A new study has shown that a common chemical used to protect crops from fungus is reducing immunity in honey bees, leading to a condition known as colony collapse disorder.

The study, conducted by researchers at University of Maryland and the U.S. Department of Agriculture, found that chemicals used in agriculture are reducing bees' ability to defend themselves from a lethal parasite.

This is the first time that fungicides have been linked to bee deaths. Earlier, insecticides such as those containing Neonicotinoid were found to be associated with the decreasing population of honeybees.

Recently, the EU decided to impose a two-year ban on the pesticide in Europe from April, 2013 amid fierce opposition from chemical industries. The ban, some people say, is based on little evidence.

In the present study, researchers collected pollen from bee hives in fields from Delaware to Maine. The pollen samples helped the scientists identify the flowering plants the bees were visiting. They then analyzed chemicals used in that particular flowering plant.

Researchers then fed the pesticide containing pollen to healthy honeybees and checked their ability to fight infection from Nosema ceranae, which is a parasite that causes the colony collapse disorder.

All the pollen samples contained nine or more kinds of fungicides, insecticides and miticides, with one sample containing about 21 different pesticides. The most frequently found fungicide was chlorothalonil (used for dusting apple crops) while fluvalinate was the most common insecticide.

What surprised the researchers was the finding that the fungicide reduced the bees' resistance against the parasite than any other chemical.

"We don't think of fungicides as having a negative effect on bees, because they're not designed to kill insects," said Dennis vanEngelsdorp from University of Maryland and senior author of the study.

"There are Federal regulations that restrict use of insecticides when honey bees are feeding, but there are no such restrictions on fungicides, so you'll often see fungicide applications going on while bees are foraging on the crop. This finding suggests that we have to reconsider that policy," he added. 

Also, honeybees weren't able to get any nutrition from the agricultural crops and depended on other non-crop plants to feed the colony. Researchers said that the honeybees are probably finding it difficult to gather nutrients from the New World crops, even though they pollinate these flowers.

The study is published in the journal PLOS ONE.