The Pattern of Pathogen Infections and Its Potential Impact on Red Imported Fire Ant (Solenopsis invicta) in Asian-Australian Areas

The present study aims to survey the previously reported pathogens of Solenopsis invicta in Asian-Australian areas, such as Kneallhazia solenopsae, Wolbachia sp. and two species of viruses. With this research, it could not only test the enemy release hypothesis (ERH) to the successful invasions in Asian-Australian areas, but also build the basic data to help to formulate the strategy of integrate management in the future. By using specific PCR, RT-PCR and microscopic checking, no infections of K. solenopsae and Wolbachia sp. was found in populations sampled from Taiwan, China, Hong Kong and Australia. The pattern seems consistent with the ERH and may explain the successful establishment of S. invicta in these regions. In contrast, surprisingly, SINVs possess relatively higher prevalence and found in most of sampled populations. The infection rates of SINV-1/1A in different regions range from 48.4 to 55.6%, with only nests from Hong Kong found infected by SINV-1. The SINV-2 has only discovered in Taiwan with 16% infection rate. Lower prevalence of SINV-2 may provide a provisional hypothesis that the susceptibility to environmental stress of SINV-2-infected nests is relatively stronger. Accordingly, further hypothesis regarding negligible effect of SINV-1/1A on the establishment of propagule of fire ant could be considered. This hypothesis is subsequently supported by normal performance of infected nests in newly-infested spots that resulted from human transportation. The insecticide test showed that SINV-2 infected colonies were more sensitive to spinosad (by feeding) than either SINV-1A infected- or the healthy ones. In contrast, neither SINV-1A- nor SINV-2 infected colonies showed more susceptible to indoxacarb (by feeding) than healthy ones. More tests associated with fitness effect of virus infection on its host should be performed to address this issue. This is the first study to comprehensively survey the prevalence of known fire ant pathogens in recently non-American invaded areas which reinforces the role ERH involved in successful invasion of S. invicta, as well as provides a new perspective of biocontrol in Taiwan.