The European Union has a bug problem.

After regulators in late 2013 banned pesticides called neonicotinoids, linked in some studies to the unintended deaths of bees, farmers across the continent applied older chemicals to which many pests had developed a resistance, allowing them to survive. Now, infestations may lead to a 15 percent drop in this year’s European harvest of rapeseed, the region’s primary source of vegetable oil used to make food ingredients and biodiesel, according to researcher Oil World.

“When we remove a tool from the box, that puts even more pressure on the tools we’ve got left,” said farmer Martin Jenkins, who has seen flea beetles for the first time in almost a decade on his 750 acres of rapeseed outside Cambridge, England. “More pesticides are being used, and even more ridiculous is there will be massively less rapeseed.”

At issue for the EU was protecting bees that farmers rely upon to pollinate more than 80 percent of Europe’s crops and wild plants, valued at 22 billion euros ($26 billion) annually. While research on how neonicotinoids affect beneficial insects hasn’t been conclusive, regulators said the risks were worth imposing a two-year ban that began in December 2013. The Canadian province of Ontario proposed similar restrictions last year, and new rules are under review in the U.S., the biggest oilseed producer.

Corn, Sunflowers

The ban left European farmers without effective alternatives, leading to widespread insect damage, Hamburg-based Oil World said in a December report. Output of rapeseed may fall to a three-year low of 20.5 million metric tons in 2015, down from a record 24 million last year, it said. The EU is the world’s largest producer of rapeseed, which is known in North America mostly as canola.

Rapeseed for February delivery rose for a fourth day, adding 0.5 percent to 362 euros a ton on Euronext in Paris as of 2:11 p.m. local time.

French corn and Spanish sunflowers may also be affected, said Copa-Cogeca, the Brussels-based lobbyist for the continent’s growers.

The EU restricted the main types of neonicotinoids, a class of chemicals similar to nicotine, while still permitting two less-toxic varieties. Bayer AG, which markets the products as Poncho and Votivo, and Syngenta AG make the pesticide. Monsanto Co., DuPont Co. and Dow Chemical Co. (DOW:US) sell seeds coated in it.

Older Chemistry

“Farmers have had to go back to older chemistry and chemistry that is increasingly less effective,” said Nick von Westenholz, the chief executive officer of the U.K.’s Crop Protection Association, an industry lobbyist. “Companies would like to innovate and bring newer stuff, but the neonicotinoid example is not a tempting one.”

While the EU’s approval process for new pesticides can take years, some research is under way. The U.K. last month granted over 650,000 pounds ($979,485) in funding to a project led by Arch UK Biocides Ltd. for a chemical based on spider venom that is harmless to bees.

Some studies, including one in May from the Harvard School of Public Health, have linked neonicotinoids to Colony Collapse Disorder, a syndrome marked by bees abandoning their hives in winter and dying. Bayer scientists dubbed the research “seriously flawed,” noting that colony failures observed in the study were prompted in part because bees were fed artificially high levels of pesticides.

Question Mark

Other research was less conclusive. Some versions of the insecticide were harmful in lab experiments and had little effect on healthy colonies in the field, according to a report by Wageningen University in the Netherlands.

“The risk to bee populations and the wider environment from using this chemical that has a very big question mark over it is not a risk worth taking,” said Helen Browning, the chief executive officer of the Soil Association, a U.K. charity focused on sustainable farming. “There are alternative approaches,” such as barrier crops around fields, she said.

The number of approved crop chemicals has fallen in the EU by more than 75 percent in two decades, according to the Andersons Centre, a farm consultancy in Leicestershire, England.

Alternative Chemicals

In Germany, most rapeseed farmers have sprayed crops at least twice with alternative chemicals known as pyrethroids this season, said Manuela Specht, a division head at oilseed trade group known as UFOP in Berlin. In past years, they only sprayed once or not at all, she said. Prolonged exposure to some pyrethroids can stunt bee growth, a University of London study showed last year.

For Jenkins, the U.K. farmer, he’s balancing a fight against pests that grow stronger over time with trying to maintain food production. In addition to flea beetles in rapeseed, he’s got an infestation of black grass, a weed that chokes his wheat fields. Two of the chemicals that he used to use are now banned, and the plant is resistant to permitted treatments of Bayer’s Atlantis, he said.

“We’re growing less tons of food on our farm than we were 10 years ago,” Jenkins said. “An attack 10 years ago we could remedy with an alternative bit of chemistry, but that is no longer the case.”