Tonic effects of stationary luminous slits on the discharge rates of some locust visual interneurones

The presence of an illuminated slit in the visual field of a locust compound eye produced changes in the tonic discharge rate of the DCMD and three other visual interneurones, recorded in a connective. The DCMD discharge peaked initially in the range of low slit subtenses, but over a period of minutes of exposure its character changed so that there was a rise at high subtenses also. When the luminance of a slit of fixed subtense was increased in steps, there was an initial rise then a sharp fall in discharge, indicating an abrupt onset of inhibition. Lateral spread of inhibition could account for the peak in response to slits, at a subtense falling well within the acceptance angle of a single ommatidium. The results show the ability of some visual interneurones to maintain a changed level of discharge in the presence of a stationary object in the visual field of the eye.     

Responses of locust visual interneurones to transiently-illuminated slits,paired spots,annuli and disc arrays

One compound eye of an immobilised locust viewed a large screen on to which could be projected a slit of variable width, parallel thin slits of variable separation, large discs or annuli, pairs of small discs or large arrays of small discs. The on-response in the contralateral cervical connective, for both the DCMD and a smaller axon group (M-spikes), was recorded over a period of 2 sec coinciding with the period of illumination. The normal spontaneous discharge of the connective is described. For a single slit the DCMD response peaked in the range 0.02–0.7° of width subtense, the most common result being 0.05°. The M-axon group showed a negative peak at a corresponding subtense. Comparing the responses to single bars and paired slits of the same overall subtense, it was found that below about 1° these were not discriminated by either type of neurone. At higher subtenses the DCMD showed preference for paired slits, the M-axons for solid bars. Comparing responses to arrays of spots with those to uniformly illuminated areas, neither the DCMD nor the M-axon group showed discrimination at angles less than 1°, but at higher angles the DCMD showed preference for arrays and the M-axons for solid areas. Annuli were more effective stimuli than were discs of the same size. Near the edge of large-area targets it was possible to detect spatial transients in excitability. Two small spots produced interaction over a wide range of separations, affording evidence for wide-range mutual inhibition affecting both types of interneurone, and for short-range facilitation for the M-axon group only.     

Parallel effects of joint receptors on motor neurones and intersegmental interneurones in the locust

Summary At the distal end of a mesothoracic tibia of the locust,Schistocerca gregaria, is a chordotonal organ which monitors the position and movement of the tarsus relative to the tibia. It contains approximately 35 receptors that variously encode different spatial and temporal parameters (position, velocity and direction of movement). Some excite intersegmental interneurones that respond phasically or tonically, with directional sensitivity to active or imposed movements of the tarsus. Some of these interneurones are also excited by intrinsic movements of the tarsal segments. Others, besides being excited by tarsal proprioceptive inputs, are also excited by exteroreceptors on the tarsus.When stimulated mechanically or electrically, chordotonal afferents evoke excitatory postsynaptic potentials with a central latency of between 0.9 and 1.4 ms simultaneously in the intersegmental interneurones and in tarsal motor neurones. The central arborizations of the afferents, the intersegmental interneurones and the tarsal motor neurones overlap in certain neuropilar regions of the mesothoracic ganglion. Other afferents cause an inhibition of the motor neurones, with a longer and non-consistent latency suggesting the involvement of other intercalated interneurones.These results indicate that proprioceptive inputs from the tarsal joint receptors are transmitted in parallel and monosynaptically to tarsal motor neurones and to the intersegmental interneurones.     

Temperature related effects on embryonic development of the Mediterranean locust, Dociostaurus maroccanus

Laboratory studies were conducted to assess the effect of temperature on the development of the eggs of Dociostaurus maroccanus (Thunberg) (Orthoptera, Acrididae) during anatrepsis (stages I–XIV) and during catatrepsis (stages XV–XX). The developmental rates of anatrepsis were studied at five constant temperatures ranging from 10 to 30°C. Egg development occurred over the entire range but at 10°C the embryos were unable to complete anatrepsis. The relationship between temperature and developmental times for completing anatrepsis was analysed by the non‐linear Logan type III model. The optimal temperature estimated for the development of eggs during anatrepsis was 24.7°C; the lower and upper thermal thresholds were 9°C and 31°C, respectively. Once the embryos completed anatrepsis, only those incubated at 15°C continued morphogenesis beyond stage XIV (diapause stage) without a low‐temperature exposure period. The developmental rate of catatrepsis was studied at four constant temperatures ranging from 15°C to 30°C after exposure to low‐temperature, 10°C, for 30, 60 or 90 days. For catatrepsis, temperature and developmental time were linearly and inversely related. Linear regression was used to estimate the lower developmental threshold and the degree days requirements for catatrepsis. Both decreased with longer exposure to the low temperature; the former from 13.8°C to 10.5°C and the latter from 212.8 to 171.5 degree days, following 30 and 90 days at 10°C, respectively. Our results improve the ability of decision support systems for Mediterranean locust pest management by providing better forecasts to land managers and pest advisors.     

