While bumblebees buzz purposefully from flower to flower, thousands of unseen inhabitants thrive alongside them, hidden within the nest material.
Bumblebees, particularly Bombus terrestris, have become indispensable partners in modern agriculture. These efficient pollinators are reared commercially and deployed to greenhouses worldwide to ensure the production of tomatoes, peppers, and other crops. However, a hidden ecosystem operates within the commercial nests we place in these controlled environments. Mites, tiny arachnids, often inhabit these nests, raising questions about their identity, origin, and impact. Recent scientific investigations have peeled back the layers of this miniature world, revealing a story of local infestation rather than foreign invasion, with significant implications for the health of our pollinators and the ecosystems they support.
The use of commercially reared bumblebees is a cornerstone of contemporary agriculture. For over two decades, the global business of bumblebee rearing has provided farmers with a powerful tool for pollination 1 . These insects are remarkably effective, especially for crops like tomatoes that require "buzz pollination"—a technique where bumblebees vibrate their flight muscles to dislodge pollen that is otherwise tightly held by the flower 6 .
Bumblebees perform "buzz pollination" by vibrating their flight muscles at a specific frequency to release pollen from flowers.
The rearing process itself, however, creates unique conditions. Colonies are maintained at high densities in facilities where they are supplied with ample sugar solution and pollen 1 . This creates an ideal environment not just for bees, but for other organisms that can exploit these rich resources. When these colonies are transported across national borders, there is a potential risk of introducing non-native mite species into new regions, much like the way the endoparasitic mite Locustacarus buchneri was spread from Europe to Japan via commercial bees 1 . This concern prompted scientists to investigate exactly which mites are living in these commercial nests and where they come from.
Nests of social insects like bumblebees are rarely sterile environments; they are typically inhabited by a variety of mite species. These mites can have different lifestyles:
Feed on pollen, nest materials, or fungi.
Prey on other small arthropods in the nest.
Feed directly on the host bumblebee.
In natural settings, these mite communities are part of a balanced ecosystem. However, the stable, warm, and food-rich environment of a commercial bumblebee nest can allow certain mite populations to flourish in unexpected ways. The high density of nests in greenhouses also facilitates easier transfer of mites between colonies, potentially leading to population booms 1 .
To determine whether commercial bumblebee nests were introducing foreign mite species into Poland, a team of researchers conducted a meticulous study on 37 commercial nests from two suppliers (Dutch and Israeli) after their use in greenhouses in southern Poland 1 4 . A further 20 colonies obtained directly from suppliers were also examined to see if infestation originated from the rearing facilities.
The research methodology was designed to thoroughly extract and identify every mite present:
Nests were gathered after 8-18 weeks of use in greenhouses for pollinating tomato crops 1 .
The nests were dismantled and placed on Tullgren funnels. This apparatus uses heat and light to gently drive mites out of the nest material and into a collection vessel over a period of two weeks 1 .
Collected mites were preserved in alcohol, mounted on microscope slides, and identified to species level using taxonomic keys. The most abundant species, Tyrophagus putrescentiae, was counted using a grid-based method for accuracy 1 .
The findings were surprising. No foreign mite species were discovered in any of the commercial nests. Instead, the researchers found seven mite species, all of which are common and native to Europe 1 4 .
| Mite Species | Family | Abundance | Notes |
|---|---|---|---|
| Tyrophagus putrescentiae | Acaridae | Very High (Predominant) | A stored product mite that feeds on fungi and organic matter 1 . |
| Hypoaspis marginepilosa | Laelapidae | Low | |
| Hypoaspis hyatti | Laelapidae | Low | |
| Hypoaspis bombicolens | Laelapidae | Low | |
| Parasitellus fucorum | Parasitidae | Very Low | |
| Parasitellus crinitus | Parasitidae | Very Low | |
| Parasitellus ignotus | Parasitidae | Very Low |
Most notably, mites were not detected in any of the 20 nests obtained directly from the suppliers 1 . This crucial piece of evidence pointed to a clear conclusion: the commercial nests were not bringing mites with them from the rearing facilities. Instead, they were being invaded by local mite species after being placed in the greenhouses 1 . The nests, filled with pollen, wax, and other organic resources, simply presented an attractive new habitat for mites already present in the local environment.
| Reagent/Material | Function in Research |
|---|---|
| Tullgren Funnel | An extraction apparatus that uses heat and light to drive mites and other micro-arthropods out of substrate samples for collection 1 . |
| Hoyer's Medium | A mounting medium used to fix mites on microscope slides. It clears the mite's body, making internal structures visible for identification under a microscope 1 . |
| 75% Ethanol | A standard preservative solution used to store collected mite specimens before they are mounted on slides for long-term study 1 . |
| Microscope Slides & Coverslips | Essential for mounting mite specimens for detailed examination under a compound microscope 1 . |
| Taxonomic Keys | Specialized reference guides that allow scientists to identify mite species based on physical characteristics like body shape, setae (hairs), and other morphological features 1 . |
The discovery that mite infestations are local has significant positive implications. It suggests that the international trade of commercial bumblebees may not be a primary vector for spreading novel mite pests, allaying one major concern for biosecurity 1 . However, the study also highlights other, more subtle risks associated with moving bee colonies.
Even if mites aren't being spread, other pathogens can be. Furthermore, the introgression of genes from commercial greenhouse bumblebees into wild populations has been documented in Poland, showing that greenhouse bees do escape and interbreed with local populations, potentially altering the genetic makeup of wild bees 6 . This, combined with the potential for disease spillover, means that the placement of commercial bumblebee colonies must be managed with care to protect endemic pollinator communities 6 .
The hidden world within a commercial bumblebee nest is a microcosm of a larger ecological story. The research in Polish greenhouses demonstrates that the most numerous mite inhabitants, like Tyrophagus putrescentiae, are not foreign invaders but local opportunists, moving into a comfortable new home rich in resources 1 . This finding shifts the focus from global biosecurity to local nest management. Understanding these dynamics is more than academic; it is crucial for ensuring the health of the pollinators our food systems rely on. As we continue to harness the power of bumblebees for agriculture, it is our responsibility to monitor these tiny roommates and the complex relationships they represent, ensuring that our agricultural practices remain in harmony with the broader environment.