by Finbarr G. Horgan, Enrique A. Mundaca, Buyung A. R. Hadi, and Eduardo Crisol-Martínez
The high use of chemical pesticides at large scales and the co-dependence of technologies, such as hybrid rice varieties and direct-seeded rice, are associated with higher pesticide use than traditional varieties and establishment methods have resulted in a technological lock-in for pesticide use, whereby the increasing use of pesticides reduces farmers’ willingness to adopt more environmentally friendly pest and weed management options.
In well-managed rice fields, a diversity of generalist and specialist natural enemies, a high degree of intraguild predation, and a range of interconnected negative feedback loops regulate arthropod densities such that rice herbivores normally occur in relatively low numbers and decline in abundance as the crop matures.
Rice is the main staple food for over half of the world’s human population. Much of rice production occurs in the tropical coastal lowlands of South and Southeast Asia. Rapid population growth (i.e., the global population is estimated to exceed 9 billion by 2050), particularly in tropical Asia, has increased pressures on Asian farmers to intensify rice production.
In response, rice intensification practices including the use of high-yielding rice varieties, increased mechanization, and an increasing use of agrochemical inputs, have been promoted by national and international agricultural development institutes, often in partnership with the private sector.
Pesticide use, in particular, has increased dramatically among Asian farmers in recent decades: this is partly due to massive increases in global chemical production since the beginning of the millennium and intense marketing by agrochemical companies.
High use of chemical pesticides at large scales and the co-dependence of certain technologies (i.e., hybrid rice varieties and direct-seeded rice are associated with higher pesticide use than traditional varieties and establishment methods has resulted in a technological lock-in with respect to pesticide use, whereby the increasing use of pesticides reduces farmers’ willingness to adopt more environmentally friendly pest and weed management options.
In well-managed rice fields, a diversity of generalist and specialist natural enemies, a high degree of intraguild predation, and a range of interconnected negative feedback loops regulate arthropod densities such that rice herbivores normally occur in relatively low numbers and decline in abundance as the crop matures.
However, natural enemies are often highly vulnerable to insecticides and other pesticides. Indeed, outbreaks of key rice pests such as planthoppers, stemborers, and leaffolders have been linked to excessive pesticide use throughout Asia.
These outbreaks were associated with a declining abundance of natural enemies, particularly during early rice crop stages. In response to insecticide-related perturbations of rice arthropod communities and the consequent widespread and large-scale outbreaks of rice pests, researchers proposed that farmers should avoid resurgence-causing insecticides and reduce overall insecticide.
For example, largely in response to severe outbreaks of planthoppers in Thailand between 2009 and 2011, the Thai government, with support from the Thai Agro-Business Association (TABA), campaigned against the use of abamectin and cypermethrin in rice.
A range of rice sustainability programs throughout Southeast Asia have also called on farmers to limit pesticide use, particularly during early crop stages when natural enemies must build up their numbers in rice fields. Furthermore, agricultural research and extension services throughout Asia continue to promote integrated pest management (IPM) and the adoption of alternatives to pesticide use such as community-based biological control, synchronized rice planting, and the use of resistant or tolerant rice varieties.
Because the large-scale use of pesticides over many years could be linked to a reduction in the diversity and abundance of natural enemies, several researchers have promoted the diversification of Asian rice landscapes using ecological engineering approaches to provide habitat and refuges for natural enemies and to restore regulatory ecosystem services.
Ecological engineering is defined as the design of ecosystems using engineering principles to promote benefits for both human societies and the environment [24]. In crop production systems, ecological engineering often relies on the use of functional plants (e.g., trap plants, repellent plants, or plants that provide alternative food sources for natural enemies) to increase the diversity and abundance of predatory arthropods.
For example, the use of Lobularia maritima (L.) Desv. as a selective food plant for Trichogramma carverae Oatman and Pinto improved the biological control of Epiphyas postvittana (Walker) in Australian vineyards.
In rice ecosystems, farmers are encouraged to plant strips of vegetation on bunds as a key ecological engineering practice. Reports from China, Thailand, Vietnam, Cambodia, the Philippines, and Bangladesh have shown that flower strips and planted bunds can increase natural enemy diversity and abundance, increase the mortality of rice herbivores due to egg parasitoids, mirid bugs, and spiders, thereby reducing pest densities, and bring added benefits to rice production systems such as increasing the diversity of insectivorous and snail-eating rice land birds, providing additional farm products for home use or sale to markets, and improving farm aesthetics.
In 2013, the Philippine Department of Agriculture—Bureau of Agricultural Research (DA-BAR)) initiated a program to develop and promote ecological engineering as a means to diversify rice production systems and reduce insecticide use among rice farmers. This initiative would complement ongoing activities in the country to improve rice farm productivity through diversification and to meet the proposed biodiversity targets for sustainable rice systems as set out in the country’s National Biodiversity Strategy and Action Plan.
As part of the program, demonstration rice farms were established in four rice-producing provinces (Laguna, Rizal, Iloilo, and Bukidnon) to promote ecological engineering among DA staff and local farmers. However, even before initiating the DA-BAR program, it was apparent that many Filipino rice farmers already planted flower or vegetable strips on their rice bunds (levees) without any formal knowledge of the principles and practices of ecological engineering.
In this context, we conducted surveys of farmers in the four regions to establish a baseline for monitoring and to determine existing crop and pest management actions that affected pesticide use by the rice farmers.
We also assessed whether the farmers’ recognition of the functions of rice arthropods was associated with pesticide inputs in rice and other crops and whether the farmers’ adoption of sustainable pest management practices such as the use of biological control agents, crop rotations, the rearing of livestock, or the planting of flowers on bunds, was associated with reduced pesticide use.
Based on our results, we provide a series of recommendations to adapt ecological engineering to the existing practices for sustainable pest management used by farmers in the targeted regions.
The rice farmers we interviewed frequently produced other crops and livestock on their farms. These included a diversity of plant and animal species. Furthermore, the farmers occasionally wild-harvested a range of animals including fish, frogs, and snails for home consumption.
These approaches to intensifying their farm productivity while at the same time diversifying their products and optimizing the environmental capital of their farms contributed to reduced pesticide applications to the rice crop. In cases where farmers produce crops as supplementary food, these activities can also reduce the overall pesticide inputs in farms, in part because farmers view diversified farms as healthier environments for natural enemies and because they tend to avoid pesticides on produce for home use by applying concoctions and other alternative management practices, including the use of biological control agents.
The survey results indicate that farmers who practice ecological engineering might therefore be encouraged to explore the use of concoctions that they can derive from the planted rice bunds, thereby increasing the benefits of the planting of vegetation or flower strips.
The results of this case study have implications for rice production systems not only in the Philippines but also in other parts of South and Southeast Asia where farmers operate small, diversified farms.
Read the study:
Horgan FG, Mundaca EA, Hadi BAR, Crisol-Martínez E. (2023) Diversified Rice Farms with Vegetable Plots and Flower Strips Are Associated with Fewer Pesticide Applications in the Philippines. Insects; 14(10):778.
