Appendix ES-11 Alien Snail Control in Nurseries

Home , Agriolimacidae, Fernery, Gastrodontidae, Limacidae, Zonitidae

Alien snail control in nurseries

Report to the Oahu Army Natural Resources Program (OANRP)

Prepared by Norine W. Yeung and Robert H. Cowie

30 November 2012

Pacific Biosciences Research Center University of Hawaii 3050 Maile Way, Gilmore 408 Honolulu, Hawaii 96822 Phone: (808) 956 4909/0956 E-mail: [email protected] [email protected]

Appendix ES-11 Alien Snail Control in Nurseries

BACKGROUND AND PURPOSE

From the basic perspective of habitat restoration, non-native species should not be introduced to areas where they are not present. Specifically, non-native snails and slugs (hereafter ‘snails’) may impact both native vegetation (Joe & Daehler 2008) and native snails (Meyer & Cowie 2010a, b, Sugiura et al. 2011) in areas to which they are introduced. Therefore, it is important that plants to be outplanted, as well as equipment and vehicles used to transport plants, are free of non-native snails. This requires appropriate management practices and control measures to be adopted in the nurseries.

For some time the OANRP has been planning to outplant native Hawaiian plants on military land on Oahu as part of its ecological restoration efforts. A major problem associated with this effort is that the plants grown in the nurseries for outplanting can become infested with non- native snails (Cowie et al. 2008), some of which, especially as juveniles, are very small (on the order of 1-2 mm). Preliminary discussions and visits to the Schofield baseyard and the nursery at the Nike site took place prior to the implementation of this agreement and the start of the project. The following two main issues were identified as needing addressing.

Salt Barriers: Currently, the legs of the greenhouse benches are placed in pots filled with salt, which acts as a barrier preventing snails from climbing up the legs and into the pots on the benches. The problems with this method are 1) increased corrosion of the posts used to support the frame structure, and 2) the potential for damage caused by the long-term accumulation of salt in the ground at the nursery sites.

Facility Sanitation: It is important that non-native snails are not transported on equipment as well as on the actual plants to be outplanted. To reduce the possibility of this happening, there should be no areas in or around the OANRP facilities suitable for snails to live.

PROPOSED WORK

Ideally, the use of salt barriers, though apparently effective, would be stopped. In order to do this, it would be necessary to demonstrate that snails are no longer able to access the greenhouse benches. Alternative barriers to salt should be considered, or at least methods of preventing the salt from dissolving by blocking rain and water draining from the benches. However, if thorough surveys of the nurseries showed that snails were not found either inside the nursery or for some distance outside it, then once they were eradicated from the plants, the salt barriers could be removed.

The objectives originally proposed under this agreement were as follows.

1) Thoroughly inspect all baseyards and nurseries (including nurseries supplying plants to OANRP under contract) to identify management practices that may facilitate contamination by snails of plants for outplanting as well as areas that may act as

Appendix ES-11 Alien Snail Control in Nurseries

sources for ingress of snails into the facilities, and provide a report detailing these findings. 2) Undertake surveys to establish which species of snails, if any, occur in and around all baseyards and nurseries, and incorporate the results into the report in 1), above. 3) Perform experiments to test whether, once snails have been eradicated from plants, the plants can be re-colonized in the absence of bench leg barriers, given appropriate facility sanitation (to be done at the Nike site nurseries). 4) Undertake studies of life-cycles of key snail species (e.g. Zonitoides arboreus, Succinea tenella, Oxychilus alliarius) in order to develop post-control inspection protocols to declare plants clean of snails that adequately account for the length of time required for growth and reproduction, and test these protocols (to be done in the laboratory at UH). 5) Develop and write revised MIP sanitation guidelines for snails, appropriate for all baseyards and nurseries, to include inspection protocols. 6) Develop and write control strategies focused on key target species. 7) Collaborate with OANRP personnel in writing up the protocols and procedures for publication in the pest management literature.

