How Nutrients Mediate the Impacts of Global Change on Locust Outbreaks

Locusts are grasshoppers that can migrate en masse and devastate food security. Plant nutrient content is a key variable influencing population dynamics, but the relationship is not straightforward. For an herbivore, plant quality depends not only on the balance of nutrients and antinutrients in plant tissues, which is influenced by land use and climate change, but also on the nutritional state and demands of the herbivore, as well as its capacity to extract nutrients from host plants. In contrast to the concept of a positive relationship between nitrogen or protein concentration and herbivore performance, a five-decade review of lab and field studies indicates that equating plant N to plant quality is misleading because grasshoppers respond negatively or neutrally to increasing plant N just as often as they respond positively. For locusts specifically, low-N environments are actually beneficial because they supply high energy rates that support migration. Therefore, intensive land use, such as continuous grazing or cropping, and elevated ambient CO2 levels that decrease the protein:carbohydrate ratios of plants are predicted to broadly promote locust outbreaks.

Deep histories of food systems in eastern Africa and current patterns of food insecurity

Central to successful attempts to address food insecurity in Africa are understandings of the historical contexts and meanings of food systems. However, much research into current challenges remains separated from deeper agrarian and alimentary histories. Using qualitative data on food within the historical record alongside the wider multidisciplinary record of the past, this Review traces long-term patterns and drivers of continuity and change in eastern African food systems. Considerable dynamism in place-based and regional trends in the integration of new foodstuffs, agricultural commercialization, resistance and transformations in diets, and diversification and specialization as livelihood strategies is found-each of which emerged within imbricated contexts of African agency, transoceanic exchanges and colonial incursions. Such historical data provide important deep-time perspectives for interventions to address modern food insecurity, as demonstrated through examples of agricultural value chains, 'under-utilized' crops and major infrastructure projects in southeast Africa.

Field bands of marching locust juveniles show carbohydrate, not protein, limitation

Locusts are grasshoppers that migrate en masse and devastate food security, yet little is known about the nutritional needs of marching bands in nature. While it has been hypothesized that protein limitation promotes locust marching behavior, migration is fueled by dietary carbohydrates. We studied South American Locust (Schistocerca cancellata) bands at eight sites across Argentina, Bolivia, and Paraguay. Bands ate most frequently from dishes containing carbohydrate artificial diets and minimally from balanced, protein, or control (vitamins and salts) dishes-indicating carbohydrate hunger. This hunger for carbohydrates is likely explained by the observation that local vegetation was generally protein-biased relative to locusts' preferred protein to carbohydrate ratio. This study highlights the importance of studying the nutritional ecology of animals in their environment and suggests that carbohydrate limitation may be a common pattern for migrating insect herbivores.

Eco-friendly postharvest irradiation strategy with 131I isotope for environmental management of populations of migratory locust, Locusta migratoria

PURPOSE

Irradiation of food is promising for control of pests to minimize postharvest losses of yields and thus improvement of food safety, shelf life of produce. It is a method of choice that induces a series of lethal biochemical and molecular changes culminating into the engagement of a downstream cascade to cause abnormalities in irradiated pests. In this study, the effects of iodine-131 (131I) isotope radiation on the male gonad development of the migratory locust, Locusta migratoria, were evaluated.

MATERIALS AND METHODS

Newly emerged adult male locusts, less than one-day-old, were divided into two groups, control and irradiated. Locusts in the control group (n = 20 insects) didn't drink irradiated water and were reared under normal environmental conditions for one week. Locusts in the irradiated group (n = 20 insects) were exposed to irradiated water at a dose of 30 mCi and they were subsequently observed until they drank the whole quantity.

