Electrophysiological and behavioral responses of red imported red ants (Hymenoptera:Formicidae) to an essential balm and its components

Authors: WEN, CHAO - South China Agricultural Univerisity; Chen, Jian; HE, YINGHAO - South China Agricultural Univerisity; WANG, FANG - South China Agricultural Univerisity; WEN, XIUJUN - South China Agricultural Univerisity; WANG, CAI - South China Agricultural Univerisity

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2020
Publication Date: 12/30/2020
Citation: Wen, C., Chen, J., He, Y., Wang, F., Wen, X., Wang, C. 2020. Electrophysiological and behavioral responses of red imported red ants (Hymenoptera:Formicidae) to an essential balm and its components. Pest Management Science. https://doi.org/10.1002/ps.6225.
DOI: https://doi.org/10.1002/ps.6225

Interpretive Summary: The red imported fire ant is a notorious invasive pest. Repellants can be useful to exclude fire ants from certain sensitive areas where the use of synthetic insecticides may not recommend, such as hospitals, schools, and electrical equipment. An earlier laboratory study showed that an essential balm from China effectively repelled red imported fire ants. However, it is not clear which compounds account for the repellency, and whether they can effectively repel fire ants in the field. In this study, five components, eucalyptol, camphor, menthol, methyl salicylate, and eugenol were identified in essential balm and olfactory response of fire ants to all all five components was confirmed. Each component showed repellency against fire ant workers in the field. However, only eugenol significantly suppressed both foraging and particle-covering behavior within 24 h, which was comparable to that of N,N-diethyl-m-toluamide (DEET), the gold standard of insect repellents. Eugenol may be a good active ingredient for developing fire ant repellant products. The particle-covering behavior has been largely ignored in studying fire ant repellents. Our study demonstrated that it is necessary to consider such behaviors in ant repellent bioassays in the future.

Technical Abstract: BACKGROUND: An over-the-counter traditional medicine product of China known as essential balm effectively repelled red imported fire ants, Solenopsis invicta Buren. However, it was not clear which chemical component(s) accounted for the repellency, and whether they would effectively repel S. invicta in the field. METHODS: The composition of essential balm was analyzed by gas chromatography-mass spectrometry (GC-MS). The olfactory responses of S. invicta to each major component of essential balm was studied using electroantennography (EAG) and gas chromatography - electroantennographic detection (GC-EAD). The behavioral response of S. invicta to each component was investigated in the field. A comparative field evaluation was also conducted for eugenol, the strongest fire ant repellent among essential balm components, with N,N-diethyl-m-toluamide (DEET), the standard for insect repellants. RESULTS: Five components, eucalyptol, camphor, menthol, methyl salicylate, and eugenol, were identified in essential balm. Each component elicited concentration-dependent EAG response. Under field conditions, all components showed repellency against foraging ants. Interestingly, foraging ants managed to access the food items placed on a surface smeared with eucalyptol, camphor, menthol, eugenol, or methyl salicylate by depositing soil particles on the surface and then walking on soil particles. However, they failed to do so when the surface was smeared with eugenol. Repellency of eugenol lasted for > 24 h, which was much longer than that of the other four components of essential balm and is comparable to that of DEET. CONCLUSION: Olfactory response of S. invicta to all five components of the essential balm was confirmed. Each component showed repellency against S. invicta workers in the field. However, only eugenol significantly suppressed both foraging and particle-covering behavior within 24 h. The repellent effect of eugenol lasted much longer than the other four components. Particle-covering behavior has been largely ignored in studying fire ant repellants. Our study demonstrated that it is necessary to consider such behaviors in ant repellent bioassays in the future.