There are considerable technical difficulties in measuring urine flow rates in intact locusts, and fluid uptake in the ileum (Phillips et al. 1988), from where urine was collected, or a forward movement of fluid into the midgut (Dow, 1980) might mean that urine production was underestimated. However, it is questionable whether tubule secretion alone can account for the rapid reduction in haemolymph volume. Interestingly, the haemolymph volume of fifth-instar Locusta migratoria nymphs falls by 13 % (18 m l) after a full meal (Bernays and Chapman, 1974). This was associated with a 9 % increase in haemolymph osmotic pressure, which led Bernays and Chapman to conclude that it was unlikely to be due to increased secretion of an isosmotic primary urine. Rather, they suggest that the reduction in volume was caused by the secretion of a copious and dilute saliva. The time course and extent of the change in haemolymph volume were similar to those observed after injection of Locusta-DP into adult locusts, and one effect of the peptide may be directly or indirectly to stimulate salivation. Volume recovery might then be due to fluid reabsorption from the midgut caecae (Dow, 1981).
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Insects were reared as described by Andersen et al. (2017b). Briefly, fourth to fifth instar nymphs of Locusta migratoria (Linnaeus 1758) were obtained from a commercial supplier (Peter Andersen Aps, Fredericia, Denmark) and maintained at 25°C under a 12 h light:12 h dark light cycle. During light hours, locusts had access to a heating lamp, allowing behavioural thermoregulation up to >45°C. Locusts were fed commercial wheat bran and fresh wheat sprouts and had access to water ad libitum. All experiments were carried out on adult L. migratoria of both sexes, 1 – 3 weeks past their final moult. Prior to experiments, locusts were placed at constant 30±1°C for 3 days without food but with water available (unless otherwise stated), and are referred to as warm acclimated.
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Two candidates for these additional diuretic factors are DP-I and DP-II: these partially characterised factors were shown to be present in the brain and corpora cardiaca of Locusta migratoria (Morgan and Mordue, 1984). Recently, a diuretic peptide (Locusta- DP; see Fig. 1E) extracted from Locusta migratoria heads was fully sequenced (Kay et al. 1991b; Lehmberg et al. 1991) and shown to be present in corpora cardiaca (Kay et al. 1991b). Because synthetic Locusta-DP stimulates cyclic AMP production in isolated tubules, it is probably one of the partially characterised factors (DP-I) described by Morgan et al. (1987). Locusta-DP has no structural similarity to the AVP-like IDH, but has significant sequence homology to vertebrate corticotropin releasing factor (CRF) and, more importantly, has considerable homology with identified diuretic peptides in Manduca sexta (Blackburn et al. 1991; Kataoka et al. 1989), Acheta domesticus (Kay et al. 1991a) and Periplaneta americana (Kay et al. 1992). These data provide evidence for a family of CRF-like diuretic peptides in insects.
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Chill tolerance of insects is defined as the ability to tolerate low temperature under circumstances not involving freezing of intracellular or extracellular fluids. For many insects chill tolerance is crucial for their ability to persist in cold environments and mounting evidence indicates that chill tolerance is associated with the ability to maintain ion and water homeostasis, thereby ensuring muscular function and preventing chill injury at low temperature. The present study describes the relationship between muscle and haemolymph ion homeostasis and time to regain posture following cold shock (CS, 2 h at −4°C) in the chill- susceptible locust Locusta migratoria. This relationship was examined in animals with and without a prior rapid cold-hardening treatment (RCH, 2 h at 0°C) to investigate the physiological underpinnings of RCH. CS elicited a doubling of haemolymph [K + ] and
In locusts, olfaction plays a crucial role for initiating and controlling behaviours, including food seeking and aggregation with conspecifics, which underlie the agricultural pest capacity of the animals. In this context, the molecular basis of olfaction in these insects is of particular in- terest. Here, we have identified genes of two orthopteran species, Locusta migratoria and Schistocera gregaria, which encode the olfactory receptor co-receptor (Orco). It was found that the sequences of LmigOrco and SgreOrco share a high degree of identity to each other and also to Orco proteins from different insect orders. The Orco-expressing cells in the antenna of S. gregaria and L. migratoria were visualized by in situ hybridization. Orco expres- sion could be assigned to clusters of cells in sensilla basiconica and few cells in sensilla trichodea, most likely representing olfactory sensory neurons. No Orco-positive cells were detected in sensilla coeloconica and sensilla chaetica. Orco expression was found already in all nymphal stages and was verified in some other tissues which are equipped with chemosensory hairs (mouthparts, tarsi, wings). Together, the results support the notion for a decisive role of Orco in locust olfaction.