RESULTS

At the end of the experiment, scanning and electron microscopic examination of testes obtained from irradiated locusts revealed several major abnormalities, including malformed nuclei of spermatozoa, irregular plasma membranes, shrinkage of testicular follicles, vacuolated cytoplasm, disintegrated nebenkern and agglutinations of spermatids. Flow cytometry analysis revealed that 131I radiation induced both early and late apoptosis, but not necrosis, in testicular tissues. Testes of irradiated insects also exhibited a burst in reactive oxygen species (ROS), as indicated by significant elevation in amounts of malondialdehyde (MDA), a marker for peroxidation of lipids. In contrast, irradiation coincided with significant reductions in activities of enzymatic antioxidant biomarkers. Relative to controls, a three-fold upregulation of expression of mRNA of heat shock protein, Hsp90, was observed in testicular tissue of irradiated locusts. 131I-irradiated insects exhibited genotoxicity, as indicated by significant increases in various indicators of DNA damage by the comet assay, including tail length (7.80 ± 0.80 µm; p < .01), olive tail moment (40.37 ± 8.08; p < .01) and tail DNA intensity % (5.1 ± 0.51; p < .01), in testicular cells compared to the controls.

CONCLUSION

This is the first report on elucidation of I131-irradiation-mediated histopathological, biochemical and molecular mechanisms in gonads of male L. migratoria. Herein, the findings underscore the utility of 131I radiation as an eco-friendly postharvest strategy for management of insect pests and in particular for control of populations of L. migratoria.

Nutrient supply and accessibility in plants: effect of protein and carbohydrates on Australian plague locust (Chortoicetes terminifera) preference and performance

In contrast to predictions from nitrogen limitation theory, recent studies have shown that herbivorous migratory insects tend to be carbohydrate (not protein) limited, likely due to increased energy demands, leading them to preferentially feed on high carbohydrate plants. However, additional factors such as mechanical and chemical defenses can also influence host plant choice and nutrient accessibility. In this study, we investigated the effects of plant protein and carbohydrate availability on plant selection and performance for a migratory generalist herbivore, the Australian plague locust, Chortoicetes terminifera. We manipulated the protein and carbohydrate content of seedling wheat (Triticum aestivum L.) by increasing the protein:carbohydrate ratio using nitrogen (N) fertilizer, and manipulated the physical structure of the plants by grinding and breaking down cell walls after drying the plants. Using a full factorial design, we ran both choice and no-choice experiments to measure preference and performance. We confirmed locust preference for plants with a lower protein-carbohydrate ratio (unfertilized plants). Unlike previous studies with mature wild grass species, we found that intact plants supported better performance than dried and ground plants, suggesting that cell wall removal may only improve performance for tougher or more carbohydrate-rich plants. These results add to the growing body of evidence suggesting that several migratory herbivorous species perform better on plants with a lower protein:carbohydrate ratio.

Herbivory by Atta vollenweideri: Reviewing the significance of grass-cutting ants as a pest of livestock

The grass-cutting ant Atta vollenweideri is well suited for studies examining the negative effect leaf-cutting ants have on livestock production in South American grasslands because they forage on the same plants as cattle. This study investigated the impact of A. vollenweideri on livestock production in Argentinean rangelands. First, we assessed A. vollenweideri herbivory rates and its economic injury level (EIL). Second, using satellite imagery in a region covering 15,000 ha, we estimated the percentage of this area that surpassed the calculated EIL. Results showed that A. vollenweideri consumed approximately 276 kg of dry plant weight/ha/year, foraging mostly on grasses (70%). Additionally, ants cut 25% of herbs and 5% of trees. In summer and autumn, ants consumed more grasses, while in winter and spring, herbs and trees were also significantly cut. Ants consumed 7% of the forage demand needed to raise a calf according to the management regime applied by farmers. Our calculated EIL (5.85 nests/ha) falls in the range of previous studies. Colonies were absent in 93.6% of the surveyed area, while their density was below the EIL in 6.2% of the area. A. vollenweideri populations surpassed the EIL in only 0.2% of the area, which corresponds to 2.6% of the locations holding colonies. These results question the perception that Atta leaf-cutting ants are a pest of livestock production. Although ants consume a small percentage of cattle's forage demand, evidence that ants and cattle are competing in the few cases in which density surpasses the EIL is arguable. First, grass-cutting ants are capable of consuming herbs and trees in addition to the grasses on which cattle mostly feed. Second, there is no evidence indicating that both are cutting the same plant portions when preferences overlap. Third, evidence suggests that ants are not displaced under high-pressure grazing regimes by cattle. In the countries where A. vollenweideri is present, decision makers have promulgated several acts making its control mandatory. It is time to revisit the pest status of A. vollenweideri and include the use of EIL as a control criterion.

