Occurrence of Distinct Carabid Beetles (Coleoptera: Carabidae) in Eastern Visayas, Philippines

Tropical forests, which include a considerable component of terrestrial biodiversity (Myers et al. 2000), are rapidly decreasing (Chazdon 2003, Dudley et al. 1998, Laurance 1999, Tole 1998). Specifically, the tropical forests of Southeast Asia are among the most disturbed because of excessive logging and continuous slash-and-burn agriculture (Fu 2003, Giri et al. 2003, Laurance 1999). The forested regions of Southeast Asia showed a decline of more than 16 million ha in 1990s, with an annual loss of 1.2% (FAO 2019). Among the highly affected are biodiversity “hot spots” of the Philippine archipelago, which contain a high number of endemic species (Brooks et al. 2002). Indeed, the Philippines has one of the most astounding deforestation rates in the last decade, with a loss of 30,350 ha annually (Kincaid 2002).

Changes in land use, for example, forest conversion to agricultural land, has been identified as the leading source of variation in species composition at both local and regional scales (Adams 2010, Huston 1993, Myers and Knoll 2001) and has been influential in the decrease of responsive species like carabid beetles in various parts of the world (Brooks et al. 2002, Kotze and O'Hara 2003, Vanbergen et al. 2010). Carabid beetles are noticeably distributed and taxonomically acclaimed with a solid systematics, and their ecological behavior has been widely studied (Homburg et al. 2014, Lövei and Sunderland 1996). Their importance resides in: (1) experimental evidence proposes they may be used as keystone indicators (Kotze et al. 2011); (2) they are responsive to anthropogenic-induced conditions, such as pesticide use in agroecosystems or contamination of soils by heavy metals (Butovsky 2011, Menalled et al. 2007); (3) they are associated with various species that are representative of a specific habitat types or successional stages, making them potential bioindicators (Lövei and Sunderland 1996); (4) they serve as early-warning indicators, as suggested by recent studies linking climate and carabid distributions (Pozsgai and Littlewood 2014); and (5) they react to natural and human-induced disturbances and management (Lövei and Sunderland 1996).

Despite its small geographic surface area, the Philippines ranks fifth globally in terms of carabid diversity and third in the level of endemic species (after Madagascar and Australia) (Cassola 2011, Cassola and Pearson 2000, Cassola and Ward 2004). However, the Philippines ranks first globally in terms of number of endemic carabid species per unit of land area. Yet, little consideration has been given to the nation's carabid fauna, to their conservation status, and the presumable impact of environmental changes and human activities likely have on these groups.

Carabids are cosmopolitan, with species richness highest in the tropical regions (Erwin 1985). However, our knowledge stems from research conducted in temperate regions of the northern hemisphere, resulting in inevitable bias. Despite their significant role in the ecosystem, ecological studies of ground-dwelling beetles are rather scarce in the northeastern hemisphere, particularly in Asia (Magagula 2003, Padayachi et al. 2014, Samways et al. 1996). The majority of studies focus on beetles in the northern hemisphere, where the taxonomy and ecology of this group of beetles are well known (Atlegrim et al. 1997, Fahy and Gormally 1998, Jukes et al. 2001, Thiele 1977, Woodcock et al. 2003). Although sporadic studies of ground-dwelling beetles have been conducted in the Philippines, these have focused primarily on the tiger beetles (subfamily Cicindelinae) and cannot be used to account for the total number and diversity of carabids in the country. The Philippines is characterized by considerable insect diversity; thus, the study of insect diversity is of great value. Baltazar (2001) reported that Coleoptera in the Philippines included 87 families, 1,567 genera, and 7,375 species, with 5,840 being endemic. However, very little attention has been given to the beetle communities, their conservation status, and the likely influence of habitat fragmentation and anthropogenic activities on these communities in the Philippines.