The dark-colour-inducing neurohormone of locusts: strain-dependent and phase-independent effects on adults of the migratory locust, Locusta migratoria

Abstract.  An albino strain that had originated from Okinawa, Japan, and a normally coloured strain that had originated from West Africa, were used to study the darkening response to injection of graded doses of dark-colour-inducing neurohormone of locusts (DCIN) ([His⁷]-corazonin) of gregarious and solitarious adults of the migratory locust, Locusta migratoria (L.). By repeated crossings, congenic albinos and normal phenotypes were obtained, both with a 99.6% West African genome, and their darkening response was compared with the original Okinawa and West African strains. Within each of these four strains, no difference was found in DCIN-induced darkening between gregarious and solitarious adults despite previous publications in the literature claiming an absence of 'fire-darkening' in gregarious adults of this species. Okinawa albino adults showed a markedly higher darkening response than the other three strains, including albinos with a 99.6% West African genome. This finding demonstrates that the differential darkening response of the Okinawa albinos is caused not by albinism, but by the geographical origin (Okinawa) of the strain. This is the first report of geographical-strain-dependent differences in the response of an insect to a neurohormone. The darkening response of adults reached a maximum on day 10 after injection; subsequently, the dark colour faded slowly. Adults injected 1 day after their moult showed a greater darkening response than those injected after 14 or 28 days.     

基于LAI的东亚飞蝗发生面积的预测模型

20世纪80年代以来东亚飞蝗在我国再度猖獗危害,及时、准确地监测东亚飞蝗的危害状况,对于东亚飞蝗的有效防治有重要意义.以河北省黄骅市为研究区,从光学模型的建立机理为着眼点,定量分析和对比了4种由植被冠层孔隙度反演LAI的算法.结果表明,LAI与植被指数之间呈明显的正相关关系,即随着LAI的增大,植被指数也在增大;在4种估算方法中,LAI-2000算法最适用于研究区植被LAI的估算.此外,还分析了LAI与飞蝗发生面积的关系,发现两者呈负相关.并在此基础上建立了飞蝗发生面积的预测模型,即：ALO=-aln（LAI）＋b,其中,a、b为调节系数.     

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.     

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.     

The paradoxical effects of nutrient ratios and supply rates on an outbreaking insect herbivore, the Australian plague locust

1. The Australian plague locust, Chortoicetes terminifera, develops following rainfall in an environment dominated by two host plants, the annual Dactyloctenium radulans and the perennial Astrebla lappacea. This simple system provides an ideal opportunity to explore the relationship between plant quality, individual herbivore performance and population responses. 2. We compared the two grasses chemically and structurally, and the behavioural, physiological and developmental responses of locust nymphs to these diets. 3. The grasses appeared to be of similar nutritional quality in terms of their chemical composition, although they differed in their physical properties. Early instar nymphs performed equally well on both grasses. However, older nymphs consuming D. radulans developed faster, survived better and attained a higher body weight compared with those consuming A. lappacea. 4. The differences in performance by the older nymphs related to the rate and ratio of supply of carbohydrate and protein from the two grasses, with less carbohydrate being assimilated from A. lappacea than D. radulans per unit of protein assimilated. Experiments showed that these differences arose as a direct result of the physical barrier to nutrient extraction provided by cell walls and indirectly through the amount of water contained within each cell. Paradoxically, nitrogen did not limit performance in the traditional sense through shortage,but rather its relative excess in A. lappacea appeared to impede intake and assimilation of adequate carbohydrate. 5. As a consequence, we predict that the length of time D. radulans remains available following rainfall will influence plaguing dynamics, although not for the reasons previously thought. 6. The results highlight the need to consider nutrient balance and actual rates of supply (rather than simply measuring the chemical composition of the plant) when attempting to understand herbivore nutritional ecology.     

Muscle contraction and relaxation-response time in response to on or off status of visual stimulus

Background

It is unclear whether response time is affected by a stimulus cue, such as a light turned on or off, or if there are differences in response to these cues during a muscle contraction task compared with a muscle relaxation task. The objective of this study was to assess the response time of a relaxation task, including the contraction portion of the task, to a stimulus of a light turned on or off. In addition, we investigated the effect of the pre-contraction level on the relaxation task.

