Team:Toulouse/project/context

iGEM Toulouse 2015

Context

Content

Bees and pollination

Bees excel in pollination and thus play an essential role in maintaining ecosystems. By gathering pollen, they allow the reproduction of 84% of the plants that grow in Europe. Bees are also responsible for the production of 35% of edible fruits and vegetables. Without bees, tomatoes, apples, vines and many more would be as good as gone (see Figure 1 for some examples). Among all bees, the domestic bee, Apis mellifera, which builds its swarm in hives provided by man, is directly responsible for the production of honey, wax and propolis. Very often, the swarms are selected for their honey production yield.

Figure 1: Examples of products dependent of bee pollination to reproduce

According to the French INRA (Institut National de la Recherche Agronomique), the bee extinction would represent an economical worldwide loss of 163 billion USD. This huge number reflects the bees’ importance in the global ecosystem.

Domestic bees

There are three types of bees living in a beehive: the worker bees, the queen bee and the male bees. In the colony, the work is divided in such a way that each caste is specialized in its activities. The worker bees are infertile female and represent the most numerous caste in the beehive. Their main activities are cleaning the beehive cells, ventilate the beehive, cap the beehive cells containing the bee eggs, feed the larvae, gather pollen and defend the colony.

The queen bee ensures the renewal of the bee colony. The male bees represent the infertilized eggs. Their main activity is the reproductive function with the queen bee outside of the beehive.

The Queen, a Worker and a male (coming soon)

Collapse of Bees

Over the last few decades, a decline in the honeybee population has been observed. In Europe 24% of the domestic bee species are threatened of extinction. The more indicators you consider, the more alarming appears the situation. The bee loss has a multifactorial origin. Among these factors, the Colony Collapse Disorder (CCD) is one of the most important. CCD corresponds to a massive loss of bee colonies. The causes of this syndrome are numerous: pesticides, viruses, parasites… among those, a mite wisely named Varroa destructor is one of the bee’s fiercest enemies.

Varroa destructor

Varroa destructor is an obligatory ectoparasite of bees. This means it is an external parasite and it cannot survive without its host, the bee. The varroa development cycle takes place in the beehive cells in parallel of the bee development cycle. The key individual of the varroa development cycle is the adult female commonly named “founder”. The founder reproduces exclusively in a brood cell that represents the beehive cell containing a bee larva. The founder reproduction occurs during the phoretic phase where the varroa is moved from one bee colony to the other by an adult bee.

Figure 2: Synchronized life cycle of Honeybees and Varroa destructor.

The mite varroa is originally an ectoparasite of Apis cerana, the Asian honey bee. The first contact between varroa and Apis mellifera occurred in the 1950s in Asia. During the following years, the infestation spread to Europe, Africa and America. The first signs of this infestation were observed in Europe and North America in the early 1980s. The varroa mite is a particularly virulent parasite of Apis mellifera since the European honeybee did not have time to develop an adaptive response to it. In Asia on the contrary, Apis cerana and Varroa destructor co-evolved over the centuries and reached a certain balance. Interestingly, the Asian honeybee is capable of detecting the parasite’s presence and of getting rid of it.

Figure 3: Effects exerted by Varroa destructor on honeybee and their consequences.

Outbreak of Varroa destructor in the Western World

The mite varroa is originally an ectoparasite of Apis cerana, the Asian honey bee. The first contact between varroa and Apis mellifera occurred in the 1950s in Asia. During the following years, the infestation spread to Europe, Africa and America. The first signs of this infestation were observed in Europe and North America in the early 1980s. The varroa mite is a particularly virulent parasite of Apis mellifera since the European honeybee did not have time to develop an adaptive response to it.

In Asia on the contrary, Apis cerana and Varroa destructor co-evolved over the centuries and reached a certain balance. Interestingly, the Asian honeybee is capable of detecting the parasite’s presence and of getting rid of it.

Means to fight Varroa destructor

There are three types of methods usually implemented to fight against varroas:

Search of tolerant or resistant bees through selection.
Use of “zoo-technic” or “bio-technic” means (Trapping of varroas in empty male broods or installation of fenced entries).

References

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