| Channeled-type applesnails are aquatic invaders in many subtropical areas and are important agricultural pests. South American channeled-type applesnail (Pomacea insularum) has been first reported in Texas in 1989. We documented the distribution and spread of Pomacea insularum in southeast Texas in 2006 and used GIS mapping to analyze the distribution patterns and compare the spread between 2005 and 2006. By the end of 2006 the presence of P. insularum was confirmed in 7 southeastern counties (Harris, Chambers, Brazoria, Galveston, Fort Bend, Waller, and Austin). The snails are currently found in 18 waterways, including Buffalo, Mustang, Chocolate, Dickinson, New, and Whites Bayou, Brazos River, and American Canal. A GIS analysis of the spatial distribution of P. insularum revealed two major clusters concentrated in the southern outskirt of the Houston metropolitan area. In Texas, we found two different modes of population dynamics for P. insularum. In permanent water bodies the populations were stable, the size structure remained constant throughout the year, and the densities were low. However, in an agricultural environment the same species displayed different population dynamics with an unstable population size, a wide-ranging size structure, and significantly higher densities. The unlimited resources during rice field flooding, lack of major predators, and high reproductive abilities of snails may be the most important factors that allow P. insularum to create large densities in rice fields. |
