Effects of parental and progeny rearing densities on locomotor activity of 1st-stadium nymphs in the migratory locust, Locusta migratoria: An analysis by long-term monitoring using an actograph

The effects of parental and progeny rearing densities on locomotor activity in 1st-stadium nymphs of the migratory locust, Locusta migratoria, were observed over a 24- or 36-h period using an actograph. Newly hatched nymphs showed a small activity peak shortly after hatching and the peak level was significantly higher in offspring (gregarious nymphs) of crowd-reared adults than in those (solitarious nymphs) of isolated-reared adults. However, no significant difference was found between the two groups in maximum activity levels exhibited after the initial peak. Post-hatching crowding enhanced locomotor activity during 2-5 h of measurements in 2-day-old nymphs. In this case, the parental density resulted in no significant influence on locomotor activity. However, the maximum activity level shown later in the observation period was higher in gregarious nymphs than in solitarious nymphs. Interestingly, this parental effect was more pronounced in nymphs reared in group than in those reared in isolation. The parental density appeared to affect the degree of response to crowding in the progeny. No evidence was found for the phase accumulation in terms of locomotor activity. The variation observed in locomotor activity among geographical populations did not correspond to their phylogenetic relationships.     

Clouds,shadows or twilight? Mayfly nymphs recognise the difference

1. We examined the relative changes in light intensity that initiate night‐time locomotor activity changes in nymphs of the mayfly, Stenonema modestum (Heptageniidae). Tests were carried out in a laboratory stream to examine the hypothesis that nymphs increase their locomotion in response to the large and sustained reductions in relative light intensity that take place during twilight but not to short‐term daytime light fluctuations or a minimum light intensity threshold. Ambient light intensity was reduced over a range of values representative of evening twilight. Light was reduced over the same range of intensities either continuously or in discrete intervals while at the same time nymph activity on unglazed tile substrata was video recorded. 2. Nymphs increased their locomotor activity during darkness in response to large, sustained relative light decreases, but not in response to short‐term, interrupted periods of light decrease. Nymphs did not recognise darkness unless an adequate light stimulus, such as large and sustained relative decrease in light intensity, had taken place. 3. We show that nymphs perceive light change over time and respond only after a lengthy period of accumulation of light stimulus. The response is much lengthier than reported for other aquatic organisms and is highly adaptive to heterogeneous stream environments.     

Phase-dependent locomotor activity in first-stadium nymphs of the desert locust, Schistocerca gregaria: effects of parental and progeny rearing density

This study examined the effects of parental and progeny rearing density on locomotor activity of 1st-stadium nymphs of the desert locust, Schistocerca gregaria, using an actograph. Progeny obtained from solitarious (isolated-reared) or gregarious (crowd-reared) locusts were reared in isolation or in a group of 30 nymphs. Crowding after hatching had a slight influence on mean activity shortly after the start of measurements, but no clear effect was detected until day 2, when maximum activity during the 6-24 h of observation was significantly higher than that of the nymphs kept in isolation. On the other hand, the effects of parental rearing density on locomotor activity manifested at all ages examined (0-2 days old). Progeny of gregarious locusts showed consistently higher activity than those of solitarious locusts. In newly hatched nymphs, the effect of parental rearing density was explained by variation in body size at hatching, one of the phase-dependent characteristics. Hatchling body color was also correlated with locomotor activity and body weight. Similar levels of locomotor activity were exhibited when green, solitarious and black, gregarious nymphs were similar in body weight. These results suggested that parental rearing density indirectly influences locomotor activity in the progeny shortly after hatching by affecting their body size as eggs or hatchlings.     

