Assessing Invasion Intensity of the Yellow Crazy Ant (Anoplolepis gracilipes) Through Foraging Behaviour

Yellow crazy ants ( Anoplolepis gracilipes ) have invaded many areas of conservation concern, including Kinabalu Park, Borneo, Malaysia, where populations occur around substation in the lowland areas. Assessing invasion intensity in protected areas is essential for timely management, yet reliable behavioural indicators remain poorly explored. In this study, we examined the foraging behaviour of A. gracilipes to assess invasion intensity at the Sayap substation in Kinabalu Park using a gel-baiting approach. Infested areas were identified, and active foraging periods were surveyed prior to deploying empty gel baits (without insecticide) measuring approximately 1 cm in width. Baits were monitored at 1-hr intervals to record ant species occupancy and bait monopolisation. Anoplolepis gracilipes workers monopolised only 16.7% of bait stations (3 out of 18), although queens were observed foraging at baits. Most bait stations were visited by six non-target ant species (two Nylanderia species, Cardiocondyla sp., Pheidole comata , Myrmicaria sp., Tetramorium sp.), indicating continued access to resources by native ants. These behavioural patterns suggest that A. gracilipes has not yet reached an invasion intensity sufficient to exclude native ant species at the study site. This study demonstrates that foraging behaviour and bait monopolisation can serve as practical behavioural indicators of invasion intensity in protected tropical environments, supporting early detection and informing timely management of invasive species.