Insects using plants as phones
A team of Dutch ecologists has found that subterranean and aboveground herbivorous insects use plants to communicate. 'Subterranean insects issue chemical warning signals via the leaves of the plant. This way, aboveground insects are alerted that the plant is already occupied.' This means that by using 'green telephone lines,' the two kinds of insects can avoid to compete for the same plant, allowing for faster growth for both species. Fascinating, but read more...
You can see above an example of interaction between aboveground and belowground insects, using plant leaves as 'green phone lines.' (Credit: Roxina Soler, NIOO-KNAW) Here is a link to a larger version of this picture.
Let's look first at the short Netherlands Organisation for Scientific Research (NWO) news release. "In recent years it has been discovered that different types of aboveground insects develop slowly if they feed on plants that also have subterranean residents and vice versa. It seems that a mechanism has developed via natural selection, which enables the subterranean and aboveground insects to detect each other. This avoids unnecessary competition. Via the 'green telephone lines', subterranean insects can also communicate with a third party, namely the natural enemy of caterpillars. Parasitic wasps lay their eggs inside aboveground insects. The wasps also benefit from the volatile signals emitted by the leaves, as these reveal where they can find a good host for their eggs."
This research work has been conducted at the Netherlands Institute of Ecology (NIOO-KNAW) in the Department of Multitrophic Interactions (MTI) of the Centre for Terrestrial Ecology. For those of you who don't know what 'multitrophic' means, please read this page at Wikipedia. You'll discover that 'trophic' comes from a Greek word meaning food or nutrition. "Multitrophic interactions are those which involve more than two trophic levels in a food web. The term is most often applied to interactions among plants, herbivores and predators."
This particular project was led by Roxina Soler Gamborena, a PhD student at NIOO. Here is how she describes her expertise in plant-insect multitrophic interactions. "Plants and insects are part of a complex multitrophic environment, in which they closely and actively interact. However, a systematic tendency to study mainly aboveground insect interactions limited the ability to develop more predictive models to achieve a better understanding of ecology and evolution in a more realistic frame. In the project I am working in, we are interested in study the interactions between below and aboveground insects, and how they can affect each other."
Her project, "A multitrophic approach linking below and aboveground organisms," is described in the MTI's student subjects page. Here is one part of the introduction. "Recently, there is an increasing interest in studying the interaction of aboveground and belowground compartments as a whole, rather than isolated aboveground studies. It is now acknowledged that insects can interact even when they feed on the host plant in different moments and parts of the plant, and some experiments had been carried out to study the interactions between belowground and aboveground insect herbivores. The main aim of this study is to determine if the oviposition behaviour of aboveground hyperparasitoids (and parasitoids) is affected by feeding damage by herbivores in the soil, as these affect parasitoid host and plant quality, using the follow multitrophic system as target for the study." The above figure has been picked from this document.
For more information, you can read one of the technical paper co-authored by Soler and published in Functional Ecology under the title "Foraging efficiency of a parasitoid of a leaf herbivore is influenced by root herbivory on neighbouring plants" (Volume 21, Issue 5, Pages 969-974, October 2007). Here is an excerpt from the abstract. "Our results show that the interaction between an above-ground foliar feeding insect and its parasitoid can be influenced by the presence of non-host herbivores feeding on the roots of neighbouring conspecific plants."
You also can read a paper published in Oikos, another Blackwell Publishing journal, under the title "Root herbivores influence the behaviour of an aboveground parasitoid through changes in plant-volatile signals" (Volume 116, Number 3, Pages 367-376, March 2007). Here is the last paragraph of the abstract. "Our results provide evidence that the foraging behaviour of a parasitoid of an aboveground herbivore can be influenced by belowground herbivores through changes in the plant volatile blend. Such indirect interactions may have profound consequences for the evolution of host selection behaviour in parasitoids, and may play an important role in the structuring and functioning of communities."
Sources: The Netherlands Organisation for Scientific Research (NWO), April 11, 2008; and various websites
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