Discharge patterns of locust visual interneurones

The spike discharges of the descending contralateral movement detector (DCMD) neurone, and of some smaller visual interneurones (S-units), were recorded in the ventral nerve cord of adult Schistocerca gregaria Forsk., in response to a stationary disc (25^o) or a small spot (0.2^o) stimulus. The discharge rate of each neurone was plotted over a period of 5 s exposure; the total number of spikes in this period was also noted. The DCMD response to the 25^o disc was a high-frequency burst falling off quickly to a low rate; the 0.2^o spot evoked a prolonged discharge with an early peak in rate. In S-units the discharge was prolonged with both targets; the rate rose to an early peak in each case, with a much higher rate for the larger disc. For the DCMD the total number of spikes per stimulus (5 s) was greater for the 0.2^o spot; for S-units it was greater for the 25^o disc. Thus an increase of about 30-fold in the number of ommatidia stimulated resulted in a fall in the total DCMD response to about one-quarter; a similar increase evoked a rise of about 6-fold in the S-unit response. When the 25^o disc was presented at progressively reduced intensities the total spike response of the DCMD rose steadily to a maximum at about 2.9 μ W m^-2; using the same procedure the spike output of S-units, initially high, declined monotonically. The role of inhibition in these results is discussed.     

Rhythmic behaviour and pattern-generating circuits in the locust: Key concepts and recent updates

There is growing recognition that rhythmic activity patterns are widespread in our brain and play an important role in all aspects of the functioning of our nervous system, from sensory integration to central processing and motor control. The study of the unique properties that enable central circuits to generate their rhythmic output in the absence of any patterned, sensory or descending, inputs, has been very rewarding in the relatively simple invertebrate preparations. The locust, specifically, is a remarkable example of an organism in which central pattern generator (CPG) networks have been suggested and studied in practically all aspects of their behaviour. Here we present an updated overview of the various rhythmic behaviours in the locust and aspects of their neural control. We focus on the fundamental concepts of multifunctional neuronal circuits, neural centre interactions and neuromodulation of CPG networks. We are certain that the very broad and solid knowledge base of locust rhythmic behaviour and pattern-generating circuits will continue to expand and further contribute to our understanding of the principles behind the functioning of the nervous system and, indeed, the brain.     

Aspects histologique,histochimique et ultrastructural des péricaryones neurosécréteurs latéraux du protocérébron de Locusta migratoria migratorioides (Insecte: Orthoptère)

Résumé L'étude histologique, histochimique et ultrastructurale des péricaryones neurosécréteurs latéraux de Locusta précise leur nombre et leur localisation. Elle révèle que le neurosécrétat latéral est semblable morphologiquement (forme et diamètre des granules élémentaires) au neurosécrétat A de la pars intercerebralis. Cependant, il en diffère histochimiquement par la présence d'une composante glucidique. Elle confirme l'hypothèse émise pour les péricaryones neurosécréteurs de la pars intercerebralis (Girardie et Girardie, 1967), de l'unicité cellulaire chez Locusta des types A et B selon la nomenclature de Johansson (1958). Elle suggère que les péricaryones latéraux pourraient être des cellules neurosécrétrices très actives.

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Histological, histochemical and ultrastructural aspects of the lateral neurosecretory cells of the protocerebrum in Locusta migratoria migratorioides (insect: orthoptera)

Summary The number (8 to 12) and position of the lateral neurosecretory cells have been established in Locusta by a histological, histochemical and ultrastructural study. The neurosecretory material of the lateral cells contains glycoprotein and is, in this way, histochemically different from medial A cells neurosecretory material. However, the morphological aspect (shape, diameter) of elementary dense core vesicles in the lateral and medial A neurosecretory cells is similar. This study confirms the idea (Girardie and Girardie, 1967) that, in Locusta, A cells and B cells (Johansson, 1958) are in fact two physiological aspects of one cell type. It also suggests that the lateral cells could be very active neurosecretory cells.

