As kids, we were taught the importance of a balanced diet with colorful food pyramids published by the USDA and now a plate is used to illustrate five major groups. But the message is still the same: variety. We get essential nutrients like vitamins and protein from different aspects of our diet. Deficiencies in any number of diet components can make children very susceptible to illness and cause them to develop mental impairments. In adults, malnutrition can cause fatigue, joint pain, problems with concentration and various other issues. As simple creatures as they seem, insects also have a variety of nutritional needs to live well and produce healthy offspring. However, insects have restricted diets; for example, some ants and termites only feed on wood, and ticks and lice feed only on blood. But insects with poor diets don’t have the time or the means to search out other food sources to supplement their diet.
What’s an insect to do?
Insects have their own version of a multivitamin in the form of tiny organisms (microorganisms) living inside them that provide essential amino acids, nitrogen and various others. True, humans also harbor bacteria that help us break down food we eat into more useable forms; but we have several kinds of bacteria capable of performing the same tasks and insects that have formed intimate relationships with microorganisms cannot survive without them – think of it like a very long term relationship. The story about how and why their relationship started is not well understood. The bacteria also benefit, using things that only the host can provide and most of these bacteria can no longer survive outside their host.
A few very well studied examples are:
Buchnera and Aphids. Pea aphids feed on a specialized compartment of plant tissue called the phloem; from here aphids acquire sap that is sugar rich, but a poor source for amino acids. Aphids acquire essential amino acids from a friendly bacterium, Buchnera aphidicola, that lives inside aphid cells. The bacteria and aphid have been in this relationship so long (150-200 million years!) that the bacteria have physically lost of pieces of their DNA normally needed in free living bacteria. However, Buchnera acquires these missing parts from the insect, including energy, carbon and nitrogen. Despite losing genes, Buchnera has managed to keep those needed to make amino acids for the insect. There is also evidence that the bacteria can listen in to the needs of the aphid and accordingly adjust how many amino acids to make. This is important, because aphid needs can vary depending on how much nutrition it was able to get from the plant (which also varies with environmental factors like temperature and water availability).
Trichonympha and termites. We generally find termites chewing through wood in our homes or dying trees in our yards. Wood and plant fiber is made up of cellulose, which termites can’t digest. Termites have formed a relationship with a small organism, the Trichonympha protist, that helps break down cellulose into substances that the insect can use for energy. In return, the protist gets some of the generated energy for it’s own survival and reproduction. Moreover, there are bacteria inside and attached to the protists that help provide the termite with other necessary things like nitrogen, that is is unable to get from plant materials. The bacteria also benefits from energy sources provided by the protist.
So, this is interesting but why do we care? There are a number of obligate relationships between insects and their microorganisms. I should point out that these organisms not only provide nutrition, but can also be necessary for reproduction or survival. Research focus has been placed on pest insects (like termites and aphids) and insects that transmit disease (like the tsetse fly). Understanding these relationships gives us information to develop new strategies to control insects re looking for alternatives to using chemicals for insect control, creative new methods have been suggested and studied. this way we can disrupt the relationship either by killing the insects, or stopping them from feeding on crops or transmitting disease.
For instance, vampiric kissing bugs (Triatomes) have bacteria that provide essential nutrients, much like the examples above. Scientists have identified these bacteria, genetically modified them to produce special molecules, introduced them back to the insects (via a spray), and the insects are unable to transmit the parasite Trypanosoma, the causative agent of Chagas Disease. Though some of this research is at its infancy, there are other areas being studied.
Keep on the look-out for any scientific breakthroughs in this area! I think we have a chance of making one of these ideas work.