Candidula intersecta
(wrinkled dune snail)

C. intersecta can be invasive in its countries of origin and is considered an agricultural pest in Europe where it can feed on cereal and horticultural crops (some pome and stone fruit) and is responsible for yield losses. Even if its economic and environmental impact has not been determined, it has the potential to cause damage in the USA, New Zealand and Australia, where it is listed as an “A pest” of quarantine concern in the Plant Quarantine Act 1997.

Meissner et al. (2009) have identified several pathways for the movement and introduction of several species of Candidula, including C. intersecta. These species can hitchhike onto containers, limestone, marble, quarry product, stones, terracotta (and other) tiles, farming machinery, cut flowers and plants.

C. intersecta has been intercepted in 2007 at port of entry in the USA on containers. Hitchcox (2007) reports interceptions on cargo containers from Italy, Colombia, and Chile. Candidula infestations have also been found near port areas in Oregon and Washington state. A report from the Oregon Department of Agriculture (2008) states that C. intersecta was detected for the first time in Douglas County, at a site much further inland than any previous surveys, indicating the species is being moved domestically. It was concluded that eradication is not an option anymore (ODA, 2008). However, no direct impacts on agriculture, nor economic damage have been reported.

Populations of several land snail species have already become established at several US seaports. They fasten on containers in rail yards and can be transported by rail to new destinations where they escape into the environment and impact on local crops.

C. intersecta originates from Europe where it is found in Portugal, Spain, Italy, the United Kingdom (including the Isle of Man, Hebrides, the Orkney Islands, and the Shetlands), France, Belgium, the Netherlands, and Ireland. It has also been reported in Holstein (northernmost state of Germany), Denmark and on the island of Öland.

The species is mostly found in the south central plain in Ireland and confined to the coast in northern parts. In Northern Ireland it is present only sparingly on dune grassland or other calcareous soils near the coast (Anderson, 1996).  

It has been introduced into South America, USA (Washington State and Oregon), Australia (South Australia, Victoria and Tasmania) and New Zealand.

Although intercepted by the US Department of Agriculture in shipments to the USA from Colombia (Robinson, 1999), Colombian colonies of C. intersecta had not been found (Hausdorf, 2002).

Land snails are excellent hitchhikers. They can climb up on sea containers and machinery and spread to new destinations and can be transported both short and long distances. The risk of introduction and spread increases with trans-shipment: transhipped containers enter a country through one port, and are unloaded for various periods of time before they are loaded again onto a different vessel and exit for their final destination. Hitchhikers can leave the unloaded containers and spread in the vicinity via port machinery or vehicles. As not all ports record departing, arriving and transhipped containers in separate categories, it is difficult to estimate the percentage of containers to screen for the presence of hitchhikers (Cowie and Robinson, 2003; Meissner et al., 2009).

Land snails including C. intersecta also have the potential to enter via imported cut flowers and plants.

C. intersecta is a temperate species of European origin (Godan, 1983; Hitchcox, 2007). It favours limestone areas and mild coastal climates. This species of land snail can invade and naturalize in a range of environments including cooler maritime climates (e.g., Ireland, UK, Tasmania and New Zealand) and dry, open and exposed habitats. C. intersecta can aestivate during long dry periods and is well adapted to drier climates such as the ones found in Southern Australia (Barker, 1999; 2002).

C. intersecta is considered to be a potential agricultural pest. Sternberg (2000) reports that C. intersecta feeds on leaves of young annual seedlings and tissues of forbs and legumes. In Europe, Candidula snails are known to feed on apples, pears, plums and peaches, damaging unripe and forming fruit on the tree. Once damaged, fruit succumb to fungal, bacterial and yeast attack and rot before maturity. C. intersecta also feed on seeds, seedlings and young plants of spring cereals (Godan, 1983).

Reproductive Biology

Land snails including C. intersecta are hermaphrodites (Godan, 1983). Many species can store sperm and produce fertile eggs for several weeks after mating. Land snails usually mate and lay eggs in the autumn as conditions are getting cooler and wetter. In temperate climates, the egg stage can be the overwintering period in the life cycle of land snails.

Physiology and Phenology

This species requires calcareous environments for the formation of its shell (Barker, 2002).

C. intersecta populations can reach high numbers and exhibit massing behaviour: large numbers of snails become arboreal, and climb up branches of trees and shrubs, and stems of cereals, to eat, mate, or aestivate and to escape from the ground heat. They are also attracted to cool, dark and humid places and favour environments where calcium is available. 

Nutrition

C. intersecta is a polyphagous species feeding on pome and stone fruit, grains, shrubs and new fresh shoots of a range of plants. 

Environmental Requirements

C. intersecta can tolerate a range of temperatures (from cool European climates in the UK to dry and hot conditions in southern Australia). It is found at altitudes from 0 to 800 m.

In its natural habitat, C. intersecta is found under stones and in crevices, particularly in limestone areas or in sand dunes (Barker, 1999; 2002). In the UK and Ireland, Gastropod species usually associated with calcareous grassland (including Candidula) are found in sandy areas where the coastal conditions and humid environment (particularly in dune slacks: hollows between the dune ridges) are favourable for their development.

C. intersecta can be found in exposed limestone outcrops, open scrub areas and dry environment in the southern part of Australia. As an agricultural pest, it can feed on pomes (apple, pears) and stone fruit (plum and peaches) and attacks grains and seedlings as they emerge. As a hitchhiker species it can seal itself on the hard surfaces of containers, machinery and vehicles and crawl into dark and cool crevices.

Some species of Mediterranean origin such as Candidula favour calcareous grasslands and sand dunes. These habitats should be checked first for accidental introductions.

In the USA, C. intersecta has been intercepted repeatedly on Italian, Spanish, Chilean and Colombian terracotta tiles, and granite, and travertine from Spain (Hitchcox, 2007; Meissner et al., 2009).

Gittenberger (1993) notes that C. intersecta differs from Trochoidea geyeri in the finer ribbing of the shell and a microsculpture with relatively prominent spiral striae and no hairpits. In T. geyeri, the body whorl is more regularly inflated. Compared to C. gigaxii, C. intersecta has coarser and less regularly arranged radial 5 riblets and a more roundish umbilicus. Shea (2007) states that C. intersecta is similar to Microxeromagna armillata but is larger and more tightly coiled with less deeply impressed sutures.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Control

There is little information regarding the specific control (chemical or not) of C. intersecta. Most protocols developed for the control of other land snails could be applied to this species (see the case of the Giant African Snail, USDA-APHIS, 2005). 

Cultural control and sanitary measures

Strategies including the reduction of habitat, field burning, and crop rotations are possible. 

Physical/mechanical control

The use of physical barriers such as copper strips is an option for gastropod control but is not always practical on a large scale. 

Chemical control

Molluscicides are often used to target invasive and exotic land snails. They are usually in the form of pellets and are used as baits. Unfortunately some molluscicides have been reported to have non-target effects. Methiocarb and metaldehyde are amongst the potential chemical control options for C. intersecta; however, there is evidence that methiocarb is detrimental to earthworms (Barker, 2002) and some cases of pet poisonings have been reported with metaldehyde. New products available contain iron phosphate (1%) and have proved to be as effective as metaldehyde (Rosetta, 2005). 

IPM

Small mammals, reptiles, amphibians, birds, and predatory insects feed on land snails and might reduce the population in the environment. Some entomopathogenic nematodes are natural enemies of some slugs and snails and are sold in Europe and Britain (Rosetta, 2005).

11/08/10 Original text by:

CRCNPB Australia, CRC for National Plant Biosecurity, Canberra, Australia