Site occupancy and detection probability of Argentine ant populations

Effective sampling and detection plays an important role in the surveillance and management of invasive species. Invasive ants are prime candidates for imperfect detection because of their small size, cryptic nature and also because of their strong association with human transportation around the globe. We examined site occupancy, colonization-extirpation dynamics and detection probability of Argentine ant populations in the Auckland region of New Zealand. Comparison of 175 sites from 2002 to 2007 shows the dynamic nature of Argentine ants, with an extirpation rate of 33% and a colonization rate of 8%. Baited vials gave relatively poor detection for Argentine ants, despite repeated sampling. If Argentine ants were present at a location, their probability of detection using baited vials was, on average, only P=0.55 (+/- SE=0.04). However, this probability depended on the duration that baited vials were left out. Detectability was highest for vials set out for three (P=0.520.75) or 6h (P=0.530.82). Detection probability for visual searching was 0.895. We use these data to suggest improvements in the design of surveys for Argentine ants. Research on detection theory and its applications for surveillance and eradication is a major gap for invasive ants.