Flight of the bum­ble­bee

Other bees may en­joy a sweeter rep­u­ta­tion, but there are many rea­sons why the hum­ble bum­ble­bee is the true rock star of the in­sect pol­li­na­tor world.

NZ Gardener - - CONTENTS - STORY: MICHELLE COURSEY

The su­per-pol­li­na­tor in your gar­den

if ever there was a mis­nomer, it is the poorly un­der­stood bum­ble­bee. This su­per-ef­fi­cient pol­li­na­tor has some­how be­come synony­mous with any­thing in­ept, clumsy and in­ef­fec­tive. Yet, the bum­ble­bee is any­thing but. With 50 times the pol­li­nat­ing power of hon­ey­bees, the hum­ble Bom­bus is, in fact, a cru­cial link in the pollen chain and is fast be­com­ing es­sen­tial to some of our most lu­cra­tive hor­ti­cul­tural pro­duc­ers.

The story of bum­ble­bees in New Zealand started some 130 years ago, when they were in­tro­duced from Eng­land specif­i­cally to pol­li­nate red clover ( Tri­folium pratense), a pop­u­lar pasture choice for new farms. Four species were im­ported: Bom­bus

ter­restris, now the most com­mon species in the coun­try; Bom­bus rud­er­a­tus, liv­ing in most re­gions ex­cept Ste­wart Is­land; Bom­bus hor­to­rum, found ev­ery­where ex­cept north of Hamil­ton and West­land; and Bom­bus sub­ter­ra­neus, our rarest bum­ble­bee, found only in in­land Can­ter­bury and cen­tral Otago.

Each species has dis­tinct vari­a­tions of black, yel­low and or­ange mark­ings.

Bom­bus ter­restris, com­monly called the large earth bum­ble­bee, boasts a black waist with a broad yel­low-or­ange band across its ab­domen. Bom­bus rud­er­a­tus can range from al­most com­pletely black, to black with broad yel­low waist colour­ing. Bom­bus hor­to­rum has a yel­low waist. Bom­bus sub­ter­ra­neus, also known as the short-haired bum­ble­bee, has black hairs on the front yel­low band.

Two fea­tures they all have in com­mon are a long tongue (pro­boscis) to plunge into the throats of ver­ti­cal flow­ers such as fox­gloves or del­phini­ums, and the abil­ity to buzz so vig­or­ously they dis­lodge up to 50 times the amount of pollen that a hon­ey­bee can man­age.

They’ve long been un­der­es­ti­mated by the pub­lic, says New Zealand Bum­ble­bee Con­ser­va­tion Trust’s (NZBCT) Ge­off Bruns­den, “be­cause when ob­served they seem to just be go­ing about their busi­ness qui­etly. But that busi­ness is very pow­er­ful, be­cause one bum­ble­bee will do the work of 50 hon­ey­bees.”

Not only that, bum­ble­bees can work in con­di­tions hon­ey­bees can’t. Bum­ble­bees can work at tem­per­a­tures just above freez­ing, in the rain and fog, from first light un­til dark. They can fly in cov­ered ar­eas such as glasshouses or within shrouded crops and they can pol­li­nate up to 450 flow­ers per hour in such a space. “Their mis­sion is to just get out there and work as many flow­ers as pos­si­ble in the day­light hours,” says Ge­off.

In fact, the hard­work­ing in­sects are only ever 40 min­utes from star­va­tion due to the speed at which they travel (up to 54 kilo­me­tres an hour), and the strength re­quired to carry their own weight plus up to 90 per cent of their body weight in food.

Along with their long tongues, the in­sects use “buzz pol­li­na­tion” or son­i­ca­tion, mean­ing they vi­brate their bod­ies to cause pollen to be re­leased, some­times in a vis­i­ble cloud. In this way, they gather more pollen than many other in­sects and cre­ate ex­tremely ef­fec­tive cross-pol­li­na­tion as they move on to the next tar­get while lit­er­ally cov­ered in pollen.

And if all else fails, these lit­tle power puffs have yet another clever tac­tic. For par­tic­u­larly deep-throated flow­ers such as broad­beans, they sim­ply use their long pro­boscis to nip a hole in the base and go straight to the source of oth­er­wise in­ac­ces­si­ble nec­tar.

