Rediscovering biological pest control

In nature there are no pests but some species become pests when they start to compete with humans for resources or when they affect the welfare, aesthetics or profit, especially food production.

In most cases, insects become pests when something changes in their environment. Very often the change happens when an animal is moved from one area to a new one where it is no longer controlled by its enemies. These introductions often follow the spread of host plants through human civilisation.

Sometimes insects increase in number when one or more of their enemies disappear. The system of checks and balances which have evolved over millions of years of evolution is known as biological control.

A hundred years ago the government authorities, particularly the Department of Agriculture, were fully aware of the importance of biological control in the Maltese islands and monitored the appearance of pests and their biological control agents. Among these were several species of aphids and the ladybirds which fed on them and kept them in check. The system worked and it was only occasionally in years with unusual weather, that aphids and other insects increased so much as to cause problems.

Soon after World War II it was believed that a solution had been found to eliminate all pests. The Department of Agriculture started to promote the use of new chemicals such as DDT to combat all pests. At first the new chemicals gave excellent results but within a year or so the pests appeared in larger numbers than ever before because apart from killing pest species the insecticides also killed predator species such as the ladybirds which had been keeping other insects in control.

They also killed biological control agents such as the vedalia beetle which was introduced 30 years earlier to control the fluted scale insect, an Australian species, which was threatening the survival of Malta’s orange groves.

The ladybird is a well known insect loved by almost everybody. In the past it used to appear in large numbers in time to control aphids before they could cause harm to agriculture. Today the ladybird is not as common as it used to be but it could become more common if we had to stop relying on dangerous chemicals to control insect numbers and rediscover biological pest control.

portelli.paul@gmail.com