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Group living has various benefits, but it also carries costs, such as risk of cannibalism. Molting is a vulnerable period of being cannibalized in juvenile arthropods, but how gregarious arthropods avoid this threat is poorly understood. Here, we examined how actively migrating gregarious nymphs of desert locust, Schistocerca gregaria , avoid cannibalism during molting, in the Sahara Desert of Mauritania. In the field, gregarious nymphs cyclically march and feed on grass during the day. Our field observations found that marching behavior helped separating pre-molting and cannibalistic non-molting nymphs. Cannibalistic non-molting nymphs marched away from roost plants, leaving sedentary pre-molting nymphs behind, creating cannibal-free spaces. Some non-molting nymphs reached a pre-molting state after daytime marching, thus both pre- and non-molting nymphs roosted on same plants at night. However, pre-molting nymphs moved away from conspecifics prior to molting. Starvation experiments confirmed that food-satiation decreased cannibalistic necrophagy. Physiological surveys of diel feeding and molting patterns revealed that nymphs molted at times when conspecifics were food-satiated rather than hungry. Hence, our results indicate that behavioral and physiological traits of gregarious locusts could function to spatiotemporally separate molting locusts from cannibalistic conspecifics, thus reducing molting-associated cannibalism. This is the first report of migration-dependent molting synchrony as a mechanism reducing costs of aggregation in gregarious arthropods. [ABSTRACT FROM AUTHOR]

Upsurges of desert locusts can cause heavy economic and agricultural losses and threaten the food security of millions of people over dozens of countries. Therefore, monitoring and spatial delimitation of their habitats are necessary for biological control studies and sampling, especially on large surfaces. This study aimed to assess and map suitable biotopes for desert locusts in southern Algeria, through a GIS tool, by integrating multicriteria analysis (Analytical Hierarchy Process) as a decision-making tool for preventive methods, biological control and research. The result is a resolution map, classified into four different zones according to pixel values. The results revealed that 28.51% of the study area is an unsuitable biotope for desert locusts, 35.92% is a survival biotope, 19.5% is a suitable biotope mainly for breeding and eggs lying and 16.05% is highly suitable for desert locust gregarization and concentration. This study offers a simplified mapping procedure to assess locust habitats for decision-making and studies in large areas. [ABSTRACT FROM AUTHOR]

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All terrestrial ectotherms are constrained to some degree by their thermal environment and the extent to which they can behaviorally buffer variable thermal conditions. New biophysical modeling methods (NicheMapR) allow the calculation of the body temperature of thermoregulating animals anywhere in the world from first principles, but require detailed observational data for parameterization and testing. Here we describe the thermoregulatory biology of marching bands of the desert locust, Schistocerca gregaria, in the Sahara Desert of Mauritania where extreme heat and strong diurnal fluctuations are a major constraint on activity and physiological processes. Using a thermal infrared camera in the field, we showed that gregarious nymphs altered the microhabitats they used, as well as postural thermoregulatory behaviors, to maintain relatively high body temperature (nearly 40°C). Field and laboratory experiments demonstrated that the preferred body temperature accelerated digestive rates. Migratory bands frequently left foraging sites with full guts before consuming all vegetation and moved to another habitat before emptying their foregut. Thus, the repertoire for behavioral thermoregulation in the desert locust strongly facilitates foraging and digestion rates, which may accelerate developmental rates and increase survival. We used our data to successfully parameterize a general biophysical model of thermoregulatory behavior that could capture hourly body temperature and activity at our remote site using globally available environmental forcing data. This modeling approach provides a stronger basis for forecasting thermal constraints on locust outbreaks under current and future climates. [ABSTRACT FROM AUTHOR]

