Aggression in imported fire ants: an explanation for shifts in their spatial distributions in Southern United States?

Abstract

1. The imported fire ants, Solenopsis invicta Buren (red), S. richteri Forel (black), and their hybrids (S. invicta × S. richteri) are sympatric congeners with overlapping but shifting spatial distributions in northern Alabama and Mississippi, United States. 2. The abilities of workers of the three ant forms (or species) to recognise non‐nestmate conspecifics and heterospecifics were compared in separate aggression bioassays using three group sizes of competitor numbers (battles): 1‐1, 5‐1, and 5‐5 resident–intruder battles. 3. Workers of all three forms showed significant aggression toward non‐nestmate conspecifics and heterospecifics. The results of the intra‐specific aggression bioassays showed that S. invicta had the lowest aggression threshold, whereas S. richteri was the least aggressive. Survival rates 1 day after intra‐specific encounters were higher for S. richteri than for S. invicta or hybrids, consistent with its lower aggressiveness. 4. In inter‐specific interactions, S. invicta workers showed the greatest aggression and were more aggressive towards S. richteri than to hybrids. Furthermore, survival 1 day after inter‐specific encounters was highest for S. invicta workers, whether they were the intruders or residents. The hybrid form was intermediate between both parental forms in aggression and post‐aggression survival. 5. The live 1‐1 and 5‐5 battles produced similar and consistent results, but differences were amplified in the 5‐5 battles, suggesting an effect of group size on aggression. These results may explain the observed shifts in the spatial distributions of the three forms and range restriction of S. richteri in southern United States.

Lethality of Red Imported Fire Ant Venom to Argentine Ants and Other Ant Species

“…Our data confirms that whole body soaking with hexane was an effective method for venom alkaloid extraction Ross et al 1987;Fadamiro et al 2009;Eliyahu et al 2011), and fully represents the alkaloids found in the venom sac. It has been proposed that the ratio of cis-C11 to trans-C11 in venom sampled by milking was always higher than that obtained by soaking (Lai et al 2009).…”

Similarity in Venom Alkaloid Chemistry of Alate Queens of Imported Fire Ants: Implication for Hybridization between Solenopsis richteri and S. invicta in the Southern United States

“…Each colony was confirmed to be S. richteri, S. invicta, or hybrid by using both alkaloid and hydrocarbon characters [4] [52]. About 50 randomly selected worker ants from each colony were soaked in 1 ml of hexane for 2 h. One ml of hexane extract was directly injected into a Shimadzu GC17A equipped with an Rtx -1MS column.…”

Evolution of cuticular hydrocarbon diversity in ants

“…, 2009). Colony mates are usually ignored, whereas other hetero‐ and conspecifics typically elicit an aggressive response (Stuart, 1993; Fadamiro et al. , 2009; Menzel et al.…”

“…Workers inspect the hydrocarbon profiles of other workers with their antennae and are thought to discriminate according to the degree to which it overlaps their own template (Suarez et al, 2002;van Zweden et al, 2009). Colony mates are usually ignored, whereas other hetero-and conspecifics typically elicit an aggressive response (Stuart, 1993;Fadamiro et al, 2009;Menzel et al, 2009).…”