Burlakova et al. (2009) found a significant negative correlation between snail size and consumption of the control plant (lettuce)a per mass basis, supporting other work that small snails can have a larger impact on plants. Because smaller sized island apple snails will consume macrophytes at a higher mass-specific rate than the larger snails, controlling the younger life stages is most important for protecting aquatic vegetation. However, because larger snails will consume more biomass on an individual basis, it is important to know the size structure and the density of snails to estimate their likely impact (Burlakova et al. 2009).

Feeding studies reviewed by Howells et al. (2006, as cited in Baker et al. 2010) suggest that P. insularum feeds on a wide range of submerged and emergent plants; Elodea canadensis is avoided by either P. canaliculata or P. insularum (taxonomy of the snails used in these studies was not certain) (Rawlings et al. 2007). Gettys et al. (2008) found P. insularum preferred H. verticillata, Najas gaudalupensis, and a freshwater alga Chara, while Myriophyllum aquaticum was consumed only when no other food was available and Egeria densa was not consumed at all (as cited in Baker et al. 2010). An absolute selectivity (yes/no) study by Howells (2002) found that no macrophyte species was rejected, although neither E. densa nor E. canadensis were tested (as cited in Baker et al. 2010). Baker et al. (2010) conducted a quantitative assessment of the potential impacts of P. insularum by evaluating consumption rates as well as feeding preferences on 22 common aquatic macrophytes in Florida, including eight nonindigenous species. The most heavily consumed plants were two native species: Limnobium spongia and Chara sp.. Nonindigenous Panicum repens, H. verticillata and Ceratophyllum demersum and native Sagittaria latifolia, N. guadalupensis and Vallisneria americana were also heavily consumed. Nonindigenous Eichhornia crassipes was consumed at a relatively low rate while nonindigenous Colocasia esculenta and Pistia stratiotes were not consumed at detectable levels. Burlakova et al. (2009) quantified the feeding rate of the island apple snail for three species of invasive macrophytes and 13 species of native macrophytes that are important for wetland restoration and health. They found that the submersed macrophytes, C. demersum and Ruppia maritima, were consumed at a significantly higher rate than emergent plants. The tissues of submersed macrophytes contain small amounts of lignin and often have higher protein concentrations than emergent plants; vontrary to submersed plants, emergent macrophytes have heavy cell walls and very thick cuticles (Wetzel 1975, as cited in Burlakova et al. 2009). Additionally, submersed flora are more accessible to snails and thus more likely to suffer greater damage. The emergent species that were found to be consumed at moderate rates (Canna glauca, Hymenocallis liriosme, Panicum hemitomon, S. graminea, and S. lancifolia) had broad, succulent leaves and stems allowing easy consumption.

Economic impact: The ability of snails to escape population control and explode in ephemeral habitats could drive the types of impacts seen in agricultural crops (Burlakova et al. 2010). Several Pomacea species have become serious agricultural pests of wetland crops (Cowie 1995 2002, Naylor 1996, in Baker et al. 2010). In Hawaii taro represents a valued resource threatened by the island apple snail (Van Dyke 2009c, as cited in Burks et al. 2010). Apple snails are significant agricultural pests of rice and taro in South East Asia, Japan, the Dominican Republic, Hawaii, and the Philippines (Cowie 2002, Ranamukhaarachchi & Wickramasinghe 2006, as cited in Burlakova et al. 2009). In Texas, farmers are facing increased maintenance costs for levees in fields with large populations of P. insularum due to constant burrowing by the snails (Burlakova Unpub. Data. 2009). The main food for island apples snail in rice fields in Texas was ducksalad and other rice weeds, and farmers reported that the snails were very efficient at clearing the fields from the weeds (Burlakova et al. 2009). However in general these invaders are pests (Joshi & Sebastian 2006, in Baker et al. 2010).

