Invasives Blog

The destructive force of desert locusts and grasshoppers can devastate crops across many regions of Africa and Asia, with swarms of locusts capable of causing widespread damage to crops, severely damaging livelihoods and increasing the risk of acute food instability. CABI has been using its extensive expertise in managing invasive insects, through early action and prevention to manage the spread of locusts.

As part of a new CABI Podcast series, we interviewed CABI experts Dr Belinda Luke and Dr Ivan Rwomushana, who explained how they are controlling the spread of desert locusts through their work. 

Desert locusts
(Schistocerca gregaria) in East Africa © CABI

Welcome Dr Luke and Dr Rwomushana. Please, introduce yourselves…  

Dr Belinda Luke: I’ve been working for CABI for the last 24 years. And part of that time has been looking at locust control. My first job when I started at CABI was working on the Lubilosa project, which was looking at the biological control of locusts and grasshoppers in Africa. And when I started 24 years ago, I was in the labs carrying out experiments related to the fungus that controls locusts. 

Dr Ivan Rwomushana: I’m a senior scientist for invasive species management. I’ve been working in CABI for the last three years and I’m based at CABI Africa regional centre in Nairobi, Kenya. My background is entomology and lately working on integrated pest management of invasive species and recently I’ve started working on locusts. 

A desert locust has two types of behaviour – solitary and gregarious. What does this involve? 

Dr Belinda Luke: Normally desert locusts are solitary. They don’t like to be near each other. But when you have very favourable conditions, so you had the rains that came in, that meant that the eggs – more eggs actually hatched, and then you will then have this density of locusts. And because the locusts are together, what happens is that they rub each other’s back legs and that stimulates them to move from a solitary phase into a gregarious phase.  

How large can swarms grow to? 

Dr Ivan Rwomushana; On average a swarm size can be about 40 million locusts. That’s an average, it could be more than that. And so, our readings, some quick calculations and to try and give you an indication of actually how big these swarms can be. If you imagine that a typical locust, I mean a female, lays about three times in her lifetime. And each time she lays, you get about 200 – 250 eggs. So, if you have a swarm of 40 million locusts, and each female, assume that half of those are females, so you’d – if they went through one cycle, you’re talking about 12 billion individuals of desert locusts.   

Has climate change had an effect on the size of swarms in Africa, their frequency or any other impacts? 

Dr Belinda Luke: We can be sure that climate change is certainly warming up and our data in Africa, because we’ve got 20 years’ worth of data, shows that it is, the temperature is increasing. So that will have an effect on the speed that the locusts can go through their development stages to become adults. And we also know that because of climate change, you get more erratic weather patterns. So, you’ll get unusual rain patterns, which is what triggered the outbreak for 2020 was unusual rain patterns in 2018. So, we certainly know that climate change is having an effect.  How much it’s having an effect on how often locusts will swarm, we don’t know yet. 

desert locust
A desert locust © CABI

CABI developed a safe and effective fungus-based biopesticide, now licensed as Green Muscle, which specifically targets locusts and is environmentally friendly.  How does it work? 

Dr Belinda Luke: The fungus is naturally occurring in the environment and it was actually isolated from a dead locust in Niger quite a few years ago…we’re [now] mass-producing it, we’re putting lots of spores onto the locusts that are in the field, whether they’re nymphs or whether they’re adults.   

Green Muscle is specific only to grasshoppers and locusts. Once it touches that locust, it will then start to grow. Within 24 hours, it will have physically pushed its way through the cuticle of the insect and will start growing in the inside of the insect, in what’s called the haemolymph. It then mass grows inside the insect and then effectively it’s eating the insect from the inside out.    

Dr Ivan Rwomushana: Locusts are cannibalistic. They feed on each other and so when one is sick, the stronger one will feed on it and also get infected but this and as a consequence of course the infection spreads from one insect to another. One locust to another and you get a better effect.  

Drone tackling desert locusts in East Africa © CABI

CABI is trialling the use of drones to spray biopesticide on locusts that would not usually be reached by traditional aircraft. How does this work? 

Dr Ivan Rwomushana: Our approach is to target immature hoppers…rather than the flying locusts because they are more susceptible to infection by the biopesticide. But also, over a unit area, if you can think of the size of a mature locust and the size of a hopper, in terms of size, you get more hoppers in a unit area than you get in terms of mature locusts. So, in terms of efficiency, it’s much better.  

How effective has it been? 

Dr Ivan Rwomushana: From the last mission that we did on trying to experiment with a drone, we’ve been getting anywhere close to 75% efficiency. So, it has ranged from about 47% to 97% kill rate, and so on average comes to about 75% efficiency. So, we think that this is a promising approach in terms of desert locust control in the future, in Kenya and other countries where locusts are a big problem. 

Thank you to Dr Belinda Luke and Dr Ivan Rwomushana for outlining the threat of desert locusts, and CABI’s work to combat the problem. This interview was taken from the CABI Podcast Series.  You can listen to this episode via the link below.

Listen to this podcast episode

CABI podcast mini-series

The CABI podcast is a series of four podcasts dedicated to discovering more about the devastating economic, environmental and social impacts invasive species have and what we can do to manage them.

You can listen via the link below or find them on all the major streaming services – just search CABI podcast invasive species.

Listen now

Further reading on desert locusts

Find out more about desert locusts and their management on the Invasive Species Compendium

Current CABI desert locust projects

https://www.cabi.org/projects/biospace-using-space-enabled-remote-sensing-for-long-term-sustainable-growth-of-biopesticide-use/

https://www.cabi.org/projects/drones-for-desert-locust-control-in-east-africa/

Read more about CABI’s work on invasive species: https://www.invasive-species.org/

Green Muscle biopesticide

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