A ladybird larva perched on a cactus in Valencia is the target of a troop of ants. The worker ants approach to attack it, but they don’t count on the fact that it knows how to defend itself: it prepares itself, tensing its white, hairy body with force to expel a drop of thick, bright red liquid. The strategy works and the predators flee as if it were an insecticide. The intense color of its venom suggested to the researchers who observed the behavior that what it was spewing was carminic acid, a chemical substance that has been used for centuries as a red dye in textiles and cosmetics. But this species is not capable of producing it. “So, where did it get it from?” asked Ángel Plata, an entomologist at the Valencian Institute of Agricultural Researchwho together with his team, discovered that the larva had kidnapped the poison of its prey: a cochineal.
This practice is known as toxin stealing and is common in some insect and frog species. The animals sequester toxins from their prey and then use them to defend themselves. Poison frogs, for example, build up reserves of harmful alkaloids when they feed on toxic insects, explains Plata. This can happen as long as the predator and prey exchanging the toxins have co-evolved, as only then do they have the mechanisms necessary to tolerate, store and then use the poison. What is surprising is that this was not the case with the ladybird and the woodlouse.
The interaction between the ladybird and the cochineal demonstrates an unprecedented ability that was not thought possible: predators can sequester and use novel toxins, even when there is no mutual evolutionary adaptation. The scientists have published the results of this research in the journal Proceedings of the Royal Society B.
As humans spread, they introduce species wherever they go, leaving many animals exposed to biochemical defenses they have never encountered before. The cochineal, for example, is an invasive species that arrived in Europe on prickly pears brought from Mexico in the 16th century.
The ladybug (Cryptolaemus montrouzieri)The insect, which plays both the role of prey and predator, is also an exotic species. Originally from Australia, it now lives in at least 64 countries. Plata became interested in the insect’s chemical defenses during his field work observations around his city, when he noticed that tuna is served for breakfast, lunch and dinner, where cochineals are abundant.
White ladybird larvae exhibit a behavior known as reflex bleeding, in which they expel hemolymph when attacked. This is usually a yellow liquid, but during experiments in the lab, when Plata and his team rubbed the larva to activate its defensive mode, the venom turned red. It contained the cochineal’s carminic acid, which turned out to be an effective weapon against hungry ants.
The discovery not only has interesting implications for understanding interactions between species in environments invaded by exotic species, but also suggests that organisms have a remarkable capacity for adaptation and flexibility in response to changes in their environment. Gema Trigos, a researcher at the Department of Social and Myrmecophilous Insects at the University of Granada, said the same. Museum and Institute of Zoology in Poland who has not participated in Plata’s study, but finds it “fascinating.” For Trigos, the article, which It has also been published in the magazine Sciencereveals adaptations that were not thought possible: “We think that nature is totally structured and immutable, but all interactions are susceptible to change.”
Even in new environments, animals can adapt to available toxins and use them to defend themselves against even more powerful enemies, the study shows. In addition, according to Trigos, the results raise new perspectives in the search for agricultural pest control strategies that could take advantage of the organisms’ ability to use and manipulate toxins from exotic prey. An idea that Plata also highlights. He explains that the ladybird was introduced to the Mediterranean with the purpose of protecting citrus orchards from scale insects, which represented a great threat and is even known as the “scale insect destroyer.” Although it can be useful in different ecosystems, he warns that its effectiveness can be limited by the presence of ants and other predators. However, the research shows that its capacity goes further, as it is capable of taking advantage of other non-native species to strengthen itself in unknown environments.
The findings also serve as a warning about the potential unintended consequences of species invasions. Plata notes that the spread of toxin-producing insects can disrupt the structure of food webs and have additional effects on native ecosystems.
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