     

Escapes with and without preparation: The neuroethology of visual startle in locusts

Locusts respond to the images of approaching (looming) objects with responses that include gliding while in flight and jumping while standing. For both of these responses there is good evidence that the DCMD neuron (descending contralateral movement detector), which carries spike trains from the brain to the thoracic ganglia, is involved. Sudden glides during flight, which cause a rapid loss of height, are last-chance manoeuvres without prior preparation. Jumps from standing require preparation over several tens of milliseconds because of the need to store muscle-derived energy in a catapult-like mechanism. Locusts’ DCMD neurons respond selectively to looming stimuli, and make connections with some motor neurons and interneurons known to be involved in flying and jumping. For glides, a burst of high-frequency DCMD spikes is a key trigger. For jumping, a similar burst can influence timing, but neither the DCMD nor any other single interneuron has been shown to be essential for triggering any stage in preparation or take-off. Responses by the DCMD to looming stimuli can alter in different behavioural contexts: in a flying locust, arousal ensures a high level of both DCMD responsiveness and glide occurrence; and there are significant differences in DCMD activity between locusts in the gregarious and the solitarious phase.     

The annual cycle of Saharan populations of Locusta migratoria cinerascens (Orthoptera: Acrididae: Oedipodinae) in Algeria

Until recently, the Algerian populations of Locusta migratoria cinerascens were considered as sedentary and solitarious. In the Central Sahara and bordering areas, the extension of pivot-irrigated areas since 1980, has resulted in the creation of biotopes favourable to the reproduction of this acridid, particularly in the cereal crops of the Adrar and Ouargla regions. From analysis of the archives of the National Institute of plant Protection, and our personal work carried out from 1995 to 2004, we can provide new information on the life cycle of L. m. cinerascens. We show that, in the cereal crops of the regions studied, there are three generations of this acridid per annum: the first one developing on corn in the spring, until the harvest; the second a spring-summer generation in market gardens in the vicinity of wheat stubble, or in early-growth Sorghum crops, and a third, summer-autumn generation, that develops on summer cereal crops and probably over-winters as diapausing adults until the following February.     

Laboratory and field investigation of a mixture of Metarhizium acridum and Neem seed oil against the Tree Locust Anacridium melanorhodon melanorhodon (Orthoptera: Acrididae)

The in vitro compatibility of Metarhizium acridum strain IMI 330189 with different concentrations of Neem seed oil Azadirachta indica A. Juss. was investigated under laboratory conditions. Water, diesel and ground nut oil dilutions of M. acridum were inoculated into semi-synthetic culture medium with Neem oil and incubated for 10 days at 20, 28, and 34°C. Fungus vegetative growth and conidia production were estimated and compatibility calculated according to the in vitro classification model [T]. Field tests were also conducted during two successive years, where fourth instar nymphs of the Tree Locust, Anacridium melanorhodon melanorhodon, were sprayed with Metarhizium, Metarhizium/Neem mixture, Neem, or Malathion, on a plantation of Acacia senegal. Samples of the treated nymphs were taken 24 h after application, placed in cages and their mortality observed daily for 3 weeks. The compatibility test revealed that at 28°C, all Neem concentrations below 2% were compatible with M. acridum and concentrations of 2 and 2.5% were moderately toxic, while at 20°C, 1.0% Neem was not compatible with the fungus. In the field, Metarhizium+Neem resulted in 74 and 92% mortality during two successive years compared to 64 and 83% for Metarhizium alone. These findings clearly reveal that Neem concentration on the mixture could be increased to just under 1.0% Neem without negative impact on the fungus and that mixing Metarhizium with small quantities of Neem oil accelerates locust mortality and increases efficacy.     

