Home » Entomology/Ecology/Evolution » Living on the edge with Wolbachia

Living on the edge with Wolbachia

The welfare of our planet and of the human species has become a major focus of many nations. One of the greatest challenges we face is food security. We are running out of space for growing food but we continue to grow in population. Farmers face the mighty challenge of growing more and losing less, when all the while climate change is expected to create new pest and disease threats, decrease crop yields and exacerbate water shortages. Our concern for the environment and sustainability has tightened pesticide regulations and fostered research into alternative methods. Consequently, biological controls, touted as an environmentally safe way to regulate pest populations, are becoming ever more popular. But how safe are these biological controls?

Enter Wolbachia. These symbiotic bacteria inhabit the intracellular space of arthropods and nematodes. They are estimated to have invaded over a million insect species alone by wreaking havoc on their hosts’ reproductive system. These parasitic bacteria are thought to be a major tool driving speciation, providing us with the great diversity of insect life we enjoy today, but they also wield the magic key to help us save millions of people from famine and from pestilence. A Wolbachia strain from D. melanogaster, wMelPop, is life-shortening to its host and can be used to control the major vector of dengue fever, a species of mosquito called Aedes aegypti. On top of shortening its life, it causes the mosquito to consume fewer and smaller bloodmeals as it ages, lowering the risk of disease transmission. This same principle can be applied to insect vectors of crop disease. Then there are some Wolbachia strains that induce cytoplasmic incompatibility on their hosts. Infected males produce sperm that only create viable offspring with eggs infected with the same Wolbachia strain. Such Wolbachia strains can be exploited as an alternative to sterile insect technique; pest populations would be swamped with Wolbachia infected males and no offspring would result from their mating.

However, Wolbachia walk the fine line of symbiosis, where parasitism and mutualism are but faces of the same coin. Despite hijacking the reproductive system of their hosts, mutualistic associations come to light day by day. For example, Wolbachia are known to confer resistance to viruses on their hosts. And amazingly, the artificial Wolbachia infection in Drosophila simulans began with a fecundity deficit but evolved a fecundity advantage after only twenty years! What would the consequences be if Aedes aegypti and its Wolbachia biological control evolved a mutualism?

An alternative method of pest control is to disrupt the mutualisms that already exist between pest and Wolbachia. The disruption of Wolbachia mutualisms in elephantiasis and river blindness gives scope for this technique in crop protection. These human diseases are major causes of global morbidity and the culprits are filarial nematodes, which depend on Wolbachia for biosynthetic pathways that only exist in the bacteria’s genome. Common antibiotics, such as doxycycline, have the potential to eradicate filariasis within just eight weeks. As our understanding of these enigmatic bacteria continues to grow, disruption of other mutualisms in the light of crop protection are sure to come to light.

Yes, research into Wolbachia is yielding exciting and promising results but before we go and save the world there is something we must remember. Millions of insect species benefit from Wolbachia and are experiencing speciation by their action, the consequences of interfering with these processes are hard to fathom. At worst, the large scale use of artificial Wolbachia or antibiotics against Wolbachia has the potential to harm ecosystems by infecting non-target organisms with a novel Wolbachia strain or by damaging mutualisms in non-target organisms, which may ironically lead to lower biodiversity and negatively affect the functioning of  our ecosystems.

A few decades ago, the world was gripped with the fear of war and conquest. Now we live in an age of pestilence and famine. Wolbachia is but a single candidate of many offering vast benefits to mankind with caveats for the environment. At a time like this, I wish I could turn to mother earth and ask: “do our own lives matter more than the lives of our brother and sister species?” It’s a tough question and can only be answered if investment in research continues and if the public and the scientific community engage ever more in this turbulent century. 

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