Carnivorous plants don't just seduce with their strange appearance: they actively manipulate the behavior of their prey. This is the case of Nepenthes khasiana, a rare species from northeast India, which traps ants with a sweet… poisonous nectar. A study carried out by researchers at the Jawaharlal Nehru Tropical Botanic Garden and Research Institute (JNTBGRI), in collaboration with Indian institutions such as the University of Kerala, reveals that this nectar contains a neurotoxin, isoshinanolone, capable of disrupting the nervous system of insects.
Published in May 2025 in the journal Plant Biology, this research calls into question the idea that this nectar would be used to feed visitors. On the contrary, it is a very elaborate chemical lure, designed to weaken prey and facilitate their capture. A plant strategy of formidable effectiveness, at the crossroads of ecology, biochemistry and evolution.
A nectar attractive in appearance, but designed to manipulate
At the house of Nepenthes khasianaan endemic species of the Khasi hills in India, the production of nectar is not intended to nourish, but to trap. Unlike traditional floral nectars, used to attract pollinators, the nectar of this plant is extrafloral, produced on the edge of its urns, called peristomes, as well as on their lids. It is distinguished by a sweet composition that is very attractive to insects, particularly ants, the plant's main prey.
This nectar contains three major sugars: glucose, fructose and sucrose. These compounds, in addition to attracting with their sweet taste, are hygroscopic. That is to say, they absorb ambient humidity. This increases the slipperiness of the peristome, making the surface unstable for insects. Nectar thus plays a dual role: a food signal to lure prey and a physical element favoring their fall.
But this strategy is not limited to texture. As the authors point out, nectar acts as a real chemical lure. It appears nutritious, but contains almost no free amino acids and very little protein. However, it is these elements that offer insects real nutritional value.
By acting on several levels – taste, chemical and physical – the plant diverts signals usually associated with a reward. This complex trap is based on coevolution between the plant and its prey. Nepenthes khasiana attracts without giving, uses without nourishing, by exploiting the innate behaviors of its visitors to lead them to their ruin.
A toxic molecule targeting the nervous system of insects
The key to the effectiveness of the trap Nepenthes khasiana
relies on the presence of a powerful chemical component in its nectar: isoshinanolone. This compound belongs to the naphthoquinone family, already known for their biological properties. Its main action consists of inhibiting a crucial enzyme of the nervous system: acetylcholinesterase (AChE).
This enzyme is involved in the degradation of acetylcholine, a neurotransmitter essential for the proper functioning of neuromuscular junctions. When the enzyme becomes blocked, acetylcholine builds up, leading to nerve overstimulation. A progressive paralysis follows. In the ants tested, researchers observed motor slowing, muscle weakness, increased grooming (stress behavior), spasms, and even death.
The team confirmed these effects via direct bioassays. Ants fed natural nectar or purified isoshinanolone showed the same symptoms. The analysis also made it possible to isolate another naphthoquinone, plumbagin. It is a volatile molecule also active against acetylcholinesterase, although less concentrated.
These results, unprecedented in the context of extrafloral nectars, reveal a functional and targeted use of a plant neurotoxicant. Unlike the defensive toxins found in certain plants to repel herbivores, here the objective is offensive. We weaken the prey to make it easier to capture.
The study therefore calls into question the vision of nectar as a simple tool of passive attraction. This is a neurobehavioral manipulation tool, oriented towards predation. This finding suggests that some carnivorous plants don't just trap. They actively disrupt the nervous systems of their targets to better consume them.
A multifactorial trap that goes beyond simple nectar
Nectar toxicity represents only one element in the complex strategy of capturing Nepenthes khasiana. The plant combines several structures and mechanisms, all optimized to guide prey towards the fall, then their digestion.
The peristome, the circular surface at the entrance to the urn, is moist, smooth and covered with wax, minimizing adhesion. When an insect tries to stay there to consume the nectar, physical instability adds to the disorientation caused by the neurotoxin. Further down, an intermediate waxy zone precedes the main cavity. This area acts like a corridor of no return.
The bottom of the urn contains an acidic viscoelastic liquid. Unlike simple digestive juices, this fluid has a texture that delays the escape of fallen prey. Acidity (pH generally less than 3.5) then allows effective tissue degradation. This process ensures the plant optimal absorption of the mineral elements released: nitrogen, phosphorus, potassium.
This system evolved to respond to a nutrient-poor environment. Nepenthes khasiana grows in acidic soils, poor in nitrogen. Each digested ant represents a precious resource. The plant therefore exploits all parameters – chemical, mechanical, environmental – to maximize its nutritional yield.
© Lathika, CC, et al., 2025
Prey capture strategies adopted by Nepenthes urns.
This multifactorial trap results from a fine integration between biochemistry and morphology. It highlights the evolutionary intelligence of plants, capable of developing sophisticated strategies without a nervous system or brain, but with fine adaptation to their ecosystem.
The influence of internal CO₂ on the carnivorous strategy of the plant
Another major discovery of the study concerns the presence of high concentrations of CO₂ inside the ballot boxes.
Nepenthes khasiana. This carbon dioxide is not just a residual product. It plays an active role in regulating the carnivorous functions of the plant.
The measurements taken by the researchers reveal CO₂ levels of up to 6000 ppm inside the urns, much higher than those in the ambient air (~400 ppm). This accumulation comes from the cellular respiration of the plant itself, but also from the microbial decomposition of captured prey. However, this CO₂ directly affects nectar production.
Urns enriched with CO₂ show an increase in the volume and toxic composition of the nectar. CO₂ also influences the growth of internal tissues, particularly those responsible for enzyme production. The researchers suggest that this altered internal atmosphere acts as a regulator of carnivorous strategy.
Furthermore, the acidic and CO₂-rich environment inhibits certain pathogenic microbes. This allows for more effective conservation of digestive fluid, while promoting the release of nutrients. The plant thus creates a microclimate favorable to the slow and controlled digestion of prey.
This interaction between gases, chemistry and physiology shows that
Nepenthes khasiana don't just trap. She actively modifies the internal parameters of her trap to improve its effectiveness.
Source: Lathika, CC, et al. (2025). “Bait, not reward: CO2-enriched Nepenthe pitchers secrete toxic nectar”. Plant Biol J, 27: 1022-1034.
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