Results

Contraction response time was significantly shorter during the light-on status than during the light-off status (P <0.01), and relaxation response time in each maximum voluntary contraction was significantly longer during the light-on status than during the light-off status (P <0.01). The relaxation response time became longer in order of 25% to 75% maximum voluntary contraction regardless of light-on or -off status, and was significantly longer than the contraction response time (P <0.05-0.01).

Conclusions

This study found that as the contraction level increased, the relaxation response time became longer than the contraction response time regardless of light status. However, contraction response time or relaxation response time findings were opposite to this during the light-on status and light-off status: contraction response time became shorter in the light-on status than in the light-off status and relaxation response time became longer in the light-on status than in the light-off status. These results suggest that the length of each response time is affected by motor control in the higher order brain and involves specific processing in the visual system.     

黄土高原不同密度刺槐（Robinia pseudoacia）林地水分生产力与土壤干燥化效应模拟

应用WinEPIC模型模拟研究了1957～2001年期间黄土高原半湿润区长武和半干旱区延安不同密度刺槐(Robinia pseudoacia)林地水分生产力演变规律和深层土壤干燥化效应.结果:(1)长武和延安高密度(6000株/hm2)、中高密度(4500株/hm2)、中低密度(3000株/hm2)和低密度(1500株/hm2)等4种处理刺槐林地逐年生物量模拟值均呈现快速增加、达到最大值后又逐年波动性降低的变化趋势,林地密度越高早期逐年生物量越高,后期逐年生物量差异缩小,两地均以低密度处理逐年生物量平均值和累积生物量模拟值最高;(2)4种密度处理45年生刺槐林地年均耗水量值基本相等,长武和延安分别为603mm和566mm,但生长前期年耗水量明显高于后期,并高于同期年降水量,林地密度越高前期耗水量越高,中期以后各密度处理耗水量基本接近且波动趋势基本一致,林地密度越高干旱胁迫程度越重;(3)模拟生长初期,4种密度处理刺槐林地0～10m土层逐月土壤有效含水量均呈现强烈的波动性降低趋势,长武各密度处理刺槐林地分别在7～23年生、延安分别在7～17年生之后逐月土壤有效含水量均在0～200mm较低水平上随降水量变化而波动;(4)4种密度处理林地0～10m土层土壤湿度剖面分布年度变化剧烈,土壤湿度逐年降低且土壤干层逐年加厚,密度越高土壤干层加厚速度越快,长武在26年生、延安在17年生时低密度处理刺槐林地土壤干层厚度均已超过10m,此后2～10m土层土壤湿度保持相对稳定的干燥化状态;(5)长武和延安刺槐林地适宜种植密度分别以1500～3000株/hm2和1500株/hm2为宜,刺槐林地土壤水分可持续利用最大年限分别为26a和18a.     

The glycosaminoglycans of the thoracic ganglia of the nymphal stages of the cockroach, Periplaneta americana, and the locust, Locusta migratoria: A histochemical study

The glycosaminoglycans of the connective tissue matrices of the developing meso- and metathoracic ganglia of locusts and cockroach nymphs have been characterized. The neural lamella contains only chondroitin sulphate in the early nymphs, but gradually keratan sulphate accumulates in the later nymphs. The glial lacunar system cannot be detected histochemically in first instar locust nymphs, but it can be seen in the youngest cockroach nymphs; it is clearly visible in the older nymphs of both species. It contains only hyaluronate.A stereological analysis of the developing meso- and meta-thoracic ganglia of the cockroach shows that the relative volumes occupied by the neurones, neuropile, glial cells and glial lacunar system change during post-embryonic development.The physiological functions of the glycosaminoglycans in the neural lamella and glial system are discussed.     

A visual circuit related to the periaqueductal gray area for the antinociceptive effects of bright light treatment

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Quantitative studies on anti-allatin and lethal effects of a synthetic precocene in different larval instars of the desert locust

