Where Have All The Insects Gone?

  • Written by Andrew Davis
  • Posted on Jun 22, 2018
  • Articles

The summer solstice, the longest day, is now passed and the hours of daylight will shorten.  However, high summer has a couple of months still to run, lazy days sitting in the garden sipping a cup of tea or glass of wine hearing birdsong and the hum of busy insects.  And yet there is an eerie quiet.

Looking back through rose tinted spectacles to days of yore, driving through the countryside at this time of year resulted in a windscreen spattered with bugs that had to be washed off after any long trip.  Not so today.  The number of insects has dropped alarmingly.  Indeed, there was an article in the Observer recently entitled ‘Where have all the insects gone?’ which claimed a catastrophic collapse in numbers over the past forty years.  For example, larger moths in southern Britain have declined by 40%; 76% of the UK’s resident and regular migrant butterflies have declined in either population or range with similar data for other species.

The populations of pollinators have been widely debated in the media with claims that bee numbers, in particular, have been decimated.  Over the past couple of decades much of the blame has been ascribed to neonicotinoid insecticides, of which there are three main types.  The chemicals were developed in the early 1990s and first used on sunflowers in France in 1994, before introduction into the USA and UK around 1998.  The main use in this country has been as a seed dressing, particularly on brassicas such as oilseed rape and kale to control cabbage stem flea beetle.  The active ingredient is translocated throughout the plant but it was not at first believed to get into the flowers to contaminate the pollen or nectar and thus have an impact on pollinators.  Research has now shown that it does and has been blamed for the death of millions of bees.  The chemical destroys the immune system of insects and thus the actual cause of death may be an infection that the insect cannot withstand rather than direct poisoning.

As a result of this further research, the use of neonicotinoids was partially banned in 2013 by the EU on flowering plants that rely on insects for pollination such as oilseed rape, but was still used on other crops such as cereals which are self-pollinating.  However, it now appears that the insecticides have spread more widely in the environment.  When drilling, some of the seed dressing may be blown away as dust; further, the compounds are soluble and are thus washed into the soil and into watercourses.  The active ingredient has been detected in wild flowers, again having an impact on pollinators.

It is increasingly being found in rivers across the country, particularly the Waveney and Wensum in East Anglia, both of which flow into the Norfolk Broads.  In the South, the Test has found to be contaminated.  This is of special significance to a river than some claim to offer the finest fly fishing for brown trout in the world as the fish rely on invertebrates and insects for their food.  It is also suggested that the decline in insect numbers may be partially responsible for the falling population of farmland birds in recent years.  It is clear that a mass extinction of insects would be catastrophic for the environment.

Earlier this month EU member states agreed a total field ban on neonicotinoid insecticides which is likely to come into force by the end of this year.  However, use in greenhouses will still be allowed as will use on domestic pets for the control of fleas and ticks.  Campaigners suggest that this is a mistake as the latter is thought to cause a significant spread of the pesticides in the environment.  However, the debate has become increasingly polarised with some environmentalists warning of catastrophe if a complete ban is not imposed whilst farmers ask how they can grow food for the nation if critical pesticides are banned.  The danger of proscription is that older, less effective chemicals are used instead in greater quantities also with detrimental effects.

There are those who challenge the doomsday scenario.  The Game and Wildlife Conservation Trust has been conducting research in Sussex for decades into grey partridge and the insects required for their food.  Over the past fifty years total insect abundance has declined by 35%, but in recent years it has shown an increase.  Twenty six insect groups were assessed in cereal crops, of which twelve had declined in abundance, two increased and the remainder show variability over time.  Extreme weather, insecticides and herbicides were all shown to affect insect abundance.  The widespread uptake of agri-environment schemes and greater awareness of the impact of insecticides by farmers is helping to support insects. Remedial measures should focus on encouraging greater plant diversity, upon which so many insects depend, in crops, pastures and urban areas.

The evidence seems to support a total ban on the use of neonicotinoids but it is equally important to provide farmers with the tools to allow them to grow our food.  The alternative is to import food from other countries that may have a more cavalier attitude to the environment.  In a previous column, I suggested that the age of chemical farming is coming to an end and that we will rely in future of wider rotation of crops, on biotechnology and biological means of control.  The sooner we make real progress in that direction, the better for food production and the environment.