|SIDERHURST, M. - Eastern Mennonite University|
Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2014
Publication Date: 11/5/2014
Citation: Siderhurst, M.S., Jang, E.B., Yu, Y. 2014. Differential Field Responses of the Little Fire Ants, Wasmannia auropunctata(Roger), to Alarm Pheromone Enantiomers. Journal of Chemical Ecology. 40(9):955-1062.
Interpretive Summary: The little fire ant,Wasmannia auropunctata(Roger)(Hymenoptera: Formicidae),is an invasive ant with negative impacts on both biodiversity and agriculture in invaded area, throughout the tropics and subtropics. The little fire ant delivers a painful sting when disturbed. Welts can last for weeks. The little fire ant also infests agricultural fields and farms,where they damage crops and sting workers. It promotes plant pests such as aphids, white flies and scale insects,which secrete plant sap that the ants eat. In turn,the ants protect these insects from natural predators and parasites. The little fire ant can also infest houses, beds, furniture and food. Peanut butter traps are widely used to detect the presence of the little fire ant, which method broadly attracts all species of ants. The compounds have been previously identified as alarm pheromones of W.auropunctata. However,the behavioral effects of the left or right "handed"(enantiomer) pheromones towards W.auropunctata in the field assays has not been determined previously. We,therefore synthesized both the left and right "handed" pheromone compounds from a commercially available precursor or one prepared using an enzyme. Field assays demonstrated that W.auropunctata had the significant preference towards the (S)-enantiomers than to the (R)-enantiomers. This is the first instance of differential attraction of ants to the enantiomers of chiral pyrazine pheromones by W.auropunctata. This "handedness" preference can be adopted to make species specific traps to identify and monitor the spreading of the little fire ants.
Technical Abstract: The little fire ant,Wasmannia auropunctata(Roger)(Hymenoptera: Formicidae),is an invasive ant with negative impacts on both biodiversity and agriculture throughout the tropics and subtropics. Since the discovery of W.auropunctata in Puna in 1999,it has established across the eastern side of Hawaii Island. The early detection of W.auropunctata is critical for both stopping the spread and eradication in small infestations. The W.auropunctata species specific trap has the advantage that anyone can tell the presence of W.auropunctata if the trap captures the ants. The alarm pheromones of W.auropunctata were identified previously as the alkyl pyrazines 2,5-dimethyl-3-(2-methylbutyl)pyrazine(2-MeBu-diMePy) and 3-methyl-2-(2-methylbutyl)pyrazine(2-MeBu-MePy). The synthetic racemic pyrazines generally attracted as many W.auropunctata workers as were attracted to a single crushed ant. Both pheromones have a single stereocenter on the side alkyl chain. However,the enantioselectivity of these pheromones towards W.auropunctata in the field assays has not been determined previously. We therefore synthesized both enantiomers of 2-MeBu-diMePy and 2-MeBu-MePy starting from commercially available (S)-2-methylbutan-1-ol,and kinetically resolved (R)-2-methylbutan-1-ol using Pseudomonas cepacia lipase(PCL). Both (S)-2-methylbutan-1-ol and (R)-2-methylbutan-1-ol had more than 98% enantiomer excess according to the GC analysis using an Rt-ßDEXm chiral column. The enantiomer excess of pyrazines should be the same as the precursors because the coupling reaction did not involve chiral center of the alkyl chain. When 1 mg chiral pyrazines were added into the rubber speta (S)-2-MeBu-diMePy attracted more than two folds ants than (R)-2-MeBu-diMePy and (S)-2-MeBu-MePy attracted more than five folds ants than (R)-2-MeBu-MePy. All pyrazines significantly attracted more ants than solvent control. This is the first instance of differential attraction of ants to the enantiomers of chiral pyrazine pheromones by W.auropunctata. This enantiomer specific preference can be adopted to make species specific traps to identify and monitor the spreading of the little fire ants.