The lethal and anti-allatin effects of various doses of 7-ethoxy-precocene II (PIII), topically applied to crowdedSchistocerca gregaria nymphs, 0–27 h after the previous moult, were investigated for the five nymphal instars. The LD (lethal dose) probit lines were parallel for the different instars. The ED (effective anti-allatin dose) probit lines were also parallel. But for each instar the LD and ED probit lines seemed to be convergent toward the higher doses. The LD₅₀ and the ED₅₀ (g PIII/g fresh weight) were not widely separated; the LD₅₀/ED₅₀ ratio was instar dependent and varied between 1.26 (Vth instar) and 5.35 (IIIrd instar). Thus, separation between lethal effect, anti-allatin effect and no effect was rather poor; indeed in many instances all these types of results were obtained in a group of hoppers treated with the same dose in the same instar. A low precocene susceptibility was observed for the Ist instar and for each subsequent instar the susceptibility further decreased; the LD₅₀ and the ED₅₀ were respectively 886 g/g and 328 g/g for the Ist instar, but increased to 14 307 g/g and 11 367 g/g for the Vth instar. The anti-allatin effect of the precocene induced various morphogenetic responses: (1) permanent adultiform in the instar next to that treated; (2) death in the moult from the next to the second consecutive instar; (3) permanent adultiform in the second consecutive instar. The occurrence and/or distribution of these responses were instar dependent and for the first three instars also limitedly dose dependent. The anti-allatin effect of the precocene applied to Vth (last) instar nymphs became overt by sterility and lack of yellow colour in the adult. An overt anti-allatin effect was always coupled with a response dependent increase of the duration of the instar treated and/or of the next instar.

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Etudes quantitatives des effets létaux ou antiallates d'un précocène de synthèse sur différents stades larvaires du criquet pélerin

Résumé L'étude a porté sur les effets létaux ou antiallates de différentes doses de 7-éthoxy-précocène II (PIII), déposées de 0 à 27 heures après la mue sur la surface dorsale de l'abdomen de larves groupées de chacun des 5 stades larvaires deSchistocerca gregaria. Les courbes des doses létales (LD) ont été parallèles pour les différents stades. Les courbes pour les doses antiallates (ED) étaient elles aussi parallèles. Cependent pour chaque stade, ces deux courbes semblaient converger et même se croiser vers les doses les plus fortes. Les LD₅₀ et ED₅₀ (en g de PIII par gramme de poids frais) n'étaient pas nettement séparées; le rapport LD₅₀/ED₅₀ dépendait du stade et variait entre 1,26 (5è stade) et 5,35 (3è stade). Ainsi la distinction entre effet létal, effet antiallate et absence d'effet était plutôt faible; à la vérité, dans de nombreux cas, tous ces effets ont été obtenus dans un groupe de criquets traités avec la même dose au même stade. Une sensibilité assez faible au précocène a été observée, même au ler stade, et pendant chaque stade suivant la sensibilité ultérieure diminuait; LD₅₀ et ED₅₀ ont été respectivement 886 g/g et 328 g/g pour le ler stade, mais ont augmenté à 14 307 g/g et 11 367 g/g pour le 5è stade. Les effets antiallates ont induit différentes conséquences morphologiques: (1) des adultiformes permanents lors du stade suivant immédiatement le stade traité; (2) mort pendant la mue du ler ou 2nd stade suivant le traitement; (3) des adultiformes permanents dans le 2nd stade après le traitement. L'apparition et/ou la distribution de ces réponses dépendaient du stade, et pour les 3 premiers stades étaient partiellement dépendantes de la dose. L'effet antiallate du précocène au 5è stade (dernier) devenait évident avec la stérilité et la perte de la coloration jaune de l'adulte. Un effet antiallate manifeste était toujours associé à un accroissement d dépendant de la dose de la durée du stade traité et/ou du stade suivant.

     

The relationship between visual working memory and attention: retention of precise colour information in the absence of effects on perceptual selection

We examined the conditions under which a feature value in visual working memory (VWM) recruits visual attention to matching stimuli. Previous work has suggested that VWM supports two qualitatively different states of representation: an active state that interacts with perceptual selection and a passive (or accessory) state that does not. An alternative hypothesis is that VWM supports a single form of representation, with the precision of feature memory controlling whether or not the representation interacts with perceptual selection. The results of three experiments supported the dual-state hypothesis. We established conditions under which participants retained a relatively precise representation of a parcticular colour. If the colour was immediately task relevant, it reliably recruited attention to matching stimuli. However, if the colour was not immediately task relevant, it failed to interact with perceptual selection. Feature maintenance in VWM is not necessarily equivalent with feature-based attentional selection.     

