In recent years, the sudden disappearance of bees has concerned scientists. When many bees are absent from the earth, this will have a great impact on people's life because many kinds of food such as fruits, vegetables, meats, milk, and eggs will be gone with bees. As a result, many scientists have already found out the reasons why many bees are vanishing from the earth. Some of these causes include climate change and serious food shortages for bees. But a major risk is the use of pesticides that can make bees become puzzled, bring less pollen home, and even unable to find their way home. In some of the worst cases, pesticides can harm bees' immune systems and make them endangered by the threats of parasites. In order to save the bees and protect our environment, some people have already gone organic by not using pesticides when planting flowers, vegetables, and fruits. And to our great delight, scientists have also discovered the way to kill those parasites that are deadly to bees. Despite these great efforts made to save the bees, it is still the increasing awareness of environmental protection that can eventually protect our bees from disappearing. According to the passage, what is the major cause for the disappearance of many bees?