Locusts: Ancient migratory pests

by Praveen Kumar | Jun 25, 2020 | Fauna, Featured, Species

They came, they saw, they plundered. They settled on every tree and on every blade of grass; they settled on the houses and covered the bare ground. The skies went black and the Pink city turned brown. It had not happened for many a long year; alas it’s happening now and about 23 countries are under their direct impact with many more to join. And the locusts have the impression of not moving away anytime soon all the while working as if sent to destroy humanity…

Much before the humans took over the world, insects have reigned the planet. These ubiquitous creatures can be found under the ground, as low as life could get; and over the ground, as high as our mountains could reach and are very much associated to human life as both useful and harmful creatures. Among the harmful insects are the Desert Locusts defying the zenith of challenges for humans. As per the estimates of Food and Security Organisation, desert locusts affect the livelihood of one in ten people on the planet and hence are deemed to be the deadliest pests infesting the world. The challenges created by them are not new, they find mentions throughout history and have references of existence through early paintings of pre-historic period.

On an average locust hit once in every six years, the hit so intense it seems they have come all together, to end humans all at once. They cover houses, swing against the windows, collapse against moving vehicles, acting as if they are assigned the only task to plunder greenery and cause destruction.

The highly mobile locusts’ swarms cover a huge area ranging from Mauritania to India, Turkmenistan to Tanzania affecting the lives and crops of people inhabiting these countries. World Bank along with various other development-oriented agencies help the countries in coping with the damaging effects and control locusts, however, there is no significant improvement in lives of people as their attack is unconditional, they are not bound to appear every year and don’t follow a determined specific time to attack instead they appear at irregular intervals, many a time after a gap of several years. This is called periodicity of locust activity. India has witnessed several locust plagues and locust upsurges and incursions during the last two centuries including at least 15 recorded cycles since 1812. During recent past India has witnessed 2 major swarms in 1968 and 1993 and the story continues to date with them appearing at regular intervals.

The year 2020, so far, has proved to be miraculously challenging with various natural calamities including one of a kind THE NOVEL CORONA VIRUS, cyclones, earthquakes and floods. While the whole world is fighting the novel coronavirus epidemic by putting humans under lockdown to limit the spread of the virus, nature has created an equally challenging, but not so new, threat in the form of locusts plague in some African and Asian nations, proving humans can be dethroned from earth anytime, without any warning if the interference with nature is not controlled.

These locusts are once again in front of us in their macabre form and wreaking havoc on crops. People this time speculating various causes for their emergence, some say changing land use pattern might be responsible, some other blaming increased greenery in the deserts, yet another group advocating the rising temperature of the Earth. Before getting to know about their arrival, let’s get acquainted with Locust briefly.

Locusts are mainly grasshoppers found in dry grasslands and desert areas. They are the world’s oldest and highly noticeable migratory pests due to their extreme destruction potential. Mistakenly, people also consider long-horned grasshopper to be locusts as they also breed in favourable summer conditions to increase numbers and destroy crops in a limited area.

Locust is the swarming stage of some species of short-horned grasshopper from the family Acrididae. There is no taxonomic difference between locust and grasshopper species, they look similar to grasshoppers but in practice are completely different from them. Grasshoppers are found on agricultural land while locusts are found in desert and arid conditions. No morphological changes are seen in Grasshopper, whereas many changes are seen during the 90 days life cycle of Locusts.

These grasshoppers are usually solitary but under certain circumstances, when their numbers increase, they witness some behavioural changes and undergo phenotypic shift and change phase to turn gregarious and start migrating. This phase change is the only basis of their definition. This change is called “density-dependent phenotypic plasticity” in scientific terms.

Boris Uvarov first described two stages of phage polymorphisms, the solitaria (independently living hoppers) and the Gregoria (hopper living as bands of immature hopper). These are also known as statary and migratory forms although, in true form, their swarms are nomadic rather than being migratory.

