Locust invasion in East Africa

Locust invasion in East Africa – a conversation with Dr Christiaan Kooyman

Capture d’écran 2020-02-17 à 09.16.07

Christiaan Kooyman, retired field scientist, grasshopper specialist, well-known for his ground-breaking work in the biological treatment of insects, has granted us an exclusive interview in order to grasp a much better understanding into the locust invasion that East Africa is now facing. His insights are not only very informative, but also thought provoking.



  • Dr Kooyman, could you please explain to us the difference between locusts and grasshoppers? 
    In general, locusts are grasshoppers that occur in two phases, solitary and gregarious. Individuals live a solitary existence only coming together for the purpose of mating. However, when numbers, and especially population densities, increase, individuals can no longer avoid each other, which triggers behavioural, physiological and morphological changes that lead to the gregarious phase. Individuals now attract each other through the excretion of a gregarization pheromone, so that they form hopper bands or flying swarms.
  • What type of locusts are present at the moment in East Africa, that are causing this humanitarian crisis? 
    The current plague is caused by the desert locust, though migratory locusts have also greatly multiplied in areas along the African Red Sea coast. Desert locusts live in desert areas during their solitary phase, which is called a recession. During periods of abundant rainfall, several generations can occur in quick succession causing population densities to rapidly increase. The resulting swarms can fly up to 200 km per day. This is an outbreak. Swarms entering new areas are called invasions.
  • How many locusts are in a swarm? 
    The number of locusts in a swarm depends on its size. Small swarms contain thousands of locusts and up to more than 100,000. Large swarms contain millions of locusts and huge swarms can contain billions. In Kenya, the swarms were large to huge. One swarm was reported to measure 40×60 km. Each adult locust eats about its own weight in vegetation per day, about 2 g.  Very large areas of crop land and pasture have been devastated, which is likely to lead to local food shortages.
  • Do we know the exact cause of the plague? 
    This plague is the result of unusually heavy rainfall. Locust numbers started increasing after the passing of several cyclones in the Gulf of Aden and the entrance of the Red Sea. Subsequent seasonal rainfall in the entire affected area made the situation reach plague proportions. Most experts agree that global warming/climate change has played an important role, though that can of course not be proven for a single plague. However, if the duration and frequency of plagues increase, then climate change would be the obvious culprit.
  • How long could the invasion last for? 
    Nobody can predict how long this plague will last. From experience, we know that control measures do not normally end plagues. They can only reduce the pain locally. Plagues end when weather conditions become unfavourable. There have been plagues in Africa during the 1930s, 1940s and 1950s, which lasted up to 8 years.
  • We hear about chemicals being sprayed from planes. Is it an effective method to counter the swarms and stop the crises? 
    In principle, the chemicals recommended by the FAO are effective against flying locusts, but to obtain more than 90% mortality their application should also be correctly done. Pilots should be properly trained in ultra-low volume application, which relies on wind to carry the droplets to their target. During the early stages of locust outbreaks, one could theoretically eliminate all swarms, but the practical challenges should not be underestimated. Once an outbreak has passed a certain threshold, it becomes very difficult to stop by spraying the swarms. As stated in my previous answer, adverse weather conditions usually end outbreaks and plagues.
  • Does the spraying of such large quantities of chemical insecticides not have a negative effect on the environment? Are there alternatives? 
    It is obvious that chemical control of locusts has undesirable side effects, especially on non-target insects and their predators, like birds and reptiles. Mammals, including humans, are also affected. On the other hand, the total affected area is still relatively small compared to the unaffected area. The problem is that chemical control is already rampant in all agricultural areas and also in parks, gardens and homes. Chemical locust control just makes things worse. Unfortunately, there are no obvious alternatives to swarm control, though some people are now advocating the large-scale harvesting of locusts for human and animal consumption. Whether that is economically feasible, remains to be seen. The only alternative to chemical control of hopper bands is the use of Metarhizium acridum, i.e. NOVACRID, GREEN MUSCLE, or similar products that contain this pathogenic fungus. It is specific to locusts and grasshoppers. It infects the hoppers by penetrating their skin and kills 90% in 2-3 weeks. Where predators are abundant, especially birds, hopper bands are often eliminated within 10 days, because when the hoppers get sick, they become much easier to catch.
  • What would be the most relevant strategy to avoid this type of natural disaster upstream? 
    Countries that are prone to locust outbreaks and invasions, should invest in stockpiling appropriate insecticides, either in the country, in the region or with the manufacturer. Each country should have a permanent, well-funded locust control unit that monitors weather and environmental conditions and carries out regular surveys when conditions are right for breeding. In the regular outbreak areas, sufficient numbers of trained people should be available for when the need arises. Of course, appropriate spray equipment should also be available and in good state of repair. Regional organisations, like the Desert Locust Control Organisation of East Africa (DLCO-EA), should be well funded to be able to assist member countries with advice, training and spray equipment, especially helicopters for surveying and aeroplanes for spraying. Countries should also take note of the forecasts by the locust unit of the FAO and their timely warnings. Finally, the use of drones for surveying and spraying should be looked into, because modern drones can make flights of considerable length and carry pesticide loads that are sufficient to deal with hopper bands and small roosting swarms.