The status and future of the Lake Naivasha fishery,Kenya

I describe a laboratory system for investigating the role of light as a proximate cue for diel changes in locomotor activity and vertical location on the substrate of stream macro-invertebrates. The system consisted of computer-controlled halogen lamps positioned over a laboratory stream in which video-recordings were made of Stenonema modestum mayfly nymphs located on the undersides of unglazed tile substrates. Locomotor activity of study organisms in response to light changes were quantified during computer-programmed and reproducible light/dark (LD) cycles. The system provided the flexibility to simulate a variety of light environments so that the separate influences of light intensity and light change on diel activities of individuals and populations could be examined, which is difficult under natural light conditions. As a group, nymphs responded similarly to simulated twilight (light decrease from 7.9 × 10² to 6.9 × 10^–2 W cm^–2 at a constant –1.9 × 10^–3 s^–1 rate of relative light change) and to natural twilight, suggesting that proposed mechanisms of light control of diel activities in nature can be adequately tested in the simulated environment. However, locomotor activity and vertical movements among individual mayflies were highly variable under controlled conditions, suggesting that physiological differences influence their responses to environmental conditions.     

Effects of elevated CO2 on the nutrient compositions and enzymes activities of Nilaparvata lugens nymphs fed on rice plants

Elevated CO 2 may reduce the tolerance of Nilaparvata lugen (N. lugens) to adverse environmental factors through the biological and physiological degeneration of N. lugens. In an artificial climate box, under 375 and 750 μL L 1 CO 2 levels, the rice stems nutrient content, the nutrient content and enzyme activities of N. lugens nymph fed on rice seedlings exposed to ambient and elevated CO 2 were studied. The results showed that rice stems had significantly higher protein and total amino acid levels under ambient than elevated CO 2 levels. Nymphs had significantly higher protein levels in the ambient CO 2 treatment, while their glucose levels were significantly lower under ambient CO 2 conditions. Significantly higher trypsin activity was observed in nymphs grown in elevated CO 2 . Significantly lower activities of the protective enzymes total superoxide dismutase and catalase were observed in the nymphs under ambient CO 2 . Meanwhile, the activity of the detoxification enzyme glutathione S-transferase was significantly higher in the ambient CO 2 treatment. Measuring how energy and resources were allocated to enzymes in N. lugens nymphs under elevated CO 2 conditions can provide a more meaningful evaluation of their metabolic tolerances to adverse climatic conditions.     

Metabolic rate in diapause and nondiapause brown locust eggs correlated with embryonic development

Insects use dormancy to survive adverse conditions. Brown locust Locustana pardalina (Walk.) eggs offer a convenient model to study dormancy (diapause and quiescence), which contributes to their survival under arid conditions. The metabolic rates of developing nondiapause, diapause and quiescent eggs are compared in the present study using closed‐system respirometry. The embryo becomes committed to continue development and hatch or to enter diapause 6 days after the eggs are placed on moist soil. The metabolic rate of nondiapause eggs increases exponentially until hatching, whereas that of diapause eggs is low and stable. The metabolic rate of diapause laboratory eggs (1.9 ± 0.6 µL CO₂ mg^?1 h^?1) is significantly higher than that of field eggs (0.5 ± 0.3 µL CO₂ mg^?1 h^?1), although the ranges of metabolic rate overlap and the embryos are all in late anatrepsis. The metabolic rate of quiescent eggs is similar to that of diapause eggs but decreases with time. Low metabolic rates during arrested development allow eggs to persist over long periods before hatching.     

The effect of temperature on the behaviour and development of Triatoma brasiliensis

Abstract. The effects of temperature on the development of early stages and the thermopreference of nymphs and adults were analysed in the haematophagous bug Triatoma brasiliensis Neiva, 1911 (Hemiptera, Reduviidae). Egg hatching, mortality of nymphs, feeding and moulting success of the early stages of T. brasiliensis were all affected by temperature. While high rates of egg hatching were observed between 25 and 27 °C, no hatching occurred at 12, 19 and 38 °C. The mortality of first‐instar nymphs was highest at 38 °C, at which no insects survived after 10 days of exposure. Feeding success was only affected at the lowest temperature (12 °C). No ecdysis was observed in the groups exposed to 12, 19 and 21 °C. Recently fed fourth‐instar nymphs preferred to stay at a temperature of approximately 30 °C. The preferred temperature began to decline gradually to approximately 27 °C during ecdysis, reaching 26 °C at 30 days after ecdysis. After a second blood meal, the insects' preferred temperature was again approximately 30 °C. The thermopreference pattern of females was similar to that of nymphs. Nymphs and females showed a daily fluctuation in their preferred temperature, moving towards higher values at the beginning of the dark phase, and choosing lower ones after this time interval, at which they remained until the end of the light phase. The females laid their eggs in all sectors of the arena, although the largest numbers of eggs were found between 28 and 32 °C.     

