Effect of sodium phenoxide on trail-following and aggregation behaviors of Formosan subterranean termites and its potential in termite control

Attracants can trigger the trail-following and aggregation behaviors of termites. When combined with pesticides, attracants can lure and kill termites, increasing the termite control efficiency. Our previous studies showed that phenol and its derivatives had trail-following activity for the Formosan subterranean termite, Coptotermes formosanus. However, these chemicals are non-polar chemicals that are volatile and insoluble in water, which limited their application in termite control. We hypothesized that the polar molecule, sodium phenoxide, could also trigger the trail-following and aggregation behaviors of C. formosanus, and attracted termites when combined with imidacloprid. Y-path tests showed that the trails treated with sodium phenoxide (0.1 μg/cm, 1 μg/cm, 10 μg/cm) had trail-following activity for C. formosanus. In contrast, sodium phenoxide with low (0.01 μg/cm) or high (100 μg/cm) concentrations could not cause the trail-following behavior. In addition, different castes (worker, soldier and nymph) of C. formosanus showed similar trail-following behaviors responding to sodium phenoxide (10 μg/cm) treated trail, and there was no significant difference in the crawling distance along the sodium phenoxide line. Aggregation-choice tests showed that sand blocks treated with sodium phenoxide (1 μg/g, 10 μg/g, 100 μg/g, and 1000 μg/g) could cause the aggregation preference of C. formosanus. In addition, 1000 μg/g sodium phenoxide significantly decreased survival rate of termite. The number of C. formosanus gathered on sand treated with imidacloprid (50 μg/g) was lower than that of untreated sand significantly. However, the combination of sodium phenoxide (1 μg/g) and imidacloprid (50 μg/g) still triggered the aggregation preference, indicating that sodium phenoxide demised the repelling effect of imidacloprid. Our study provides a theoretical basis for developing insecticide formulations that attract termites.