral locusts and grasshoppers was determined by denaturing gradient gel electrophoresis (DGGE) analysis of bacterial 16S rRNA gene fragments. The study revealed an effect of phase polymorphism on gut bacterial diversity in brown locusts from South Africa. A single bacterial phylotype, consistent with Citrobacter sp. dominated the gut microbiota of two sympatric populations of Moroccan and Italian locusts in Spain. There was evidence for Wollbachia sp. in the meadow grasshopper caught locally in the UK. Sequence analysis of DGGE products did not reveal evidence for unculturable bacteria and homologies suggested that bacterial species were principally Gammaproteobacteria from the family Enterobacteriaceae similar to those recorded previously in laboratory reared locusts.