In Africa, there are two well-known subspecies of the desert locust; the Sahara subspecies, Schistocerca gregaria gregaria (Forskål, 1775), and the southern African subspecies, Schistocerca gregaria flaviventris (Burmeister). The northern locust, S. g. gregaria, extends across the Sahara desert to western Asia. The invasion area of the southern subspecies, S. g. flaviventris, extends to Namibia, Angola, South Africa, Ascension Islands and Botswana. Four different locust populations were selected, three populations for the northern S. g. gregaria (f, e, r) from different localities and one population for the southern S. g. flaviventris (s). Three characters were selected, the length of the forewing (E), the length of the posterior femur (F), and the widest part of the head capsule (C). Two ratios (E/F, F/C)were also calculated and compared for the different populations. The univariate analysis technique using the ANOVA test was performed for the four locust populations. The means of the different measured characters and the two ratios indicated significant differences between the southern population and the other three northern populations. The mean values of E, F,C, and E/F ratio were lower for the southern population compared to the three northern populations. Multivariate analysis of variance indicated that the four locust populations were highly significantly different (P< 0.0001). Standardised canonical coefficients for the three characters and the two ratios were given. The Mahalanobis distance (D2) between the centroids of the different populations for the three measured characters and the two ratios were significantly different (P < 0.0001). The distances recorded between the southern and the three northern populations were higher than the distances between the three northern populations. The results indicated that the southern males and females are more morphologically closer to each other than to either sex of the northern locusts. Also, the two sexes of the northern populations are more or less similar in their morphological features than the southern locust population. We may suggest that the southern population may categorise an evolutionary dichotomy that has arisen on the African continent and may separate the two locust populations into two distinct species. [ABSTRACT FROM AUTHOR]

Aims: The Desert Locust (Schistocerca gregaria) occupies vast territories in the Saharan part of Africa. Its habitats have been described separately in several localities, yet a synthetic view is lacking. Previous researchers have provided lists of plants for each study site but rarely the corresponding information about their phytosociological context. The aim of this work was to give insights into the classes and alliances hosting the Desert Locust throughout the Saharo-Sindian and Saharo-Sahelian area. Location: We investigated four regions in the center and in the southern parts of Algerian Sahara, with altitudes ranging from 300 to 1050 m a.s.l. We also considered six localities taken from literature, of which two and four were selected in the Saharo-Sindian and Saharo-Sahelian regions respectively. Methods: We sampled 466 relevés between 2007 and 2013 to record the abundance-dominance of plants, and the density of Desert Locust. Sampling dates were adjusted to insect presence. The plant assemblages were defined by Ward's clustering method to obtain a balanced number of samples. The fidelity (phi coefficient) of plant species in the assemblages found was calculated. The link between Desert Locust density and different environmental parameters, including vegetation alliance proportions, was estimated through correlation analysis. Results: Hierarchical classification revealed 16 plant assemblages that do not clearly fit into the phytosociological system. Each assemblage contains species belonging to several alliances, highlighting the difficulty in defining plant associations in desert ecosystems. Desert Locust abundance was positively linked to the percentages of Saharo-Sindian plants and of the Antirrhino-Pithurantion scopariae alliance, but negatively so to plants associated with saline-gypsum soils. As with the Acacio-Panicion, the Antirrhino-Pithurantion scopariae is a desert steppe developed on oued edges (temporary river) but with a slightly higher annual rainfall. There is a set of stations, particularly near Bordj-Badji-Mokhtar, where the density of Desert Locust is not linked to preferred plants, suggesting that they constitute only survival biotopes. We also provide a wider view on the requirements of the Desert Locust to enter a gregarious phase, by including several literature stations of tropical Africa, in order to compare the different vegetation types. Even where the dominant vegetation remains the Acacio-Panicion, the flora is mainly Saharo-Sahelian and Sahelo-Sudanian, and not Mediterraneo-Saharo-Sindian. Conclusions: The habitat of Desert Locust is clearly defined by plant assemblages linked to the Acacio-Panicion alliance. There are significant differences between the vegetation associated with solitary and gregarious individuals. [ABSTRACT FROM AUTHOR]

The desert plant, Lotus corniculatus (Fabaceae), inhabits the Saudi Arabian Sahara Desert. In these areas the desert locust, Schistocerca gregaria (Orthoptera, Acrididae), feeds on L. corniculatus containing the plant allelochemical linamarin; a cyanogenic glucoside that is usually toxic to polyphagous insects. Under laboratory conditions this plant was fed to S. gregaria. Haemolymph proteins and allelochemicals detoxification in S. gregaria, fed on L. corniculatus were assessed. Female 5th instar nymphs were reared on L. corniculatus or on wheat seedlings, Triticum aestivum, as control. In insects, glutathione-S-transferase is one of the most important detoxifying enzymes. The activity of glutathione-S-transferase (in units /gram) in the mid-gut tissues of 5th instar nymph females fed on L. corniculatus was significantly higher than in those fed on T. aestivum. The quantity of haemolymph proteins (in mg 100µl1) in adult locust females resulting from nymphs fed on L. corniculatus was significantly less than it was in females fed on T. aestivum. Decreasing protein synthesis in the adult females of S. gregaria might be related to detoxifying toxic compounds in L. corniculatus. [ABSTRACT FROM AUTHOR]