Solitary locusts are forced to live together during the dry season due to the limited greenery in the area. Increased tactile stimulation of the posterior leg leads to an increase in serotonin levels that causes the grasshopper to change colour, eat more, and breed easily. Locusts breed in desert areas and often coincide with forests, agricultural areas, and pastoral livelihoods. In all locusts have three breeding seasons: winter breeding (November to December), spring breeding (January to June) and summer breeding (July to October). There is only one season of grasshopper breeding in India, i.e., the summer breeding while our neighbour, Pakistan has both spring and summer breeding seasons.

The life cycle of locusts consists of three distinct stages, egg, hopper and adult. Locusts lay eggs at a depth of 10 cm in moist sandy soil. Gregarious females usually lay eggs in 2-3 pods with 60–80 eggs in a pod. The solitary female mostly lays an average of 150–200 eggs in 3–4 pods. The rate of growth of eggs depends on soil moisture and temperature. There is no growth below 15°C. Incubation period during the optimum temperature of 32–35°C is between 10–35 days.

There are about 28500 species of grasshoppers worldwide, of which only 500 exist in the form of agricultural pests, and only 20 have the potential to become locusts. India is mainly affected by four species of locusts, the desert locust (Schistocerca gregaria), the African migratory locust (Locusta migratoria), the Bombay locust (Patanga succincta), and tree locust (Anacridium spp).

After the incubation is complete the eggs hatch and nymphs come out which are called “hoppers”. The gregarious stage consists of 5 instars and the Solitarius population consists of 5–6 instars. Each instar has different growth and special colour changes. The growth rate of the hopper depends on the temperature. Where it takes 22 days at an average temperature of 37°C, the same can be delayed up to 70 days at an average temperature of 22°C.

Hoppers become adults after the fifth instar stage. This change is called ‘fledging’ and the young adult is called ‘fledgeling’ or ‘immature adult’. The duration of sexual maturity varies. In the appropriate condition, the adult can mature in 3 weeks and can take up to 8 months in frost and/or drought conditions. During this stage, adults fly to search for favourable reproductive status and can travel thousands of kilometres. During this time, if favourable conditions are found at any time, they can become gregarious

Younger grasshoppers are solitary at the time of hatching and are green and brown to fit with their surroundings. When the food is in abundance, dessert locusts increase the number by breeding and achieve a “gregarious state”. Younger immature adults are pink in colour while older adults turn dark red or brown in cold conditions.

As the locusts grow larger and denser, they act in a group with behavioural changes to form a flying flock known as a swarm. The change of grasshopper form is induced by several contacts per minute over a period of four hours. A large swarm spread over an area of thousands of square kilometres can contain billions of grasshoppers, with a population of about 80 million per square kilometre. At this point, the grasshoppers are fully mature and adult. Adults become bright yellow at maturity. Males mature earlier than females. Changes in locust behaviour and physical symptoms are reversible, which can eventually change their original form or pass on to their offspring.

Locusts hatch from an egg to adulthood after a breeding cycle of about three months and can increase in number up to 20 times. It can increase 400 times after six months and up to 8,000 after nine months. They come in swarms of thousands of millions to eat all the leaves, flowers, fruits, seeds, and bark of trees, plants or crops. They sit on trees in such a number that under their weight the tree can even break. A grasshopper makes a meal equal to its weight i.e. at least two grams. The locust of the flying band also shows the cannibalistic action of biting each other during food shortages. Migrations in desert locusts are influenced by their cannibalism. Research by Sepideh Bazzazi suggests that grasshopper swarms are formed because they like to stay one step ahead of their cannibalistic neighbours to protect themselves.

Their emergence as swarms cannot be attributed to a single factor entirely. They follow a sequence. Yes, changing land use pattern and other factors play an important role, but at a particular point following the sequence. For example, the greenery is essential but only after the eggs have hatched into nymphs, to keep them alive.

