Tracking Behavior in the Snail rosea: First Evidence of Preference for Endemic vs. Biocontrol Target Pest Species in Hawaii Author(s): Brenden S. Holland , Taylor Chock , Alan Lee and Shinji Sugiura Source: American Malacological Bulletin, 30(1):153-157. 2012. Published By: American Malacological Society DOI: http://dx.doi.org/10.4003/006.030.0113 URL: http://www.bioone.org/doi/full/10.4003/006.030.0113

BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder.

BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. Amer. Malac. Bull. 30(1): 153–157 (2012)

RESEARCH NOTE

Tracking behavior in the snail : First evidence of preference for endemic vs. biocontrol target pest species in Hawaii

Brenden S. Holland1, Taylor Chock2, Alan Lee3, and Shinji Sugiura1,4

1Center for Conservation Research and Training, Pacifi c Biosciences Research Center, University of Hawaii at Manoa, 3050 Maile Way, Gilmore 408, Honolulu, Hawaii 96822, U.S.A. 2Whitman College, 345 Boyer Ave., Walla Walla, Washington 99362, U.S.A. 3Depauw University, P.O. Box 37, Greencastle, Indiana 46135-0037, U.S.A. 4Department of Forest Entomology, Forestry and Forest Products Research Institute (FFPRI), 1 Matsunosato, Tsukuba, Ibaraki 305-8687, Japan Correspondence, B. S. Holland: [email protected]

Abstract: The predatory snail Euglandina rosea (Férussac, 1821) is native to the southeastern U.S.A. and has been widely introduced as an attempted biological control agent for agricultural pest gastropods, often targeting the giant African snail Achatina fulica Bowdich, 1822. However, E. rosea may impact native land snails rather than A. fulica, particularly in Hawaii. Laboratory prey preference trials for E. rosea were conducted using three prey taxa, including the endemic endangered Oahu tree snail Achatinella lila Pilsbry, 1914, the giant African snail A. fulica, and the introduced Asian trampsnail Bradybaena similaris (Rang, 1831). Trials were conducted in the laboratory on branches of ohia lehua trees, Metrosideros polymorpha, an important component for Hawaiian tree snails. Y-shaped ohia branches were used to simulate tree snail habitat and test E. rosea’s ability to track and pursue prey via slime trails on branches, and to evaluate prey choice by offering trails of two different species simultaneously and slime trail vs. water. Euglandina rosea signifi cantly favored branches with slime trails vs. water, choosing the branch with slime trail 90% of the time (P < 0.001). Predatory snails exhibited no signifi cant preference between B. similaris and A. fulica (P = 0.820), or B. similaris and A. lila (P = 0.260). However, E. rosea showed a signifi cant preference for native Achatinella lila over invasive Achatina fulica (P = 0.040), the intended target species of the biological control program.

Key words: Hawaiian tree snails, predatory snails, Achatinella lila

Euglandina rosea (Férussac, 1821) is a carnivorous, primary destructive agent of native Hawaiian and other island terrestrial pulmonate snail native to the southeastern U.S.A. snails including arboreal species (Christensen 1984, Cowie that preys exclusively on gastropod molluscs (reviewed in 2001). The conservation and resource management community Barker and Efford 2004). Euglandina rosea was introduced to in the Hawaiian Islands has been intent on fi nding effective Hawaii and many other Pacifi c islands as a biological control ways to attract, capture, and kill E. rosea for a number of years method, targeting primarily the terrestrial agricultural pest (Brenden Holland, pers. obs.). Although very little is presently species Achatina fulica Bowdich, 1822, the giant African snail known about the prey tracking and feeding behavior of this (Mead 1979, Cowie 2001). Together with a number of other species in Hawaii, gaining understanding of these underlying infamous, attempted bio-control programs in Hawaii that mechanisms and strategies will provide important information failed to control the intended pest species, this effort backfi red that ultimately should be applicable to control efforts. catastrophically (Howarth 1991, Henneman and Memmott As in many groups, gastropods track and locate 2001, Holland et al. 2008), and has led directly to range mates and food resources by detecting and following chemical reductions and of the native terrestrial island snail trails (Chase 1986, Clifford et al. 2003, Shaheen et al. 2005). fauna (Clarke et al. 1984, Cowie 2001, Lydeard et al. 2004). Trail tracking behavior is known from both predatory and non- Euglandina rosea was fi rst released in Hawaii in 1955 by the predatory snails. Predatory snails have been shown to follow Board of Agriculture and was subsequently introduced mucous trails in terrestrial, marine, and aquatic ecosystems throughout the Pacific and Indian Oceans by officials in (Chase 1986, Levri 1998, Davis 2005). At the present time, French Polynesia, Samoa, Mauritius, Micronesia, and elsewhere although an important topic, the underlying physiological (Mead 1979, Griffiths et al. 1993, Civeyrel and Simberloff and biochemical basis for prey mucous trail recognition by E. 1996, Cowie 2001). Euglandina rosea has since become a rosea is poorly understood and warrants further investigation. 153 154 AMERICAN MALACOLOGICAL BULLETIN 30 · 1 · 2012