MODIFICATIONS TO THE PROPOSED WORK

As the project progressed, and in discussion with OANRP personnel, the above objectives were modified as follows. Objectives 1, 2 and 6 were retained and the combined report detailing our findings and recommendations is provided as part of this overall project report. Objective 3 was modified and divided into two parts: 1) laboratory experiments to test alternative nursery bench leg barriers, and 2) provision of a protocol for monitoring the area around the nurseries, to be implemented by OANRP personnel at the Nike site nursery. The results of the experiments and the protocol provided to the OANRP are provided as part of this overall project report. Objective 4 was scaled back to focus only on Zonitoides arboreus as the major species of concern. Following a literature search, we determined that sufficient information was available regarding the life-cycle of Zonitoides arboreus and the relevant citations were provided to OANRP personnel. These citations are listed as part of this overall project report. Objective 5 was addressed as requested and the revised MIP sanitation guidelines are provided as part of this overall report. Objective 7 will be addressed in the future following discussion with OANRP personnel regarding which aspects of the overall project warrant publication in the peer-reviewed literature.

Appendix ES-11 Alien Snail Control in Nurseries

BASEYARD AND NURSERY SURVEYS AND MANAGEMENT PRACTICES

Surveys

Surveys were carried out by experienced snail biologists at four nurseries (Table 1). Surveys at the Nike nursery encompassed the OANRP section and the DLNR (State of Hawaii, Department of Land and Natural Resources) section as well as areas in the immediate vicinity but outside of the nursery. The results from these three surveys were kept separate. The other OANRP nursery surveyed was that at the East Base. In addition, Kay’s Fernery and the Lyon Arboretum rare plant nursery were also surveyed, these being nurseries from which OANRP would like to obtain certain plant species for outplanting.

Results

The species found during the surveys are listed in Table 1. Some species could not be identified to species and in the case of Tornatellidinae and Pacificellinae only to subfamily.

Summary

Only one live snail (Euglandina rosea) was found in the OANRP greenhouse at the Nike nursery. Several live non-native snails were found in the DLNR Nike greenhouse as well as in areas around both greenhouses. At the East Base nursery, no live snails were found in the nursery area, but one live non-native snail (Bradybaena similaris) was found immediately outside the nursery area, in a patch of grass on the side of the road. Many live non-native snails were found at Kay’s Fernery and Lyon Arboretum (rare plant nursery/greenhouse). In particular, a non-native snail (Sinployea sp.), previously not recorded in the Hawaiian Islands, was found at the Lyon Arboretum nursery.

Management practices

The baseyards and OANRP nurseries are generally clean and tidy and probably not major sources of contamination of plants by snails. However, the DLNR Nike greenhouse, Kay’s Fernery and Lyon Arboretum need substantial improvement to minimize snail infestation. The DLNR Nike greenhouse is a concern as the facility is located only several meters away from the OANRP greenhouse and may be a continual source of non-native snails. The following practices should be followed to minimize the potential for contamination. The key is to maintain the facilities free of snails this is done primarily simply by minimizing places for them to hide. Please see also the modified MIP Sanitation Guidelines (below).

 Minimize hiding places for snails, especially those that provide high humidity microhabitats not exposed to direct sunlight, in and around the facility. This might include removing (best) or raising off the ground (better than leaving on the ground) various materials and objects such as stacks of plant pots, piles of wood, packing materials, fencing equipment, plastic sheeting, junk and trash.

Appendix ES-11 Alien Snail Control in Nurseries

 Remove weedy vegetation in and around the facility. If there are lawn areas, keep them well mown. Remove moss growing on or around equipment (e.g. concrete blocks, nursery bench siding) and on the surface of soil in pots.  Monitor the facility on a regular basis to look for snails or signs of snail presence. Look for slime trails and damage to plants. Empty shells may indicate the presence of live individuals. Check around pots in nurseries, in the immediate vicinity of greenhouses and around the perimeter of the nurseries and baseyards. Check likely hiding places for snails, under the various items mentioned above but also in weedy vegetation (which ideally should have been removed), water supply on/off tap housings (i.e. Buffalo boxes) and in vegetated areas at the bases of building walls and sidewalk edges. In nurseries check the undersides of plant pots as well as the upper two centimeters of earth/medium in pots.  In nurseries keep the area around plants and in pots clear of leaf litter.  If feasible, establish an inhospitable buffer area (e.g. bare concrete, gravel) 3-4 m wide around the facility.  Manually dispose of any snails found. Wear gloves or use a suitable implement to handle them as they may contain parasites that could infect humans.  Set up traps to lure snails then dispose of them.  Use commercially available baits to kill snails if necessary, following the directions and taking the precautions detailed on the product label.

Appendix ES-11 Alien Snail Control in Nurseries

Table 1. Snail species found at the nurseries and greenhouses. Native species asterisked.

