Ceylon Journal of Science 48(2) 2019: 177-184 DOI: http://doi.org/10.4038/cjs.v48i2.7622 RESEARCH ARTICLE The distribution of terrestrial pest gastropods and their damage to agricultural crops in Kandy and Nuwara Eliya districts in Sri Lanka P.W.D.B. Maheshini, K.G.D.D. Thilakarathne, G.N. Hirimuthugoda, K.B. Ranawana and S. Kumburegama* Department of Zoology, Faculty of Science, University of Peradeniya, Peradeniya, Sri Lanka Received: 01/01/2019 ; Accepted: 13/05/2019 Abstract: An island wide survey from 1999 to 2002 in Sri Lanka are endemic to the country. In addition to the endemic, highlighted the presence of 18 species of exotic snails and slugs, non-endemic native species, this study also highlighted of which most were identified as pests of agriculture crops. the presence of 18 exotic species that were introduced However, since this survey, no studies on pest gastropods have accidentally or intentionally to the country (Naggs and been carried out in the country. Hence, the present study was Raheem, 2000; Ranawana et al., 2012). Some of these carried out in Kandy and Nuwara Eliya districts in approximately species are known to adversely affect agriculture and 15 hectares of agricultural land to determine the current status horticulture in many countries world over (Naggs et al., of these gastropods. During the study, a total of 14 terrestrial 2003; Jayaratne et al., 2015). gastropod species were recorded from agricultural lands of Since this survey, there have been no follow up studies which eight species were recognized as exotic pest gastropods. on the pest gastropods and their affects to agriculture in Sri They were Deroceras reticulatum, Laevicaulis altae, Mariaella Lanka (Kumburegama and Ranawana, 2001; Kumburegama dussumieri, Milax gagates, Lissachatina fulica, Bradybaena and Ranawana, 2002). Thus, the present study was carried similaris, Allopeas gracile and Subulina octona. The damage from out to assess the present distribution of the pest gastropods pest gastropods was observed in many crops and especially in the in Kandy and Nuwara Eliya districts in the central province seedling or nursery stage plants. The highest damage to crops in and to evaluate the degree of damage caused by these pest Nuwara Eliya and Kandy districts were caused by D. reticulatum gastropods to agriculture crops in these districts. and Lissachatina fulica respectively. The study indicated that the distribution range of many of these pest gastropods, especially MATERIALS AND METHODS Laevicaulis altae and Lissachatina fulica has increased during the past fifteen years. Elevation is a key environmental factor that Study site selection affects their distribution in these districts. Field visits in agricultural lands including green houses were carried out in six Divisional Secretariats (DS) (Doluwa, Keywords: Pest gastropods, Kandy, Nuwara Eliya, distribution, Kundasale, Pasbage Korale, Udapalatha, Medadumbara agriculture, crops. and Yatinuwara) in the Kandy district and five DS (Nuwara Eliya, Kothmale, Haguranketha, Ambagamuwa and INTRODUCTION Walapane) in the Nuwara Eliya district for a period of ten Members of Class Gastropoda are the most diverse months from January to October 2017. This study period and arguably the most successful group within Phylum included both the dry (January to March) and the rainy Mollusca (Pearce and Őrstan, 2006). This group consists (May to September) seasons. Sampling for pest gastropods of the snails that typically have an external shell and the was carried out every two weeks in approximately 15 slugs that lack an external shell. Among the snails and hectares of agricultural land. During field visits, a field slugs relatively few species are considered to be pests of was defined as the land owned by a single farmer. With agriculture and horticulture (Kozlowski, 2012). In many the consent of the farmer, each field was sampled for countries these pests cause severe economic losses to terrestrial pest gastropods during the night when the pest agriculture and horticulture. Often these species are non- snails and slugs are most active. Geo-coordinates, altitude, natives of that region or country (Wiktor, 2001). Given temperature and relative humidity of each agricultural land the opportunity, these species are able to spread rapidly in visited (including greenhouses) were recorded. The owners a short amount of time and some species even penetrate were interviewed to record the history of pest gastropod natural habitats (Wiktor, 2001; Kozlowski, 2012). outbreaks in their fields and current pest gastropod control practices. Sri Lanka has a rich gastropod diversity. This diversity was brought into focus by the Darwin