Introduction
Recent decades have seen an increase in global attention being given to agricultural practices and their consequences for food safety and biodiversity (Foley et al. Reference Foley, DeFries, Asner and Barford2005, Tschnarke et al. Reference Tscharntke, Clough, Wanger, Jackson, Motzke and Perfecto2012). Intensive agriculture increases yield (Seufert et al. Reference Seufert, Ramankutty and Foley2012) but has been associated with declines in species diversity across all taxonomic groups (e.g., Kehoe et al. Reference Kehoe, Kuemmerle, Meyer, Levers, Václavík and Kreft2015, Outhwaite et al. Reference Outhwaite, McCann and Newbold2022). Organic agriculture, on the other hand, can promote biodiversity in terrestrial and aquatic ecosystems (Bengtsson et al. Reference Bengtsson, Ahnström and Weibull2005, Fuller et al. Reference Fuller, Norton, Feber, Johnson, Chamberlain and Joys2005) and is key to maintaining ecosystem services and multifunctionality, leading, for instance, to increased levels of soil organic matter and microbial activity (Paudel et al. Reference Paudel, Wang, Poudel, Acharya, Victores, de Souza and Wang2023). While there has been a push for the development of organic agriculture in high-income countries, where crop systems are largely intensive, there is also concern about the ongoing conversion of land to intensive agriculture in middle- and low-income countries, where traditional agricultural practices have been maintained until now. This concern is particularly relevant in the context of Lao PDR, where economic pressures and policy influences continue to drive the shift towards more intensive agricultural practices.
Insects play diverse roles in ecosystem services, such as acting as indicators of ecosystem functional change, facilitating pollination, aiding decomposition and serving as a food source for other organisms. Beetles specifically (order: Coleoptera) play crucial ecological roles (Jones et al. Reference Jones, Fu, Reganold, Karp, Besser, Tylianakis and Snyder2019); however, like other insects, they are at particular risk from agricultural intensification (Sánchez-Bayo & Wyckhuys Reference Sánchez-Bayo and Wyckhuys2019, Eggleton Reference Eggleton2020). Beetles can serve as effective indicators of the impacts of agricultural practices on ecosystem functioning (Gallé et al. Reference Gallé, Happe, Baillod, Tscharntke and Batáry2019, Chouangthavy et al. Reference Chouangthavy, Sanguansub and Das2021). Importantly, polyphagous predators (including carabid beetles), which serve as biological control agents for managing pests in cultivated areas (Diekötter et al. Reference Diekötter, Wamser, Wolters and Birkhofer2010), are particularly favoured by organic agriculture (Gallé et al. Reference Gallé, Happe, Baillod, Tscharntke and Batáry2019).
In recent years, agricultural land area has increased rapidly across Lao PDR, driven by foreign investments; there was a doubling in the number of foreign companies or factories in Lao PDR from 2009 to 2015 (Wentworth et al. Reference Wentworth, Pavelic, Kongmany, Sotoukee, Sengphaxaiyalath, Phomkeona and Manivong2021). The conversion of organic agriculture to intensification practices has been particularly noticeable in large-scale banana plantations (NAFRI 2016), revealing a steady transition from subsistence to commercial production, in which chemical fertilizers and pesticides are used. The conversion of natural forests into plantations reduces beetle abundance and diversity (Chouangthavy & Fourcade Reference Chouangthavy and Fourcade2023), showing that agriculture expansion is an obstacle to the preservation of insect biodiversity in Lao PDR. In response to concerns over suspected health risks for farm workers and consumers, as well as water contamination associated with the heavy use of agrochemicals on farms, the promotion of organic agriculture in Lao PDR has been supported by rural development non-governmental organizations and private-sector enterprises seeking access to premium markets; the Lao PDR government has played a role in this from its early stages (Panyakul Reference Panyakul2012). An important remaining question is whether this approach can also promote the maintenance of ecosystem services and the conservation of the country’s biodiversity, including its rich beetle fauna. In addition, understanding seasonal variation in beetle communities is essential for assessing how farming systems, such as organic and conventional ones, interact with factors like resource availability and climate. We therefore compared the diversity and abundance of beetles between organic and conventional farms in Vientiane, the capital of Lao PDR. Agricultural intensification is known to significantly impact the distribution, diversity and abundance of coleopteran communities in many tropical agricultural ecosystems, but it remains unclear how seasonal variations and range shifts may influence the local fauna in Lao PDR. Understanding these patterns is important for interpreting the temporal dynamics of beetle populations, as changes in seasonality could affect beetle abundance and community composition. Our objective was to analyse the beetle community composition in these contrasting farming systems and in different months.