Dr S. Pradhan in 1967 put forth the Biotic theory of periodicity of locust cycles, who was at that time head of the division of Entomology at the Indian Agricultural Research Institute, New Delhi. Locusts breed in semi-desert areas where sandy soil is suitable for thrusting the eggs up to a depth of 15 cm. While locusts lead a marginal existence in these areas, their vertebrate predators, namely, lizards, snakes, birds, shrews, hedgehogs, moles etc. find it difficult to sustain themselves in the extreme conditions of deserts and semi-deserts and hence gradually move out to the more tolerant areas on the periphery.

But in desert areas, once in a decade or so, there is sufficient rainfall that triggers the growth of sedge grass and other weeds and locust gets a chance to realise its full biotic potential and its population shoots up in the absence of predators that are present outside the breeding areas and cannot move in fast enough to contain its population. Unchecked by the natural enemies, locust moves from the solitary phase to migratory phase and develops into large congregations and eventually to swarms that migrate out of the breeding areas causing immense destruction. Locust swarms having gone out of the desert areas, scattered population of adults and nymphs is left behind which then persists as solitary phase, throughout Mauritania and India, till the arrival of another phase of tolerant environmental conditions.

Grasshoppers are major components of grassland ecosystems around the world and play an important role in trophic mobility and nutrient cycling. But when green grasslands develop due to good rains, locusts take advantage of the greenery and multiply rapidly to increase in number within a month or two and take the shape of a terrible swarm.

If not controlled on time, small groups of wingless hoppers or bands can form a small group or swarm of winged adult grasshoppers called an OUTBREAK and is typically spread around 5,000 square kilometres in a part of a country. If an outbreak or multiple outbreaks concurrently are not controlled and there is widespread or unusually heavy rainfall in the surrounding areas, a series of breeding seasons may occur that would later lead to the formation of hopper bands and adult swarms. This is called UPSURGE and generally affects the entire region.

if an Upsurge is not controlled, and the environmental condition remains favourable for reproduction, locust populations continue to increase in number and size developing into a PLAGUE. Most infestations occur in the form of bands and swarms at the time of the Plague. A major Plague occurs when two or more regions are affected simultaneously.

Locusts outbreaks are common and frequent, with only a few of these outbreaks taking the form of upsurge, and some of the upsurges turn into plagues. The last Plague was observed in 1987–89 and the last major upsurge in 2003–05. Upsurges and plagues do not emerge on a single night, they may take several months to a year or two to develop.

Globally, Locusts are monitored by the Local Watch Department in guidance of Food and Agriculture Organization (FAO) of United Nation, according to which the current locust attack story began in the year 2018 with cyclonic storms and heavy rains on the Arabian Peninsula. The storm of May caused so much water that for the next six months the desert saw the emergence of green landscapes capable of sustaining two generations of locusts. Subsequently, due to the October storms, locusts got another few months to breed and thrive where their three generations grew up. They became dangerous from here and targeted Africa starting in 2019. Locusts increased their populations in remotely undeveloped areas such as Oman and Yemen due to cyclones.

According to FAO’s locust’s expert Keith Cressman, the organization monitors the attacks of locust through human resources and satellites but has failed in this case. Monitoring network collapsed. According to Cressman, no one knew what was happening in the remote area of ​​the Earth then. There is nothing in this area, no roads, no infrastructure, no Facebook, nothing. Some are large mounds of sand, which are no less than skyscrapers.

When locust swarms develop a tendency to live in groups and become gregarious, they rely primarily on carbohydrate-rich foods. The land from which successive crops have been taken and which have been over-grazed lack Nitrogen. Due to this lack of essential nutrient from the soil carbohydrate-rich grasses develop. Experts have found this in studies on South American locusts.

At the end of 2018, when people saw locusts in Oman, the news reached Cressman’s organization and alerted the situation. But it was too late by then. From here locust swarms had reached Yemen and Iran and were continuously coming out of Oman. War-torn Yemen had the crisis of not having the force to fight the locust attack. Yemen received heavy rainfall during these conditions and the locust swarm found a favourable environment to breed and flourish. The locust disaster reached Somalia from here during the last spring and summer seasons (2019) and then wreaked havoc in Ethiopia and Kenya. Last March saw heavy rain in East Africa, which again proved to be a boon for locusts. Over the last forty years, control of desert locusts with preventive strategy has proved effective, but due to negligence and organizational problems, locust swarms have once again become a serious problem.

