Of Bees and Flowers

After all, bees and flies aren’t as dumb  as we thought, nor  flowers  naive.  Did you know that the flower petal is like a touch screen?  Only,  we don’t know how to decode the responses.  But bees and flies are much smarter and they know  how to  carry out   small talk with  flowers.   In brief  such  electrical interactions facilitate communication between   flowers and their  pollinators.

As early as 1900’s Jagadish Chandra Bose had detected the electrical activity in plants.   Compilation of  his findings could be found in his  book RESPONSE IN THE LIVING  AND NON-LIVING written in 1902 ( currently available on line , thanks to gutenberg projectt ). Plant electrophysiology  has since then developed into a very interesting and active area of research.  April 8^th issue of Science  carries a paper by Clarke  et al   which   describes how bumble bees can detect,  read and respond to  floral electric fields.  In combination with color,  texture, scent and  nectar,   the electrical impulses are powerful  signals which  greatly influence the bee behavior.

Normally bees carry a slight positive charge and the flower petals complement with a mild negative charge.  With very sensitive and specialized  instruments Clarke and his team  measured the  charge  carried by the bees. Of the 51 bees   94% of bees were positively charged as expected but  6% proved to be rebels, they carried a  negative charge.( I am certain, experiments are on way to understand more about this rebel group).  An equally delicate set up  was used to  monitor the electrical signature of the flowers. For field trials  the  conformists were let out into a  field of petunias. Averaged over  about 50 bee touch downs,   the team  registered a maximum  value of 25mV  which lasted for roughly 100 seconds in a flower.  In addition the team was amazed at the quickness of the petal   response which occurred within seconds. Perhaps  an instant  signal  to  other visitors that they are not welcome?.

The researchers tried to tempt and confuse  the bees with artificial flowers, which had  steel stems and plastic petals.  Two sets were considered.  One set carried the minimal biologically relevant  electric field  and also sucrose solution as substitute for nectar.   The other set was dummy, no electrical signal and the  sugar solution was replaced with bitter quinine solution.  Naturally bees flocked to the  charged  plastic  flowers. But when both sets were grounded  bereft of a " come, hither" signal the bees strayed away .

Well that is not the end of the story. While reading this paper I was reminded of  another one  which had appeared a month ago on how clever and crafty  the  dainty flowers could be. Wright leading a team  comprising of members from both sides of Atlantic  was intrigued by the presence of  minute amounts of caffeine  in the nectar of  citrus  and  coffee  flowers.  Copious secretion of such bitter alkaloids  is an evolutionary trick perfected by plants to ward of herbivores. But  why traces of it  in the nectar? Within the citrus family Wright and team focused on   grapefruit, pomelo,  and orange blossoms and  among the coffee family  Arabica, liberica and canephora.   They began with the assumption that by providing nectar laced with caffeine, the flowers might be enticing  the bees to return to them, in  other words ensuring  their fidelity. Seems like stretching  a bit too much, isn’t it ?  Well not at all.  Their  carefully controlled experiments  proved  precisely  the same  assumption. I suggest you read the whole paper to fully appreciate  the very logical and time consuming experiments.  

Tailpiece

Did you know  fruit flies  immunize their off springs  at larval stage against possible parasites?.  When mother flies suspect  such a  possibility, they lay their eggs in an alcohol enriched medium. Prof  Prof Schlenke is a pioneer in this field 

1. Detection and Learning of Floral Electric Fields by Bumblebees  D. Clarke   et al Science 5 April 2013: Vol. 340 no. 6128 pp. 66-69 

2.Caffeine in Floral Nectar Enhances a Pollinator's Memory of Reward:                                        G. A. Wright et al Science 8 March 2013: Vol. 339 no. 6124 pp. 1202-1204

3. Fruit flies medicate offspring after seeing parasites                                                                  

Kacsoh etal Science  22 February 2013 Vol.339,  6122, pp 947-950