Recent reviews and publications on the carabid fauna of the Philippines were conducted by Cassola (2000, 2011), Cassola and Ward (2004), Cassola and Zettel (2006), Ceniza (1994), Deuve (2015), Dheurle (2015), Naviaux (1992, 2002), and Wiesner (1980, 1988a, 1989, 1992a, 1992b, 2015). Several new species have been recognized and described, including Thopeutica milanae (Weisner) in Leyte, Elaphropus schawalleri (Baehr), E. surrulipennis (Dejean), E. martensi (Baehr), and Paratachys leytensis (Baehr) in Leyte, and Brachinus bendanilloi and Pheropsophus azoulayi (Lassalle & Schnell) in Leyte and Cebu. These and other studies have served as impetus for further studies of the carabids in the forests of Eastern Visayas. We undertook this investigation to identify the occurrence and habitat preferences of carabid beetles in Lake Danao, Mount Ncolod, Kuapnit Balinsasayao, Asug Forest, City Forest, and Closed Canopy Forest in Eastern Visayas to provide baseline data for the conservation of carabid beetles and their forest habitats.

Site selection. The study was conducted in selected forests of Eastern Visayas: (1) Lake Danao National Park of Ormoc City, Leyte; (2) Kuapnit Balinsasayao National Forest of Abuyog and Baybay City, Leyte; (3) City Forest and Marble Park in Calbayog City, Samar; (4) Asug Forest Reserve, Biliran; (5) Mount Nacolod Forest in Silago, Southern Leyte; and (6) Borongan-Llorente Closed Canopy Forest in Borongan, Eastern Samar (Fig. 1). These forests were chosen based on (1) slope position (incline extending from ≥8–18% can be utilized for regular and lasting yield generation), (2) cultivated area is located near the forest, (3) portions of the forest have been formed by slash-and-burn practices, and (4) forest contains areas under current cultivation. These forests are either declared as protected areas or proposed protected areas by the Department of Environment and Natural Resource of Eastern Visayas.

Survey methods. Carabid beetles were collected using pitfall trapping and manual collection and/or searching the ground. The pitfall traps were 500-ml plastic containers (11.4 cm long × 11.4 cm wide × 8 cm high) that were half-filled with bait substance and were buried in the ground so that the top of the trap was at the soil surface. One hundred traps were placed in every habitat type at each forest, with a total of 200 pitfall traps placed in every study site. The traps were arranged in square grids with 20 m between adjacent traps to avoid trap interactions (e.g., the “digging in” effect [Hoekman et al. 2017]).

After a 2-week comparison of baits, we decided to use vinegar, vinegar with catsup, fermented fish with vinegar, and ground meat as attractants in the traps. Pitfall traps captured carabid beetles using these bait materials, while previously used baits did not effectively capture any carabid beetles. A 13 × 13-cm piece of metal was secured over each trap as a shield from rain, litter, and disturbance by animals. Traps were emptied and refilled twice weekly at which time carabids were collected and returned to the laboratory for sorting and identification.

Meanwhile, hand-picking/searching on the ground was conducted by actively searching for the beetles on the ground, in leaf litter, under logs and other substrates, under tree bark, and in rotting deadwood. Sixty man-hours were spent in active searching for each visit at each site, occurring primarily between 2000 and 2300 hours, as most carabid beetles are nocturnal. Collections were made four times a month over 6 mo (i.e., January–June 2019) for each site.

A 0.5-cm mesh screen was used to sift dry leaf litter for carabid beetles. Moist leaf litter was scooped onto white cloths and a pair of forceps was used to collect beetles. Likewise, resting and running beetles were sampled by manual searching under logs, stones, and tree bark. Collecting took place both during the day and at night. All specimens were transferred into a killing agent preservative (9.0:0.5:0.5 parts of 70% ethyl alcohol, table vinegar, ethyl acetate [3:1]) as per Hoekman et al. (2017).

Identification. Carabids were identified to the species level when possible using the works of Thiele (1977), Lindroth (1949), Scholtz and Grebennikov (2005), Luff (1987), Kirschenhofer (2008), and Trautner and Geigenmüller (1987). All identifications were confirmed by Dr. Bernard Lassalle (French Entomological Society, France) and Dr. Rainer Schnell (University of Duisburg Essen, Germany). Representative specimens are stored in the Biology Laboratory, Leyte Normal University, Philippines.

