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News :: Environment
Africa faces giant plague of locusts
by Brent Herbert
11 Jul 2004
Exceptional rains over the Sahel, and record breaking harvests have created ideal conditions for a plague of locusts. The focus is currently on pesticide usage to curtail the plague and the resulting famine, but up to the present, chemical pesticides have never been known to end a desert locust plague. A collection of links to stories on this developing plague...
Locust plague threatens Africa
A plague of locusts is poised to sweep into western Africa and destroy precious food crops, the UN Food and Agriculture Organization (FAO) warned this week. Can they be stopped in time? Nature.com investigates what it takes to control the voracious insects.
Two days of torrential rains in western Africa last October encouraged the insects to breed and lay their eggs in wet sand. They later moved northwards to Morocco, Algeria, Tunisia and Libya. This year, favourable weather conditions have vastly increased their numbers. Despite efforts to control them, the first swarms are forming and heading back to northwestern countries, including Mauritania, Senegal and Mali. The locusts are soon expected to spread east towards Niger, Chad and Sudan.
How serious is the threat?
Extremely serious, according to experts. So far, the scale of the infestation is on a par with the growth of the last plague in 1987-89, which affected 28 countries. The worst-case scenario is that they will strip subsistence crops in areas that are already suffering severe food shortages because of civil war or drought. "It's the most serious situation we have had in the past fifteen years," says Keith Cressman of the FAO, who forecasts locust infestations.
Locusts are mainly curbed using chemical pesticides, such as the organophosphate malathion, which is sprayed from vehicles and aeroplanes. Unfortunately, this kills insects and the toxin can accumulate in birds, lizards and other animals that feed on the poisoned insects.
What will happen next?
Whether the early swarms develop into vast ones partly depends on the weather: rains will escalate the problem and dry weather could assuage it. But some say that a plague is almost unavoidable without drastic intervention. We will see much bigger swarms in the coming weeks, predicts Cressman.
Africa braced for giant plague of locusts
A shadow will fall over Africa this week. Vast tracts of land will be darkened and destroyed and the sky will turn black. The day of the locust has returned.
The United Nations describes the situation as 'extremely critical'. Swarms big enough to engulf London, and containing 50 million insects, were monitored by UN analysts last week.
They watched with mounting concern as swarms of locusts began to sweep southwards from breeding grounds in North Africa. Their rate of travel is astonishing. Wind conditions forecast this week will see locusts moving 60 miles a day
Radar has helped track the first insects to central Senegal, almost 1,300 miles from their starting point south of the Atlas mountains in Morocco and Algeria.
Mauritania, Mali, Chad, Niger and western Sudan are next in line. Eventually, a swath of scavenging insects 6,000km wide could straddle Africa.
23 African countries face food shortages this summer. Just £6m in aid has been pledged, a sum the UN believes is insufficient.
Locust swarms may spiral into plague
The insects could breed to plague proportions and ruin the livelihoods of poor African farmers and affect food security. The last African locust plague lasted from 1986 to 1989 and struck 40 countries.
In 2003, exceptionally wet rainy seasons in the Sahel and northern Africa meant that the desert locust species (Schistocerca gregaria (Forskal)) was able to breed more generations of offspring than usual, leading to a population boom.
"It's important to control in terms of protecting crops in the Sahel and trying to prevent it from getting any bigger," Elliott told New Scientist. "Possibly this summer is the last chance to do so. Once it really gets going it's extremely difficult to deal with as the population gets larger and larger."
Previous plagues of the 1940s and 1950s lasted 10 or 15 years, and hit as many as 65 countries, says Elliott. "It would be fairly horrendous if we moved into that scale," he warns.
The north African countries currently suffering swarms - Morocco, Algeria, Tunisia and Libya - are making "tremendous efforts" to control the insatiable pests, he says. But because the locusts cover such a huge area, Elliott predicts that substantial numbers of swarms will escape and move back into the Sahel later in 2004.
Whether the locusts have another successful breeding round will depend on the summer rains in the Sahel, he says. But reports suggest the rains may have already started. "Then we would expect that by the end of 2004 that a full blown plague will have developed."
The FAO is also trying to develop more environmentally friendly "biopesticides".
It has tested a biopesticide spray consisting of a natural fungus called Metarhizium. This kills the locusts within three to four weeks. Other products affect the insect growth regulators and disrupt the moulting process, so the locusts never reach adulthood.
