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THECOMMERCIAL GREENHOUSEGROWER • APRIL 2018
POLLINATION •
SinceNatural England refused to renew theprevious class
licence topermit the release of non-nativebumblebees
when it expired at the endof December 2014, growers of
tomatoes and certainother greenhouse crops have looked
for ways tomaintainpollination levels for an industry
under increasing financial pressure.With a recently
completedproject on the issuedue topublish its final
report this year, RichardCrowhurst looks at some of the
issues surrounding thepollinationof greenhouse crops.
Withbumblebees beingwidespread for greenhouse
pollination since 1992, the loss of certain sub-species has
come as ablow to tomatogrowers inparticular. “Since
thebeginningof 2013 the importationof non-native
bumblebee species into theUK has been restrictedby
Natural England,” explains Jasper Hubert, Technical
Consultant withKoppert Biological Systems. “Thismeant
that the suppliers of bumblebees had to switch their
UKproduct to the naturally occurringUK sub-species
Bombus terrestris audax, from theEuropeanmainland
speciesBombus terrestris terrestris. This change allowed
growers tousebumblebees on their outdoor crops, but
alsomeant that greenhouse growers had to stopusing a
bumblebee species that they hadgrown accustomed to
overmany years.”
The reasons for Natural England’s decisionwerebased
around threemainperceived risks: that non-native
bumblebees could escape fromgreenhouses and
polytunnels andbecome established in theUK; that
escapednon-native species couldhybridisewith the
nativeBombus terrestris audax, resulting in the loss of
a specieswhich is unique toBritain and Ireland; and
that importedbumblebees could introducediseases,
pathogens andparasiteswhich could infect other native
wildpollinators andbee species. However, entomologists
point out that there couldwell be regular flights of non-
audax bees from northernFrance to southernEngland,
but that there is no evidence of hybridisation.
According toAHDBHorticulture, commercial trials
in the 1980s resulted in the commercial selectionof
two non-native sub-species; B. terrestris terrestris
andB. terrestris dalmatinus, while the nativeBritish
sub-species, B. terrestris audaxwas dismisseddue to
inferior performance. Subsequently the twoEuropean
sub-species becamewell used ingreenhouse tomato
productionwithAHDB adding that, ‘In the 27 years since
the first release of non-nativebumblebees inUK tomato
crops, there has been no evidence of their establishment
outside glasshouses or any detrimental effect on natural
bumblebeepopulations.’
However, Jasper stresses that this does notmean that
growers are now stuckwith an inferior bee. “It is important
to keep inmind that bumblebees by nature are not warm
weather pollinators, but are specialised in adapting to
cooler conditions. The temperature thresholds of audax
andmainland terrestris are very close to eachother. Often
there are stepswhich the grower couldundertake tomake
the environment in the greenhouse nicer for thebees, like
providing adequate shading, lowering the hives toground
level where it is cooler, insteadof having themhigh up in
the greenhouse.”
Since 2015 some growers have reportedpoor pollination
results from using audax compared toother species, with
some resorting to handpollination to achieve satisfactory
results.While admitting that it is difficult togeneralise,
AHDBHorticulture estimates that poor fruit set could cost
POLLINATIONOPTIONS LIMITED
FORGREENHOUSEGROWERS
Bumblebee on tomato flower. [Biobest].