Euglandina rosea feeds on slugs and other snails by tracking their prey through detection of small, water-soluble components in prey slime using specialized elongated lips (Clifford et al. 2003). Although most commonly encountered on the ground in Hawaii, E. rosea is known to climb trees in pursuit of prey (Davis et al. 2004), including of course, tree snails (Hadfi eld et al. 1993). Therefore, as in experiments focusing on tracking behavior in snail-eating fl atworms (Sugiura and Yamaura 2009), studies of trail tracking behavior of E. rosea were conducted on tree branches. However, E. rosea behavior has previously not been observed on such materials, but has been studied on polyethylene sheets or glass plates (Cook 1985, Clifford et al. 2003, Shaheen et al. 2005). In addition to Achatina fulica and Achatinella spp., E. rosea have also been observed to prey on the common introduced snail Bradybaena similaris (Rang, 1831) (Davis and Butler 1964). The Oahu tree snail Achatinella lila Pilsbry, 1914 was included in the trials as a representative of the endemic Hawaiian malacofauna. Laboratory prey trail preference choice trials were Figure 1. Schematic of experimental set-up, showing y-junction and conducted on y-shaped ohia lehua (Metrosideros polymorpha) relative dimensions of ohia lehua branch components. Laboratory prey trail preference trials were conducted on y-shaped ohia (Metro- tree branches to simulate arboreal conditions where the sideros polymorpha) tree branches. native tree snails live and where Euglandina rosea tracks and hunts native tree snails. Y-shaped branches stripped of leaves were suspended 15 cm off the lab bench to simulate the arboreal environment. Snail trails were carefully placed from show direction of travel. Within each of the four pairwise the beginning of the y-junction to the tip of each branch trials, B and C were randomized, to account for any inherent without overlap (Fig. 1), yet at the y-junction the two trails left-right bias in E. rosea. Prey choice experiments in pairwise were close enough that E. rosea could taste both trails trials were conducted with pairings of Achatina fulica vs. simultaneously with their specialized sensory palps (Fig. 1). Achatinella lila, A. lila vs. Bradybaena similaris, B. similaris vs. The sides (left or right of the y-junction) of the prey trails A. fulica, and A. fulica vs. water. were randomized during each set of trials to avoid any All Euglandina rosea specimens were collected from the directional bias that may have resulted from light sources or same locations in the Waianae Mountain range in Hawaii on other visual or magnetic cues that could affect the snails’ the island of Oahu. Individual weight and shell length was choice of direction. Branches were changed between trials. recorded upon arrival to the lab. Euglandina rosea specimens On the occasions when branches were reused, branches were (N = 52) were kept in plastic terraria in the laboratory (22 °C) vigorously scrubbed in scalding water and detergent, then and were fed Bradybaena similaris collected from various rinsed and air dried, effectively removing all traces of slime locations around the University of Hawaii (UH) at Manoa trails. Fresh trails were produced prior to each pairwise trial. campus approx. once a week (Table 1). Previous studies For each trial series, 20 E. rosea individuals were used (Table indicate that trail following by E. rosea was not infl uenced by 1); each predatory snail was used only once per day. hunger (Clifford et al. 2003), but regular feedings were Ten tree branches were used. Tree branch dimensions conducted to maintain the health of the specimens. The were as follows: mean length of straight element, labeled A, common Achatina fulica (N = 5) were also obtained on the was 8.75 cm (SE 3.06), mean length of split elements after UH campus. Achatinella lila (N = 5) occurs in the central y-junction was 9.79 cm (SE 2.31) the average angle between Koolau Range on Oahu, and were kept in environmental branches B and C was 40° (Fig. 1). Foliage was removed before chambers in the UH Tree Snail Conservation Lab. Achatinella trials began, and snail mucous trails were removed between lila was kept under permit by the USFWS and no individuals trials, or new branches were used. Dimensions of y-junction were harmed during these trials. of branches used was such that as Euglandina rosea moved Since prey were not consumed by Euglandina rosea in along the straight portion to the junction, it was allowed to these trials, one important consideration in our experimental choose which direction, either B or C (Fig. 1), to pursue. design was the possibility that, since Achatina fulica is Point A shows the starting point for predatory snails, arrows substantially larger than the other two experimental prey PREY TRACKING IN EUGLANDINA 155

