Forty per cent of world's insect populations declining, could become extinct, new study finds

Forty per cent of insect species are suffering dramatic declines in their populations that could lead to extinction, a review of global insect numbers has found.

And that result, scientists say, could be catastrophic for our planet. 

Bees, ants and beetles are disappearing eight times faster than mammals, birds or reptiles, while other species of insects including houseflies and cockroaches are likely to boom, the study says.

The majority of creatures that live on land are insects and they perform a number of roles which benefit other species, including humans.

They pollinate around 75 per cent of global crops, keep the numbers of pests in check and provide a food source for birds, bats and small mammals.

The causes of the dramatic decline include intensive agriculture, pesticides and climate change.

The new paper, which was published in the journal Biological Conservation, takes a broader look at overall insect populations.

It reviewed 73 existing studies published around the world in the last 13 years.

The study found that declines in almost all regions may end in the extinction of as many as 40 per cent of insects.

"The main factor is the loss of habitat, due to agricultural practices, urbanisation and deforestation," Dr Francisco Sánchez-Bayo, the lead author from the University of Sydney, told BBC News.

"Second is the increasing use of fertilisers and pesticides in agriculture worldwide and contamination with chemical pollutants of all kinds. Thirdly, we have biological factors, such as invasive species and pathogens; and fourthly, we have climate change, particularly in tropical areas where it is known to have a big impact."

The study highlights the recent massive decline in Puerto Rican tropical forests and the and drop in flying insects in Germany.

"It's not just about bees, or even about pollination and feeding ourselves - the declines also include dung beetles that recycle waste and insects like dragonflies that start life in rivers and ponds," said Matt Shardlow from UK campaigners Buglife.

"It is becoming increasingly obvious our planet's ecology is breaking and there is a need for an intense and global effort to halt and reverse these dreadful trends. Allowing the slow eradication of insect life to continue is not a rational option."

Experts have also said that pest insects will thrive in the warmer conditions.

"Fast-breeding pest insects will probably thrive because of the warmer conditions, because many of their natural enemies, which breed more slowly, will disappear, " the University of Sussex’s Professor Dave Goulson, who was not involved in the review, told BBC News.

"It's quite plausible that we might end up with plagues of small numbers of pest insects, but we will lose all the wonderful ones that we want, like bees and hoverflies and butterflies and dung beetles that do a great job of disposing of animal waste."

Professor Goulson encouraged people to make more insect-friendly gardens and to stop using pesticides and buy organic food.