Assessment on Potential Suitable Habitats of the Grasshopper Oedaleus decorus asiaticus in North China based on MaxEnt Modeling and Remote Sensing Data

Grasshopper populations can quickly grow to catastrophic levels, causing a huge amount of damage in a short time. Oedaleus decorus asiaticus (Bey-Bienko) (O. d. asiaticus) is the most serious species in Xilingol League of the Inner Mongolia Autonomous Region. The region is not only an important grassland but also a site of agricultural heritage systems in China. Therefore, projecting the potential geographic distribution of O. d. asiaticus to provide an early warning is vital. Here, we combined temperature, precipitation, soil, vegetation, and topography with remote sensing data to screen the predictors that best characterize the current geographical distribution of O. d. asiaticus. A MaxEnt model approach was applied to project the potential suitable distribution of O. d. asiaticus in Xilingol League (the Inner Mongolia Autonomous Region of China) combined with a set of optimized parameters. The modeling results indicated that there were six main habitat factors that determined the suitable distribution of O. d. asiaticus such as the soil type (ST), grassland type (GT), elevation, precipitation during the growing period (GP), precipitation during the spawning period (SP), and normalized difference vegetation index during the overwintering period (ONDVI). The simulated result was good, with average AUC and TSS values of 0.875 and 0.812, respectively. The potential inhabitable areas of grasshoppers were 198,527 km², distributed mainly in West Urumqi, Xilinhot City, East Urumqi, Abaga Banner, and Xianghuang Banner of Xilingol League. This study is valuable to guide managers and decision-makers to prevent and control the occurrence of O. d. asiaticus early on and this study may facilitate meaningful reductions in pesticide application.

Domestication provides durum wheat with protection from locust herbivory

Lower plant resistance to herbivores following domestication has been suggested as the main cause for higher feeding damage in crops than in wild progenitors. While herbivore compensatory feeding has also been proposed as a possible mechanism for raised damage in crops with low nutritional quality, predictions regarding the effects of plant domestication on nutritional quality for herbivores remain unclear. In particular, data on primary metabolites, even major macronutrients, measured in the organs consumed by herbivores, are scarce. In this study, we used a collection of 10 accessions of wild ancestors and 10 accessions of modern progenies of Triticum turgidum to examine whether feeding damage and selectivity by nymphs of Locusta migratoria primarily depended on five leaf traits related to structural resistance or nutrient profiles. Our results unexpectedly showed that locusts favored wild ancestors over domesticated accessions and that leaf toughness and nitrogen and soluble protein contents increased with the domestication process. Furthermore, the quantitative relationship between soluble protein and digestible carbohydrates was found to poorly meet the specific requirements of the herbivore, in all wheat accessions, both wild and modern. The increase in leaf structural resistance to herbivores in domesticated tetraploid wheat accessions suggested that resource allocation trade-offs between growth and herbivory resistance may have been disrupted by domestication in the vegetative organs of this species. Since domestication did not result in a loss of nutritional quality in the leaves of the tetraploid wheat, our results rather provides evidence for a role of the content of plants in nonnutritive nitrogenous secondary compounds, possibly deterrent or toxic, at least for grasshopper herbivores.

Predictions Based on Different Climate Change Scenarios: The Habitat of Typical Locust Species Is Shrinking in Kazakhstan and Xinjiang, China

