Resource competition assays between the African big‐headed ant, Pheidole megacephala (Fabricius) and the invasive Argentine ant, Linepithema humile (Mayr): mechanisms of inter‐specific displacement

Abstract

1. The spread of Argentine ants, Linepithema humile (Mayr), in introduced areas is mainly through the displacement of native ant species owing to high inter-specific competition. In South Africa, L. humile has not established in the climatically suitable eastern and northern escarpments dominated by the African big headed ant, Pheidole megacephala (Fabricius), probably owing to local biotic resistance.2. Inter-specific aggression, at the individual and colony level, and competition for a shared resource were evaluated in the laboratory.3. Aggression between the two ant species was very high in all of the assays. Both species suffered similar mortality rates during one-on-one aggression assays, however, during symmetrical group confrontations, L. humile workers showed significantly higher mortality rates than P. megacephala workers. During asymmetrical group confrontations both species killed more of the other ant species when they had numeric advantage. Both ant species located the shared resource at the same time; however, once P. megacephala discovered the bait, they displaced L. humile from the bait through high inter-specific aggression, thereafter dominating the bait for the remainder of the trial.4. The results demonstrate the potential of P. megacephala to prevent the establishment and survival of incipient L. humile colonies through enhanced resource competition and high inter-specific aggression. This is the first study to indicate potential biotic resistance to the spread of L. humile in South Africa.

The Attractiveness of Toxic Bait is not Always Accompanied by Increased Mortality in Laboratory Colonies of Argentine Ants,Linepithema humile(Hymenoptera: Formicidae)

“…Recruitment intensity for each of the toxic baits was averaged across the eight experiments per time interval for the 6 h (after which foraging rates dropped off rapidly), and recruitment curves (showing mean and standard error) were generated. Recruitment effort over time (recruitment pattern) of workers to the toxic bait and corresponding food control was compared, as well as the recruitment intensity over time for ants foraging on the toxic bait compared to ants foraging for a food resource in control colonies, using two-way repeated measures ANOVA with Greenhouse-Geisser correction (Mothapo & Wossler 2014). The Greenhouse-Geisser correction is used when the assumption of sphericity or equal variances are violated, and corrects by calculating new degrees of freedom and a new significance value (P) so that a valid F-ratio can be obtained.…”

Now you see me, now you don’t: verifying the absence of alien invasive yellow crazy ant Anoplolepis gracilipes in South Africa

“…This could have been a result of A. gracilipes not being able to compete with the abundant L. humile (Argentine ants) present at this site ( 13 ). Linepithema humile is one of the most widespread ant invasive species in South Africa that has successfully invaded at least six of the nine provinces in South Africa ( 15 , 30 ). This species is also listed as one of the world’s 100 worst invaders ( 7 , 31 ).…”

“…Sampling sites were chosen based on previously recorded sites (Durban: 12 ; Gansbaai, Knysna, Table Bay, and Kalk Bay: 13 ; Kalk Bay: https://www.inaturalist.org/observations/1160269 ). The other records of A. gracilipes included Gansbaai and Knysna ( 15 ), but due to logistical constraints, these sites could not be sampled. Nevertheless, the four harbours sampled were representative of the major harbours and most confirmed records of this species in South Africa to date.…”