Influence of Light Intensity on Plasma Melatonin and Locomotor Activity Rhythms in Tench

Melatonin production by the pineal organ is influenced by light intensity, as has been described in most vertebrate species, in which melatonin is considered a synchronizer of circadian rhythms. In tench, strict nocturnal activity rhythms have been described, although the role of melatonin has not been clarified. In this study we investigated daily activity and melatonin rhythms under 12∶12 light‐dark (LD) conditions with two different light intensities (58.6 and 1,091 µW/cm²), and the effect of 1 h broad spectrum white light pulses of different intensities (3.3, 5.3, 10.5, 1,091.4 µW/cm²) applied at middarkness (MD) on nocturnal circulating melatonin. The results showed that plasma melatonin in tench under LD 12∶12 and high light conditions displayed rhythmic variation, where values at MD (255.8±65.9 pg/ml) were higher than at midlight (ML) (70.7±31.9 pg/ml). Such a difference between MD and ML values was reduced in animals exposed to LD 12∶12 and low light intensity. The application of 1 h light pulses at MD lowered plasma melatonin to 111.6±3.2 pg/ml (in the 3.3–10.5 µW/cm² range) and to 61.8±18.3 pg/ml (with the 1,091.4 µW/cm² light pulse) and totally suppressed nocturnal locomotor activity. These results show that melatonin rhythms persisted in tench exposed to low light intensity although the amplitude of the rhythm is affected. In addition, it was observed that light pulses applied at MD affected plasma melatonin content and locomotor activity. Such a low threshold suggests that the melatonin system is capable of transducing light even under dim conditions, which may be used by this nocturnal fish to synchronize to weak night light signals (e.g., moonlight cycles).     

Substrate relations of the African wood‐burrowing mayfly Povilla adusta Navás (Ephemeroptera,Polymitarcyidae)

Colonization of an artificial substrate (polyurethane foam) by nymphs of the wood‐burrowing mayfly Povilla adusta was studied in a natural West‐African lake (Opi Lake). Nymphs readily colonized the substrate in densities up to 11,000 m^‐2 (early instars) and at depths ≤ 1.5 m. Blocks with rough surfaces and those in close proximity to oviposition sites near‐shore, had larger densities of nymphs than did those with smooth surfaces or those placed off‐shore. The upper surfaces of submerged blocks had smaller numbers of larger nymphs than did lower surfaces. Differences in the abundance of periphyton on the various surfaces may account for some of these patterns. The generation time of P. adusta is estimated to be three months in Opi Lake.     

Effects of temperature on growth of Vallisneria americana in a sub-tropical estuarine environment

The submersed aquatic vegetation (SAV) species Vallisneria americana Michx. (tape grass) is a valuable resource in the Caloosahatchee estuary and in many other aquatic systems. Given the variable nature of freshwater inflows and environmental conditions in the Caloosahatchee, it is necessary to understand how tape grass will respond to high and low salinity conditions at different light and temperature levels. Specifically, quantitative information is needed as input to modeling tools that can be applied to predict growth and survival of tape grass under a range of environmental conditions present in the estuary. We determined growth rates for small and medium sized tape grass plants obtained from the Caloosahatchee estuary, southwest coastal Florida, USA in freshwater (0.5 psu) under high (331 μE m^?2 s^?1) and low light (42 μE m^?2 s^?1) and at 10 psu under high light conditions. We ran six treatments at five temperatures spanning 13–32 °C for 8–9 weeks. The optimum temperature for growth was roughly 28 °C, with a minimum threshold temperature of 13 °C and a maximum threshold temperature of 38 °C. Plants grew fastest in freshwater, at high light and temperatures greater than 20 °C. The slowest growth rates were observed at 13 °C regardless of salinity, light or plant size. Our results suggest that tape grass growth is strongly influenced by water temperature and that additional stressors such as low light and elevated salinity can reduce the range of temperature tolerance, especially at colder water temperatures.     