Most terrestrial animals are constrained by extreme heat conditions such as midday desert environments, while a few terrestrial ectothermic insects are active in such ecological niches. Sexually mature males of the desert locust (Schistocerca gregaria) in the Sahara Desert remain on the open ground, despite the ground temperatures exceeding their lethal limit, to form leks and to mate incoming gravid females during the daytime. Lekking male locusts apparently suffer from extreme heat stress and greatly fluctuating thermal conditions. The present study examined the thermoregulatory strategies of the lekking male S. gregaria. Our field observations showed that lekking males changed their body orientation toward the sun depending on the temperature and time of day. In the relatively cool morning, males basked by orienting perpendicular to the sun's rays, maximizing the area of body surface exposed to the sun's rays. In contrast, around midday, when the ground surface temperature exceeded lethal high temperatures, some males tended to shelter inside the plants or remain in the shade. However, the remainder stayed on the ground, stilted (i.e., extending their legs to raise their bodies off the hot ground) and oriented parallel to the sun's rays, which minimized radiative heating. Measurements of body temperature throughout the hot middle period of the day confirmed that the stilting posture prevented overheating. Their critical lethal body temperature was as high as 54.7 °C. In this lekking system, gravid females enter male leks by flying. These incoming females usually landed on open ground, whereupon nearby males immediately approached, mounted, and mated the female, implying that males with greater heat-tolerance can increase mating chance. These results suggest that behavioral thermoregulation and physiologically high heat tolerance of male desert locusts allows them to endure extreme thermal conditions for lekking. [Display omitted] • Thermoregulatory strategies of the lekking desert locust male were investigated. • Lekking males exhibited behavioral and physiological strategies to tolerate heat. • Stilting posture prevented overheating. • Desert locust males have one of the highest known thermal tolerances of the species of insects. [ABSTRACT FROM AUTHOR]

The desert locust, Schistocerca gregaria, is a major migratory pest that causes substantial agricultural damage. Flying adult swarms disperse widely during the daytime, but they densely roost on plants at night. Swarm control operations are generally conducted during the daytime, but night-time control is a significant potential alternative. However, the night-roosting behavior of swarms is poorly understood. We determined night-roosting plant preferences of migrating sexually immature swarms of S. gregaria at four different sites in the Sahara Desert in Mauritania during winter. The night-roosting sites were divided into two types based on presence or absence of large trees. Swarms tended to roost on the largest trees and bushes at a given site. Swarms used medium-sized plants when large trees were not locally available, but the same medium-sized plant species were hardly used when large trees were available. Plant choice influenced roosting group size—large locust groups roosted on larger plants. Night-roosting locusts rarely fled from approaching observers. These results suggest that swarms of S. gregaria exhibit plasticity in their utilization patterns of night-roosting plants depending on the plant community encountered and they selectively use larger plants. We propose that this predictable plant-size dependent night-roosting can be used to particularly ease locust swarm control and to generally adopt anti-locust night control strategy. [ABSTRACT FROM AUTHOR]

Animals often aggregate at certain sites during vulnerable periods such as night-roosting as an anti-predatory strategy. Some migratory gregarious animals must regularly find new night-roosting sites, but how they synchronously choose such sites is poorly understood. We examined how gregarious nymphs of the desert locust, Schistocerca gregaria Forskål (Orthoptera: Acrididae), aggregate at certain plants for night-roosting in the Sahara Desert. Migratory bands of last instar nymphs climbed trees around dusk and roosted there overnight. A spatial autocorrelation analysis of plants indicated that the larger locust groups formed at the larger plants within the local plant community. Other large groups were not formed near the large tree, but smaller groups were patchily distributed. Plant height was the primary cue used by migratory bands to choose night-roosting plants. A nearest-neighbor distance analysis showed that single conspicuous large trees with scattered smaller plants were distributed locally. This plant community structure and negative geotactic ascending behavior of gregarious nymphs may force them to concentrate at the landmark plant from all directions and afar. This plant-size-dependent roosting site choice may contribute for developing artificial trapping systems for locusts and inciting to a new environment-friendly night control approach. [ABSTRACT FROM AUTHOR]