A new scientific study has found "dramatic" and "alarming" declines in insect populations in areas in Germany, which researchers say could have far-reaching consequences for the world's crop production and natural ecosystems.

The study, published on Wednesday in peer-reviewed journal PLOS One has found that, in German nature reserves, flying insect populations have declined by more than 75% over the duration of the 27-year study.

"The flying insect community as a whole... has been decimated over the last few decades," said the study, which was conducted by Researchers from Radboud University in the Netherlands and the Entomological Society Krefeld in Germany.

"Loss of insect diversity and abundance is expected to provoke cascading effects on food webs and to jeopardize ecosystem services."

Co-author Caspar Hallman said he and his colleagues were "very, very surprised" by the results.