Locust swarms, the curse of Africa
READERS WOULD have read the alarming news item that appeared in this newspaper four weeks ago about the calamitous swarms of desert locusts sweeping across Northern and Western Africa. There was also a photograph seven days ago in this newspaper of such a swarm wreaking peril and pestilence on Chad, with a pitiful farmer grieving over the disaster wrought on his field by the flying army of pests.
The numbers and the havoc they are causing are staggering. A typical swarm contains as many as 20-50 million insects and causes the daytime sky to darken. The Food and Agriculture Organization (FAO) of the U.N. has described the situation as extremely critical; swarms big enough to engulf an area as big as London and containing 50 million locusts were monitored to sweep southwards from their breeding grounds in Northwest Africa.
Straddling Africa
Starting from Morocco, they are moving towards Mauritania, Mali, Chad, Niger and Western Sudan. The Guardian of London reports that a swathe 6000 km-wide could straddle Africa. To get a feel for the enormity, let us recall that a full-grown locust, wings wide flung, spans an area less than 100 square cm. An army of 10 million insects flying as a close pack would thus cover about a square km; that is about the size of a small cricket field.
One can thus get an idea of how many such `formations' would be involved in the current locust invasion. Twenty- three African countries are feared to be affected this summer and apprehended to face severe food shortage.
Get a feel for this too. A typical locust weighs 2-5 grams and consumes its own weight of vegetation in a day. A swarm would thus be able to finish off fields and fields of crops and vegetation in a single day- food that would have fed thousands of people for weeks. The last time such a locust swarm hit Africa and deprived its people of their food was in 1986; the invasion lasted a full three years and starved 40 of the 54 countries of the African continent. No wonder they refer to such swarms as locust plagues.
Locust plague
Such plagues seem to hit Africa regularly, though not in well-defined intervals or cycles. Also, how long a plague would last, and where all it will spread are not certain. The swarm flight across the Red Sea in 1889 is recorded in the Encyclopedia Brittanica to have been 2000 square miles in size. And in 1869, the desert locust swarm was reported to have reached as far as England from West Africa. The ones in the 1940s and 1950s lasted 10 and 15 years, and hit 65 countries of Africa and the Near East. That they have been with us for millennia is apparent.
The Bible talks about how when such locust swarms came, `the land was darkened and ate all the plants in the land so that nothing green was left'. The ancient Egyptians referred to them as an army in the sky. Interestingly, while locust swarms have been hitting West Asia, the Punjab, Sind and the edges of Western India, no legends or ancient texts mention this pestilence.
Perhaps we should sigh in relief and thank the biology of the locust for this. Belonging to the grasshopper family (insectologists call this the Acrididae: appropriate, since the Latin word acer refers to sharp and sour), the locust prefers hot and dry climes. Indeed, it is also called the desert locus (schistocera gregaria; etymologically, schist comes from the word to split and gregar means belonging to a flock or group). Larger in size than the garden grasshopper , it breeds in the wet rainy season.
Breeding ground
Areas of Northern Africa- Morocco, Algeria, Tunisia, Libya and the Sahel — with their wet rainy seasons are the breeding grounds of this pest, where tons of eggs are deposited during breeding season. Once hatched and ready, the desert locust flies downwind to low pressure areas where rains have recently fallen, eat up all vegetation and move on to the next low pressure area.
The growth dynamics of the locust is interesting.
Two phases are defined, the solitary and the gregarious. While in the solitary phase, it does not collect into groups, is somewhat camouflaged in colour with the surroundings, is sluggish with low metabolism and breathing rate, and has short wings, narrow body and long legs. When a solitary matures in the presence of many others, it changes to become gregarious. This phase is distinguished by colour, form, physiology and behaviour. Turning to black or yellowish orange, the gregarious form is metabolically highly active, physiologically larger with bigger wings and a fatter body, nervous in behaviour and turns totally social. When the crowding is sufficiently dense and long in duration, the migratory phase starts.
This switch between the solitary and the gregarious is reversible. When a gregarious locust is young, it can revert to the solitary phase if matured in isolation. This suggests that the switching phenomenon might be driven chemically, through a pheromone, released and received between locusts which drives their physiology and behaviour.
Attacking it chemically
Two such locust pheromone candidates have been reported: phenylacetonitrile and a Z-9-pentacosene derivative. Whether these indeed drive locusts is yet to be rigorously confirmed. But the idea of the involvement of chemicals would lead to ways to contain and destroy locust crowding and swarming.
While research towards these aspects are going on at and through the FAO and the Anti-Locust Research Centre at London U.K., and other places, current efforts use mechanical removal using `hopperdozers', and insecticides, larvicides and poisons such as 2,4-D and Dieldrin. These are used both to kill the egg clutches at breeding spots and across lands where the swarms hold sway. FAO is also trying to use biopesticides, which are more environment friendly.
Shaoni Bhattacharya writes in the New Scientist that one such bioinsecticide is a natural fungus, metarhizium, which is effective against locusts and kills them within four weeks. Other products affect the insect growth by disrupting the moulting process, so the locusts never reach adulthood. Reading this makes me wonder whether our Indian companies which make Neem extracts should not go to help the beleaguered Africans.
An active chemical in these extracts is azadirachtin, which is an excellent insect anti-feedant, which causes the insects to lose all appetite and starve themselves to death. Such a gesture would be in the noble tradition set by Dr Yousuf Hameid of Cipla, who has manufactured anti-HIV drugs and offered them to African governments at rock bottom prices, in the battle against AIDS.
D. Balasubramanian
dbala@lvpei.org
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