Methods
Study area and farm selection
The study was conducted in three organic farms across an area of 2.5 ha and three conventional farms across an area of 5.7 ha in Vientiane in 2023, where organic farming encompasses 175 ha of land and over 1000 tonnes of organic products are grown and sold annually (National Statistics 2020). Conventional farming remains dominant, covering c. 340 ha, but it involves cultivation of a range of vegetables similar to those grown on organic farms.
The organic farms were in Non-Tare village (18°7′18.39″N, 102°42′27.21″E), situated c. 7 km away from three selected conventional farms in Pakxab Kao village (18°8′45.54″N, 102°46′38.14″E). The organic farms were c. 200–300 m apart, located within the same general area where farmer groups practise organic farming, adhering strictly to the regulations and guidelines of Lao Ministry of Agriculture and Forestry organic certification. This form of organic farming uses composted and fresh manure (e.g., cow and chicken dung) for organic inputs and does not employ chemical or synthetic fertilizers and pesticides.
The vegetables grown in the three conventional farms are treated with synthetic fertilizers (e.g., NPK), pesticides, insecticides and herbicides. Located along the Nam Ngum River, where a convenient water supply for agriculture is available, they are surrounded by paddy rice fields, fruit orchards (predominantly tamarind, jackfruit and mango trees) and ponds. They are also situated in close proximity to other intensive agricultural practices, such as deforestation for cassava plantation, expansion of grazing areas for cattle and road construction.
Beetle sampling and identification
Pitfall traps were set and collected over a 7-month period (January–July) in 2023 following the methodology of Chouangthavy & Fourcade (Reference Chouangthavy and Fourcade2023). The traps were positioned along a transect line through the centre of each farm in areas with the most densely planted crops, with a total of 10 traps per farm, placed at least 10 m from each other and in the middle of each month (10 traps × 6 farms × 7 months = 420 traps). Beetles (Coleoptera) were collected from the traps after 7 days. This approach ensured that our traps were representative of the primary cropping patterns while capturing the influence of crops within close proximity.
Specimens were dried in an oven at 45°C for 7 days, then transferred to wooden insect collection boxes – one for each family – and sorted into morphospecies. Some beetle species could be identified thanks to comparisons with Laotian beetles from the families Curculionidae and Bostrichidae, identified by Dr Roger Beaver (Chiang Mai, Thailand). Specimens belonging to the Carabidae, Chrysomelidae, Coccinellidae and Scarabaeidae families were forwarded to the Plant Protection Center, Department of Agriculture and Forestry in Vientiane and identified by Dr Phoukaothong Sikaisone. These specimens were then compared with older samples from lowland agricultural ecosystems in Lao PDR (Rapusas et al. Reference Rapusas, Schiller, Heong, Barrion, Sengsoulivong, Inthavong and Inthavong2006) housed at the Center. The remaining families were cross-referenced with voucher specimens housed in the Faculty of Forestry at the National University of Laos (Lee et al. Reference Lee, Bae and Won2017). For specimens unidentified at the genus or species level, we assigned them morphospecies codes such as ‘sp’ or ‘sp1, 2, 3 …’ for each family – for example, Scirtidae sp1.
All specimens were assigned to nine functional feeding guilds: phytophages, dung feeders, fungivores, omnivores, pests, pollen feeders, predators, saprophages and scavengers (Chenchouni et al. Reference Chenchouni, Menasria, Neffar, Chafaa, Bradai, Chaibi and Si Bachir2015). These feeding guilds aided our understanding of the ecological roles of the beetle families within ecosystems and how they might contribute to ecosystem dynamics (Tscharntke et al. Reference Tscharntke, Sekercioglu, Dietsch, Sodhi, Hoehn and Tylianakis2008). Beetle data from the 10 traps in each farm were pooled to form one sample per sampling farm per month.