Ecosystem change: Aquatic plants are the most important components of wetland structure, therefore, herbivores can have profound impacts on community and ecosystem structure in these systems (Sheldon 1987, Lodge 1991, Lodge et al. 1998, Van Donk 1998, as cited in Burlakova et al. 2009). Nonindigenous apple snails represent a significant threat to wetland ecosystems (Carlsson et al. 2004, Carlsson & Lacoursiere 2005, Carlsson 2006, in Baker et al. 2010). In experiments conducted by Burlakova et al. (2009) P. insularum consumed substantial amounts of seven of 13 species that are important for wetland restoration. In some invaded wetlands P. canaliculata and/or P. insularum (as per Rawlings et al. 2007) have been associated with a shift from macrophyte-dominated communities to phytoplankton-dominated communities (Carlsson et al. 2004, in Baker et al. 2010).

The ecosystem impacts of P. insularum in Florida have not yet been resolved (Gettys et al. 2008, in Baker et al. 2010; Rawlings et al. 2007). Cattau et al. (2010) found that the island apple snail significantly affects the foraging behavior and activity pattern of the endangered Everglades snail kite (Rostrhamus sociabilis plumbeus) in Florida. Populations of the native Florida apple snail P. paludosa could be negatively impacted by the island apple snail (Connor et al. 2008).

Human health: Apple snails are an intermediate host for the rat lungworm (Angiostrongylus cantonensis) a nematode that can cause meningitis in humans (Carter et al. 2009).

Interaction with other invasive species: Burks et al. (2010) studied oviposition trends of the island apple snail and found that snails laid more clutches on wild taro (Colocasia esculenta) than expected by the exotic plant’s availability.

In contrast to Southeastern Asia, at present, there is no documented agricultural damage in Texas from P. insularum (Burlakova et al. 2009). Agricultural practices common in Texas could explain this difference. Recent studies have concluded that the magnitude of crop damage depends on the technique used to grow rice (Teo 2003, Wada 1999, Sanico et al. 2002, Wada 2006, in Burlakova et al. 2009). Snail damage to rice seedlings is correlated with the depth of water on the field, and damage decreases as seedling age increases. Increasing seedling age from two to five weeks resulted in significant reductions in snail damage (Sanico et al. 2002, as cited in Burlakova et al. 2009). Limited moisture conditions immobilise and prevent the snail from causing severe damage even at high densities. Dry direct seeding, which uses a minimal amount of water in the early stages of growth, minimizes snail damage as compared to other methods (Teo 2003, as cited in Burlakova et al. 2009). Wada (1999, as cited in Burlakova et al. 2009) found that draining after sowing greatly reduces snail damage, and three weeks of drainage can almost prevent all damage due to snails.

Education and awareness: Even though the aquarium industry is one of the five major sources for introduction of all aquatic invaders it has received relatively little attention from scientists and policy makers (Padilla & Williams 2004, Ruiz et al. 1997, as cited in Karatayev et al. 2009). Karatayev et al. (2009) highlight the importance of this vector and the need for special attention from the scientific community as well as policy makers and managers. Measures are needed both in terms of regulation and public education to reduce the negative consequences of future introductions and the spread of exotic species.

Integrated Management: Understanding of the trends in the abundance of clutches on different plant species such as wild taro (C. esculenta) may yield important information about island apple snail establishment patterns (Byers 2002, as cited in Burks et al. 2010). However Burks et al. (2010) do not suggest that the presence of an avoided or less-preferred plant would limit suitable oviposition sites for the island apple snail. Recent management plans for wetland habitats suggest that egg mortality resulting from failed hatching (presumably due to laying on surfaces subject to water stress) may reduce egg supply of this invasive snail (Van Dyke 2009b, as cited in Burks et al. 2010). Researchers have not yet found a plant or substrate that will effectively deter P. insularum oviposition (Burks et al. 2010). On the other hand Burlakova et al. (2009) recommend restoring wetland areas (where island apple snails are present) by planting emergent flora with a low risk of damage from apple snails due to low palatability: island apple snail consumption was lowest for Thalia dealbata, Spartina alterniflora, Typha latifolia, and Scirpus californicus.