More social insects may have different immune responses than solitary ones. Scientists have found that insects like ants, bees and termites actually have weaker immune responses.
Eusocial insects are insects that live in groups. Living at close quarters with many other individuals may make you suspect that these insects would be at increased risk at contracting disease. However, eusocial insects are incredibly successful, which raises the question of how they are able to thrive.
The "social group hypothesis" argues that the eusocial lifestyle has given eusocial insects stronger immune systems. A second hypothesis, known as the "relaxed selection hypothesis," argues that eusocial insects have evolved specific behaviors that reduce the risk of disease transmission.
In this case, the researchers wanted to test the social group hypothesis to see which of these hypotheses were accurate. In order to do so, the researchers tested the "encapsulation response" in 11 different insect species. These included six eusocial insects, including ant, eusocial bee, eusocial wasp and termite species; and five non-eusocial insects, including non-eusocial bee, non-eusocial wasp and cockroach species.
The encapsulation response is an immune response in which hemocytes in an insect's hemolymph engulf and immobilize any foreign substances that enter the insect's body. Hemocytes are roughly analogous to white blood cells, while hemolymph is roughly analogous to blood in mammals.
The researchers inserted a probe into insect samples and measured how strong the encapsulation response was. They found that eusocial insects generally had a less pronounced immune response than non-eusocial insects. In addition, they found that the larger the colony size associated with a species, the weaker its immune response.
"This tells us that the behaviors we see in eusocial insects-like grooming each other or bringing antifungal materials into nests or hives-are playing an important role in colony health," Margarita Lopez-Uribe, postdoctoral researcher at NC State and lead author of the study, said. "And this argues in favor of the relaxed selection hypothesis.
The findings reveal a bit more about insects that form social groups and colonies. This is especially important to note when considering insects like bees, which are currently in steep decline around the world. The study was published in the journal Biology Letters.