Site Family Genus Species Snails found Nike Nursery (OANRP greenhouse area) Spiraxidae Euglandina rosea live Vitreidae Hawaiia minuscula shells only Nike Nursery (DLNR greenhouse area) Achatinellidae Tornatellidinae sp.* live Agriolimacidae Deroceras laeve live Gastrodontidae Zonitoides arboreus live Limacidae Limax maximus live Subulinidae Allopeas clavulinum live Subulinidae Paropeas achatinaceum shells only Veronicellidae Veronicella cubensis live Nike Nursery (beyond greenhouse area) Achatinellidae Achatinella mustelina* shells only Achatinellidae Tornatellidinae sp.* live Gastrodontidae Zonitoides arboreus live Spiraxidae Euglandina rosea live Subulinidae Allopeas clavulinum live Subulinidae Paropeas achatinaceum live Vitreidae Hawaiia minuscula shells only East Base Achatinidae Achatina fulica shells only Bradybaenidae Bradybaena similaris live Polygyridae Polygyra cereolus shells only Streptaxidae Gonaxis kibweziensis shells only Subulinidae Allopeas clavulinum shells only Subulinidae Paropeas achatinaceum shells only Subulinidae Paropeas achatinaceum shells only Subulinidae Subulina octona shells only Subulinidae Subulina octona shells only Vertiginidae Gastrocopta servilis shells only Kay's Fernery Achatinellidae Pacificellinae sp.* live Achatinellidae Tornatellidinae sp.* live Achatinidae Achatina fulica live Agriolimacidae Deroceras laeve live Euconulidae Liardetia doliolum live Spiraxidae Euglandina rosea live Subulinidae Allopeas clavulinum live Subulinidae Paropeas achatinaceum live Subulinidae Subulina octona live Succineidae Succinea tenella live Veronicellidae Veronicella cubensis live Zonitidae Oxychilus alliarius live Lyon Arboretum (Rare Plant Nursery) Achatinellidae Tornatellidinae sp.* live Achatinidae Achatina fulica live Agriolimacidae Deroceras laeve live Charopidae Sinployea sp. live Euconulidae Liardetia doliolum live Spiraxidae Euglandina rosea live Subulinidae Subulina octona live Veronicellidae Veronicella cubensis live

Appendix ES-11 Alien Snail Control in Nurseries

LABORATORY EXPERIMENTS TO TEST ALTERNATIVE NURSERY BENCH LEG BARRIERS

Methods

Three barriers were chosen for their known use as successful snail barriers: Tex-R© (fabric with a coating of latex bound copper hydroxide that cannot be leached out), copper metal tape, and salt. Four snail species known to be nursery pests (i.e. Veronicella cubensis, Zonitoides arboreus, Succinea tenella, and Deroceras laeve) were tested. They were collected from various locations on Oahu and housed in the laboratory in Gilmore Hall, University of Hawaii. Prior to each trial, they were starved for 48 hours.

Barrier experiment

Experiments were carried out in 70 x 40 x 40 cm (W x L X H) plastic bins with 2 cm of soil on the bottom of the bins. Plastic bags were placed on the soil to provide shelter. Polyvinyl chloride (PVC) pipes (28 cm high, 5 cm diameter) were used to mimic greenhouse bench legs. Three pipes, one with each of the three barriers, were placed along the center line of the bin (Figure 1). The barriers were attached 15 cm from the bottoms of the pipes. A piece of lettuce was placed on top of each pipe, as an attractant. Five snails were placed on the soil along each side of the barrier setup for a total of 10 snails per trial (3 trials per species). The bins were sprayed with water prior to the introduction of the snails. The behavior of the snails was observed for the first hour. If they did not breach the barriers, the bins were covered and snails were observed again 10-12 h later. Snails were observed for a week or until the barriers were breached. Bins were sprayed twice a day, 1 hour prior to each recording event (morning and evening, 10-12 h apart). Each trial had one control with the same setup as the experimental trials but with no barriers (Figure 2).

Snail (downward) movement experiment

These trials assessed whether snails would breach barriers when placed on top of the PVC pipes. No shelter or food was provided on top of these pipes (Figure 3) and three individuals were placed on top of each pipe. The bins were sprayed with water prior to the placement of snails. Behavior of the snails was observed for 3 h. Each trial had one control with the same set up as the experimental trials but with no barriers (Figure 4).