Climate change, especially climate extremes, can increase the uncertainty of locust outbreaks. The Italian locust (Calliptamus italicus (Linnaeus, 1758)), Asian migratory locust (Locusta migratoria migratoria Linnaeus, 1758), and Siberian locust (Gomphocerus sibiricus (Linnaeus, 1767)) are common pests widely distributed in the semidesert grasslands of Central Asia and its surrounding regions. Predicting the geographic distribution changes and future habitats of locusts in the context of climate warming is essential to effectively prevent large and sudden locust outbreaks. In this study, the optimized maximum entropy (MaxEnt) model, employing a combination of climatic, soil, and topographic factors, was used to predict the potential fitness areas of typical locusts in the 2030s and 2050s, assuming four shared socioeconomic pathways (SSP126, SSP245, SSP370, and SSP585) in the CMIP6 model. Modeling results showed that the mean area under the curve (AUC) and true statistical skill (TSS) of the MaxEnt model reached 0.933 and 0.7651, respectively, indicating that the model exhibited good prediction performance. Our results showed that soil surface sand content, slope, mean precipitation during the hottest season, and precipitation seasonality were the key environmental variables affecting locust distribution in the region. The three locust species were mainly distributed in the upstream region of the Irtysh River, the Alatao Mountain region, the northern slopes of the Tianshan Mountains, around Sayram Lake, the eastern part of the Alakol Lake region, the Tekes River region, the western part of Ulungur Lake, the Ili River, and the upstream region of the Tarim River. According to several climate projections, the area of potential habitat for the three most common locust species will decrease by 3.9 × 10⁴-4.6 × 10⁴ km² by the 2030s and by 6.4 × 10⁴-10.6 × 10⁴ km² by the 2050s. As the climate becomes more extreme, the suitable area will shrink, but the highly suitable area will expand; thus, the risk of infestation should be taken seriously. Our study present a timely investigation to add to extensive literature currently appearing regarding the myriad ways climate change may affect species. While this naturally details a limited range of taxa, methods and potential impacts may be more broadly applicable to other locust species.

Evaluation of the Toxicity of Chemical and Biogenic Insecticides to Three Outbreaking Insects in Desert Steppes of Northern China

The locusts Oedales asiaticus (Bey-Bienko) and Myrmeleotettix palpalis (Zubovski) (Orthoptera Acrididae) and the leaf beetle Galeruca daurica (Joannis) (Coleoptera, Chrysomelidae) are economically devastating insect species in the desert steppes of Northern China. Control is mainly and frequently dependent on highly toxic chemicals. To date, there have been no complete and comprehensive reports of insecticide applications to these key pests. In this study, laboratory bioassays were carried out to determine and compare the toxicity of twelve insecticides to three outbreaking insects, O. asiaticus, M. palpalis, and G. daurica, from three typical desert steppe regions, SZWQ, XHQ and WLTQQ, respectively. The responses of the two locust species and the leaf beetle were evaluated by topical application and leaf dip bioassay techniques across a range of concentrations to develop dosage–mortality regressions. The insecticides tested included six chemical insecticides (β-cypermethrin, imidacloprid, phoxim, λ-cyhalothrin, methomyl, chlorantraniliprole) and six biogenic insecticides (spinosad, avermectin, rotenone, matrine, azadiracthin, and methoxyfenozide). The results showed that phoxim, λ-cyhalothrin, β-cypermethrin and spinosad showed highly toxic activity to O.asiaticus, M. palpalis, and G. daurica, while methonyl, chlorantraniliprole, and rotenone were moderately toxic to both locust species and the leaf beetle. The LC₅₀ values of matrine, azadiractin, and avermectin were more than 1 μg a.i./adult for O. asiaticus and M. palpalis, the LC₅₀ values of which were higher 2 g/L for G. daurica. Our findings complement information from previous similar studies and will inform future studies relating to the control of outbreaking insects, such as O.asiaticus, M. palpalis, and G. daurica in desert steppes of northern China. This study is also expected to provide basic data on the use of chemical and biogenic insecticides for application in desert steppes.

The Handsome Cross Grasshopper Oedaleus decorus (Germar, 1825) (Orthoptera: Acrididae) as a Neglected Pest in the South-Eastern Part of West Siberian Plain

Simple Summary

The handsome cross grasshopper is one of the most abundant and widely distributed grasshopper species over the steppe and semi-desert territories of Eurasia. In many areas, especially in east Mongolia and north-east China, it is a very common and dangerous pest on agriculture fields and pasturelands. However, the species was relatively rare in the steppes of west Siberia until the 1960s, but by the end of the last century, the geographic and ecological distribution of the handsome cross grasshopper was changed significantly. Nowadays, it often occurs across all steppes of the south-eastern part of West Siberian Plain, its abundance is high, and its populations are found in the forest-steppes and also on the eastern side of the Ob River. The authors tried to use ecologo-geographic modelling to estimate how species distribution may change in the near future.

