Dr. Md. Mahfuz Alam
The brown planthopper (Nilaparvata lugens), commonly referred to as BPH, is one of the most devastating pests in rice production, especially in South and Southeast Asia, where rice is a primary food source. Bangladesh, as a major rice-producing nation, is highly vulnerable to BPH infestations due to its warm, humid climate, which is conducive to the pest’s growth and reproduction. The insect damages rice directly by sucking sap from the phloem, weakening plants and reducing yields and indirectly by acting as a vector for viral diseases like grassy stunt and ragged stunt virus, which further compromise plant health. BPH outbreaks can lead to total crop failure if left unmanaged, especially during warm and humid conditions that favor its proliferation. Effective management strategies are crucial to minimizing crop losses and ensuring food security in Bangladesh, where rice is a staple crop and essential to the diet of approximately seventeen million people.

A. Nature of Damage
1. Direct Effects of BPH on Rice Plants
BPH causes direct damage to rice plants primarily by feeding on the plant's phloem sap, which drains the plant's nutrients and energy and leads to the following issues:
1. Sap Depletion and Nutrient Drainage: BPH nymphs and adults insert their stylets into the rice plant's vascular tissues to suck sap, which depletes essential nutrients (Picture 1&2). Continuous feeding weakens plants, leaving them unable to perform basic functions like photosynthesis effectively.
2. Hopperburn:
BPH feeding weakens the rice plants, leading to a condition known as "hopperburn." Hopperburn is characterized by yellowing, browning, and ultimately wilting of leaves. As BPH populations increase, hopperburn spreads quickly through the field, causing large areas of plants to die off prematurely (Picture 2). In severe cases, entire fields can be destroyed within a few days, resulting in total crop failure.
3. Reduced Photosynthetic Ability: The continuous sap-sucking activity by BPH weakens the plant's leaves, reducing chlorophyll content and the plant's ability to photosynthesize effectively. With a compromised photosynthetic rate, plants become less efficient in energy production, which slows growth, reduces vigor and limits grain production.
4. Stunted Growth: When BPH infestation begins at early growth stages, plants often exhibit stunted growth, which affects their ability to develop healthy stems and leaves. The stress induced by BPH feeding can cause a noticeable reduction in plant height and tiller numbers, which directly impacts the plant’s potential to produce grains.
5. Reduced Grain Formation: BPH feeding stresses the plant, often leading to fewer and smaller grains. When feeding occurs during the reproductive stage, it can disrupt panicle formation and filling, resulting in poor grain quality and reduced yield.
2. Indirect Effects of BPH as a Disease Vector
In addition to direct feeding damage, BPH also acts as a vector for viral diseases that further damage rice plants and compound yield losses. These include:
1. Rice Grassy Stunt Virus (RGSV): BPH transmits the rice grassy stunt virus, which causes infected plants to become stunted and to produce thin, grassy-looking leaves. Infected plants display excessive tillering but fail to produce mature grains, leading to a complete loss of marketable yield.
2. Rice Ragged Stunt Virus (RRSV): The rice ragged stunt virus, also transmitted by BPH, results in characteristic ragged leaves, with serrated edges and twisted leaf blades. Infected plants exhibit reduced tillering and may produce poorly formed panicles or no panicles at all, leading to yield reductions of up to 100% in severely affected areas.
3. Cumulative Effect of Viral Infections: Viral infections transmitted by BPH can spread rapidly through rice fields, particularly in densely planted areas where BPH populations can proliferate easily. These viral infections not only reduce yield potential but also affect grain quality, resulting in lightweight, unmarketable rice grains. Moreover, infected plants can act as sources of infection for subsequent planting seasons if not managed properly.
3. Economic Impact on Rice Production in Bangladesh
BPH infestations and the associated diseases have substantial economic impacts on rice farming in Bangladesh:
1. Yield Loss and Financial Losses: Severe BPH infestations during the tillering to booting stages can cause yield losses of up to 80-100%. This is especially critical for Bangladesh, where aman rice is a major staple and a significant component of the annual rice yield. In Bangladesh, rice production losses from BPH outbreaks can reach alarming levels, directly affecting farmers' incomes and increasing the nation’s vulnerability to food shortages. In 2024, yield reductions due to BPH can result in economic losses amounting to millions of dollars, placing additional stress on smallholder farmers who may not have access to effective control methods.
2. Increased Production Costs: Managing BPH requires additional inputs, including labour and control measures, which increase production costs. Farmers often resort to chemical insecticides to control BPH, which, while costly, may not always be effective due to BPH’s growing resistance to common pesticides. This reliance on chemical control increases production expenses and reduces profit margins for farmers.