Table 1. Total numbers of predator and prey snail specimens used. Shell length, width, and weight given are mean values with standard errors in parentheses.

Species N Shell length (cm) Shell width (cm) Weight (g) Achatina fulica 5 53.36 (14.59) 28.8 (7.41) 21.03 (12.3) Bradybaena similaris 10 8.35 (1.37) 4.66 (0.73) 0.16 (0.10) Achatinella lila 5 15.83 (3.75) 7.76 (0.41) 0.76 (0.16) Euglandina rosea 52 34.92 (9.54) 15.83 (3.75) 2.84 (2.07) species, its slime trail could be wider, potentially causing Finally, in trials of Achatinella lila vs. Achatina fulica, the confounding factors by the amount of trail material, rather native Hawaiian tree snail was chosen 15 times out of 20 (P = than the intended variable. However, the tree branches used 0.040). While not strongly signifi cant, the results show for the were standardized by their width to approx. 5–6 mm in fi rst time that Euglandina rosea preferred an endemic, diameter (within the width range of labial palps), so that endangered species rather than its intended biocontrol target. branches were narrower than prey foot width, limiting prey Previously published laboratory choice and gut content size as a factor in the preference experiments. studies of fi eld-collected individuals indicated that adults of To place slime trails on branches, Achatina fulica, Achatinella Euglandina rosea preferred snail species much smaller than lila, and Bradybaena similaris were placed on the branch in an themselves (Cook 1985, Griffi ths et al. 1993, Meyer and Cowie active state with foot protruding and were allowed to crawl 2010). Whether E. rosea can discriminate among prey snail along the length of the branch, with occasional directional species using mucous trails had until now remained unclear prodding if the snail was inactive. Because of A. fulica’s large although E. rosea has been known to discriminate between size relative to the tree branch, individuals occasionally required conspecifi c and prey snail trails (Clifford et al. 2003). Our trail- manual assistance to remain upright as they crawled along choice experiments indicated that E. rosea can discriminate the length of the branch. Each trial was considered complete between Achatinella lila and Achatina fulica trails. once Euglandina rosea made a choice and crawled to the tip of Interestingly, Euglandina rosea showed no preference the branch furthest from the y-junction (Fig. 1). In all cases, between the Oahu native Achatinella lila and introduced slime trails were applied to branches, then prey snails removed, Bradybaena similaris. Implications here suggested that in and predators immediately placed at the y-junction for the areas where both prey species are present, neither had any choice trial. Efforts were made to present fresh mucous trails immediate survival advantage over the other. However, B. to predators, normally less than 15 minutes old. similaris develops, matures, and reproduces at a much faster Three trials with 20 Euglandina rosea each were conducted rate than Achatinella spp., giving the introduced species an with two prey species presented one at a time. In addition, an advantage over the live bearing and late maturing Achatinella experiment was performed using 20 E. rosea with Achatina spp. There are forest regions on Oahu where both species co- fulica slime on one side of the branch and tap water on the occur, such as Puu Hapapa, where the majority of the E. rosea other (Fig. 1). These trials were a control to ensure that E. rosea used in this study were collected. The E. rosea used in this was following mucous rather than following the branch for an study may have fed on both species in the wild and were opportunity to hydrate. Tracking frequencies were analyzed therefore locally adapted to feeding on these prey. This could using a two-tailed binomial test (Iwai et al. 2010). be a confounding factor causing preference of locally available The results of the control trial showed clearly that prey over Achatina fulica though no preference was exhibited Euglandina rosea pursued the Achatina fulica path signifi cantly more often (18 out of 20 replicates) than the water path, supporting that E. rosea was indeed attracted to slime rather Table 2. Trail preference results showing the number of times each prey trail was chosen by Euglandina rosea. Each trial series consisted than water (Table 2). of 20 replicates, table includes P values from two-tailed binomial However, no signifi cant preference between Bradybaena tests, where P values with asterisk (*) were statistically signifi cant. similaris and Achatina fulica was observed, with nine predatory snails selecting A. fulica and 11 choosing B. similaris out of 20 Trial series Total number of times chosen P value replicates (two-tailed binomial test: P = 0.820). In trials between B. similaris and Achatinella lila, Euglandina rosea chose B. 1 Achatina (11) vs. Bradybaena (9) 0.820 similaris 13 times and A. lila 7 times out of 20 trials (P = 0.260), 2 Achatinella (7) vs. Bradybaena (13) 0.260 3 Achatinella (15) vs. Achatina (5) 0.040* suggesting that E. rosea had no preference between B. similaris 4 Achatina (18) vs. water (2) <0.001* and A. lila (Table 1). 156 AMERICAN MALACOLOGICAL BULLETIN 30 · 1 · 2012