A total of 7,844 individuals belonging to 41 species, 25 genera, 13 tribes, and 2 subfamilies were collected in this survey of six selected forests in Leyte and Samar. Specifically, 26 species were collected from Lake Danao, 32 species from Mt. Nacolod, 20 species from Kuapnit Balinsasayao Forest, 11 species from Asug Forest, 19 species from City Forest, and 26 species from Closed Canopy Forest (Table 1). The survey recorded 19 endemic species, of which 12 are endemic to the Philippines, 6 are endemic to Leyte, and 1 is endemic to Samar. The most commonly encountered and abundant species were Pheropsophus hassenteufeli (Straneo), P. lumawigi (Hrdlicka), Tricondyla aptera punctipennis (Chevrolat), T. ovicollis (Motschulsky), and T. conicicollis (Chaudoir). Their abundance and ubiquity suggest their high resiliency to the presence of anthropogenic disturbances. These species were observed to prefer open riparian ecosystems with diverse vegetation, a characteristic of all study sites where they were collected.

The most dominant tribe recorded was Brachinini (Subfamily Carabinae) with eight species, followed by Cicindelini with six species. Five species from Tribe Collyridini were collected, and four species each representing Lebiini and Chlaeniini were collected.

Six new records of carabid species occurrence in Leyte were noted. These included Brachinus leytensis (Lassalle & Schnell), Trigonotoma goeltenbothi (Lassalle, Roux & Schnell), Pheropsophus lumawigi (Hrdlicka), Pheropsophus azouleyi (Lassalle & Schnell), Pheropsophus uliweberi (Lassalle & Schnell), and Pheropsophus sp. (Lassalle & Schnell). The latter two species appear to be previously undescribed species, are designated as species nova herein, and will be formally described in an ensuing publication (Fig. 2A, B). Lesticus samarensis (Dubault, Lassalle & Roux) was reported as a new record for Samar Island.

Low numbers of carabid species were observed in the forests of Samar, which might be attributed to less tree canopy cover in those forests. Carabid beetles are known to be highly associated with forested habitats. Farming and conversions of forest land to agricultural land may cause disturbance of the larvae of carabids, further reducing their diversity in the area. Nevertheless, these forests seem to be a suitable habitat for carabid beetles due to the open and sandy riverine ecosystem that is preferred by some species of carabid beetles from the Tribe Cecindelini. Conversion of land usage from forests to agricultural land and human settlements might have caused the observed reduction in species richness and diversity.

Conversely, higher numbers of carabid beetles were observed in the Leyte forests. This might be attributed to sparse vegetative cover in comparison to the forests of Samar. The preference of some carabid beetles, like tiger beetles, to sandy soil with sparse vegetation was also reported by Hoback et al. (2000), who noted that sandy areas are conducive to female reproductive activities. Because this study on carabid distribution and occurrence is the first to be conducted and/or reported from Leyte and Samar, there are no other studies for comparisons.

Notwithstanding the diverse anthropogenic disturbances in the six forests studied herein, carabid beetles flourish, thus demonstrating how these groups of species continually adapt to their environments. Yet, land conversions (e.g., disturbances as well as human settlements stripping the forests because of unlawful logging of timber) pose threats to the carabid beetles inhabiting these six forests. Slash-and-burn farming, which destroys growth on the steepest slopes, poses further threat to the species dwelling in these ecosystems. Some carabid beetles, which are habitat specific and have a narrow geographic distribution, should be subject to protection and conservation priority as the current loss of our forest ecosystems has a profound effect on their survival. Special attention should be given to species that are endemic, rare, and occupy small areas or habitats are at special risk of extinction. Interventions, such as the implementation of the forest warden system, would be an effective strategy in deterring illegal activities in the forest.

We thank the chairpersons of the different barangays where collections were conducted, farmers Rogelio Amay, Juan Santiago, Robert Daclitan, Roy Albuera, Christian Magno, Alvin Yodico, Mario Samson, Leo Samson, Rey Lacdao, and Martin Pascua for the help in data collection, local guides from the different forest sites, barangay officials for granting permission to survey the areas, the Department of Environment and Natural Resources Regional Office VIII and Protected Area Management Board for granting us the necessary permits, and the Commission on Higher Education for the funding.