Researchers in Malaysian Borneo studying tropical forests have discovered that predatory wasps are increasingly occupying the hollow stems of Macaranga pearsonii plants, a disruption tied to human-altered environments like oil palm plantations, according to a study published in PeerJ.
Disrupting a Ten-Million-Year Partnership
For at least 10 million years, Macaranga pearsonii trees have maintained a close partnership with ants. The plants produce hollow chambers to shelter the insects and supply them with nutritious food bodies. In return, the ants aggressively defend their host plants against leaf-eating insects such as caterpillars.
That ancient mutualism is being disrupted. An international team of scientists from Queen Mary University of London, the Royal Botanic Gardens, Kew, and the Biology Center of the Czech Academy of Sciences found that predatory wasps are increasingly occupying those exact hollow stems.
Nurseries Built for Wasp Larvae
Scientists examined young Macaranga pearsonii trees growing across two distinct habitat types: logged forests and oil palm plantations. When the team dissected the plant stems, they uncovered an unexpected use of the specialized structures.
Mr. Lestina, the lead author of the study, described the findings:
While surveying these ant-plants, I noticed that many stems had been hollowed out in an unusual way. When we opened them, they were full of flies being eaten alive by wasp larvae. Adult wasps hunt and paralyze the flies, then store them inside the plant’s cavities as food for their young. Mr. Lestina
Instead of functioning as homes for protective ant colonies, some of the chambers inside the plants had effectively become nurseries stocked with prey for developing wasp larvae.
How Landscapes Altered by Humans Favor Wasps
The field work revealed a strong connection linking wasp occupation to habitat disturbance. Plants growing within oil palm plantations were much more likely to contain wasps than those located in logged forests.
Trees occupied by wasps consistently supported much smaller ant colonies. While these observations raise the possibility that the predatory wasps are displacing the ants completely, researchers emphasize that experiments will be required to confirm whether that is actually happening.
Dr. Kalsum M. Yusah, a co-author on the study, contextualized the findings:
Human activities are transforming habitats worldwide, and this kind of shift in species interactions is exactly what we expect to see. We don’t yet know whether this wasp is native or introduced, but its spread is clearly linked to disturbed landscapes. Kalsum M. Yusah
Consequences for Tropical Forest Regeneration
The ecological ramifications extend beyond the immediate interaction between ants, wasps, and individual plants. Macaranga plants frequently take root first in zones that have suffered destruction or clearing.
If the loss of their ant defenders makes these plants less healthy, the broader process of forest regeneration could potentially be influenced. Dr. Yusah cautioned that ecosystem recovery after a disturbance might be slowed if the vegetation loses its ant protectors and experiences a decline in vitality.
Senior author Dr. Fayle from Queen Mary University of London pointed out that the breakdown of these mutualistic benefits can drive long-term evolutionary change. If plant structures become less valuable because wasps exploit them, the plants may stop investing in them.
These subtle alterations serve as an initial signal that natural networks can undergo quiet transformations long before any organisms vanish completely. Inside the hollow stems of tropical plants, the first sign is unfolding as a partnership that has lasted millions of years may be starting to come apart.