Results

Barrier experiment

No snails except Veronicella cubensis breached the two copper-based barriers (Tex-R© and copper tape; Figure 5). Within the first hour many of the snails were observed moving up the PVC pipes. Snails retracted slightly when they touched the barriers and subsequently moved

Appendix ES-11 Alien Snail Control in Nurseries

down the PVC pipe or remained on the pipe below the barriers (Figure 6). Several snails in the control bins reached the lettuce within 30 min (Figure 7). No snails breached the salt barrier.

Snail (downward) movement experiment

Within the first hour, all snails were observed moving down the PVC pipes. Veronicella cubensis and Deroceras laeve individuals breached the copper-based barriers but not the salt barrier (Figure 8). Several individuals of each species were observed moving across the salt barrier and each of these snails died while trying to cross the barrier (Figure 8).

Summary

Copper-based barriers were effective in barring some but not all species of snails, but the most effective barrier was the salt. No snails breached this barrier and those that attempted to cross it all died.

Appendix ES-11 Alien Snail Control in Nurseries

Veronicella cubensis Figure 5. breaching Figure 1. Snail barrier experimental setup. the two copper-based barriers. Left: Tex- Left to right: Tex-R©, copper tape, salt. R©, right: copper tape.

Veronicella Figure 6. No snails except for Figure 2. Snail barrier control setup. cubensis breached the two copper-based barriers.

Figure 3. Snail (downward) movement experimental set up.

Figure 7. Snails reaching the lettuce in the control setup.

Figure 4. Snail (downward) movement control setup. Figure 8. Snails attempting to cross the salt barrier. All snails died while crossing.

Appendix ES-11 Alien Snail Control in Nurseries

NIKE/PAHOLE NURSERY SNAIL INVASION DETECTION PROTOCOL

1) Approximately 80 plastic containers (length 13 cm, width 10 cm, height 5 cm) will be put into the ground surrounding the nursery, approximately 5 meters out from the nursery and positioned 1 meter apart (Figure 9) by OANRP personnel. 2) Approximately 120 plastic containers (length 13 cm, width 10 cm, height 5 cm) will be put into the ground surrounding the Upper Building, approximately 5 meters out from the building and positioned 1 meter apart (Figure 1) by OANRP personnel. 3) Each container will have a hole cut out of its bottom, approximately 6 x 4 cm to permit drainage. Each container will contain a piece of lettuce (food) and a piece of cardboard (shelter), each approximately 4 x 4 cm. 4) Containers will be monitored by OANRP personnel every 3-4 days for any snails. Each container should be searched for at least 30 seconds, to ensure finding very small snails. On each occasion the lettuce and cardboard will be dampened as needed. Replace lettuce also as appropriate (if it has dried out or become rotten). 5) Collect any snails found for confirmation of identification by UH personnel, as necessary. 6) Monitor for 1 month.

Figure 9. Approximate placement of potted lettuce plants around the Nike/Pahole nursery. Base map provided by Lauren Weisenberger.

Appendix ES-11 Alien Snail Control in Nurseries

LIFE-CYCLE OF ZONITOIDES ARBOREUS

Three publications dealing with control of Zonitoides arboreus as pests of orchids in Hawaii and that also provide information about the life-history of these snails were provided to OANRP personnel. They are:

Hollingsworth R.G. & Sewake, K.T. 2002. The orchid snail as a pest of orchids in Hawaii. Miscellaneous Pests, College of Agriculture and Human Resources, University of Hawaii at Manoa 1: 1-2. Hollingsworth, R.G. & Armstrong, J.W. 2003. Effectiveness of products containing metaldehyde, copper or extracts of yucca or neem for control of Zonitoides arboreus (Say), a snail pest of orchid roots in Hawaii. International Journal of Pest Management 49 115-122. Hollingsworth, R.G., Follett, P.A. & Armstrong, J.W. 2003. Effects of irradiation on the reproductive ability of Zonitoides arboreus, a snail pest of orchid roots. Annals of Applied Biology 143: 395-399.

Appendix ES-11 Alien Snail Control in Nurseries

REVISED MIP SANITATION GUIDELINES

The current guidelines regarding snails and slugs are as follows.