Notes on paternal care and sibling cannibalism in the giant water bug, Lethocerus deyrolli (Heteroptera: Belostomatidae)

Males of the giant water bug, Lethocerus deyrolli, care for egg masses on vegetation above the water surface. They supply the developing eggs with water and guard them against predators. In the present study, mechanisms by which paternal care is extended were found. Males were found situated just below the water on the natal substrate (usually a stick), and the first instar nymphs were aggregated around the substrate. When disturbed, the males showed aggressive behavior, threatening the intruder with their forelegs. Nymphs up to 12 h old did not attack the offered sibling nymphs or anuran larvae, which are common prey in the field. The 24 h‐old nymphs attacked both prey animals; however, they preferred anuran larvae. Cannibalistic behavior in the nymphs was well developed 72 h after hatching, when the nymphs had already dispersed from the natal substrate. The suppression of sibling cannibalism in younger nymphs would promote the maintenance of tight nymphal aggregations and consequently extend male care in this predatory species.     

Hunting behaviour of the perlid stonefly nymph Dinocras cephalotes (Plecoptera) under different light conditions

The hunting behaviour of Dinocras cephalotes nymphs was studied during two different light intensities, darkness and twilight (0·1 cd m^?2). Nymphs of the mayfly Baetis rhodani were provided as food. In darkness the predator moved slowly without stopping, encountering the prey with the antennae and the hair fringes on the tibiae. Little time was spent in a shelter. There was little tendency to pursue the prey after a missed first attack and the pursuing distance was short. In twilight the speed of the predator was higher and the movement was interrupted by long periods of rest. The number of successful attacks was higher and more attacks were initiated when the predator was immobile. Time of activity outside the shelter was short. There was a greater tendency to pursue the prey after a missed first attack and the pursuing distance was longer compared with that in darkness. There are two main advantages of changing strategy from ‘searcher’ in darkness to ‘ambusher’ in the light: to avoid being detected by predators hunting by vision and to avoid being detected by potential prey species relying on visual cues for the detection of predators. The optical design of the eye revealed that only those parts of the eye directed upwards and backwards were optimized to the light conditions at which the predator preferred to be active, suggesting that the main function of these areas is to detect predators, though an additional gain in detecting prey could also be seen.     

The levels of ecdysteroids in uninjured and leg-autotomized nymphs of Blattella germanica (L.)

The levels of ecdysteroids in control and leg-autotomized first-instar nymphs of Blattella germanica were determined by radioimmunoassay from hatching to the time of the first ecdysis. Uninjured nymphs showed a distinct release of ecdysteroids half-way through the stadium, and this resulted in the commencement of the moult cycle which formed the cuticle of the second instar. Cockroaches which had legs autotomized at 48 h after hatching (i.e. before the control ecydsteroid release) had their instar duration increased by that time period. Releases of ecdysteroids and events of the moulting cycle were also postponed by the 48 h period. The titre of ecdysteroids in injured animals was double that of controls. Nymphs were also autotomized at 96 h (i.e. after the normal release of ecdysteroids) but no changes in instar duration, ecdysteroid releases, or events of the moult cycle were recorded. The effects of injury, prothoracicotropic hormone activity and ecdysteroid release are discussed.     

Diurnal rhythms of locomotory activity in isolated desert locusts (Schistocerca gregaria (forsk.))

Abstract

The results of aktograph experiments suggest that S. gregaria is primarily day‐active although its circadian clock can, to some extent, be synchronized by changes in both light and temperature. Low temperatures exert a threshold effect on activity. The nycthemeral rhythm of the desert locust is feeble in LD 12:12, even with fluctuating temperatures. This, is probably of adaptive significance. It certainly accords with the plastic and opportune nature of locust behaviour, upon which survival depends under the unpredictable conditions of the desert climate. For the insect must always be ready to exploit temporary and irregular amelorations of its harsh, arid environment. The desert locust, therefore, cannot afford to adopt rigid rhythms or behaviour patterns that might cause it to lose the benefits of a chance shower or to miss the temporary appearance of green grass. It is argued that the persistence of a rhythm fora short while could be due to an endogenous ‘clock’ or to an exogenous periodicity that continues briefly in constant conditions. It has been shown experimentally, however, that although locusts do not exhibit a marked periodicity under field conditions they, nevertheless, possess good circadian ‘clocks’ whose disclosure can be elicited by subjecting the insects to unnatural light‐dark régimes.     

