The title of this post is a summary of a talk I’m giving today! It's a departmental seminar day, so I'm presenting some results from one chapter of my thesis. (The actual title is "Effects of defoliation by the edible caterpillar Cirina butyrospermi on yields of maize and shea" but I don't think that's quite as catchy.)
Here’s an edited version of the talk, which covers a bit of my fieldwork in the past two years:
Here’s an edited version of the talk, which covers a bit of my fieldwork in the past two years:
This is what we want to do - to feed the world sustainably
Of all the people i know, I’m on the naive and optimistic end of the spectrum, but even i cant look at this image without dying a little inside.
Because this is the exact opposite of what we’re doing.
The current global food system is overrun with problems. Our growing population and growing demand for protein are fuelling widespread environmental degradation and species extinction, public health epidemics such as malnutrition, obesity and heart disease, and exacerbating economic inequality between producers and consumers.
So how does conservation fit into this context? We want food - and we want to save wild species. How can we best do this?
There are many ideas out there, but the one that inspired me to do this research was that of edible insects. Insects, we’re told, have a low environmental footprint, are nutrient rich, and are a highly valued resource currently controlled by some of the world’s poorest people.
Some edible insects are wild-harvested, some are farmed. Yet others are present in existing agricultural systems - and are harvested as a by product.
I felt like these by-product insects were particularly interesting - we’ve sort of been semi farming them for thousands of years, because we’ve been propagating their food source across large areas of land. We’re living in an era of accelerating agricultural intensification and the disintegration of traditional food cultures - what does this mean for semi-farmed edible insects?
Of all the people i know, I’m on the naive and optimistic end of the spectrum, but even i cant look at this image without dying a little inside.
Because this is the exact opposite of what we’re doing.
The current global food system is overrun with problems. Our growing population and growing demand for protein are fuelling widespread environmental degradation and species extinction, public health epidemics such as malnutrition, obesity and heart disease, and exacerbating economic inequality between producers and consumers.
So how does conservation fit into this context? We want food - and we want to save wild species. How can we best do this?
There are many ideas out there, but the one that inspired me to do this research was that of edible insects. Insects, we’re told, have a low environmental footprint, are nutrient rich, and are a highly valued resource currently controlled by some of the world’s poorest people.
Some edible insects are wild-harvested, some are farmed. Yet others are present in existing agricultural systems - and are harvested as a by product.
I felt like these by-product insects were particularly interesting - we’ve sort of been semi farming them for thousands of years, because we’ve been propagating their food source across large areas of land. We’re living in an era of accelerating agricultural intensification and the disintegration of traditional food cultures - what does this mean for semi-farmed edible insects?
I chose to do my fieldwork in Burkina Faso, West Africa, because this is a country in which many of the problems facing the global food system are really acute - widespread destruction of habitat to clear land for agriculture, prevalent malnutrition among those who produce the food. Also, they have one particular edible insect that really intrigued me!
As the satellite image above shows (thank you Google maps), the agricultural fields in Burkina Faso are filled with trees, and the vast majority of the trees are shea trees. Shea trees produce nuts that can be ground and churned to make shea butter, a product that’s used in cosmetics and confectionary worldwide. The nuts fetch high prices at market and it’s Burkina Faso’s third biggest export crop. It’s been called ‘women’s gold’, because the shea nuts are traditionally a crop that is harvested by women.
The most dominant crop that’s grown in the fields is maize, which is the dietary staple in the region. Men are traditionally responsible for the maize crop, although in practice both women and children often contribute a lot of the physical labour.
So, the agricultural system in southwestern Burkina Faso can be most accurately described as maize- and shea-dominant agroforestry.
So, the agricultural system in southwestern Burkina Faso can be most accurately described as maize- and shea-dominant agroforestry.
The reason for my excitement when i first heard about this potential study system was the insect that eats the leaves of the shea tree. It’s an edible caterpillar, collected in large numbers (as you can see from the above photo) and sold in huge quantities at markets.
African edible caterpillars are delicious, fascinating creatures. Many of them are highly seasonal, but very abundant when in season. However, the vast majority are only found in forest environments. This was the first time i’d ever heard of an agricultural system that had edible caterpillars. Looking into it, i found papers that referred to the caterpillar as a ‘pest’ of shea. i had endless unanswered questions, and decided a pilot trip would be necessary to try and understand which of my questions would be most relevant to those living in the region.
Methods
Farmer interviews & consultations
In 2016 I spent a couple of weeks visiting villages and interviewing men and women whose primary income source was smallholder farming. I consulted them about their priorities, and it was clear that one of the most important questions to people here was: what are effects of defoliation by caterpillars on yields of shea and maize?
I decided to ask this as the driving research question for one of the chapters of my thesis.
