The insect world is in crisis. Insect diversity has suffered a disastrous decline as the result of progressive loss of habitat, extreme weather phenomena and the use of pesticides. Nevertheless, these not-so-cuddly animal species fulfil indispensable functions in their respective ecosystems. Professor Hans Jacquemyn from the Faculty of Science outlines how we can turn the tide of devastation.
In 2017, German and Dutch researchers came to an alarming conclusion: insect abundance will have decreased by no less than 75% over the past three decades. Yet that finding came up against a great deal of criticism, as the insect counts were done in a limited number of non-randomised places.
More recently, a meta-analysis was published in the scientific journal Science in which 166 studies – comprising 1,700 researched locales in 41 countries – were compared. According to Professor Hans Jacquemyn (Ecology, Evolution and Biodiversity Conservation Section), that analysis also offers a stark picture, ‘There is a worldwide decline of almost 10% per decade. Terrestrial insects in particular are affected, whilst the number of aquatic insects has on the contrary increased in recent years.’
Fatal habitat loss
The decrease has a strong regional connection, as research shows that insect decline has occurred mainly in Europe and North America. ‘Loss and fragmentation of suitable habitats through intensification of agriculture, drainage, deforestation and urbanisation are probably the main culprits,’ says Professor Jacquemyn. ‘Grasslands with flowering plants are switched out for intensively fertilised fields or highly urbanised environments. This leads to a huge loss of habitat for insects.’ Insects that nest in forests are also struggling with a significant reduction in their habitat.
Moreover, the quality of remaining habitat fragments is deteriorating due to intensive agriculture. ‘For example, fertiliser discharge can lead to eutrophication, or an excess of nutrients,’ says Professor Jacquemyn. ‘As a result, certain plant species will run rampant and dominate less competitive species.’ For insects, that means a more limited supply of food.
But pollution can also take other forms. It has recently been demonstrated that light and sound pollution from increased urbanisation can have a negative effect on insect populations. ‘Another factor is the frequent use of monocultures, or large areas where the same type of crop is grown. Such intensive agricultural areas put great pressure on the diversity of insects’ food sources.’
To make matters worse, the use of pesticides has increased enormously since the 1960s, and many new pesticides have been introduced that affect insect populations. ‘For example, it has recently been established that pesticides unintentionally cause enormous damage to multiple types of bees,’ says Professor Jacquemyn. ‘Pollinators do not die immediately, but they suffer from amnesia due to certain pesticides and can therefore no longer find food.’
For the time being, climate change is primarily a threat to specialist insects that depend on a specific plant species. ‘Rising temperatures create a temporal mismatch between the flowering of a plant and the hatching of insect eggs, making it impossible for an insect to find food sources.’ Professor Jacquemyn also warns that extreme weather conditions will increasingly ravage insects populations. ‘Heavy rainfall can completely wash away and destroy insect nests, for example.’
‘Rising temperatures create a temporal mismatch between the flowering of a plant and the hatching of insect eggs, making it impossible for an insect to find food sources.’
No pollination, no harvest
Should the speed at which insects disappear worry us? According to Professor Jacquemyn, we cannot live without insects because they perform so many useful functions. ‘First of all, there are about 300,000 plant species dependent on insects for pollination. That is almost 90% of all plants that appear on earth.’
When a certain insect species disappears at the base of the food pyramid, there are detrimental consequences for plants and animals that depend on it for food or reproduction. This also applies to agricultural crops, as approximately 84% of all crops in Europe are critically dependent on pollinators. ‘Cherry, apple, plum, raspberry, blackberry … these are all examples of fruit-bearing plants that need insects to form a fruit,' explains Professor Jacquemyn. ‘But chocolate, kiwi, mango, avocado, tomato and artichoke also depend on insects for pollination. If pollinators disappear, this would have an immense impact on the production of those crops.’
Some insects feed specifically on pests, making them an efficient and sustainable alternative to chemical pesticides. ‘Parasitic wasps eat insect pests, such as aphids and whitefly, and thus remove pests from the ecosystem in an organic manner.’ Ants, another insect with a bad image, also help fight harmful insects and are an important food source for other organisms. ‘The green woodpecker mainly feeds on ants. So if they disappear, that’s also the end of the woodpecker population,’ explains Professor Jacquemyn. In addition, ants spread the seeds of a number of plant species and play an important role in the nutrient cycle.
Flower gardens for recovery
Can we stop or even reverse the progressive decline of insects? Japanese researchers have developed a drone that can fertilize flowering plants by sprinkling them with soap bubbles full of pollen grains. Such an artificial pollination method can maintain the agricultural harvest and replace pollinators, but does not address the problem at its root.
Researchers offer a high-tech alternative, whilst according to Professor Jacquemyn, a natural solution is available. ‘Bring back habitat, such as unfertilised grasslands and flower meadows, and reserve, for example, the edges of arable lands for insects and sow them with flowers.’ Roadside berms can also play a role in habitat restoration: ‘The enormous volume of berms along our roads and highways, if managed appropriately, can serve as food sources for insects.’
‘The enormous volume of berms along our roads and highways, if managed appropriately, can serve as food sources for insects.’
As far as our gardens are concerned, we’re better off exchanging neatly manicured lawns for something a little more wild. According to Professor Jacquemyn, cutting the grass less often and allowing wild flowers to flourish results in more food sources and therefore larger insect populations. ‘If I have just a few flowering plants in my own garden, I notice that they’re immediately visited by a lot of insects.’
Providing nesting opportunities also contributes to the recovery. ‘This can be done by replanting small landscape elements, such as hedges and rows of trees. Or by leaving dead trees in forests; dead wood is a highly suitable habitat for many insects.’ Other helpful practices include cutting back on pesticides, pushing for greater landscape heterogeneity and devising specific conservation plans for species that are currently doing poorly.
Professor Jacquemyn hopes that this turnaround will come soon, ‘I don't think we’ll be immediately exchanging insects for drones in large numbers, but if we continue like this, it could lead to a dramatic outcome. It’s time for people to make themselves aware of the usefulness of insects and realise that they can do something themselves to counteract their decline. Insects may not be the most cuddly animal species, but they do perform essential functions.’