How Plants Influence Honeybee Caste System

Is has long been known that food fed to larval honeybees influences their development and therefore their place in the hive. Larvae fed a mixture of pollen and honey, often referred to as "bee bread," develop into sterile workers whereas larvae fed special secretions termed "royal jelly" from nurses within the colony will develop into queens. Despite this knowledge, the mechanisms underpinning such drastic developmental differences have remained a mystery... until now.

A team of researchers from Nanjing University in China have uncovered the secret to honeybee caste systems and it all comes down to the plants themselves. It all has to do with tiny molecules within plants called microRNA. In eukaryotic organsisms, microRNA plays a fundamental role in the regulation of gene expression. In plants, they have considerable effects on flower size and color. In doing so, they can make floral displays more attractive to busy honeybees.

Photo Credit: [1]

Photo Credit: [1]

As bees collect pollen and nectar, they pick up large quantities of these microRNA molecules. Back in the hive, these products are not distributed equally, which influences the amount of microRNA molecules that are fed to developing larvae. The team found that microRNA molecules are much more concentrated in bee bread than they are in royal jelly. Its this difference in concentrations that appears to be at the root of the caste system.

Larvae that were fed bee bread full of microRNA molecules developed smaller bodies and reduced, sterile ovaries. In other words, they developed into the worker class. Alternatively, larvae fed royal jelly, which has much lower concentrations of microRNA, developed along a more "normal" pathway, complete with functioning ovaries and a fuller body size; they developed into queens.

All of this hints at a deep co-evolutionary relationship. The fact that these microRNA molecules not only make plants more attractive to pollinators but also influence the caste system of these insects is quite remarkable. Additionally, this opens up new doors into understanding co-evolutionary dynamics. If horizontal transfer of regulatory molecules between two vastly different kingdoms of life can manifest in such important ecological relationships, there is no telling what more is awaiting discovery. 

Further Reading: [1]

 

The Termite-Eating Nepenthes

Plants and eusocial insects have some interesting ecological relationships with one another. A vast majority of these relationships are between a plant a members of the order Hymenoptera (ants, bees, and wasps), but what about those other eusocial insects, the termites?

Despite the social similarities they share with many ants, bees, and wasps, termites are actually distant relatives of the cockroaches. As many already know, termites also have a relationship with plants. Thanks to symbiotic bacteria residing in their gut, termites are able to make a living eating wood and building massive colonies, sometimes in undesirable locations like in the framework of your house. However, there is at least one species of plant out there that has evolved a different kind of relationship with termites.

Meet Nepenthes albomarginata. Native to Borneo, Malaysia, and Sumatra, this tropical carnivore seems to have a taste for termites. However, unlike flies or ants that are attracted to sweet nectar, termites have a different palate. Feeding on plant materials, termites don't necessarily seem like the kind of insect a plant would want to attract. N. albomarginata has seemingly found a way to attract tasty termites without becoming a meal itself.

As the specific epithet suggests, there is a white ring located around the margin of the pitchers' mouths. The ring is made up of a dense coat of hairs called trichomes. It was discovered that sometimes this white ring would disappear overnight. The pitchers without the white ring were also chock-full of partially digested termites. Just how the termites find these pitchers isn't quite certain. Researchers have not yet been able to isolate a scent compound.

Either way, the termites swarm the ring. While many termites make off with a free meal, plenty more of them slip and fall into the trap. It has been found that N. albomarginata obtains upwards of 50% of its nitrogen needs from termites in this way. What's more, all of this happens in a span of a single evening. Once the ring is picked clean, the pitchers are no longer attractive to the termites. They go their way and the plant has its meal. Because of the social structure of these peculiar insects, the loss of these individuals is never high enough to represent a serious selective pressure.

Further Reading: [1]