Although bees are often lauded for their pollination prowess, other insects are just as important for the success of the world's crops, according to a new study.

The finding, reported in Proceedings of the National Academy of Sciences, suggested that non-bee pollinators such as flies, wasps, beetles and butterflies could provide potential insurance against declines in bee numbers.

An international team led by Dr Romina Rader of the University of New England set out to determine, for the first time, how non-bee insects contribute to pollination of crops.

"The reason I started on this project was because I had looked at visitors within a few crops and noticed how abundant non-bees were in particular locations and particular times of day and under particular conditions and I wondered overall how much they contribute," Dr Rader said.

The team analysed data collected for 17 pollinator-dependent crops across five continents, ranging from vast monocultures to small diverse systems.

A number of factors were measured including visitation rates, effectiveness, contribution to yield and relationship to habitat.

The researchers found that non-bees performed 25 to 50 per cent of the total number of flower visits.

While non-bees were less effective at depositing pollen, their visitation rates were much higher than bees, resulting in similar quality of pollination services.

Insects provide pollination insurance

A wasp visits a passionflower ( Catalina Gutiérrez-Chacón, University of Freiburg, Germany. )

The study also elucidated the importance of non-bees to crops that are not attractive to bees such as custard apples, soursop and mangoes.

Co-author Dr Saul Cunningham, of the CSIRO, said the study was important because it filled a gap in research that had been created through bias towards studying bees.

"This study shows that while bees are usually the most efficient crop pollinators on a per visit basis, lots of other insects are involved, especially flies, wasps and beetles," he said.

"These other insects are sometimes so numerous that can have a greater total effect than the bees. This is especially true for certain crops that don't attract bees so well.

"A good example that we all love at this time of year are mangoes, which benefit greatly from non-bee pollination."

The researchers also found non-insects responded differently than bees to the landscape structure.

While bees rely on hives and other structures that can be affected by environmental change, pollinating insects almost always lived closer to the plants either in the grass or shrubs.

Dr Rader said that with current global declines in bee populations, other, hardier insects that do not rely heavily on vulnerable habitat structures could provide a kind of "pollination insurance" in the face of environmental change.

"The honeybee is assumed to be the dominant pollinator in many crops. While this is probably true in a lot of areas, it is likely particular landscapes and habitats have more abundant non-bees that we haven't really paid attention to," she said.

"If we don't know who they are, we will not know how to protect and conserve them and whether they are impacted by our management practices or not."