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nervous system. Development of thermotolerance is especially important for poikilothermic animals that lack the physiological mechanisms for maintaining a stable body temperature, and more so for those poikilotherms that are exposed to large fluctuations in ambient temperature on a regular basis. The locust Locusta migratoria is poikilothermic and native to sub-Saharan Africa. In their desert ecology, L. migratoria are routinely exposed to extremes in heat that can surpass 40°C, and internal temperature can be as much as 10–12°C above ambient during vigorous activities such as flight (Weis-Fogh, 1956). In order to cope in this environment, it is likely that the locust has evolved physiologically relevant ways of protecting neural function from heat stress. Thus, the locust is an excellent model for studies of thermosensitivity, thermotolerance and the HS response. Moreover, its relatively simple nervous system provides a unique opportunity for examination at the cellular level in live and semi-intact preparations.
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We have recently initiated a programme to explore these issues by comparing in closely related pairs of generalist- and specialist-feeding insects the diet selection and ingestive, post-ingestive and performance-related responses to macronutrient imbalance. Previously, we have compared the solitarious and gregarious phenotypes of the desert locust, which are genetically identical but, due to their differing ecological circumstances, are likely to encounter a different range of host plants (Simpson et al., 2002). We found that the two morphs have similar optimum macronutrient requirements but that they respond very differently when confined to nutritionally imbalanced foods. Specifically, the gregarious morph, which is highly mobile and has a broader host range than the more sessile solitarious form, ingests greater excesses of the surplus nutrient in imbalanced foods. These data support the hypothesis that plant generalists are opportunistic in acquiring nutrient excesses when available and use them to complement imbalances that might exist in foods that are subsequently encountered (Raubenheimer and Simpson, 1999; Simpson et al., 2002). Here, we performed a detailed comparison of the ingestive, post-ingestive and developmental responses of the gregarious form of two species of grasshopper that differ in their host range: the generalist-feeding Schistocerca gregaria and the grass- specialist Locusta migratoria.
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So far, little is known about the nature of the sources of neuronal response variability. The most functionally important intrinsic noise source of sensory neurons may arise from the stochastic gating of ion channels. In this thesis, I investigate potential channel noise sources in the auditory receptor neurons of Locusta migratoria. The auditory system of locusts is a well-established system for studying the processing of acoustic patterns, and the anatomical and functional properties of the receptor neurons are well understood. To directly measure the noise characteristics of the underlying ionic currents, somatic recordings of sensory neurons are required. These, however, are hard to achieve in the locust auditory system without damaging the sensory transduction machinery. Here, I therefore employ an indirect approach to assess the stochastic dynamics of the sensory neurons based on interspike-interval and spike-count statistics of neuronal spike train responses. This allowed me to record the spike responses of the auditory receptor neurons intracellularly from the auditory nerve far away from the ear. The interspike intervals (ISI) of the spike responses, i.e. the time between subsequent action potentials, as well as the spike count, i.e. the number of action potentials fired in a defined time frame, are statistically analyzed. By means of simulations of integrate-and-fire and conductance-based models, different assumptions of possible noise sources are tested which explain the ISI and spike-count statistics of the experimental data.
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The electrophysiological results indicate that MNSCs from the pars intercerebralis of Locusta migratoria are rather heterogeneous with respect to membrane potential and excitability. This seems also to be the case for MNSCs of Periplaneta americana as shown in in situ recordings from the somata (Cook and Milligan, 1972). It may be that our pipette solution (I) containing calcium and EGTA was not appropriate for buffering intracellular calcium to an optimal level in all recordings. This is especially important in the context of the investigations of Pitman (1979) and Thomas (1984), who demonstrated that the properties of some insect neurones are very dependent upon intracellular calcium concentration. Chelation of intracellular calcium by injection of citrate or EGTA can enable somata that are normally passive to generate calcium-dependent action potentials. Experiments are in progress to investigate in detail the ionic current components of the action potentials of locust MNSCs.