关于蝗虫多样性与草原生态系统可持续发展的若干科学问题

蝗虫多样性既是草原生态系统演化的产物 ,反过来也影响着草原生态系统的结构与功能。蝗虫多样性状况与草原生态系统的持续发展有着密切的关联 ,这其中的科学问题包括 :(1 )蝗虫多样性及其空间变异机理 ;(2 )蝗虫多样性对草原生态系统过程的影响 ;(3 )蝗虫多样性空间格局与草原生态系统演化中的自然和人文因素的关联 ;(4 )蝗虫种群暴发的多样性阈值与草原生态系统的调控 ;(5 )蝗虫多样性和稳定性与草原生态系统的健康等。深入发掘生物多样性所包含的科学内涵 ,将一个物种的多样性与生态系统的结构和功能耦合起来研究 ,从重要物种蝗虫的生物多样性入手 ,深入探讨草原生态系统的持续发展问题 ,将为减少或减轻我国西部草原蝗灾发生提供科学的支持     

Stress-induced thermotolerance of ventilatory motor pattern generation in the locust, Locusta migratoria

Ventilation is a crucial motor activity that provides organisms with an adequate circulation of respiratory gases. For animals that exist in harsh environments, an important goal is to protect ventilation under extreme conditions. Heat shock, anoxia, and cold shock are environmental stresses that have previously been shown to trigger protective responses. We used the locust to examine stress-induced thermotolerance by monitoring the ability of the central nervous system to generate ventilatory motor patterns during a subsequent heat exposure. Preparations from pre-stressed animals had an increased incidence of motor pattern recovery following heat-induced failure, however, prior stress did not alter the characteristics of the ventilatory motor pattern. During constant heat exposure at sub-lethal temperatures, we observed a protective effect of heat shock pre-treatment. Serotonin application had similar effects on motor patterns when compared to prior heat shock. These studies are consistent with previous studies that indicate prior exposure to extreme temperatures and hypoxia can protect neural operation against high temperature stress. They further suggest that the protective mechanism is a time-dependent process best revealed during prolonged exposure to extreme temperatures and is mediated by a neuromodulator such as serotonin.     

Laboratory Testing of Metarhizium spp. and Beauveria bassiana on Sahelian Non-target Arthropods

Laboratory experiments were conducted to investigate the host specificity of 11 isolates of Metarhizium sp. and one isolate of Beauveria bassiana , all deuteromycete entomopathogenic fungi that are being tested as potential biocontrol agents against locusts and grasshoppers. Metarhizium sp. (isolate IMI 330 189) was applied topically to Pimelia senegalensis and Trachyderma hispida, two Sahelian tenebrionid beetles. No infection was observed at a dose of ca. 2.5 x 106 conidia per insect, much higher than dose rates likely to occur in the field. The hymenopteran parasitoids Bracon hebetor (Braconidae) and Apoanagyrus lopezi (Encyrtidae) were exposed to surfaces treated with the entomopathogens at a rate equivalent to ca. 5 x 1012 spores ha-1, the recommended field rate against locusts. All 12 isolates tested resulted in 100% mortality of the parasitoids. Average survival times ranged from 1.6 to 4.1 days. In all cases there was fungal outgrowth on the cadavers. Exposure time-response experiments further confirmed the pathogenicity of these fungi to the parasitoids. The possibility of these parasitoids being affected in the field is discussed.     

蝗虫染色体分带技术的研究

本文对采自长沙岳麓山的中华稻蝗〔Oxya chinensis (Thunberg)〕和采自杭州的小稻蝗〔Oxya hyla intricata (Stal) 〕进行了染色体C带、R带、N带和A带的处理研究。结果表明,C带显示结构异染色质,其位置在不同分裂相中较为稳定;R带即G带的反带,带纹较C带丰富,在粗线期最为明显,本文观察到不同的温育条件可影响R带产生的效果;N带和Ag带可相互参照比较,从而为NOR的准确定位提供依据;A带即荧光带,本文对其显带程序作了一定的改进。 Abstract:In this paperOxya chinensis (Thunberg) collected from the Yuelu Mountains in Changsha, Hunan Province andOxya hyla intricata (Stal) collected from Hangzhou, Zhejiang province were analysed by chromosomal C-banding、R-banding、N-banding、Ag-banding and A-banding. The results showed that the constitutive heterochromatin was stained in C-banding, and it relatively stable; R-banding was the reverse of G-banding, its bands were relatively obvious at the pachytene and abundent, it may be because of the selective extracts that cause the bands evident, the different effects were surveyed under the various incubation conditions; Both N-banding and Ag-banding can stain the nucleolar organizer and the two were compared in this paper; The A-banding was a little improved in the light of the banding process.