Secretions of the Frontal Gland of a Nasute Termite Soldier: The Role in the Defense against an Entomopathogenic Fungi.

One of the main characteristics of eusocial insects is an effective division of labor. Termites are one type of eusocial insect that has developed specialized defensive individuals, or soldiers. Although soldiers in termites were viewed as a "burden" due to their high energy costs and inability to feed themselves, studies have revealed that they are essential for other processes, including colony immunity. Soldiers belonging to Nasutitermitinae subfamily have frontal glands that secrete defensive substances. However, little is known about how soldiers and compounds from frontal gland contribute to colony immunity. Here, we investigated the effect of the frontal gland secretion from Nasutitermes corniger on defense against an entomopathogenic fungi. Specifically, we tested the following hypothesizes: (1) the presence of healthy soldiers positively affects the survival of infected workers; (2) the frontal gland extract increases the survivorship of N. corniger workers infected with the fungus; and (3) the growth of Metarhizium anisopliae fungus is negative affects by contact with frontal gland extract of N. corniger soldiers. In general, workers of N. corniger infected with M. anisopliae survived less than those with soldiers or uninfected (control). The groups of N. corniger workers exposed to M. anisopliae survived longer when there was the presence of the soldier's frontal gland compared to groups with only fungi, and the secretions of soldiers have an inhibitory effect on the growth of M. anisopliae. This work contributes to a better understanding of the function of the soldiers, and defense mechanisms that involve chemical secretions.