How locusts become a plague

Swarming locusts in East Africa have caused damage over the last two years and led to massive control operations using harmful pesticides. The complexities of phase change between solitary swarming behaviour are still insufficiently understood all their ramifications, from physiology through ecology. Michael Gross reports. Locust swarms devastating entire landscapes affected human societies since beginnings agriculture. Their sudden appearance destructive effects described ancient texts including Bible, as well Iliad, Quran Mahābhārata. In 2020, world was kept busy by an outbreak a different kind, swarmed Middle East, affecting many countries Kenya, Ethiopia, Uganda, Somalia, Eritrea, Iran, Yemen, Oman, Saudi Arabia, reaching even Pakistan India. Meanwhile, upsurge South American that began 2015 surpassed outbreaks seen previous 60 continued Argentina, Bolivia Paraguay. Some parts Kenya saw worst devastation 70 years. As is desert locust’s evolutionary adaptation conditions when abundant rainfall follows drought, extreme weather events facilitated climate may be contributing factor this catastrophic event. Systematic monitoring lead can enable early measures stop situation escalating. politically unstable world, however, these hindered security concerns. When fails, it did late 2019, locust plagues threaten cause food shortages for millions people beyond, large-scale spraying organophosphate insecticides used decimate swarms. report Mongabay highlighted April, products purchased Food Agriculture Organization (FAO) combat plague mostly considered harmful, chlorpyrifos fenitrothion, which listed ‘moderately hazardous’ World Health Organisation. application risks causing additional environment resident population. A biological agent based on spores fungus Metarhizium acridum, infects kills locusts, also available. It has immediate advantage affects much-narrower range species, although there concerns non-target such termites. Its use problems with country approvals, production volume economic feasibility. material, shorter shelf life than chemical agents, its cannot scaled up rapidly. connection ongoing Africa, FAO governments more 12,000 litres fungal — which, corresponds only one hundredth organophosphates acquired. become problem they switch gregarious, lifestyle, vital importance better understand find ways preventing it. Over 100 years, much research been dedicated phenomenon, but questions remain. Until 20th century, were separate species specimens. Only work Boris Uvarov (1889–1970), Russian émigré who worked London, UK, clear certain grasshopper locust, undergo dramatic phenotype favourable. While not systematic group, locusts. This coexistence phenotypes, or phases, known density-dependent polyphenism. solitarious gregarious triggered serotonin signal maintained exchange pheromones, depends population density. extent really do appear like species. Under suitable conditions, reproduce abundantly, giving rise bands wingless nymphs, later form larger adult insects. They pass offspring. Given rapid reproduction big part problem, Amir Ayali at Tel Aviv University, Israel, argues mating insects surprisingly understudied. recently, Ayali’s group reported experimental (Schistocerca gregaria) phases (J. Insect Behav. (2018) 31, 629–641). “We suggest intra- inter-phase reproductive interactions among populations major impact dynamics,” summarises. Out four possible combinations, researchers found most successful males females. offspring typically inherit status mother, mechanisms transmission yet fully understood. Another underappreciated environmental plasticity role bacterial symbionts play. recent review field microbiota, colleagues raised possibility, unproven, gut bacterium Weissella cibaria, dominant contribute phenotypic (Insects (2020) 11, 655). involved passing trait, microbiota transmitted mother via egg pod’s foam plug, larvae upon hatching, recently shown (Environ. Microbiol. (2021) 23, 2461–2472. first study tract Omar Lavy laboratory changeable density thus could play polyphenism (FEMS Ecol. 96, fiaa044). Earlier had pheromones status. addition behavioural changes induced switch, experience collective walking triggers motion observed individual insect walks own (iScience 24, 102299). For study, grown lab consistently held because living availability food. These would normally experienced movement, exposed kinematics, upheld once removed crowd. capacity demonstrating motion, “collective-motion-state”, does need learned. suggests state “released” experiencing motion. His tried induce same animals without success, suggesting elements phenotype. propensity useful swarms, means accidentally separated swarm will easier fit back catches up. Thus, while each defines set patterns, further within taken into account. definition movement suited engaging naïve challenges established thinking describes (Curr. Biol. (2019) 29, R1055–R1058) emergent property large number individuals calling specific change. physiological foundations long-term fate remain explored. showed very little interaction individuals, makes impressive tightly coordinated scale. Gregarious isolated extended period time timescale reversal varies widely process laboratory, doesn’t offer solution posed billions Once open, genie won’t go bottle long any left eat. Beyond behaviour, energy balance important handle limit cause. Arianne Cease Arizona State University (ASU) Tempe, USA, Chinese Academy Sciences, Beijing, China, prefer vegetation low protein content, focus stocking carbohydrates fuel energy-intensive migrations (Science (2012) 335, 467–469). practical terms, heavily grazed fields, higher proportion protein, promote outbreaks, crops healthy soils high nitrogen content less affected. confirmed around globe, continents (Front. Evol. 7, 263). building discovery, Marion Le Gall ASU Senegal millet plants (Pennisetum glaucum) received high, moderate no fertiliser Anim. 89, 2214–2221). show treatment increased protein-to-carbohydrate ratio plants. Senegalese grasshoppers (Oedaleus senegalensis), evolved traits independently less-extreme extent, locked highly fertilised plants, reduced survival rates compared those feeding unfertilised experiment Stav Talal America marching limited plant carbohydrate (Proc. R. Soc. B 287, 20202500). High-carb, low-protein diets supported survival, growth lipid accumulation. Rick Overson jointly Global Initiative (GLI). Launched 2018, initiative consists GLI Lab Network. network’s purpose forge new partnerships seek integrate management. supports 400 members 55 countries. Laboratory hosts projects spanning natural social sciences aiming advance fundamental understanding systems exist, helping develop local solutions global challenge plagues. joint project farmers, USAID (the US federal agency international aid), Gaston Berger McGill CIRAD Plant Protection Directorate, developing novel community-based preventative strategy West Africa. involves setting village-based soil amendment programmes create environments discouraging outbreaking grasshoppers. initiative, NSF-supported Behavioral Plasticity Research Institute (BPRI), aims connect aspects, molecular studies ecology, landscape BPRI Baylor College Medicine Texas A&M includes partners institutes. her highlighted, complex social–ecological–technological system. context, governance, often receives attention critical, explains: “Working together across boundaries, sectors, disciplines our powerful tool advancing research, response, resilience”. various enjoy eating terms efficiency turning primary calories consumption, outperform domestic cattle fivefold. strikes, consumption quite scale sheer biomass bulk phenomenon. Moreover, wouldn’t advisable deployed. Keeping eye might encourage currently way happening. particular, drought excessive rainfall, made likely change, conspire regional political instability, hinders stages, make frequent. fact favoured war chimes biblical reports kinds arriving sequence divine punishment. points out, nobody wants extinct, North Rocky Mountain (Melanoplus spretus), due land-use destroying breeding grounds. rather keep them solitary,” concludes, “if we knew how”.