Data analysis
We first compared the beetle morphospecies richness between organic and conventional farms by constructing accumulation curves based on the number of collected individuals as a measure of sampling effort (Chao et al. Reference Chao, Gotelli, Hsieh, Sander, Ma, Colwell and Ellison2014) using the ‘iNEXT’ R package (Hsieh et al. Reference Hsieh, Ma, Chao and McInerny2016).
We then examined the beetle community composition in both farming systems by employing non-metric multidimensional scaling (NMDS). A permutational multivariate analysis of variance (PERMANOVA) was also used to test for differences between the two groups and sampling months. Site identity was also included as a covariate to account for the fact that sampling was repeated several times in the same sites. NMDS and PERMANOVA were based on the Bray–Curtis distance between samples and were conducted using the ‘vegan’ R package.
We compared the relative abundance of each beetle family and feeding guild between the organic and conventional farms by summing the data in each and using Pearson χ2 tests.
Finally, we tested for seasonal patterns in beetle abundance and species richness between organic and conventional farms. To examine this, we modelled the variation in beetle abundance and species richness as a function of the farming system, considering the interaction with the sampling month. We used negative binomial generalized linear mixed models with site identity as a random intercept, implemented using the ‘lme4’ package for R. This approach allowed us to account for seasonal effects and potential overdispersion in the count data, providing robust estimates of the relationship between farming system and temporal dynamics.
Results
Among the total of 2504 individuals belonging to 99 beetle morphospecies in 23 families, almost half (1038 individuals) were Nitidulidae. We observed 1262 individuals belonging to 47 species (14 families) in conventional farms and 1242 individuals belonging to 65 species (18 families) in organic farms. The accumulation curves (Fig. 1a; additional curves based on other diversity indices in Fig. S2) suggested that we sampled 0.99 of all species present in these two farming systems, and that family richness was effectively higher in organic farms (asymptotic richness estimator: organic farms = 70.32 (95% confidence interval (CI): 65.00–84.12)); conventional farms = 51.16 (95% CI: 47.00–70.55)). The NMDS (stress = 0.19, non-metric fit = 0.97; Fig. S1) revealed vastly different compositions between conventional and organic farm samples. Only 13 species were present in both farm types, including the single most frequent morphospecies of our dataset (‘Nitidulidae sp1’); there was a significant difference between farm types in community composition (PERMANOVA, F1,30 = 4.38, R2 = 0.08, p = 0.001) and in the distribution of individuals among families (χ2 = 1110.3, df = 22, p < 0.001).
(a) Rarefaction and extrapolation curves of beetle species richness for conventional and organic farms. (b) Abundance of beetles collected in conventional and organic farms (all data merged), grouped by feeding guild.
The relative abundance of beetles among feeding guilds also differed between conventional and organic farms (χ2 = 1030.2, df = 7, p< 0.001; Fig. 1b). Conventional farms were dominated by saprophagous (638 individuals) and pest (539) species, while predators (586 individuals) and saprophagous species (429 individuals) were the most abundant in organic farms. The number of individuals sampled across the months did not vary between conventional and organic farms (effect of farming system: χ2 = 0.65, df = 1, p = 0.418; effect of month × farming system interaction: χ2 = 10.69, df = 6, p = 0.098), but there was a significant effect of sampling month (χ2 = 35.19, df = 6, p < 0.001), with fewer individuals sampled during the first (January) and last (July) months of sampling (Fig. 2a).
Mean (± standard error of the mean (s.e.m.)) (a) abundance and (b) species richness sampled in conventional (red) and organic (green) farms during the 6 months of sampling.
Locally sampled species richness was significantly higher in organic compared to conventional farms (χ2 = 10.65, df = 1, p = 0.001; Fig. 2b). Among sampling months there were differences in beetle community composition (F6,30 = 3.00, R2 = 0.29, p = 0.001) and richness (χ2 = 31.21, df = 6, p < 0.001), and there was also a significant interaction between farming system and sampling month (χ2 = 13.43, df = 6, p = 0.037).
