Morphological and ultrastructural observation of mandibles of two invasive fire ants, Solenopsis invicta Buren, Solenopsis geminata Fabricius and a native ant Tapinoma melanocephalum Fabricius.
Mandibular shape of two invasive fire ants, Solenopsis invicta, Solenopsis geminata and a native ant Tapinoma melanocephalum were observed by light microscope and scanning electron microscopy (SEM). The head width and mandible size were polymorphism and widened progressively in two invasive species, while no significant difference was found in those parameters among individuals of T. melanocephalum. The T. melanocephalum has the smallest mandibles in the three types of species. It included four sharp incisor lobes, numbers of small and obtuse incisor lobes, smooth texture of ventral regions. There was no morphological difference in major, medium, minor workers of S. invicta and S. geminate mandibles. The mandibles of three sizes of workers included four sharp small teeth, with smooth texture of ventral regions. S. geminata soldier mandibles were different from workers because of blunt small teeth, relatively deep inner concave margin and rough texture of ventral regions. It was speculated that hardness mandibles of S. invicta were evolved in relation to colony founding and defending, while mandibles of S. geminata soldier were mainly related to food grinding, instead of colony defending.