Yet for all the skills of the bum­ble­bee, it is hon­ey­bees – with their hive num­bers in the tens of thou­sands com­pared to the bum­ble­bee’s more mod­est pop­u­la­tion of 400 per nest at the most – that are the rock stars of the pol­li­nat­ing in­sect world. This is prob­a­bly be­cause “hon­ey­bees con­trib­ute in an un­der­stood way to the eco­nomic well­be­ing of peo­ple, whereas the bum­ble­bee is just out there do­ing its job, and is not vis­i­bly bring­ing us a re­source,” says Ge­off.

Iron­i­cally, bum­ble­bees work hard on many re­sources that we would no­tice the ab­sence of, in­clud­ing the farm­land plants they were first brought to the coun­try to work on. “Bum­ble­bees are es­sen­tial to pol­li­nate the in­tro­duced pasture plants that we rely on. Our an­i­mals graze on them, they ni­trify the soils for grass to grow in, and so forth,” ex­plains en­to­mol­o­gist Dr Barry Dono­van, who has stud­ied them for over 40 years.

Hard­work­ing bum­ble­bees are only ever 40 min­utes from star­va­tion, due to the speed and strength re­quired of them.

In terms of the fruit and veg­eta­bles, bum­ble­bees are vi­tal to the New Zealand to­mato in­dus­try which has a farm gate value of $100 mil­lion a year, and the Bom­bus ter­restris is bred com­mer­cially by sev­eral com­pa­nies to be used in the in­door pro­duc­tion of to­ma­toes.

Like­wise, pro­duc­ers of in­door crops such as cap­sicum, egg­plant, blue­berry and cour­gette also fre­quently look to bum­ble­bees to en­hance their yield.

An emerg­ing mar­ket is that of ki­wifruit grow­ers, who are in­creas­ingly look­ing to the bum­ble­bee as an al­ter­na­tive to hon­ey­bees, which dis­like work­ing in the shrouded or­chards and are steadily be­com­ing more ex­pen­sive. It’s also be­lieved that bum­ble­bees work the flower of the ki­wifruit much more ef­fi­ciently – nearly dou­ble the con­tact on the flow­ers’ stigma than the hon­ey­bee.

Waiuku-based bum­ble­bee pro­ducer Zonda Ben­e­fi­cials has seen “huge growth” in out­door cov­ered crops such as ki­wifruit and pas­sion­fruit which have tra­di­tion­ally re­lied on hon­ey­bees, ac­cord­ing to sales and ad­min­is­tra­tion spokesper­son Tracy Calder. “The var­roa mite has caused is­sues [with hon­ey­bee us­age], and the cost at­trib­uted to get­ting hon­ey­bee hives is get­ting quite high be­cause a lot are be­ing used pre­dom­i­nantly for manuka honey pro­duc­tion.”

Tracy says over the past four and a half years at Zonda, de­mand for bum­ble­bee hives has out­stripped sup­ply. “Be­fore, it was more the in­door to­mato grow­ers, but over the last few years it’s also been ki­wifruit, av­o­ca­dos and straw­ber­ries.”

Bum­ble­bees re­quire very lit­tle in order to flour­ish. The queen can form her nest in an old ro­dent hole or other dry space un­der­ground which can be repli­cated with a rel­a­tively sim­ple box con­struc­tion con­tain­ing nest­ing ma­te­ri­als such as in­su­la­tion pad­ding or un­der­felt.

De­spite the de­mand and grow­ing aware­ness of the in­sect, though, one species of bum­ble­bee is pos­si­bly on the verge of ex­tinc­tion. The last of its kind in the world, its plight is se­ri­ous. Ex­act num­bers of Bom­bus

sub­ter­ra­neus are un­known, but

One species of bum­ble­bee is pos­si­bly on the verge of ex­tinc­tion. The last of its kind in the world, its plight is se­ri­ous.

en­to­mol­o­gist Barry – who stud­ies the dwin­dling species – says the sit­u­a­tion “is sound­ing rather omi­nous”. The species was abun­dant in the 1960s, with one per­son catch­ing 80 queens in one day, but searches in the last two years have found just two in­sects. “The mea­gre ev­i­dence we have very strongly sug­gests that num­bers have been de­creas­ing rapidly,” adds Barry, who is try­ing to catch the bum­ble­bees and es­tab­lish man-made colonies in Christchurch in order to study and con­serve their num­bers.

