Apoptosis as a primary defense mechanism in response to viral infection in invasive fire ant Solenopsis invicta

Apoptosis is considered an innate defense mechanism of insect hosts at the early stage of pathogen infection. The present study attempts to determine whether apoptosis is involved in defending the fire ant, Solenopsis invicta from a natural viral pathogen Solenopsis invicta virus 1 (SINV-1). Results of TEM examination and TUNEL assay both revealed the signature of apoptosis in the midgut epithelium of SINV-1-infected fire ant larvae. A time course study was conducted to monitor changes in the dynamics of SINV-1 viral titers and apoptosis levels in the midgut epithelium of SINV-1-infected larvae. We found that the viral titer significantly decreases as apoptosis level increases, suggesting that the apoptotic epithelium constitutes a barrier against dissemination of SINV-1. These findings serve as the very first empirical evidence for the virus-induced apoptosis in ants and also help explain some previously observed mortality patterns and behavioral alterations associated with SINV-1 in fire ants.