Karlsruhe, Germany  - Thousands of German bee-keepers were readying claims for compensation Saturday after scientists traced the cause of mass deaths in bees: a pesticide that coated maize seed.

Vast numbers of the insects were killed in the Rhine valley area of Germany's Baden-Wuerttemberg state by the chemical clothianidin, the Julius Kuehn Institute in the northern city of Braunschweig said.

The loss of swarms has worsened a long-term collapse in bee populations in many parts of the world that is blamed on the varroa mite infesting hives.

The bee institute said late Friday 29 out of 30 dead bees it had checked had been killed by contact with the pesticide, which is harmless to humans but lethal to fruit flies and the corn rootworm (scientific name Diabrotica virgifera).

Farmers in the valley and Bavaria have used massive amounts of the pesticide this year as the pests take over. The institute said it may have blown onto wild plants, fruit trees and rapeseed crops as it was spread.

The Baden Apiarists' Association, with 7,100 members, said Saturday it would study a compensation claim against farmers or the pesticide makers and would meet Monday with the state agriculture minister, Peter Hauk. (dpa)