Addressing a 30-strong group of growers and seed company representatives at the NIAB's field trial site near Cambridge last month, Koppert consultant Jasper Hubert said the biological control specialist now supplies colonies of native bumblebees (Bombus terrestris subsp. audax) to help growers of crops such as courgettes and pumpkins to boost pollination, which leads to better yields and improved fruit quality.
Hubert explained how it is in growers' interests to have a wide range of different pollinators in their crops, saying: "If some of them fail you, others will not."
But the behaviour of bumblebees in particular benefits cucurbit crops because of their short pollination windows of just six hours, said Hubert. "Cucurbit flowers are ready just around sunrise and wanting to close at around noon," coinciding with bumblebees' main period of activity, he pointed out.
"Bumblebees need to get pollen every day in order to feed their brood, but they do not tend to like sunlight," he said. But they will tolerate winds of up to 40 miles an hour, unlike honeybees, which avoid poor weather.
In addition, bumblebees' larger size and hairy exterior suits cucurbits' large flowers, so pollen is more likely to stick to them, added Hubert. He also pointed out that because cucurbits have both male and female flowers, bumblebees' habit of hopping from flower to flower is "very nice if you want good cross-pollination".
Koppert's trials on courgette crops grown under glass have found that bumblebees transfer 2.8 times more pollen than honeybees, said Hubert, while plants pollinated by bumblebees produced 4.3kg, compared with 3kg per plant in the honey bee-pollinated crop. The bumblebees not only helped produce larger and thicker fruit but these ripened faster and were less likely to be misshapen or suffer from fruit rot, he said.
An earlier US trial found that pumpkin fields supplemented with bumblebees produced 1.55 fruits per plant, compared with just 1.14 fruits per plant in a control field.