Their dis­ap­pear­ance here echoes their story in Eng­land over the 1970s and 1980s, leav­ing the New Zealand pop­u­la­tion as the only one left in the world. “Ex­tinc­tion here is pos­si­ble. They went ex­tinct in Eng­land af­ter liv­ing there since the last Ice Age. They went ex­tinct there in just a cou­ple of decades, so there is no rea­son why the same couldn’t hap­pen here. Then that raises the gi­gan­tic ques­tion of why.”

English re­searchers be­lieve the loss of nat­u­ral habi­tats and a re­duced range of wild­flow­ers – a key food source – due to in­ten­sive agri­cul­ture were the main fac­tors. Barry says he is also con­cerned that in New Zealand, a dev­as­tat­ing dis­ease may have been in­tro­duced to the pop­u­la­tion, but no one knows for sure.

On a big­ger scale, Barry says the loss of the Bom­bus sub­ter­ra­neus sig­nals the con­tin­ued “degra­da­tion of the biota of the en­tire world”.

“We live in a gi­gan­tic eco­log­i­cal web, with ev­ery­thing in­ter­act­ing, sup­port­ing and com­pet­ing at the same time, but the more the fab­ric of that web breaks down, the more in­sta­bil­ity there is of the en­tire web. So the ex­tinc­tion of any­thing un­der­mines our own se­cu­rity.”

The NZBCT was co-founded by Ge­off Bruns­den and He­len John­son last year to raise aware­ness of the bum­ble­bee’s role in that web, and in do­ing so, en­sure that bum­ble­bees and other pol­li­na­tor in­sects re­main plen­ti­ful in New Zealand. A pas­sion­ate en­vi­ron­men­tal­ist, He­len says the trust is about us­ing “the power of the bum­ble­bee” to ed­u­cate peo­ple about the im­por­tance of pol­li­na­tion. “Many peo­ple don’t grow their own fruit and veg­eta­bles now, and so they don’t re­alise how im­por­tant in­sects such as bum­ble­bees are.”

The trust founders, along with Barry, hope home gar­den­ers around New Zealand will look af­ter bum­ble­bees, es­pe­cially those in the South Is­land who may be able to help con­serve the at-risk short-haired bum­ble­bee. Barry rec­om­mends plant­ing wild­flow­ers in­clud­ing red clover, viper’s bu­gloss and Rus­sell lupin (which is con­sid­ered weedy in ar­eas with braided river sys­tems), as well as the Weigela florida shrub, Si­lene

dioica and Robinia pseu­doa­ca­cia. For the other species of bum­ble­bee, which are not cur­rently un­der threat, wild­flow­ers are also favoured, along with laven­der, bor­age, cat mint, fox­glove, gera­ni­ums, and herbs.

Gar­den­ers can also pur­chase nest boxes or fully func­tion­ing colonies of bum­ble­bees if they wish to in­crease the num­ber of these su­per pol­li­na­tors in their own gar­dens to aid cross pol­li­na­tion, or sim­ply to help sup­port num­bers in the wild.

Bum­ble­bees can also be counted as part of NZ Gar­dener’s Great Kiwi Bee Count this month to help mon­i­tor the health of the pop­u­la­tion in re­gions around the coun­try.

Fi­nally, if a stranded or sleepy bum­ble­bee is found in the gar­den, a small con­tainer or lid of equal parts sugar and warm wa­ter, along with a help­ing hand to some nearby flow­ers, may just help it form a thriv­ing colony. Such a small ges­ture for these giants of the pol­li­na­tion world seems only right in ap­pre­ci­a­tion of the hard­work­ing flight of the hum­ble bum­ble­bee.

Bom­bus rud­er­a­tus. Bom­bus sub­ter­ra­neus.

Bom­bus hor­to­rum.

Bom­bus ter­restris.

Fox­glove.

Gera­nium.

Robinia pseu­doa­ca­cia.

Red clover.

Si­lene dioica.

Weigela florida.

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