26
THECOMMERCIAL GREENHOUSEGROWER • APRIL 2018
• POLLINATION
theBritish tomato industry asmuch as £8.1million a year.
“Natural England is able to issue emergency licences
for the release of non-native species inglasshouses and
polytunnelswhen audax is not available,” saysNeilWard,
IPM&PollinationSpecialist at Biobest Group. “However,
under normal circumstances, growers are only permitted
touse the native species.”
“Glasshouse tomatoes require efficient and effective
pollination especially as themajority of crops are now
soldon the truss requiring a full truss of pollinated flowers
producing uniform fruit and truss form,” explainsDr
PhilipMorley, Technical Officer at the TomatoGrowers’
Association (TGA). “Goodpollination also has apositive
effect on fruit shape aswell, so there are two aesthetic
requirementswhichpollination enhances. Generally the
more flowers any cultivar has, themorebees are required
to carry out pollination in crops (this is especially true
of cherry tomato typeswhich tend to have lotsmore
flowers). Bee suppliers are responsible for ensuring
efficient pollination andwill adjust the number of hives in a
glasshouse tomeet plant requirements.”
Inorder to achieve this, good communication is required
betweengrowers and their bee supplier, asCaroline
Reid, UKCommercial Manager for BiolineAgroSciences
explains: “Growers, particularly tomatogrowers, report
that nativebees are less effective than non-native ones,
particularly at high temperatures, so some loss of yield
has been experienced. We haven’t had any cases
of lack of supply toour growers as our production is
scheduled, but if extrademandwas required there could
be caseswhere not enoughof the specific species are
available. BeelineAudax (Bombus terrestris audax) is
the only species of bee that BiolineAgroSciences sell for
pollination in theUK.”
One advantage of the restrictions onbee species
has been that the ‘queen excluder’ whichwas a legal
requirement in non-native hives, does not have tobe used
with audax, resulting in an increased longevity of colonies.
“Thequeen excluder is an artificial narrowingof the hive
entrance to allowworker bees to freelymove in andout
of a hive, while locking thebigger sizedQueens inside the
hive,” explains Jasper. “However, this often resulted in the
Queens blocking the entrance to the hive, slowingdown
the traffic somuch that the colony deteriorated following
the emergence of the first Queens.”
Bees are crucial tohelpovercome the environmental
restrictions onpollination createdby protectedgrowing.
“Althoughmany plants can self-pollinate,most plants rely
on the transport of pollen fromone flower to the next,
either bymeans of windpollinationor through the use
of insects,” points out Jasper. “Since greenhouses are
protected fromwind, evenplantswhich are naturallywind
pollinatedwill have to rely on either labour-intensive hand
pollinationor the use of bumblebees. All flowers have a
pollinationwindowduringwhichpollinationneeds tobe
achieved to turn the flower into fruit. Thiswindow canbe
so short that the flower only opens for a fewhours in the
earlymorning (courgettes) or canbe relatively forgiving,
givingpollinators about aweek’s time to visit the flower
(strawberries). In all cases it is desirable topollinate the
flowers as soon as possible, as the fruit quality can suffer
in latepollinated flowers.”
Despite their smaller colony size,meaning fewer workers
are available, bumblebees haveprovedbetter for thiswork
thanhoney bees for a number of reasons, particularly their
tame temperament and their relative robustness,making
it easier to copewith larger temperature ranges and crop
protection regimes. “Very fewpeoplewill use honeybees
in a greenhouse,” he continues. “Outdoors or inopen
tunnels honeybees, bumblebees (Bombus terrestris
audax) andmasonbees (Osmia spp.) may all be used,
with the lattermost in apples and cherries.”
There are alsobotanical reasons for favouring
bumblebees Jasper explains: “Very open flowers, like
peppers or strawberries present their flowers tomost
insects likebumblebees, honeybees or even hoverflies.
Other flower shapesmake itmoredifficult or even
impossible for generalist pollinators to access thepollen
andnectar inside the flowers. Flowerswhich aremore
bell-shaped, like tomatoes or blueberries, arebetter
pollinatedby bumblebees. This is due to the uniqueway
inwhichbumblebees pollinate flowers, aprocess called
buzz pollination. Bumblebeeswill attach themselves to
the flowers andwill vibrate the flowers using their wing
muscles. The vibrationswill dislodge thepollen from the
Correct hiveplacement in the crop is important.
[BiolineAgroSciences].
