It is not only group size: Soldiers also modulate the tolerance to insecticide in termites (Blattodea: Isoptera)

The survivorship of social insects is known to increase with group size, even in situations of stress, such as starvation and exposure to insecticides. However, in termites, studies have been undertaken only with workers, disregarding the possible effect of soldiers. The role of soldiers in the termite colonies goes beyond defense, mainly in Nasutitermes species. It is already known that soldiers initiate the foraging as well as improve the decision-making of food resources. Here, we evaluated the effect of group size and the presence of soldiers on exposure to sublethal doses of the insecticide imidacloprid in Nasutitermes corniger (Termitidae: Nasutitermitinae). To do so, toxicity bioassays were undertaken initially to determine the dose of the insecticide required to kill 50% of the N. corniger population (LD₅₀) to be used in the main experiments. Survival bioassays were then carried out with termite groups, with and without soldiers, in different sizes (6, 10, 14, 22, 26, 30 and 60), exposed and nonexposed to insecticide. In general, the mean time to death of termites increases linearly with group size. However, the mean time to death in groups with soldiers was significantly longer only in groups exposed to the insecticide. Our results indicate that soldiers can help to increase the tolerance of nasute termite groups to insecticides, in addition to the group size, as already shown in the previous study. The size of the group and social context could, therefore, modulate behavioral and/or physiological responses that enhance the ability to survive under stressful situations.