Infestations of locusts are one of a farmer’s many worries. Even when one has overcome many other risks of farming to get a healthy crop of say, maize, the prospect of losing it all within minutes is terrifying.
Yet minutes is all it can take for a swarm of locusts to decimate a crop field. What makes this millennia-old farmer’s enemy even more worrying a threat is that there is very little that an individual farmer can do to prevent or ameliorate it.
Among recent devastating locust plagues of what are called “desert locusts” (because they typically breed in dry regions) were those of North Africa in 1988-9, and West Africa’s in 2004-5. Although dry areas are the locust’s normal habitat, periods of high moisture levels in those areas are one of the factors conducive to changing the usual solitary habits of the locust into the huge swarms that are so agriculturally destructive.
Wide swathes of Africa experienced extensive flooding a few months ago, and there are fears that locust invasions are going to be one of the lingering after-effects. In East Africa there have been reports in recent weeks of swarms of locusts moving south from the Middle East, with fears in Kenya of the first major locust plague in several decades.
For such an ancient plague, the exact conditions that cause the desert locust to abandon its usually harmless habits and coalesce into devastatingly destructive swarms have only recently begun to be fully understood. This makes predictions of locust plagues difficult, and control measures are often employed too late to prevent the wiping out of large areas of crops. Nevertheless, survey and monitoring mechanisms have improved in recent years, allowing organizations like the Food and Agricultural Organization to alert governments against impending plagues.
It is said that during the 1988 desert locust plague, swarms crossed the Atlantic from Mauritania to the Caribbean, flying 5 000 kilometres in 10 days. With such efficient migration habits, effective control measures are clearly beyond even national governments. They must be coordinated by governments and international organizations working together in regional fashion.
The main control measure has been the aerial and hand spraying of organophosphate pesticides. But there are increasing concerns about the residual effects of these highly toxic, non-specific chemicals on human health and the environment. Many of those that remain in use in Africa have been banned in the U.S. and Europe.
In recent years there has been increasing research and experimentation on bio-control measures of locust control. Apart from avoiding the toxic effects on humans and the environment, they promise to be more effective against the locusts. Their development has been slow because unlike broad-spectrum, non-specific agro-chemicals, effective bio-controls require a detailed understanding of the biological life cycle of the organism they are employed against.
The traditional pesticides can be likened to a machine gun approach, in which the killing of the targeted pest is also accompanied by the decimation of many other organisms. Bio-controls are much more specific in their operation, and therefore largely harmless to non-targeted organisms. Bio-controls are by their nature generally quickly and harmlessly degradable, so there rarely is any concern about lingering toxic residue as is the case with synthetic agro-chemical pesticides.
One type of bio-pesticide in use in West Africa is derived from a fungus that is a naturally occurring enemy of the locust. But it is highly susceptible to breakdown under sunlight and so does not accumulate in high enough concentrations to prevent locust swarming. Research has been aimed at finding ways of making the anti-locust fungus last longer under sunlight, making it possible to increase its concentrations to levels that would make it useful as an economically significant control measure against locust swarms.
At the International Centre for Insect Physiology and Ecology (ICIPE) in Nairobi, a naturally occurring locust pheromone, or mating chemical signal, seems promising in controlling the swarming behaviour of young locust “hoppers.” Minute quantities of phenylacetonitrile (PAN) caused the hoppers to retain their normal harmless solitary behaviour. A FAO article about the research says, “Confused and disoriented, some lost their appetite altogether, while others turned cannibal and ate one other. Any survivors were easy prey for predators.”
The quantities of PAN required for effective locust control are said to be as low as 10 millilitres per hectare, a fraction of that employed with traditional chemical or biological pesticides. The prospect of huge cost savings is a big incentive for the exploration of the use of this method of locust control for poor countries. Estimated costs are as low as 50 cents per hectare as opposed to US$12 for chemical pesticides and $15-20 for other bio-control agents.
Most of these new methods of locust control are still at various experimental stages, but they promise more hope for locust control than the standard methods of the past several decades. The ability of the locust swarms to travel large distances in a short period has made even the old standby methods of debatable effectiveness. That coupled with their cost, their broad-spectrum toxicity which endangers human health and the long periods over which their residues remain active in the environment have speeded up the pace of the search for alternatives.
All these are welcome developments, as there is little the hard-working but vulnerable farmer can do by himself against a plague of locusts.
By Chido Makunike
Makunike is an Agricultural Consultant based in Dakar, Senegal
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