Dark-dependent soluble guanylyl cyclase activity in locust photoreceptor cells

The enzyme soluble guanylyl cyclase (SGC) mediates physiological effects of the gaseous signalling molecule nitric oxide by generating the second messenger molecule cyclic-GMP (cGMP). Here we have demonstrated that SGC is expressed in photoreceptor cells of locust compound eyes. However, stimulation of SGC activity in the eyes was observed only in the dark, indicating that light may cause inhibition of SGC activity in locust photoreceptor cells. Because light causes elevation of cytosolic Ca²⁺ in insect photoreceptor cells, we investigated the involvement of Ca²⁺ in mediating the inhibitory effect of light on SGC activity in the locust eye. Light-adapted locust eyes incubated with Ca²⁺-free physiological saline displayed a similar level of stimulated SGC activity to that normally seen only in dark-adapted eyes. These data indicate for the first time that Ca²⁺ may regulate SGC activity in cells. Moreover, the dark dependence of SGC activity in the locust eye suggests that SGC and cGMP may participate in dark-adaptation mechanisms in insect photoreceptor cells.     

Die Lichtempfindlichkeit der Circadianen rhythmik dreier Höhlenkäfer-arten der Gattung Laemostenus

Laemostenus terricola and oblongus are troglophile (facultative) cavernicolous animals. Laemostenus navarricus is troglobite; outside of caves and cave entrances it cannot survive. In the three species, the period of spontaneous locomotor activity is longest under LL conditions of 10^?4 and 10^?2 lux. In both. DD and more intense LL. the period becomes shorter. The precision of the animals activity periods was computed by periodogram analysis. In DD and LL of 10^?4 lux the rhythm of locomotor activity of L. navarricus is extinct or very unprecise, in LL of 10^?2 and 10⁰ lux the periods are much more exact. L. oblongus is always periodically active under DD and weak LL conditions; like L. navarricus its activity periods are more precise in brighter LL. On the other hand the activity periods of L. terricola are relatively precise in DD and LL of 10^?4 lux and become more unprecise in increasing light intensity. More than 50% of the tested animals were synchronised by LDs of $\text{0}\text{10}{}^{\mathrm{?4}}$. $\text{0}\text{10}{}^{\mathrm{?2}}$, and $\text{0}\text{10}{}^0$ lux.Because of the extreme light sensitivity of their circadian system, the three species are adapted to twilight habitats (cave entrances). Because of its aperiodicity under DD conditions L. navarricus is additionally adapted to a life in constant darkness (inside of caves). For this and other physiological and morphological reasons the troglobite L. navarricus represents a relatively early stage of regressive evolution under cave conditions.     

Phytochrome modulation of blue-light-induced phototropism

Red light enhances hypocotyl phototropism toward unilateral blue light through a phytochrome‐mediated response. This study demonstrates how the phytochromes modulate blue‐light‐induced phototropism in the absence of a red light pre‐treatment. It was found that phytochromes A, B, and D have conditionally overlapping functions in the promotion of blue‐light‐induced phototropism. Under very low blue light intensities (0.01 µmol m^?2 s^?1) phyA activity is necessary for the progression of a normal phototropic response, whereas above 1.0 µmol m^?1 s^?2 phyB and phyD have functional redundancy with phyA to promote phototropism. PhyA also contributes to attenuation of phototropism under high fluence rates of unilateral blue light, which was previously shown to be dependent on the phototropins and cryptochromes. From these results, it appears that phytochromes are required to develop a robust phototropic response under low fluence rates, whereas under high irradiances where phototropism may be less important, phyA suppresses phototropism.     

