Monocultures and honey bee health

Pollination is one of the most important ecosystem services for human kind. The worldwide demand of crops led to the presence of human maintained, artificial environments of huge areas consisting of single plant species. Several of these monocultures depend on insect pollination (e.g. almond) and due to their numbers and easiness of moving around, domestic honey bees are used for such large-scale pollination services. In recent times across the globe, populations of pollinators -including honey bees- are declining which can have dramatic effects (“pollination crisis”).

There exist many different stress factors, ranging from pathogens to toxins like pesticides or antibiotics, that negatively impact honey bee health. Considering poor nutrition from mono diet being the underlying fundament in combination with a close contact between millions of bees from different colonies and origins, which promotes the spread of disease, monoculture pollination environments likely enhance negative impacts on the health of honey bee colonies.

The microbiome and honey bee health

The current recognition that all higher organisms are closely associated with a diverse microbial community altered our understanding of animal biology and gave rise to the term “holobiont” describing the host together with all associated microorganisms acting as a unit of natural selection. The microbiota can have profound effects on host health; both detrimental and beneficial. The host-microbiome field, although being one of the “hot topics” in biological and medical research, is still largely underexplored, we are just starting to fathom the huge role that the microbiota can have on host ecology and evolution. The microbiota can provide its host with flexibility beyond that encoded in host genomes, as rapid changes in microbial community composition or individual microbial genomes can directly affect important host life history traits. Therefore, the microbiota may enable rapid acclimation to new environments and resistance to environmental disturbances

The honey bee system is also an ideal model for studying fundamental, functional, structural, and evolutionary aspects of host-associated microbial communities. Because the microbiome is simple, all core symbionts are cultivable and the system is experimentally tractable. The internal microbiota of social bees gets transmitted from older to younger bees within a hive, which likely facilitates host symbiont coevolution and emergence of a distinctive intestinal community but also let us expect a quick adaptation of the microbiome on changing environmental conditions. In addition, the system offers the attractive possibility of raising symbiont-free honey bees in the lab for controlled inoculation assays for functional tests.

Recent experimental findings support the idea that the bee microbiota is strongly involved in host health and development. Therefore, rather than exclusively focusing on the direct effects that stress factors have on honey bees, it is highly interesting and relevant to study stress factor induced changes in the microbiome and their role on host health. Especially, such negative changes (dysbiosis) or adaptations can have more long-term effects on the health of a colony as the microbiome gets transmitted from generation to generation.

Our aim is to study the role and evolution of the honey bee microbiome under relevant, and for the pollinator, extreme field conditions in almond monoculture in Australia with following controlled experiments under laboratory conditions.

1. Studying pathogen spread and microbiome evolution in the field

In order to study changes in the honey bee microbiome in relation with pathogen load and symbiont adaptations, we want to use total RNA sequencing of individuals from different colonies before, within and after monoculture pollination. This will be the first attempt to systematically study the effect of monoculture on microbiome evolution with following monitoring of long-term effects for the colonies.

2. Using controlled laboratory experiments to study, verify and disentangle effects from different factors on honey bee health

Raising symbiont free larvae in the lab will make it possible to repeat the field experiment under a complete controlled set up, comparing mono diet vs poly diet. We will be able to pass the microbiome from one generation to the other and to study if the microbiome evolves to the mono diet treatment and which changes we can see on microbiome level. The last step will be functional tests to see if the performance of the microbiome adapted to the respective food source that has been used to feed the larvae before with following tests to study a potential increased susceptibility of the host towards other stress factors (e.g. pesticides, antibiotics, pathogens).