Following pilot interviews, I randomly selected a sample of 45 households, stratified by household size, all of whom owned at least 1ha of maize. I selected three shea trees in each field - also stratified by size. I did approx 14 months of fieldwork in 2016-17.
Field data collection
In 2016 I collected observational data on shea tree defoliation and the growth of maize plants under and outside of tree canopies. In 2017 I repeated this data collection and also collected data on the abundance of shea nuts and the weight of maize cobs relative to plant height.
Field experiment
In 2017, in collaboration with two farmers, I conducted a field experiment: we planted two rows of maize (30 plants each row) and applied caterpillar faeces as fertiliser to one of the rows. We then measured the growth of each plant and weighed the eventual harvested cobs.
African edible caterpillars are delicious, fascinating creatures. Many of them are highly seasonal, but very abundant when in season. However, the vast majority are only found in forest environments. This was the first time i’d ever heard of an agricultural system that had edible caterpillars. Looking into it, i found papers that referred to the caterpillar as a ‘pest’ of shea. i had endless unanswered questions, and decided a pilot trip would be necessary to try and understand which of my questions would be most relevant to those living in the region.
Methods
Farmer interviews & consultations
In 2016 I spent a couple of weeks visiting villages and interviewing men and women whose primary income source was smallholder farming. I consulted them about their priorities, and it was clear that one of the most important questions to people here was: what are effects of defoliation by caterpillars on yields of shea and maize?
I decided to ask this as the driving research question for one of the chapters of my thesis.
Following pilot interviews, I randomly selected a sample of 45 households, stratified by household size, all of whom owned at least 1ha of maize. I selected three shea trees in each field - also stratified by size. I did approx 14 months of fieldwork in 2016-17.
Field data collection
In 2016 I collected observational data on shea tree defoliation and the growth of maize plants under and outside of tree canopies. In 2017 I repeated this data collection and also collected data on the abundance of shea nuts and the weight of maize cobs relative to plant height.
Field experiment
In 2017, in collaboration with two farmers, I conducted a field experiment: we planted two rows of maize (30 plants each row) and applied caterpillar faeces as fertiliser to one of the rows. We then measured the growth of each plant and weighed the eventual harvested cobs.
The image above shows a typical landscape in the midst of caterpillar season. All the trees are shea trees - but some look like they're dying. They're not dying! They've just been stripped of their leaves by a lot of very hungry caterpillars..
Results
The results of observations and experiments have been surprising, and as ever, I wish I had another year or so to collect more data!
I can’t publish the graphs that accompanied here because they’re being submitted for peer review, but here’s a summary of my results:
What does this mean?
Overall, my first conclusion is that caterpillars aren’t a ‘pest’ in the conventional sense – and what I mean by this is that there is no evidence that they cause any harm to yields of either shea or maize.
Secondly, it looks like defoliation by caterpillars may assist maize growth, probably due to light and/or fertilization of the soil by caterpillar faeces - but more data is needed to verify this. 2016 may have been a false positive; 2017 may have been a false negative.
Finally, the field experiment results do suggest that there may be a positive impact of caterpillar faeces on maize productivity – but again, more data is needed.
Results
The results of observations and experiments have been surprising, and as ever, I wish I had another year or so to collect more data!
I can’t publish the graphs that accompanied here because they’re being submitted for peer review, but here’s a summary of my results:
- There was no significant relationship between the extent of shea defoliation and the abundance of shea nuts on trees the following year. Given the extent of defoliation, this is really surprising.
- in 2016 there was less difference in maize height underneath trees with more defoliation, suggesting that defoliation does help crop growth. However, the same trend was not observed in 2017.
- Plants that are fertilised with caterpillar faeces grow taller - there's a significant height difference from Day 50 onwards - but there was no significant difference in maize cob weight.
What does this mean?
Overall, my first conclusion is that caterpillars aren’t a ‘pest’ in the conventional sense – and what I mean by this is that there is no evidence that they cause any harm to yields of either shea or maize.
Secondly, it looks like defoliation by caterpillars may assist maize growth, probably due to light and/or fertilization of the soil by caterpillar faeces - but more data is needed to verify this. 2016 may have been a false positive; 2017 may have been a false negative.
Finally, the field experiment results do suggest that there may be a positive impact of caterpillar faeces on maize productivity – but again, more data is needed.
So, let’s return to the first image, & the problem that made me start this study.
I think I can say something new about this now, for what it's worth:
In West Africa, edible caterpillars aren’t a pest insect.
They might even help fertilize the soil that produces the staple crop.
In order to build a more sustainable food system we need to do more research, and when we do so, we need to listen to the farmers to whom this matters most.
Thank you for reading! And thanks to those who made this study possible:
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