Discussion
We highlight the potential value of organic farming practices for preserving beetle diversity in Lao PDR, where such studies are limited (Chouangthavy et al. Reference Chouangthavy, Sanguansub and Das2021). Our findings demonstrate differences in beetle diversity between three organic farms and three conventional farms, suggesting that farming practices may influence beetle populations in this context.
Our two farm types being located in different areas constrains the generalizability of our findings. Location-specific factors such as microclimate, soil conditions or surrounding landscape features might influence the observed patterns, in addition to effects of organic farming, which primarily favoured open-field carabid species and promoted greater abundance and diversity among habitat specialists compared to generalist species (Puech et al. Reference Puech, Baudry, Joannon, Poggi and Aviron2014). The fact that Nitidulidae, Chrysomelidae, Curculionidae, Carabidae and Coccinellidae stood out as dominant among the sampled beetle families can be attributed to the exceptional dispersal abilities of these beetles, coupled with a general affinity for agricultural ecosystems (Puech et al. Reference Puech, Baudry, Joannon, Poggi and Aviron2014). Several studies have found a positive effect of organic farming on beetle abundance and species richness (Sorgog et al. Reference Sorgog, Tanaka and Baba2023), but this pattern has not been found in all cases (Hole et al. Reference Hole, Perkins, Wilson, Alexander, Grice and Evans2005). Several factors play a role in the differences between organic and conventional farming systems, including the landscape matrix (e.g., Weibull & Bengtsson Reference Weibull and Bengtsson2000, Weibull et al. Reference Weibull, Ostman and Granqvist2003, Schmidt & Tscharntke Reference Schmidt and Tscharntke2005) and habitat heterogeneity (Weibull & Bengtsson Reference Weibull and Bengtsson2000). In the present study, organic farms were associated with higher abundances of beneficial insects, especially predatory beetles, while the abundance of pest species was reduced compared to in conventional farms. There may be more effective biological pest control in the organic farms compared to in conventional farms (Östman et al. Reference Östman, Ekbom and Bengtsson2003, Török et al. Reference Török, Zieger, Rosenthal, Földesi, Gallé, Tscharntke and Batáry2021) if heightened diversity of natural enemies increases rates of predation on crop pests (Letourneau & Bothwell Reference Letourneau and Bothwell2008). The abundance of pollen feeders was also greater in organic farms, which corroborates the notion of organic farming strengthening pollination compared to conventional practices (Gabriel & Tscharntke Reference Gabriel and Tscharntke2007, Holzschuh et al. Reference Holzschuh, Steffan-Dewenter and Tscharntke2008). Our finding that species richness increased from January to February and then declined until July, leading to similar levels of richness in both organic and conventional farms from May to July, aligns with previous research on the positive impacts of organic farming on beetle diversity, while the impact on beetle abundance is less clear (e.g., Rosas-Ramos et al. Reference Rosas-Ramos, Asís, Tobajas, de Paz and Baños-Picón2022). However, none of the families showed the same seasonal variations in organic and conventional farms (see Fig. S3); the farming practices may affect the phenology of beetle communities differently.
Our findings show that organic farming practices were associated with significantly greater family richness in beetle communities, particularly among predator species. Greater predator diversity is probably responsible for the smaller insect pest populations in organic farms compared to in conventional farms. The dynamics of beetle communities in conventional and organic farming environments remain largely unstudied in Southeast Asia, but in Lao PDR organic farming appears to be helping to conserve beetle biodiversity within agricultural systems and to be bolstering the populations of species groups that provide ecosystem services such as control of pest species.
Supplementary material
The beetle sampling data in organic and conventional farming are available in the Figshare repository: https://doi.org/10.6084/m9.figshare.25019879.v1.
Acknowledgements
We thank the village heads and farmers for providing their information and facilities. Special thanks are extended to Plant Protection students Tarwanh, Teenoy, Khounkham and Samayphone for assistance with the fieldwork. We are also grateful to Mr Souphapone Rattanarasy and Associate Professor Katsuyuki Eguchi for providing their facilities.
Author contributions
BC: Conceptualization, investigation, writing original draft, methodology, writing – review and formal analysis. YF: Conceptualization, investigation, writing – review, editing, formal analysis and revised the final draft.
Financial support
None.
Competing interests
The authors declare none.
Ethical standards
Not applicable.