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Octopamine and tyramine modulate the myogenic activity of a variety of visceral muscles in insects, including tissues of the reproductive system. Octopamine decreases the basal tonus, and reduces the amplitude and frequency of neurally evoked contractions of the lateral oviducts of the locust Locusta migratoria (Lange and Orchard, 1986). Also, octopamine has been shown to decrease the amplitude of proctolin-induced contractions in a dose- dependent manner (Lange and Orchard, 1986; Nykamp and Lange, 2000). These effects appear to be mediated by an Oct/Tyr receptor shown to be expressed in the oviducts of locusts (Molaei et al., 2005). In Drosophila and the stable fly Stomoxys calcitrans, octopamine reduces the amplitude and frequency of contractions, and reduces basal tonus of the oviducts in a dose-dependent manner (Cook and Wagner, 1992; Middleton et al., 2006; Rodríguez- Valentín et al., 2006). These physiological effects could be linked to two receptors: the octopamine receptor in the mushroom bodies (OAMB) and Oct β 2-R, which have been shown in Drosophila to be expressed in the epithelial and muscle cells of the oviducts (Lee et al., 2003; Li et al., 2015; Lim et al., 2014). These receptors are involved in ovulation and fertilization of eggs, whereby mutant constructs of these receptors show reproductive sterility in females, accumulation of eggs in the ovary and reduction in the number of eggs laid (Lee et al., 2003; Li et al., 2015; Lim et al., 2014). In contrast, octopamine has also been shown to increase the frequency
The effect of previous exposure to lateral sensory stimuli in shaping the response to subsequent symmetric stimuli represents an important overlooked issue in neuroethology, with special reference to arthropods. In this research, we investigated the hypothesis to ‘ programme ’ jumping escape direction as well as surveillance orientation in young and adult individuals of Locusta migratoria as an adaptive consequence of prior exposure to directional-biased predator approaches generated by a robotic leopard gecko representing Eublepharis macularius. The manipulation of the jumping escape direction was successfully achieved in young locusts, although young L. migratoria did not exhibit innately lateralized jumping escapes. Jumping escape direction was also successfully manipulated in adult locusts, which exhibited innate lateralized jumping escape at the individual level. The innate lateralization of each instar of L. migratoria in using a preferential eye during surveillance was not affected by prior lateralized exposure to the robotic gecko. Our results indicate a high plasticity of the escape motor outputs that are occurring almost in real time with the perceived stimuli, making them greatly adaptable and compliant to environmental changes in order to be effective and reliable. In addition, surveillance lateralization innately occurs at population level in each instar of L. migratoria. Therefore, its low forgeability by environmental factors would avoid disorganization at swarm level and improve swarm coordination during group tasks. These findings are consistent with the fact that, as in vertebrates, in insects the right hemisphere is specialized in controlling fear and escape functions.
Overall, the biological life cycle of the nematode under study corresponds to earlier data (Anderson, 1962), with the only difference that we recorded three locust species, Aiolopus oxianus, Calliptamus italicus and Melanoplus frigidis as D. isabellina’s intermediate hosts. In our experiments the parasites developed in their definitive hosts much faster than in the experiments by Anderson (1962). Probably, this is because of the experimental conditions and different susceptibility in different bird species. Probably, the other species of the genus that concentrate in the organs connected with the external environment (air sacs, eye sockets and nasal cavities) will have a similar biological cycle scheme. This viewpoint is confirmed by data from a number of other researchers (Bain, Voucher, 1973; Cawthorn, Anderson, 1980), who registered locusts (Camnula pellucidа, Melanoplus bilituratus, M. fusciatus, M. sanguinipes, Locusta migratoria, Schistocerca gregaria) as the intermediate hosts of some nematode species from the genus Diplotiaena – D. agelaeus (Walton, 1927), D. tricuspis (Fedtshenko, 1874), D.tridens (Molim, 1858) and D. bargusinica (Skryabin, 1927).