ACKNOWLEDGMENTS

Thanks to Vince Costello and Stephanie Joe for providing live Euglandina rosea for use in this study and to the Oahu Natural Resources Program, U.S. Army Garrison, for laboratory support. Taylor Chock was supported during preparation of this manuscript by an internship from Whitman College. Alan Lee was supported by a grant from the USFWS to M. G. Hadfi eld. Shinji Sugiura was supported by a Japan Society for Figure 2. Adult Euglandina rosea tracking Achatinella lila that has the Promotion of Science (JSPS) Postdoctoral Fellowship for just crawled along the branch leaving a fresh mucous trail. Prey Research Abroad. We thank Donna Poscablo for providing snails were removed from the branch prior to placing E. rosea on the the photo in Figure 2. branch to avoid confounding olfactory or visual factors. Snail tracks were removed from bark between trials by scrubbing in scalding wa- ter and detergent, rinsing, and air drying. LITERATURE CITED

Barker, G. M. and M. G. Efford. 2004. Predatory gastropods as natu- ral enemies of terrestrial gastropods and other invertebrates. for B. similaris vs. A. fulica. Future studies on prey preference In: G. M. Barker, ed., Natural Enemies of Terrestrial Molluscs. in E. rosea might take prey ranges into account, and test prey CABI Publishing, Wallingford, U.K.. Pp. 279–403. collected from areas where B. similaris is present but species Chase, R. 1986. Lessons from snail tentacles. Chemical Senses 11: of Achatinella are absent, as well as areas where Achatinella 411–426. spp. are present but B. similaris is absent, to evaluate the Christensen, C. C. 1984. Are Euglandina and Gonaxis effective possible role of local adaptation in prey choice. agents for biological control of the giant African snail in Ha- waii? American Malacological Bulletin 2: 98–99. In the Hawaiian Islands, the geographic distribution of Civeyrel, L. and D. Simberloff. 1996. A tale of two snails: Is the cure Euglandina rosea ranges from sea level to mountain peaks and worse than the disease? and Conservation 5: 1231– ridges at about 1000 m, whereas Achatina fulica occurs in 1252. lower elevation , likely allopatric with Achatinella lila. Clarke B., J. Murray, and M. S. Johnson. 1984. The of In addition A. fulica is a ground-dwelling species and has not endemic species by a program of biological control. Pacifi c Sci- been observed to climb ohia trees. Therefore it is highly ence 38: 97–104. unlikely that E. rosea would encounter a choice between Clifford, K. T., L. Gross, K. Johnson, K. J. Martin, N. Shaheen, and M. native tree snails and African snails in the fi eld. A. Harrington. 2003. Slime-trail tracking in the predatory snail, Although resource managers in Hawaii have long Euglandina rosea. Behavioral Neuroscience 117: 1086–1095. speculated as to whether native island snails might be preferred Cook, A. 1985. Functional aspects of trail following by the carnivo- to the intended biocontrol target species Achatina fulica, this rous snail Euglandina rosea. Malacologia 26: 173–181. Cowie, R. H. 2001. Can snails ever be effective and safe biocontrol is the fi rst study to conclusively document this phenomenon. agents? International Journal of Pest Management 47: 23–40. The data presented here provide the fi rst concrete evidence Civeyrel, L. and D. Simberloff. 1996. A tale of two snails: Is the cure that, when offered fresh mucous trails of the giant African worse than the disease? Biodiversity and Conservation 5:1231– snail and an endemic Oahu tree snail, there is a clear preference 1252. for the tree snail. In addition, in unpublished laboratory trials, Davis, E. C. 2005. Trail Detection and Ecological Niche Modeling we observed that even when Euglandina rosea attempted to in Terrestrial Gastropods. Ph.D. Dissertation, University of attack larger A. fulica adults, it usually failed, due presumably Kansas. to the large size disparity. Yet surprisingly, well-intentioned Davis, C. J. and G. D. Butler. 1964. Introduced enemies of the giant agriculture agency personnel from island nations where A. African snail, Achatina fulica Bowdich, in Hawaii (: fulica is present periodically propose release of E. rosea as a Achatinidae). Proceedings of the Hawaiian Entomological Society solution. This study provides strong support against continued 18: 377–389. Davis, E. C., K. E. Perez, and D. J. Bennett. 2004. Euglandina rosea release of E. rosea, for any reason. (Férussac, 1821) is found on the ground and in trees in Florida. Knowledge of prey preferences of Euglandina rosea may The Nautilus 118: 127–128. ultimately help in the design and construction of attractant Griffi ths, O., A. Cook, and S. M. Wells. 1993. The diet of the intro- traps for E. rosea that could be used throughout the Pacifi c duced carnivorous snail Euglandina rosea in Mauritius and its islands to control and ultimately exterminate E. rosea to implications for threatened island gastropod faunas. Journal of preserve native and endemic fauna. Zoology 229: 79–89. PREY TRACKING IN EUGLANDINA 157

