The life cycle of the alien boatman Trichocorixa verticalis (Hemiptera, Corixidae) in saline and hypersaline wetlands of south-west Spain

Trichocorixa verticalis (Corixidae) is native to North America but is well established as an alien in the Western Mediterranean region, where it is invasive in permanent coastal wetlands with high salinities. We investigated the annual cycle and generation time of T. verticalis in the introduced range in south-west Spain, through a combination of field surveys and laboratory experiments. Field surveys were conducted on a monthly basis over 1year in three saline fish ponds in Donana and four hypersaline salt ponds in the Odiel marshes. Adults were present all year round, whereas nymphs were only absent in August, when temperatures and salinities were high. Adult sex ratios were idiosyncratic and often male or female biased for a given location and month. Adults were smaller during summer months. Laboratory experiments revealed an oviposition rate of 11.5eggsper day and a generation time of about 54days from egg to adult, suggesting T. verticalis may complete around six generations per year in permanent wetlands. A combination of a high oviposition rate and continuous reproduction throughout the year gives T. verticalis an advantage over native corixid competitors (Sigara spp), and appears to explain the success of this alien aquatic insect.