Abstract

Oedaleus decorus is a widely distributed acridid over the Eurasian semi-arid territories, from the Atlantic coast to the Pacific coast. In many semi-arid territories, O. decorus was and is the most important pest, but in the south-eastern part of West Siberian Plain, it was not considered a pest until the 1960s. We compared two sets of data on the acridid distribution in the region: before 1960 and from 1961 until 2021. Until the 1960s, the species occurred mainly in the southern steppes. Since the 1960s, its distribution changed significantly. Nowadays, it occupies almost all local steppes and the southern part of the forest-steppes and can be also found on the eastern side of the Ob River. These shifts may be explained by both climatic changes and changes in human activities. During upsurges the densities of O. decorus were often more than one to two adults per square meter. It is often abundant in the same habitats and in the same periods as the Italian locust (Calliptamus italicus)—one of the most important acridid pests. This means during joint outbreaks these two species can simultaneously damage almost all spectrum of plants.

Density-dependent mating behaviors reduce male mating harassment in locusts

Male mating harassment may occur when females and males do not have the same mating objectives. Communal animals need to manage the costs of male mating harassment. Here, we demonstrate how desert locusts in dense populations reduce such conflicts through behaviors. In transient populations (of solitarious morphology but gregarious behavior), we found that nongravid females occupied separate sites far from males and were not mating, whereas males aggregated on open ground (leks), waiting for gravid females to enter the lekking sites. Once a male mounted a gravid female, no other males attacked the pair; mating pairs were thereby protected during the vulnerable time of oviposition. In comparison, solitarious locusts displayed a balanced sex ratio in low-density populations, and females mated irrespective of their ovarian state. Our results indicate that the mating behaviors of desert locusts are density dependent and that sex-biased behavioral group separation may minimize the costs of male mating harassment and competition.

Long-Term Population Dynamics of Namib Desert Tenebrionid Beetles Reveal Complex Relationships to Pulse-Reserve Conditions

Noy-Meir's paradigm concerning desert populations being predictably tied to unpredictable productivity pulses was tested by examining abundance trends of 26 species of flightless detritivorous tenebrionid beetles (Coleoptera, Tenebrionidae) in the hyper-arid Namib Desert (MAP = 25 mm). Over 45 years, tenebrionids were continuously pitfall trapped on a gravel plain. Species were categorised according to how their populations increased after 22 effective rainfall events (>11 mm in a week), and declined with decreasing detritus reserves (97.7-0.2 g m^-2), while sustained by nonrainfall moisture. Six patterns of population variation were recognised: (a) increases triggered by effective summer rainfalls, tracking detritus over time (five species, 41% abundance); (b) irrupting upon summer rainfalls, crashing a year later (three, 18%); (c) increasing gradually after series of heavy (>40 mm) rainfall years, declining over the next decade (eight, 15%); (d) triggered by winter rainfall, population fluctuating moderately (two, 20%); (e) increasing during dry years, declining during wet (one, 0.4%); (f) erratic range expansions following heavy rain (seven, 5%). All species experienced population bottlenecks during a decade of scant reserves, followed by the community cycling back to its earlier composition after 30 years. By responding selectively to alternative configurations of resources, Namib tenebrionids showed temporal patterns and magnitudes of population fluctuation more diverse than predicted by Noy-Meir's original model, underpinning high species diversity.

Application of Remote Sensing Data for Locust Research and Management-A Review

Simple Summary

Locust outbreaks around the world regularly affect vast areas and millions of people. Mapping and monitoring locust habitats, as well as prediction of locust outbreaks is essential to minimize the damage on crops and pasture. In this context, remote sensing has become one of the most important data sources for effective locust management. This review paper summarizes remote sensing-based studies for locust management and research over the past four decades and reveals progress made and gaps for further research. We quantify which locust species, regions of interest, sensor data and variables were mainly used and which thematic foci were of interest. Our review shows that most studies were conducted for the desert locust, the migratory locust and Australian plague locust and corresponding areas of interest. Remote sensing studies for other destructive locust species are rather rare. Most studies utilized data from optical sensors to derive NDVI and land cover for mapping and monitoring the locust habitats. Furthermore, temperature, precipitation and soil moisture are derived from thermal infrared, passive and active radar sensors. Applications of the European Sentinel fleet, entire Landsat archive or very-high-spatial-resolution data are rare. Implementing new methods (e.g., data fusion) and additional data sources could provide new insights for locust research and management.