Hadfi eld, M. G., S. E. Miller, and A. H. Carwile. 1993. The decima- tion of endemic Hawaiian tree snails by alien predators. Ameri- can Zoologist 33: 610–622. Henneman, M. L., and J. Memmott. 2001. Infi ltration of a Hawai- ian community by introduced biological control agents. Science 293: 1314–1316. Holland, B. S., C. C. Christensen, K. A. Hayes, and R. H. Cowie. 2008. Biocontrol in Hawaii: Ecological and regulatory perspec- tives. Proceedings of the Hawaiian Entomological Society 40: 81–83. Howarth, F. G. 1991. Environmental impacts of classical biological control. Annual Review of Entomology 36: 485–509. Iwai, N., S. Sugiura, and S. Chiba. 2010. Prey-tracking behavior in the invasive terrestrial planarian Platydemus manokwari (Platy- helminthes, Tricladida). Naturwissenschaften 97: 997–1002. Levri, E. P. 1998. Perceived risk, parasitism, and the forag- ing behavior of a freshwater snail (Potamopyrgus antipodarum). Canadian Journal of Zoology 76: 1878–1884. Lydeard, C., R. H. Cowie, W. F. Ponder, A. E. Bogan, P. Bouchet, S. A. Clark, K. S. Cummings, T. J. Frest, O. Gargominy, D. G. Herbert, R. Hershler, K. E. Perez, B. Roth, M. Seddon, E. E. Strong, and F. G. Thompson. 2004. The global decline of non- marine mollusks. BioScience 54: 321–330. Mead, A. R. 1979. Economic malacology with particular reference to Achatina fulica. In: V. Fretter and J. Peake, eds., The Pulmonates Vol. 2B. Academic Press, London, Pp. 1–150. Meyer, W. M. III. and R. H. Cowie. 2010. Feeding preferences of two predatory snails introduced to Hawaii and their conservation implications. Malacologia 53: 135–144. Shaheen, N., K. Patel, P. Patel, M. Moore, and M. A. Harrington. 2005. A predatory snail distinguishes between conspecifi c and heterospecifi c snails and trails based on chemical cues in slime. Animal Behaviour 70: 1067–1077. Sugiura, S. and Y. Yamaura. 2010. Potential impacts of the invasive fl atworm Platydemus manokwari on arboreal snails. Biological Invasions 11: 737–742.

Submitted: 18 August 2010; accepted: 17 February 2011; fi nal revisions received: 31 October 2011