Electroantennographic And Behavioral Responses Of Workers Of The Red Imported Fire Ant, Solenopsis Invicta Buren (Hymenoptera:Formicidae) To Alarm Pheromone And Its Analogs

The red imported fire ant (RIFA), Solenopsis invicta Buren (Hymenoptera: Formicidae), is a typical medical and agricultural pest. RIFA is native to Brazil, Paraguay, and Argentina in South America. In1930s, RIFA invaded southern USA through the port of Mobile, Alabama. Since then, the fire ants rapidly spread throughout the southern United States and, more recently, have been introduced to other regions of the world, including the Caribbean, Australia, New Zealand, Taiwan, Hong Kong, Macao, and China. RIFA has been listed as one of the100most dangerous alien species in the world. The figure of RIFA is in accordance with common ants. But the size of RIFA is slightly bigger. Since2004, it has invaded several provinces in the south of China, such as Guangzhou, Guangxi, Hunan, Jiangxi and Fujian. As a member of the social insects, behaviors of RIFA are mediated by pheromones. Alarm pheromones in particular have the simplest structure of all, but are not well understood. They have low molecule weights, highly volatile, and appear to be the least specific of all pheromones. In this study, workers of S. invicta were collected from Guangdong province. The chemical components of head, mandibular gland and body extract were analyzed. The electroantennographic(EAG) and behavioral responses of the workers of S. invicta to15alkylpyrazine analogs have been tested. The main results were listed as following:The alarm pheromone components of the S. invicta were extracted from head, mandibular gland and whole body of RIFA workers. These extracts were analyzed by using GC-MS technique. According to the retention time of2-ethyl-3,6-dimethylpyrazine and the Nist08database, a chemical component named4-methoxy-3,5-dimethyl-benzenamine was found.EAG tests were performed to evaluate the responses of workers of S. invicta to15odor stimuli, including the main component of alarm pheromone and its analogs. The results showed that different doses of alkylpyrazine analogs could elicit significant EAG responses from workers of S. invicta. The EAG response was dose dependent. Workers displayed the highest EAG reaction at100μg. As the dose increased to1000ug, the reaction significantly decreased. The EAG responses elicited by2,3-diethyl-5-methylpyraizne is higher than that elicited by the RIFA alarm pheromone component,2-ethyl-3,6-dimethylpyrazine. The results of alarm behavioral test with the15pyrazine analogs to the worker of S. invicta were in accordance with the EAG responses. The alarm behavioral responses of5pyrazine analogs were similar to2-ethyl-3,6-dimethylpyrazine. The dose of100ng elicited the strongest alarm reaction. Alarm behavior is one of the most obvious behaviors of ants, but it is also one of the hardest to define. In generally, there are three levels to estimate the alarm response. Initially, the ants eluted or approached the source of the alarm. Then some of the ants running with their mandibles opened. Moreover, the ants reacted to the alarm pheromone showed grooming behavior, such as biting the source of odor.Six chemical compounds were further selected for the foraging behavior test. All the six analogs could all enhance the bait discovery efficiency, but no significant difference among these six compounds. The samples injected onto filter paper disc along with food bait could attract more workers than the samples impregnated into the food bait.