Mollusk Monitoring and Control . Look for signs and symptoms. . Identify the target pests (make sure it is a pest and not a beneficial insect). . Monitor for pests presence and their levels of abundance. . Know their life cycle . Monitor on a daily basis, usually early morning is best. . Contact your local agriculture extension agent or DOA agent for proper identification, up-to-date chemicals and current control practices.

a) Slug  DESCRIPTION: Slugs are terrestrial mollusks that do not have shells. They have slimy bodies, are usually 1 to 2 inches (some can even reach 8 inches) long and travel on a foot that leaves a trail of slime behind. The colors range from white, yellow to black. They have a rasping mouthpiece. The eggs are in translucent-white, individual sacs, which form a cluster, and are usually found in dark, cool, moist areas or underground. Slugs can produce about 6 generations per year and take about a year to mature. (Deputy and Murakami 2000).  SIGNS AND SYMPTOMS: Look for the slime trail, which is usually silver in color. Damage to the plant, such as large ragged holes in leaves, flowers, and stems, is done by the slug. They can quickly defoliate the plant if not controlled. Check the undersides of pots and in drainage hole of the pot to see if they are present. Slugs begin feeding at the bottom of plants and work their way up (Ball and Ball 1990).  CONTROL: Keep area around plant and in pot clear of leaf litter. Manually dispose of any slugs in growing area. Set up traps to lure slugs and then dispose of them. Set up a physical or chemical barrier to deter slugs. Use baits to kill slugs (Deputy and Murakami 2000).

b) Snails  DESCRIPTION: Snails are soft-bodied mollusks that are protected in a shell. They can range in color from cream, pink to gray. The markings on the shell vary from species to species. They can be found in moist, dark areas, usually coming out at night to feed with their rasping mouthpiece (Ball and Ball 1990). They produce about 80 eggs at a time, and can lay eggs up to 6 times a year. The eggs are rounded and white in color, and can be found in the upper layer of the soil. The snails mature in two years (Deputy and Murakami 2000).  SIGNS AND SYMPTOMS: Look for the slime trail, which is usually silver in color. Damage to the plant, such as large ragged holes in leaves, flowers, and stems, is done by the snail. They can quickly defoliate the plant if not controlled. Check the undersides of pots to see if they are present (Ball and Ball 1990).  CONTROL: Keep area around plant and in pot clear of leaf litter. Manually dispose of any snails in growing area. Set up traps to lure snails and then dispose of them. Set up a physical or chemical barrier to deter snails. Use baits to kill snails (Deputy and Murakami 2000).

We suggest modifying these guidelines as follows.

Snail and Slug Monitoring and Control . Look for signs and symptoms. . Identify the target pests (make sure it is a non-native and not a native species of snail - all slugs are non- native). . Monitor pest presence and abundance. . Know their life cycle. . Monitor on a daily basis, usually early morning or after rain is best. . There are many species of snails and slugs, so contact your local agriculture extension agent or DOA agent for proper identification, details of up-to-date chemicals and currently acceptable control practices.

 DESCRIPTION: Slugs are species of snails that have lost their shells through the course of evolution. Some slugs retain a small vestige of a shell, which might be visible externally, or in some cases is

Appendix ES-11 Alien Snail Control in Nurseries

completely internal. Semi-slugs have a larger shell but are unable to retract the body fully inside it. Slugs and snails have slimy bodies and travel on a foot that leaves a trail of slime behind. Snails and slugs range in size from 1-2 mm (many native and non-native species) to 15 cm or more (giant African snail). Juveniles may be much smaller. Most snails can be identified by looking at features of the shell: what shape it is; how big it is; what color it is; and so on, but in some cases dissection to reveal the internal anatomy is necessary. Slugs, which are often more difficult to identify as they lack a shell or the shell is much reduced, are identified by the color of the body (although some species are highly variable), by various other external features (e.g. location of pneumostome, size and shape of mantle, presence/absence of keel) and by dissection to reveal the internal anatomy. The main visible features of a snail’s or slug’s body are its head, generally with two pairs of tentacles, its foot and its tail. The eyes are at the tips of the upper, longer pair of tentacles. Snails and slugs have rasping mouthparts. The eggs of most snails are encased in a white shell. Some snails and many slugs lay translucent-white eggs, sometimes lacking a hard shell but surrounded by a gelatinous matrix. Most snails and slugs lay their eggs in clutches, usually in dark, cool, moist areas or underground. Species of snails and slugs differ widely in their life histories. Some are extremely fecund. For instance, the giant African snail (Achatina fulica) lays clutches of on average around 200 eggs about once a month and the snails grow to full size within a few months of hatching (Kekauoha 1966).  SIGNS AND SYMPTOMS: Look for the slime trail, which is transparent and glistening if new and dries to a usually silverish color. Damage to the plant, such as large ragged holes in leaves, flowers, and stems. They can quickly defoliate the plant if not controlled. Check the undersides of pots and in drainage hole of the pot to see if they are present. Check upper two centimeters of earth/medium in pots. Check other likely hiding places for snails and slugs in the vicinity, e.g. under various materials and objects, especially areas that provide high humidity microhabitats not exposed to direct sunlight such as piles of wood, packing materials, fencing equipment, plastic sheeting and trash, inside access housing to water on/off tap (i.e. Buffalo box), in weedy vegetation, areas between concrete structures (buildings, sidewalks) and vegetation. Note that slugs and snails access plants from the bottom but may begin to feed on younger leaves near the top, or they may begin feeding at the bottom of plants and work their way up (Ball and Ball 1990). Finding shells may indicate presence of live individuals.  CONTROL: Keep area around plant and in pot clear of leaf litter. Maintain a clean and tidy facility, minimizing possible hiding places for snails and slugs (see above). Establish an inhospitable buffer area (e.g. bare concrete, gravel) 3-4 m wide around each greenhouse and around the entire facility. Monitor frequently for signs and symptoms both around pots in nurseries, in the immediate vicinity of greenhouses and around the perimeter of the nursery. Manually dispose of any snails or slugs found. Set up traps to lure snails and slugs and then dispose of them. Set up a physical or chemical barrier to deter snails and slugs. Use baits to kill snails and slugs (Deputy and Murakami 2000).

