Behavioral Mediation On The Cotton Aphid-fire Ant Interaction By Semiochemicals

The cotton aphid(Aphis gossypii Glover)is a worldwide polyphagous agricultural pest,which has a wide range of hosts and can transmit plant viruses.The red imported fire ant(Solenopsis invicta Buren)is a highly invasive and dangerous pest.In nature,fire ants like to live with the hemipteran insects that excrete honeydew,such as cotton aphid,having a facultative mutualism.Cotton aphids produce honeydew as a fuel for ant foraging,and ants attend and protect cotton aphids against nature enemies.Ants are also known to limit aphid dispersal.This can occur through direct physical manipulation,or chemical influence.Little is known about the mediation of chemical signals between organisms.This study used cotton aphid and the red imported fire ants as target insects.A cotton aphid-ant interaction system was set up in the laboratory.The population dynamics and the aggregation patterns of aphids in the presence of fire ants were investigated.Secondly,by testing activity of fractions of the fire ant extract,of the chemical composition of the fire ant extract fractions that can cause behavioral changes in cotton aphids was further identified.Finally,a simulated symbiotic experiment was conducted to verify the effect of the fire ant extract fractions on aphids.The olfactory and behavioral responses of fire ant workers to cotton aphid induced volatiles were used to determine the volatile compounds that might by utilized by fire ants to locate cotton aphids.The main results are as follows:1.In the aphid-fire ant mutualism experiment,the total number of aphid in the control without fire ants increased all the time,while the total number of aphid in the treatment with fire ants increased in the first several days and then became stable afterwards.Aphids in both treatment and control all showed aggregation on the lower side of leave,but more obvious in the presence of fire ant.Aphids also tended to aggregate on cotton stems in the treatment with fire ants.Therefore,fire ants can significantly promote aphid aggregation,especially on leaves and stems.2.The results of Petri dish experiment on cotton aphid dispersion showed that the fire ant worker extract,trail pheromone fraction,Z,E-?-farnesene and E,E-?-farnesene could significantly prolong the dispersal time of aphids.By using EAG technique,the EAG responses of cotton aphids to these semiochemicals were measured.In line with the behavioral responses,these compounds could elicit EAG response in the apterous aphids.3.The trail pheromone fraction and its components that limited aphid dispersal were selected for simulating aphid-ant interaction experiment.The results showed that the aphid population did not increase significantly,and aphids did not aggregated on the leaves or stem.4.The results of Y-tube behavioral experiments showed that the cotton seedling damaged by cotton aphids had a very significant attractiveness to fire ant workers.The EAG responses of fire ant workers to the nine volatile compounds released by damaged cotton plant were dose-dependent,and the compounds at the dose of 100 ?g/?L triggered the highest EAG response.Among the tested compounds,methyl salicylate and 6-methyl-5-hepten-2-one caused the greatest EAG responses in the fire ants.In behavioral selection experiments,fire ants were significantly attracted to methyl salicylate,6-methyl-5-hepten-2-one and DMNT.In summary,in the aphid-ant mutualistic system,the symbiotic ants promoted the aggregation of cotton aphids,and the number of aphids also increased significantly.However,in the experiment with semiochemicals for substitution of ants,the result indicated that these chemicals could not fully function the role of fire ants in the mutualistic system.