Abstract

Recently, locust outbreaks around the world have destroyed agricultural and natural vegetation and caused massive damage endangering food security. Unusual heavy rainfalls in habitats of the desert locust (Schistocerca gregaria) and lack of monitoring due to political conflicts or inaccessibility of those habitats lead to massive desert locust outbreaks and swarms migrating over the Arabian Peninsula, East Africa, India and Pakistan. At the same time, swarms of the Moroccan locust (Dociostaurus maroccanus) in some Central Asian countries and swarms of the Italian locust (Calliptamus italicus) in Russia and China destroyed crops despite developed and ongoing monitoring and control measurements. These recent events underline that the risk and damage caused by locust pests is as present as ever and affects 100 million of human lives despite technical progress in locust monitoring, prediction and control approaches. Remote sensing has become one of the most important data sources in locust management. Since the 1980s, remote sensing data and applications have accompanied many locust management activities and contributed to an improved and more effective control of locust outbreaks and plagues. Recently, open-access remote sensing data archives as well as progress in cloud computing provide unprecedented opportunity for remote sensing-based locust management and research. Additionally, unmanned aerial vehicle (UAV) systems bring up new prospects for a more effective and faster locust control. Nevertheless, the full capacity of available remote sensing applications and possibilities have not been exploited yet. This review paper provides a comprehensive and quantitative overview of international research articles focusing on remote sensing application for locust management and research. We reviewed 110 articles published over the last four decades, and categorized them into different aspects and main research topics to summarize achievements and gaps for further research and application development. The results reveal a strong focus on three species—the desert locust, the migratory locust (Locusta migratoria), and the Australian plague locust (Chortoicetes terminifera)—and corresponding regions of interest. There is still a lack of international studies for other pest species such as the Italian locust, the Moroccan locust, the Central American locust (Schistocerca piceifrons), the South American locust (Schistocerca cancellata), the brown locust (Locustana pardalina) and the red locust (Nomadacris septemfasciata). In terms of applied sensors, most studies utilized Advanced Very-High-Resolution Radiometer (AVHRR), Satellite Pour l’Observation de la Terre VEGETATION (SPOT-VGT), Moderate-Resolution Imaging Spectroradiometer (MODIS) as well as Landsat data focusing mainly on vegetation monitoring or land cover mapping. Application of geomorphological metrics as well as radar-based soil moisture data is comparably rare despite previous acknowledgement of their importance for locust outbreaks. Despite great advance and usage of available remote sensing resources, we identify several gaps and potential for future research to further improve the understanding and capacities of the use of remote sensing in supporting locust outbreak- research and management.

Distribution Patterns of Grasshoppers and Their Kin over the Eurasian Steppes

Simple Summary

The steppe zone is the huge area in temperate Eurasia where different grasslands form the main type of vegetation. The main part of this life zone has been transformed by human activity and used for crop cultivation (mainly wheat) and livestock. Regional and local transformations and/or climate changes can result in some shifts in species and population distribution of Orthoptera. Over this area, the climatic conditions and the dominated grasslands are suitable for numerous grasshoppers and their relatives, especially the graminivorous ones. The general level of their diversity is usually high. Many species are very abundant and may become important pests. However, there are also many rare species. The main aims of this paper are to reveal general patterns of Orthoptera distribution in the Eurasian steppes, to evaluate long-term trends of changes in distribution of taxa and populations, and to estimate the potential for population changes relative to human activity and global warming trends.

