Insects in peril

Sunday, 03 March 2019

Bumble bee in the Garden of Heligan, England

In my younger gardening years, I would probably have thought, 'Yay!' on hearing that numbers of all kinds of insects are in sharp decline, with recent estimates being a 45% drop worldwide over the past four decades, and predictions that 40% of the planet's insect species will be extinct in the next few decades. A little wiser nowadays, I realise what important roles insects play in our ecosystem: as vital pollinators of plants, including important crops; as food for birds, bats, amphibians, reptiles and other creatures; as predators for destructive insects; as helpers in breaking down decaying matter in the environment; and, in some cases, controllers of weeds.

Bogong moth

Just last week an alarming report illustrated this problem close to home, noting that Bogong moth numbers in alpine areas in Australia this year are catastrophically low, leading to a lack of a key food source for the endangered mountain pygmy possum population as they breed and raise their young. The cause of the drop in moth numbers has been attributed to ongoing drought and unusually high summer temperatures in this region.

Bug on Dahlia Moonfire

Along with changes in weather patterns (particularly an issue in tropical climates), other causes of insect decline include loss of their habitat caused by deforestation, conversion of land to intensive monocultural agriculture and increasing urbanisation; use of pesticides, especially neonicotinoid chemicals that are harmful to many insects; overuse of nitrogen fertilisers in farming, which pollute the wider landscape and reduce biodiversity amongst plants, enabling only a few dominant species to prosper; and the use of herbicides that have destroyed various wild food sources for insects.

Butterfly on lavender

Unlike other environmental issues, where we gardeners can do very little to make a difference, in this case there are small steps we can all take in our own gardens to help. Probably the most important one is to stop using harmful pesticides in our gardens, especially the neonicotinoid-based ones such as Confidor, which are absorbed through the whole plant and can poison any insect that visits its flowers. Many retailers are voluntarily withdrawing them from sale in Australia, which is very commendable. It's a big step to use no pesticides at all, not even the organic ones such as horticultural oils, and I don't know if I can give these up just yet, but I am working on myself with this! Another constructive step we can contemplate taking is to eat more of organically produced food, supporting farmers who are eschewing dangerous chemicals (or grow our own without the use of harmful pesticides).

Orlaya grandiflora with rose Betty Prior, in the garden of Sandra Wilson in Sydney

Another next step we can take is to include in our gardens a diversity of flowering plants to attract insects in their search for food. Plants with single flowers (as opposed to hybridised double flowers) are preferred, and many insects are particularly drawn to the tiny flowers of the Apiaceae and Asteraceae families of plants. Plants such as Queen Anne's lace and Orlaya, along with herbs such as parsley, coriander and chervil allowed to go to flower, are some of the Apiaceae plants, and the Asteraceae family includes all the many and varied daisy plants. Plants from the broad Lamiaceae family also seem to be particularly favoured. However, all flowering plants have their insect pollinators, especially our native flora, and it is also helpful to have a succession of flowering plants throughout the year, so that there is always something in bloom in the garden. Another good reason for us gardeners to acquire more plants!

Insect hotel

Providing a water source for insects is also vital, even if it is just a shallow dish somewhere in the garden. A more challenging step is to leave some of the garden a bit 'untidy', especially over winter, to provide shelter and habitat for insect species. There are some cute insect 'hotels' that can be bought these days, or you can make your own out of lengths of bamboo and other hollow material. Allowing a few weeds here and there is another idea, as these may be a source of food for certain insects. This can be my justification for weedy areas in my garden in future!

It's easy to love butterflies, dragonflies, ladybirds and bees in the garden, but developing an ability to embrace the presence of less lovely insects is something of a greater challenge! Bronze orange beetles, lily borers and mosquitoes are just a few of the horrors that come to mind. I am going to try to find physical methods of controlling them on my plants then leave them for the birds to eat. Tolerating a few holes in leaves gnawed by insects is not the end of the world, either, as I try to tell myself. Hopefully, other creatures will come along and eat many of the less desirable insects if we can re-establish a more natural balance in our gardens over time!

Another thing that gardeners can do is to take on the role of being a 'citizen scientist' and help document the numbers of insects in your vicinity, to help scientists get a more accurate picture of what is happening. One such program, called the Wild Pollinator Count, is currently being run in Australia, and you can find more about it here. Count dates for this year are 14-21 April and 10-17 November.