Locusts are very difficult to control at the time of the attack as they are spread over a large area. Early intervention in locusts is the only successful way to prevent a swarm. Many organizations around the world monitor threats from locusts. They provide forecasts of areas likely to suffer locusts in the near future.

FAO’s Desert Locust Information Service (DLIS) monitors daily weather, ecological conditions and locust conditions from Rome, Italy. The DLIS obtains the results of field survey and control operations conducted by national teams in the affected countries and assesses the current situation by combining this information with satellite data, such as MODIS, rainfall estimates and seasonal temperatures and rainfall forecasts, etc. Information on breeding and migration during the week is estimated.

Locust Warning Organisation (LWO), Directorate of Plant Protection Quarantine and Storage is responsible for monitoring, survey and control of Desert Locust in Scheduled Desert Areas mainly in the States of Rajasthan and Gujarat. The incursion of exotic locust swarms into India is prevented through the organization of suitable control operation. LWO keeps itself abreast with the prevailing locust situation at National and International level through monthly Desert Locust Bulletins of FAO issued by the Desert Locust Information Service. Survey data are collected by the field functionaries from the fields which are transmitted to LWO circle offices, field HQ Jodhpur and Central HQ Faridabad where these are compiled and analysed to forewarn the probability of locust outbreak and upsurges. The locust situation is appraised to the State Governments of Rajasthan and Gujarat with the advice to gear up their field functionaries to keep a constant vigil on locust situation in their areas and intimate the same to nearest LWO offices for taking necessary action at their end. A lot of innovations have been made in the field of locust survey and surveillance for quick transmission of locust survey data, their analysis, decision making, mapping of survey areas through computerization, adoption of new software like eLocust2/ eLocust3 and RAMSES.

Historically, people were incapable of protecting crops from locusts, however, today we have the advantage of deeper knowledge and technology to fight locusts than ancestors, but still the spread over a huge area (16–30 million km), limited Resources, underdeveloped infrastructure and permeability of those areas, etc. make locusts difficult to control or contain.

Currently, the primary method of controlling desert locust swarm is small concentrated doses of organophosphate chemicals (the major ingredient in herbicides and pesticides). Which are done by spraying ultra-low volume (ULV) with vehicle-mounted or aerial sprayers. Locusts acquire the chemical either directly or indirectly by walking on the plant or eating their residues. These controls are carried out entirely by government agencies. DPPQ&S has approved 4 pesticides for use in scheduled desert areas of India. 11 pesticides have been approved for control of desert locust on crops and trees.

Organic pesticides made from fungi, bacteria, and neem extracts are also used to prevent locusts. The effectiveness of many biological pesticides is comparable to traditional chemical pesticides but in general, it takes a longer time to kill pests. To prevent these, farmers in the affected areas have started growing crops that can be harvested before the local swarm season. Additionally, inhibition of serotonin has succeeded in controlling the number of locusts in laboratories, but the field test of this technique is yet to be done.

Desert locust predator includes wasps and flies, parasitoid wasps, predator beetle larvae, birds and reptiles as natural enemies. Recently, Dr Dharmendra Khandal has seen Jacobin cuckoo, peahen hunting them in Sawai Madhopur. But these predators have the impression that they can be effective in keeping solitary populations under control. Due to a large number of locusts in the swarm and hopper bands, their influence against them is limited.

Although it is almost impossible to stop a grasshopper attack, their severity can be reduced by controlling the swarms, destroying a large number of eggs. Stringent efforts are being made in the affected countries to control the current ‘plague’. But how they will end up is difficult to say. At present, only the monsoon will control their swarm to some extent.

(more…)