Abstract

The main aims of this paper are to reveal general patterns of Orthoptera distribution in the Eurasian steppes, to evaluate long-term trends of changes in distribution of taxa and populations, and to estimate the potential for population changes relative to human activity and global warming trends. The main publications concerning diversity and distribution of these insects over the steppes are analyzed. The fauna of the Eurasian steppes includes more than 440 species of Orthoptera. The general distribution of grasshoppers and their kin in the Eurasian steppes reflects their common associations with different grasslands. The species richness increases from the relatively cold forest-steppes to the semi-deserts with their warm summer. There are some endemic or subendemic taxa, including the tribe Onconotini (Tettigoniidae). The populations’ distribution of Orthoptera is also analyzed. The populations of native Orthoptera extend through all the herbaceous landscapes. Under these conditions, the interrelating of colonies of each species may result in great abundance. The population distribution of three species locusts (Locusta migratoria, Calliptamus italicus, Dociostaurus maroccanus) is also discussed. Some notable changes of their populations’ distribution and dynamics are characterized. The situation with rare Orthoptera is estimated. Retrospective and prospective of the steppe fauna of Orthoptera are discussed.

A review of historical and recent locust outbreaks: Links to global warming, food security and mitigation strategies

Locusts differ from ordinary grasshoppers in their ability to swarm over long distances and are among the oldest migratory pests. The ecology and biology of locusts make them among the most devastating pests worldwide and hence the calls for actions to prevent the next outbreaks. The most destructive of all locust species is the desert locust (Schistocerca gregaria). Here, we review the current locust epidemic 2020 outbreak and its causes and prevention including the green technologies that may provide a reference for future directions of locust control and food security. Massive locust outbreaks threaten the terrestrial environments and crop production in around 100 countries of which Ethiopia, Somalia and Kenya are the most affected. Six large locust outbreaks are reported for the period from 1912 to 1989 all being closely related to long-term droughts and warm winters coupled with occurrence of high precipitation in spring and summer. The outbreaks in East Africa, India and Pakistan are the most pronounced with locusts migrating more than 150 km/day during which the locusts consume food equivalent to their own body weight on a daily basis. The plague heavily affects the agricultural sectors, which is the foundation of national economies and social stability. Global warming is likely the main cause of locust plague outbreak in recent decades driving egg spawning of up to 2-400,000 eggs per square meter. Biological control techniques such as microorganisms, insects and birds help to reduce the outbreaks while reducing ecosystem and agricultural impacts. In addition, green technologies such as light and sound stimulation seem to work, however, these are challenging and need further technological development incorporating remote sensing and modelling before they are applicable on large-scales. According to the Food and Agriculture Organization (FAO) of the United Nations, the 2020 locust outbreak is the worst in 70 years probably triggered by climate change, hurricanes and heavy rain and has affected a total of 70,000 ha in Somalia and Ethiopia. There is a need for shifting towards soybean, rape, and watermelon which seems to help to prevent locust outbreaks and obtain food security. Furthermore, locusts have a very high protein content and is an excellent protein source for meat production and as an alternative human protein source, which should be used to mitigate food security. In addition, forestation of arable land improves local climate conditions towards less precipitation and lower temperatures while simultaneously attracting a larger number of birds thereby increasing the locust predation rates.

Plagues of Desert Locusts: Very Low Invasion Risk to China

Recently, the most serious upsurge of the desert locust (Schistocerca gregaria) in the last 25 years is spreading across eastern Africa and southwestern Asia. Parts of the desert locust 'invasion area', namely the northern border areas of Pakistan and India, are very close to China, and whether locust swarms will invade China is of wide concern. To answer this question, we identified areas of potentially suitable habitat for the desert locust within China based on historical precipitation and temperature data, and found that parts of Xinjiang and Inner Mongolia provinces could provide ephemeral habitat in summer, but these places are remote from any other desert locust breeding areas. New generation adults of the desert locust in Pakistan and India present since April led to swarms spreading into the Indo-Pakistan border region in June, and so we examined historical wind data for this period. Our results showed that winds at the altitude of locust swarm flight blew eastward during April-June, but the wind speeds were quite slow and would not facilitate desert locust eastward migration over large distances. Simulated trajectories of desert locust swarms undertaking 10-day migrations mostly ended within India. The most easterly point of these trajectories just reached eastern India, and this is very close to the eastern border of the invasion area of desert locusts described in previous studies. Overall, the risk that the desert locust will invade China is very low.