However, Elliott adds that without more international funding, trials will not move into large scale use.
Locusts Head South for Rains
The first desert locust swarms have left their breeding areas in North Africa and moved south to Mauritania, Senegal, and Mali.
Donors have so far pledged only half of the US $17 million that the FAO appealed for in April to help it run an existing campaign through the spring breeding period and extend it across the West African region in the summer.
Crops in North African countries like Morocco have already been damaged by the flying pests. The Moroccan Press Agency said the country's agricultural authorities had warned on Tuesday that this year's infestations were of "an exceptional magnitude".
The locust upsurge started in the Sahel last summer when breeding was encouraged by extremely heavy rainfall. The insects then headed north across the Sahara to Morocco and Algeria, but are now making their way back south.
"Last summer's exceptional rains in Northwest and West Africa created very favourable conditions for locusts to develop."
"A dramatic increase in locusts could threaten crop production during the coming months."
However, this is not a very eco-friendly process. Conventional pesticides used to combat locusts can damage the environment and are harmful to some birds.
With the summer rains washing through the Sahel, agricultural officials everywhere agree on the urgency of the situation.
As Lemine told IRIN from Mauritania: "If we do not intervene on time to decrease the economic, social, environmental impact of the locust plague, we will spend more to control it, with no guarantee of success."
Links to discussions of the use of chemical pesticides to control locust plagues...
Locust plague could cripple Africa
The United Nations Food and Agriculture Organisation warned on Monday that a devastating new plague of locusts may be about to descend on a large part of Africa.
FAO said additional international aid is urgently needed to monitor and control the infestation, which it added would have to be carried out with conventional pesticides.
In a PDF paper discussing locust control in Africa the authors address the question, "Chemical controls : do they work?" and note that to the present, chemical control has never been known to end a desert locust plague.
"Older organochlorine pesticides used to spray on locusts were hazardous to the environment. Newer pesticides can be hazardous to humans and wildlife. The FAO’s Pesticide Referee Panel provides information about recognised locust control chemicals. There is little evidence that chemical controls—as opposed to winds, rain or lack of food—have wiped out plagues."
They also comment on the FAO strategy of 'pre-emptive spraying' currently underway in Northern Africa by commenting,
"The preventative approach seeks to monitor locust breeding areas and spray as gregarising populations of locusts are identified. This is difficult in practice, as many of the principal breeding zones are difficult to reach.The cost and effort of infrastructure and communications required is very considerable. In many areas— Mali, Niger, Chad, Ethiopia and Sudan—there is or has been until recently civil strife."
Describing the varieties of chemical control agents available, they note that,
"Dieldrin and other organochlorine insecticides were eventually banned because of persistence, environmental effects, and bioconcentration in fatty tissues. Replacement insecticides included the organophosphate products fenitrothion, malathion and diazinon, and the carbamates carbaryl and propoxur. These were less hazardous to the environment but more hazardous to human and animal health. They were followed by chemicals of the pyrethroid family such as cypermethrin and lambda-cyhalothrin, and the new phenyl pyrazole fipronil. All these broad spectrum ‘knock-down’ chemicals are hazardous to non-target species."
Nevertheless, given the threat that such insects pose to human agriculture, research continues on finding the means to control these outbreaks. A paper from the Sustainable Development Organization investigates Organic methods for controlling Desert Locust Swarms.
D D T, Fipronil, Chlorpyrifros, Malathion, are all common names in the war against locusts, borers and other destructive insects. According to the FAO Emergency Center for Locust Operations, “the primary method of c o n t rolling Desert Locust swarms and hopper bands is with mainly organophosphate chemicals applied in small-concentrated doses … by vehicle-mounted and aerial sprayers and to a lesser extent by knapsack and handheld sprayers.
Yes, these pesticides will kill the insects, but they also cause damage to the environment and to the people whose crops and lands are being sprayed; as well as to those who ingest such contaminated food. In most p a rts of sub-Saharan Africa, the harvesting of maize (the staple food crop), and other cereals is done by hand. Most of the pesticides currently being sprayed in t h i rd-world countries have been banned in the United States and the EU.
For the farmer, insect control is of paramount importance. Recognising this, Organic Solutions continually researches for ways to provide the farmer with cost - effective insect control, providing maximum results with low to no risk for humans, livestock and the environment ... All tests (in the labratory) have confirmed the efficiency of Org a n i c Solutions on locusts and stemborers’.