Initiative funded, Identification and sampling of pest gastropods island wide survey conducted from 1999 to 2002 (Naggs et al., 2003). It highlighted the presence of 253 species Snails and slugs encountered during the study were of terrestrial gastropods out of which 81% (205 species) identified using field guides (Naggs and Raheem, 2002; *Corresponding Author’s Email: [email protected] http://orcid.org/0000-0002-7378-872X This article is published under the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 178 Ceylon Journal of Science 48(2) 2019:177-184 Mordan et al., 2003). Visual and time based sampling Data analysis and distribution map preparation approach was utilized to sample pest snails and slugs. For each field visited, if a single crop was cultivated, a random The relative abundance and density of each pest gastropod sampling for pest gastropods in a total of 10 plots (1 m2 species were calculated. The relative abundance data were each) from different parts of the field was carried out. If further used to determine significant differences in the several crop types were cultivated in one field, 10 plots distribution of the pest species between the two districts from each of the crop types were sampled. Each plot was using a Mann-Whitney test in Minitab 18 software. A sampled for a maximum period of 15 minutes. The number Canonical Correspondence Analysis (CCA) was carried of pest gastropods of each species per plot was recorded. out using Canaco 5 software to determine the variation of pest gastropod distribution with measured environmental In addition the margins of the fields and adjacent home variables of altitude, temperature and relative humidity. gardens were also observed for the presence of these pest The distribution map of the exotic pest gastropods was gastropods. However, the pests gastropods encountered in prepared using Arc Map 10.3 software (Figure 1). these areas were not used in density or relative abundance calculations. Kandy Nuwara Eliya Colombo Figure 1: Distribution map of terrestrial pest gastropods observed in agricultural fields in Kandy and Nuwara Eliya districts. Figure 1: Distribution map of terrestrial pest gastropods observed in agricultural fields in Kandy and Nuwara Eliya districts. P.W.D.B. Maheshini et al. 179 Evaluation of the degree of damage to crop plants All four species of slugs encountered, namely, Deroceras reticulatum (Muller, 1856) (Figure 2A), Laevicaulis altae In each field visited the type of crops cultivated were noted. (Ferussac, 1822) (Figure 2B), Mariaella dussumieri (Gray, After the pest gastropod numbers were estimated, the 1856) (Figure 2C) and Milax gagates (Draparnaaud, 1801) degree of damage to crops from these pests was evaluated (Figure 2D) are pests of agriculture and horticulture. Out by randomly examining ten plants from each of the plots. of the nine species of snails, Lissachatina fulica (Bowdich, If a single crop is cultivated, ten plots were examined to 1822) (Figure 2E), Bradybaena similaris (Ferussac, 1822) determine the extent of damage to that crop. But, if several (Figure 2F), Subulina octona (Bruguiere, 1789) (Figure crop types were cultivated in a field, ten plots from each of 2G) and Allopeas gracile (Hutton, 1834) (Figure 2H) are the crop types were examined to separately determine the the documented pest species (Figure 2). extent of damage to each of the crop types. Either direct observation of the snails and slugs feeding or indirect The remaining six are native snail species (Figure 3). evidence in the form of slime trails at the damaged or Of these, five species are endemic, namely, Satiella sp. grazing site was used to identify the damage caused by (Figure 3A), Euplecta emiliana (Pfeiffer, 1854) (Figure gastropod pests. Then by careful observation of the parts 3B), Euplecta hyphasma (Benson, 1853) (Figure 3C), damaged, an estimation of the degree of damage (%) to Eurychlamys vilipensa (Benson, 1853) (Figure 3D) and the plant was noted. At the end of the study this data was Cryptozona chenui (Pfeiffer, 1847). The remaining species pooled and analyzed to determine the degree of damage to is, Cryptozona bistrialis (Beck, 1837) (Figure 3E), which the different crops. is a non-endemic snail. RESULTS AND DISCUSSION Interestingly, it was observed that while the exotic, pest gastropods encountered in the crop fields caused direct, Gastropod species encountered and their distribution observable damage to different parts of the crop plants, with some species demonstrating voracious appetites, Since the previous study in the early 2000s, there have been the endemic and non-endemic native species caused no no studies on the distribution, ecology, biology