Characterization and analysis of full-length transcriptomes from two grasshoppers, Gomphocerus licenti and Mongolotettix japonicus

Acrididae are diverse in size, body shape, behavior, ecology and life history; widely distributed; easy to collect; and important to agriculture. They represent promising model candidates for functional genomics, but their extremely large genomes have hindered this research; establishing a reference transcriptome for a species is the primary means of obtaining genetic information. Here, two Acrididae species, Gomphocerus licenti and Mongolotettix japonicus, were selected for full-length (FL) PacBio transcriptome sequencing. For G. licenti and M. japonicus, respectively, 590,112 and 566,165 circular consensus sequences (CCS) were generated, which identified 458,131 and 428,979 full-length nonchimeric (FLNC) reads. After isoform-level clustering, next-generation sequencing (NGS) short sequences were used for error correction, and remove redundant sequences with CD-HIT, 17,970 and 16,766 unigenes were generated for G. licenti and M. japonicus. In addition, we obtained 17,495 and 16,373 coding sequences, 1,082 and 813 transcription factors, 11,840 and 10,814 simple sequence repeats, and 905 and 706 long noncoding RNAs by analyzing the transcriptomes of G. licenti and M. japonicus, respectively, and 15,803 and 14,846 unigenes were annotated in eight functional databases. This is the first study to sequence FL transcriptomes of G. licenti and M. japonicus, providing valuable genetic resources for further functional genomics research.

Nitrogen fertilizer decreases survival and reproduction of female locusts by increasing plant protein to carbohydrate ratio

Nitrogen limitation theory predicts that terrestrial plants should benefit from nitrogen inputs and that herbivores should benefit from subsequent higher plant protein contents. While this pattern has generally been supported, some herbivorous insects have shown preference and higher performance on low protein (p), high carbohydrate (c) diets as juveniles. However, little is known about the effects on reproduction in adults. Using nitrogen fertilizer, we demonstrate that high plant p:c has negative effects on Senegalese locust (Orthoptera: Oedaeleus senegalensis) reproduction and survival in an agroecological setting. For this, we measured p:c in millet plants Pennisetum glaucum that received two levels of fertilizer (high and moderate) and a control, then we caged locusts on these plants for 2 weeks. In the laboratory, we gave locusts the choice between untreated millet leaves and leaves that received one of the two fertilization treatment. We found that fertilization increased p:c ratio in a concentration-dependent fashion. We counted the number of locusts alive over the course of 2 weeks and showed that fewer females survived on fertilized plants than on control plants. Females that ate plants from the high fertilization treatment laid lighter eggs. Finally, we showed that female locusts prefer unfertilized plants to plants with a high p:c. We hypothesize that this pattern will apply broadly to species that have extensive carbohydrate needs, such as long-distance migrators. Because many ecological studies focus primarily on nitrogen or protein, and fail to consider carbohydrates, this study has important implications for how ecologists consider nutrient limitation of primary consumers in ecosystems globally.

Migratory Take-Off Behaviour of the Mongolian Grasshopper Oedaleus asiaticus

Oedaleus asiaticus is one of the dominant species of grasshoppers in the rangeland on the Mongolian plateau, and a serious pest, but its migratory behavior is poorly known. We investigated the take-off behavior of migratory O. asiaticus in field cages in the inner Mongolia region of northern China. The species shows a degree of density-dependent phase polyphenism, with high-density swarming populations characterized by a brown morph, while low-density populations are more likely to comprise a green morph. We found that only 12.4% of brown morphs engaged in migratory take-off, and 2.0% of green morphs. Migratory grasshoppers took off at dusk, especially in the half hour after sunset (20:00–20:30 h). Most emigrating individuals did not have any food in their digestive tract, and the females were mated but with immature ovaries. In contrast, non-emigrating individuals rarely had empty digestive tracts, and most females were mated and sexually mature. Therefore, it seems clear that individuals prepare for migration in the afternoon by eliminating food residue from the body, and migration is largely restricted to sexually immature stages (at least in females). Furthermore, it was found that weather conditions (particularly temperature and wind speed at 15:00 h) in the afternoon had a significant effect on take-off that evening, with O. asiaticus preferring to take off in warm, dry and calm weather. The findings of this study will contribute to a reliable basis for forecasting migratory movements of this pest.