Appendix ES-11 Alien Snail Control in Nurseries

CONCLUSION

In general, the OANRP’s efforts to maintain snail free nurseries and greenhouses are exemplary. The OANRP Nike facility is especially clean. However, even in the most well- maintained greenhouse a small number of snails were found. Nonetheless, with appropriate protection of nursery benches and vigilant monitoring, we consider that the Nike greenhouse in particular can be kept as free of snails and slugs as is practically possible. Rigorous attention to cleanliness and tidiness at all sites is crucial for maintaining a snail and slug free environment.

It is unfortunate that the best barrier to place around the nursery table legs remains salt. The other two barriers tested successfully prevented access by some of the snail species tested but at least two of them (Veronicella cubensis and Deroceras laeve) were able to breach both of these barriers (though D. laeve only breached them going down the legs). Based on these experiments it may be that the only totally effective barriers would be those that kill the snails.

Appendix ES-11 Alien Snail Control in Nurseries

REFERENCES

Ball, J. & Ball, L. 1990. Rodale’s flower garden problem solver. Rodale Press, Emmaus, p. 277- 349. Cowie, R.H., Hayes, K.A., Tran, C.T. & Meyer, W.M., III. 2008. The horticultural industry as a vector of alien snails and slugs: widespread invasions in Hawaii. International Journal of Pest Management 54: 267-276. Deputy, J. & Murakami, P. 2000. Slugs and Snails. Landscape, Floriculture, and Ornamentals News, no. 8, July 2000: 10-12. Hollingsworth R.G. & Sewake, K.T. 2002. The orchid snail as a pest of orchids in Hawaii. Miscellaneous Pests, College of Agriculture and Human Resources, University of Hawaii at Manoa 1: 1-2. Hollingsworth, R.G. & Armstrong, J.W. 2003. Effectiveness of products containing metaldehyde, copper or extracts of yucca or neem for control of Zonitoides arboreus (Say), a snail pest of orchid roots in Hawaii. International Journal of Pest Management 49: 115-122. Hollingsworth, R.G., Follett, P.A. & Armstrong, J.W. 2003. Effects of irradiation on the reproductive ability of Zonitoides arboreus, a snail pest of orchid roots. Annals of Applied Biology 143: 395-399. Joe, S.M. & Daehler, C.C. 2008. Invasive slugs as under-appreciated obstacles to rare plant restoration: evidence from the Hawaiian Islands. Biological Invasions 10: 245-255. Kekauoha, W. 1966. Life history and population studies of Achatina fulica. The Nautilus 80: 3-10, 39-46. Meyer, W.M., III & Cowie, R.H. 2010a. Feeding preference of two introduced predatory snails and their conservation implications. Malacologia 53: 135-144. Meyer, W.M., III & Cowie, R.H. 2010b. Invasive temperate species are a threat to tropical island biodiversity. Biotropica 42: 732-738. Sugiura, S., Holland B.S. & Cowie, R.H. 2011. Predatory behaviour of newly-hatched Euglandina rosea. Journal of Molluscan Studies 77: 101-102.