The action of philanthotoxin-343 and photolabile analogues on locust (Schistocerca gregaria) muscle

The effects of philanthotoxin-343 (PhTX-343; tyrosyl-butanoyl-spermine) and photolabile analogues of this synthetic toxin on locust (Schistocerca gregaria) skeletal muscle have been investigated using whole muscle preparations (twitch contractions), single muscle fibres (excitatory postsynaptic currents (EPSCs)) and muscle membrane patches containing single quisqualate-sensitive glutamate receptors (qGluR). Analogues containing an azido group attached to either the butanoyl side-chain of PhTX-343 or as a substitute for the hydroxyl moiety of the tyrosyl residue were about 6 fold more potent antagonists than PhTX-343; those with an azido group located at the distal end of the toxin molecule were generally 2–3 fold less potent than PhTX-343. When these compounds were tested in subdued light, they were reversible antagonists of the muscle twitch, EPSC and qGluR. When a muscle was irradiated with U.V. during application of photolabile toxin combined with either neural stimulation of the muscle orl-glutamate application, antagonism of the twitch, EPSC and qGluR was complete and irreversible.     

Variation in diapause potential and strength in eggs of the Australian plague locust, Chortoicetes terminifera (Walker) (Orthoptera: Acrididae)

Samples of eggs of Chortoicetes terminifera were incubated under 3 temperature regimes which would allow non-diapause eggs to develop about 50% and so take them beyond the diapause stage. Even so, many more eggs entered diapause when reared at 20°C for 3 weeks than at 32°C for 1 week. By collecting and incubating eggs at intervals after laying in autumn, diapause potential or strength of eggs at different stages of development was estimated. For eggs in pre-diapause, the proportion in diapause after rearing was used to estimate diapause “potential”; for those in diapause, the proportion was used to estimate diapause “strength”. At laying, eggs varied greatly in their potential to enter diapause. However, those with lower potential at laying often increased their potential during the pre-diapause stage so that by the time diapause was reached diapause strength varied but over a lesser range. In all eggbeds, diapause strength decreased by 7–9 weeks after laying; little or none remained by mid-winter.These variations in diapause potential and diapause strength seem to reflect how much the temperature threshold for development during diapause is increased above that for non-diapause. Both diapause potential and strength may reflect the value of some factor whose level at laying is determined by the environment experienced by the parents but which changes subsequently.     

The effects of elevated CO2 (0.5%) on chloroplasts in the tetraploid black locust (Robinia pseudoacacia L.)

Some ploidy plants demonstrate environmental stress tolerance. Tetraploid (4×) black locust (Robinia pseudoacacia L.) exhibits less chlorosis in response to high CO₂ than do the corresponding diploid (2×) plants of this species. We investigated the plant growth, anatomy, photosynthetic ability, chlorophyll (chl) fluorescence, and antioxidase activities in 2× and 4× black locusts cultivated under high CO₂ (0.5%). Elevated CO₂ (0.5%) induced a global decrease in the contents of total chl, chl a, and chl b in 2× leaves, while few changes were found in the chl content of 4× leaves. Analyses of the chl fluorescence intensity, maximum quantum yield of photosystem II (PSII) photochemistry (Fv/Fm), K‐step (V_k), and J‐step (V_J) revealed that 0.5% CO₂ had a negative effect on the photosynthetic capacity and growth of the 2× plants, especially the performance of PSII. In contrast, there was no significant effect of high CO₂ on the growth of the 4× plants. These analyses indicate that the decreased inhibition of the growth of 4× plants by high CO₂ (0.5%) may be attributed to an improved photosynthetic capacity, pigment content, and ultrastructure of the chloroplast compared to 2× plants.     

Measurements of locomotor activity in hatchlings of the migratory locust Locusta migratoria: effects of intrinsic and extrinsic factors

Abstract. The effects of intrinsic and extrinsic factors on locomotor activity in crowd‐reared first‐stadium nymphs of the migratory locust Locusta migratoria are investigated under continuous light conditions using an actograph apparatus. Nymphs show monomodal or bimodal patterns of locomotor activity with respect to the time after the start of measurements, depending on the age. Locomotor activity is suppressed by the presence of grass in nymphs aged 0–2 days old but a peak of activity observed shortly after hatching is not suppressed. The results suggest that newly‐hatched nymphs may try to disperse from the hatching site. Nymphs show higher locomotor activity levels under moist conditions than under dry conditions during the first 5‐h period of measurements. This enhanced locomotor activity may constitute attempts to avoid high humidity. Under dim‐light conditions (2 × 10^?2 Wm^?2), locomotor activity is suppressed during the first half day and increases to a high level thereafter in both grass‐fed and unfed individuals. This increased activity might indicate a possible involvement of circadian rhythms. Background colour has no significant effect on the locomotor activity. The present study provides new aspects of behaviour in nymphs as well as baseline data for behavioural analysis of locust locomotion in relation to phase polyphenism.