Organic Solutions Insecticides act just after simple contact by tearing off the insect cuticle, exposing it to pro g ressive desiccation up to the critical water point and eventually death (which means that it takes longer to have an effect than typical insecticides ... but with typical insecticides the researchers found that the insect either died right away, or lived, thus developing resistance).
If you read the rest of the article, they explain that this organic pesticide works by stabbing the insect full of tiny holes made by sharp particles of silicate earth when they are sprayed, which causes the insect to lose body moisture and die. Because the pesticide is 'mechanical' (involving stabbing the bugs to death with tiny particles of suspended silicates) there is never any chance of the insect developing immunity. Its a novel sounding idea, but would require a change in thinking (it is not possible to 'spray it and leave it' but rather the insects must be engaged in order for the method to work.)
The Locust Controversy
—alternatives to chemicals available
he devastation that locusts can cause is well-publicised and widely feared. Locusts have the ability to swarm, which occurs when solitary locusts group together and then migrate. The facility to swarm distinguishes locusts from grasshoppers (both belong to the Acrididae insect family) and is largely a function of population density. Following locust outbreaks in the 1950s there were no subsequent serious outbreaks until the 1980s. A plague formed in the period 1986-89, and large stocks of the highly persistent insecticide dieldrin were used to control swarms.
The principal strategy was barrier spraying: dieldrin was sprayed across the path that it was hoped marching bands of locust hoppers would take. As the insecticide was persistent, any hopper bands that did in fact cross the barrier strip were killed. In addition to barrier spraying, organphosphorous pesticides, such as fenitrothion, were sprayed from planes overflying a locust swarm. Both methods depended on good information of the whereabouts of the target locusts and the availability of stores, equipment and trained personnel. FAO, as the co-ordinating agency, was criticised over the level of use of pesticides, the problems of dumps of surplus stocks of older pesticides and the efficacy of the campaign.
How effective have chemical pesticides been in controlling outbreaks of locusts? How effective have the regional organisations set up to monitor and control outbreaks been?
The environmental groups in particular wanted an examination of the cost-effectiveness of chemical controls; an investigation into other solutions, including food and farmer support; and an evaluation of regional, as opposed to local, crop losses. The background paper prepared by Greenpeace International and The Pesticides Trust(5) echoed concerns of the US OTA Report. Without an examination of the longer-term goals of locust control, and consideration of alternative means of achieving the same end, the use of chemicals threatens to become an end in itself.
Biological Control Conquers Biblical Plague
The plague locust is being halted in its devastating path. Evidence is emerging of successful biocontrol of the insects that have been the scourge of farmers and agro-industrialists since biblical times.
In its first large scale operational trial, the fungal pesticide Metarhizium has successfully killed Australian plague locusts in the outback of the state of New South Wales after about 10 days exposure.
The program had been so successful that inspectors who examined treated areas said they compared with eradication rates achieved by conventional chemical insecticides, a spokesman for the Australian Plague Locust Commission said.
A representative of the United Nations Food and Agriculture Organization (FAO), Dr. Clive Elliott, said the success could encourage the FAO to conduct similar trials in sub-Saharan Africa.
The insects remain a recurring concern in sub-Saharan Africa where they have caused famine and dislocation of population since ancient times.
FAO experts have argued that conventional pesticides should be discontinued, because of their unavoidable negative environmental effect. But through the 1990s these pesticides had been the only available tactic.
The molecule behind a Biblical plague?
A simple natural molecule 2-methoxyphenol, also known as guaiacol could be a factor in the voracious swarming of locusts, which have devastated crops since before even Biblical plagues.
The compound is made by the bacterium Pantoea agglomerans which lives in the insects' guts, and according to Rod Dillon at the University of Bath, UK, this volatile chemical component is one component of a pheromone found in desert-locust faecal pellets thought to trigger swarming behaviour. Guaiacol is probably biosynthesised from the lignin-derived vanillic acid (4-hydroxy-3-methoxybenzoic acid) in the locusts' diet.
Locusts gather in vast swarms, which leave in their wake devastated human crops and starving villagers in many areas of the developing world. Understanding what makes them swarm might ultimately lead to a pesticide-free method of crop protection.
Perhaps by placing the pheromone over large areas where locusts feed we might be able to disrupt their behavior and stop them swarming. Alternatively, we could use guaiacol or the whole pheromone to trigger them to swarm when no food is available and so bump up their mortality rate.
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