Role of propagule size in the success of incipient colonies of the invasive Argentine ant

Factors that contribute to the successful establishment of invasive species are often poorly understood. Propagule size is considered a key determinan t of establishment success, but experimental tests of its importance are ra re. We used experimental colonies of the invasive Argentine ant (Linepithem a humile) that differed both in worker and queen number to test how these a ttributes influence the survivorship and growth of incipient colonies. All propagules without workers experienced queen mortality, in contrast to only 6% of propagules with workers. In small propagules (10-1,000 workers), bro od production increased with worker number but not queen number. In contras t, per capita measures of colony growth decreased with worker number over t hese colony sizes. In larger propagules (1,000-11,000 workers), brood produ ction also increased with increasing worker number, but per capita brood pr oduction appeared independent of colony size. Our results suggest that quee ns need workers to establish successfully but that propagules with as few a s 10 workers can grow quickly. Given the requirements for propagule success in Argentine ants, it is not surprising how easily they spread via human c ommerce.