Genetic and hormonal control of melanization in reddish–brown and albino mutants in the desert locust Schistocerca gregaria

The genetic and hormonal control of body colouration is investigated using two recessive genetic mutant strains, the reddish–brown (RB) mutant and an albino mutant, as well as a normal (pigmented) strain of the desert locust Schistocerca gregaria. The colour patterns of the RB nymphs are similar to those of a normal strain, although the intensity of the melanization is weaker in the former. Reciprocal crosses between the RB and albino mutants produce only normal phenotypes in the F₁ generation. In the F₂ generation, the normal, RB and albino phenotypes appear in a ratio of 9 : 3 : 4, indicating that two Mendelian units might determine the appearance of dark body colour and the intensity of melanization, respectively. In other words, at least two steps of regulation might be involved in the expression of body colour. Injections of [His⁷]‐corazonin, a neuropeptide inducing dark colour in this locust, fail to induce dark colour in albino nymphs but show a dose‐dependent darkening in RB nymphs in the range, 10 pmol to 1 nmol. Some RB nymphs become indistinguishable from normal individuals after injection of the peptide. Implantation of corpora cardiaca (CC) taken from RB mutants into other RB individuals induces darkening in the latter and CC from RB, albino and normal strains have similar dark colour‐inducing activity when implanted into albino Locusta migratoria. These results suggest the possibility that the RB mutant gene regulates the intensity of melanization, possibly through controlling the pathway of pigment biosynthesis associated with [His⁷]‐corazonin.     

Comparative analysis of thylakoid protein complexes in the mesophyll and bundle sheath cells from C3, C4 and C3–C4 Paniceae grasses

To better understand the coordination between dark and light reactions during the transition from C₃ to C₄ photosynthesis, we optimized a method for separating thylakoids from mesophyll (MC) and bundle sheath cells (BSCs) across different plant species. We grew six Paniceae grasses including representatives from the C₃, C₃–C₄ and C₄ photosynthetic types and all three C₄ biochemical subtypes [nicotinamide adenine dinucleotide phosphate‐dependent malic enzyme (NADP‐ME), nicotinamide adenine dinucleotide‐dependent malic enzyme (NAD‐ME) and phosphoenolpyruvate carboxykinase (PEPCK)] in addition to Zea mays under control conditions (1000 μmol quanta m^?2 s^?1 and 400 ppm of CO₂). Proteomics analysis of thylakoids under native conditions, using blue native polyacrylamide gel electrophoresis followed by liquid chromatography‐mass spectrometry (LC‐MS), demonstrated the presence of subunits of all light‐reaction‐related complexes in all species and cell types. C₄ NADP‐ME species showed a higher photosystems I/II ratio and a clear accumulation of the NADH dehydrogenase‐like complexes in BSCs, while Cytb₆f was more abundant in BSCs of C₄ NAD‐ME species. The C₄ PEPCK species showed no clear differences between cell types. Our study presents, for the first time, a good separation between BSC and MC for a C₃–C₄ intermediate grass which did not show noticeable differences in the distribution of the thylakoid complexes. For the NADP‐ME species Panicum antidotale, growth at glacial CO₂ (180 ppm of CO₂) had no effect on the distribution of the light‐reaction complexes, while growth at low light (200 μmol quanta m^?2 s^?1) promoted the accumulation of light‐harvesting proteins in both cell types. These results add to our understanding of thylakoid distribution across photosynthetic types and subtypes, and introduce thylakoid distribution between the MC and BSC of a C₃–C₄ intermediate species.     

The hatching time of Locusta migratoria under outdoor conditions: role of temperature and adaptive significance

The present study investigates the time of hatching of the migratory locust Locusta migratoria using egg pods that are artificially buried in the soil under outdoor conditions. Most eggs hatch in the mid‐morning, with a peak between 11.00 and 12.00 h, and none hatch before 09.00 or after 16.00 h. Furthermore, most egg pods complete hatching within a day, although some take 2 or 3 days, and egg hatching is interrupted by rain. There are no large differences in hatching time from May to September. Laboratory experiments in which the eggs are exposed to temperatures simulating outdoor conditions show that soil temperature is the main factor controlling hatching activity. The increase in temperature in the morning appears to trigger egg hatching, as confirmed by laboratory experiments, which may explain the similar hatching times between seasons. The seasonal patterns of temperature variation and hatching time suggest that the hatching time of L. migratoria eggs may be adjusted to allow the hatchlings to be exposed to high temperatures in the afternoon so that they can harden their bodies quickly.