A friend of mine has recently had confirmation from his vet that liver fluke infecting his sheep have become resistant to the flukicide drench he uses to control the parasite. Fortunately there are three types of flukicides, enabling rotation, so it’s not the end of the world - but it’s a wake-up call for him, and he will have to be careful not to allow the fluke on his farm to become resistant to the alternatives as well.

Fluke are not the only parasites to develop resistance to the drugs used to control them. Stomach worms are also becoming resistant to different groups of anthelmintics, prompting scientists to research ways of developing vaccines.

It’s much the same with antibiotics where a gene which makes bacteria resistant to a “last resort” antibiotic has been found in pigs and humans in England and Wales. The resistance gene, called mcr- 1, was first found last year in pigs in China and makes common bacteria resistant to polymixin antibiotics such as colistin, which are known as “last-line” antibiotics as they are often used as a drug of final resort to treat serious infections by multiple drug-resistant bacteria.

In China, the world’s largest pig producer, antibiotics aren’t typically administered under veterinary supervision, unlike the UK where there are strict regulations controlling their use.

The agricultural sector has for some time been blamed for its part in antibiotic resistance in both humans and animals.

Colistin is frequently used for mass medication of intensively farmed pigs and poultry, and scientists believe the resistance gene has spread from farm animals to humans because the antibiotic is used much more widely in veterinary medicine than in human medicine.

Growing concerns about antibiotic resistance prompted fast-food chain McDonald’s to announce last spring that it will phase out all use of antibiotics critically important to human health over a two-year period, and in the US will only sell poultry raised “antibiotics-free”.

German livestock and poultry producers have antibiotics use benchmarked against other farms, and restrictions placed on those with usage deemed too high under tough new legislation that came into force last July.

It’s not just bugs and parasites that are evolving to become resistant to widely used medicines, weeds are also becoming resistant to some herbicides, like glyphosate.

Many of the chemicals we have used in agriculture have turned out to be environmental disasters. Aldrin, deildrin and DDT were all effective ingredients in sheep dips that were so deadly they had to be withdrawn from use. DDT entered the food chain and caused infertility in birds of prey.

They were followed by organophosphate (OP) dips that had been developed from nerve gas used in the Second World War. From 1976 until 1992, sheep farmers were obliged by law to use them to eradicate pests like sheep scab mites. Thousands complained of becoming ill after using them, and even those who took the precautions recommended - such as wearing protective clothing - said they were often ill after dipping sheep.

Figures released in 1993 revealed that between 1988 and 1992, 450 UK farmers and farm workers became ill after exposure to OP pesticides in sheep dip, and a number went on to suffer from serious, long-term ill-health. Symptoms include excessive tiredness, headaches, limb pains, disturbed sleep, poor concentration, mood changes, and thoughts of suicide.

Then there was the disturbing damage done to bee and butterfly populations by neonicotinoids that have now been banned by the EU.

Those pesticides were widely used in seed dressings for maize, oilseed rape and sunflowers to control pests such as virus-carrying aphids and cabbage stem flea beetle.

Currently a significant proportion of the UK wheat crop is sprayed with insecticides to control cereal aphids, which reduce yields by sucking sap from plants and transmitting barley yellow dwarf virus.

Unfortunately those sprays kill beneficial species of insects as well, and consequently damage ecosystems.

For most of my life I have embraced new technology, but my faith in science has faltered in recent years.

I remember being alarmed by an EU report in 2005 that strengthened suspicion that pesticides can cause Parkinson’s Disease.

The “Geoparkinson” study was published in the New Scientist and involved nearly 3,000 people. Headed by Anthony Seaton of Aberdeen University, the research found farmers were 43 per cent more likely to develop Parkinson’s because of their exposure to pesticides.

I am not a Luddite, but have become more critical of new techniques.