Falling numbers of wild bees and other pollinating insects are hurting global agriculture, a study released on Thursday found.

Managed populations of pollinators are less effective at fertilizing plants than wild ones, the researchers said, so the dearth of pollinating insects cannot be solved by simply introducing others.

"Adding more honey bees often does not fix this problem, but... increased service by wild insects would help," said Lawrence Harder, a scientist with the University of Calgary in Canada, which led the study.

Pollinating insects usually live in natural or semi-natural habitats, such as the edges of forests, hedgerows or grasslands.

These habitats are gradually being lost as the land is cultivated for agriculture, but, as a result, the abundance and diversity of wild pollinators crucial for the crops' success is declining.

The researchers analyzed 41 crop systems around the world, including fruits, seeds, nuts, and coffee to examine the impact of wild pollinators on crop pollination.

"Paradoxically, most common approaches to increase agricultural efficiency, such as cultivation of all available land and the use of pesticides, reduce the abundance and variety of wild insects that could increase production of these crops," says Harder.

He said tomatoes, coffee and watermelon are among the key crops which are likely to suffer from the declining population of wild pollinators.

Most flowering crops need to receive pollen before making seeds and fruits, a process that is enhanced by insects -- like bees, but also flies, butterflies and beetles -- that visit flowers.

The research, which was published in the journal Science, was carried out by an international team of some 50 researchers, who collected data from 600 fields in 20 countries.

The study called for new efforts to conserve and restore the natural habitats of honey bees and wild insects.