One of the dominant pollinators in red clover is the buff-tailed bumble bee. (Maj Rundlöf/Science)

Honeybees may be sweet, but it's their wild cousins that give plants better sex — and, consequently, higher crop yields.

"Basically, the more of those wild insects there were, there more fruit was produced in that particular field," said Lawrence Harder, a University of Calgary biologist in an interview this week, "whereas for honeybees, that was only true for 14 per cent of the crops."

Harder was speaking about the results of an international study he co-authored, which was published online in the journal Science Express. It looked at the effect of honeybees and wild pollinators on yields of 41 crops in 600 fields in 20 countries, including a blueberry field on Prince Edward Island.

The crops included many grown in Canada, such as canola, strawberries, blueberries, pumpkin, tomatoes, onions, cranberries, sunflowers and red clover; as well as many familiar imports such as coffee, mango and almonds.

The findings suggest that the decline of wild insect pollinators could have a negative impact on plant yields, and that honeybees can't take the place of wild pollinators.

Many flowering plants require insects to transfer pollen — which contain sperm cells — to the female part of a flower in order to produce seeds, which are often enclosed in a fruit.

University of Calgary professor Lawrence Harder, seen here conducting field work in Japan for another research study, was one of 50 researchers involved in a study about wild insects and pollination. (Dale Hensley/University of Calgary)

Honeybees, which aren't native to North America, are sometimes hired out and trucked from field to field in order to pollinate farmers' fields.

However, many wild insects serve as pollinators also. Most of them are among the 20,000 species of bees, such as bumblebees, mason bees, and many that are less familiar.

"Most bees are kind of a centimetre long, and most people would think they were a fly or something," Harder said.

He added that flies such as hoverflies and, to a much lesser extent, butterflies also act as pollinators.

Honeybees may promote inbreeding

It's not clear why honeybees aren't as effective pollinators as other insects, since the study found that they actually transfer more pollen than wild pollinators.

However, Harder said it may be that honeybees may have a greater tendency to promote plant inbreeding, which may lead to fewer viable offspring in the form of seeds.

Because plants are hermaphroditic, that allows for "the extremely close form of inbreeding of mating with yourself," also known as self-pollination, Harder said.

"Honeybees may tend to move more between flowers on the same plant, resulting in self-pollination, whereas the wild insects visit a fewer number of flowers on an individual plant before they move to the next plant."

Wild pollinators declining

Unfortunately, Harder said, there is evidence that many wild pollinators are on the decline.

A new study by researchers at Washington University in St. Louis, also published in Friday's issue of Science, compared the bees and flowering plants near Carlinville, Il. In the late 1800s with those that existed in 2009 and 2010 and found half the bees associated with 26 spring-blooming flowers had disappeared. Meanwhile, some pollinators no longer visited their plants as often and those that did visit weren't carrying as much pollen.

Many wild pollinators nest in the ground or in hollow twigs, and their nesting sites may be disturbed when fields are plowed, harvested or otherwise worked for agriculture, Harder said.

While farmers may be tempted to clear and plant all available agricultural land, the study suggests that leaving patches of land in their natural state could improve the yields of some crops by providing habitat for wild pollinators, Harder said.

"Canola and fruit crops would benefit from this kind of practice of leaving more natural area for native flowering plants and for the stability of nesting areas."

The study was led by Lucas Garibaldi, a researcher at the National University of Río Negro in Argentina. In addition to Harder, its 50 authors included one other Canadian, Steven Javorek, a Kentville, N.S.-based scientist with Agriculture and Agri-Food Canada, who conducted the part of the study involving a blueberry field in P.E.I.