Ultrastructure of the poison gland in the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae).

The red imported fire ant, Solenopsis invicta is an exotic invasive pest which has mainly infected the southeast and coastal regions (20°N-34°N and 105°E-124°E) in China and about 7000 ha territories were infested according to the estimation of the authoritative organization. The venom plays an important role in their territory expansion, which is synthesized in the poison gland and stored in the venom reservoir during the early development stage of worker. With the aid of electron microscope, the length of the sting apparatus of S. invicta is approximate 640 μm from the tip of lancet to the base of the sting bulb. The maximum secretory cell from the venom gland tissue is approximate 16 μm in length and 3.3μm -4.4 μm in width. In the inner of the sting bulb, there were many hollow lumina where the low dose of the venom were stored and delivered into the sting lancet. The venom would be vented through the acidopore of the gaster when the foraging workers encountered the exogenous foraging competitor. A large number of fat bodies and microvillus were regularly arrayed near the pericellular membrane of the sting apparatus of S. invicta. These structures increased obviously the superficial area and the volume of venom reservoir of S. invicta.