3. Threat to National Food Security: As a staple crop, rice is essential to the Bangladeshi diet and widespread crop losses due to BPH threaten national food security. In years when BPH outbreaks are severe, the reduced domestic rice supply may lead to increased prices, impacting affordability for low income consumers. Additionally, BPH outbreaks can contribute to fluctuations in food supply, increasing Bangladesh’s dependence on imported rice.
4. Environmental and Ecological Impacts
The impact of BPH extends beyond economic losses, as BPH management often involves excessive pesticide use, which has significant environmental repercussions:
1. Disruption of Ecosystems: Over reliance on pesticides to control BPH can harm non-target organisms, including beneficial insects like predators and parasitoids that naturally regulate BPH populations. The death of natural enemies reduces biodiversity in the rice ecosystem, making fields more susceptible to future pest outbreaks.
2. Pesticide Resistance: BPH has shown a remarkable ability to develop resistance to a wide range of insecticides, including carbamates, organophosphates and pyrethroids. As a result, the effectiveness of pesticides diminishes over time, leading to an overuse cycle that further promotes resistance development and makes chemical control increasingly unsustainable.
B. Challenges of BPH Management
BPH has developed resistance to many chemical insecticides, making control difficult and often ineffective with conventional approaches. Over reliance on insecticides can disrupt ecological balances, eliminating natural predators and beneficial organisms that help regulate pest populations. Additionally, frequent use of pesticides poses health risks to farmers and contaminates soil and water resources. Sustainable, integrated pest management (IPM) approaches are therefore essential to control BPH effectively while minimizing environmental impact.
Integrated Management Strategies for BPH in Rice
A successful approach to managing BPH in Bangladesh incorporates multiple, complementary strategies, including monitoring, cultural practices, biological control and selective chemical interventions. Here are the primary components of a sustainable management strategy for BPH:
1. Monitoring and Early Detection
Early detection is vital for managing BPH outbreaks effectively:
• Field Monitoring: Regular field monitoring, particularly during the tillering and booting stages of rice growth, can help detect BPH populations before they reach damaging levels. Farmers should inspect the base of rice plants and use light traps in the evening to monitor adult BPH activity.
• Economic Threshold Level (ETL): Implementing control measures only when populations exceed the ETL (10-15 BPH per hill for lowland rice) can help prevent unnecessary pesticide applications, conserving beneficial insects and reducing production costs.
2. Cultural Practices
Proper cultural management can help create an unfavorable environment for BPH:
• Resistant Varieties: Using BPH resistant rice varieties is an effective strategy to reduce infestation. In Bangladesh, varieties such as BRRI dhan47 and BRRI dhan55 have shown resistance to BPH, offering an environmentally friendly and economically viable solution.
• Proper Fertilization: Excessive use of nitrogen fertilizer can increase BPH populations by promoting succulent plant growth, which attracts planthoppers. Applying balanced fertilizers based on soil testing can prevent excessive nitrogen use and reduce BPH risk.
• Water Management: Alternate wetting and drying (AWD) practices can help control BPH populations by periodically drying fields to create conditions less favorable for their reproduction. This also conserves water, benefiting both the crop and the environment.
• Field Hygiene and Crop Rotation: Removing crop residues after harvest can reduce BPH overwintering sites, while crop rotation can help break the pest cycle and lower BPH pressure in rice fields.
3. Biological Control
Biological control leverages natural predators and parasitoids to regulate BPH populations:
• Natural Predators: Predatory insects like spiders, lady beetles (Coccinellidae), and predatory bugs (Cyrtorhinus lividipennis) are important natural enemies of BPH. Preserving these beneficial organisms through reduced pesticide use and habitat conservation can contribute to natural pest control.
• Parasitoids and Pathogens: Fungal pathogens such as Beauveria bassiana and Metarhizium anisopliae have shown effectiveness against BPH in field conditions. These biological agents can be applied to manage BPH populations sustainably and are often less harmful to non-target species than chemical insecticides.
4. Chemical Control with Selective Pesticides
While chemical control should be minimized, selective use of pesticides may be necessary during severe infestations:
• Rotating insecticides with different modes of action can help delay resistance development in BPH populations. Insecticides such as Dimethoate 60EC 1litre/hactare, Diazinon 60EC 1 litre/hactare, Emamectin benzoate (5SG) 1 Kg/hectare are effective against BPH.
• Spot treatments targeting high density BPH areas can reduce insecticide usage, conserve natural enemies, and lower production costs (Picture 4).
5. Farmer Education and Community Based IPM Programs
Community-based IPM programs can enhance BPH management effectiveness and increase adoption rates of sustainable practices:
• Training programs can educate farmers on identifying BPH, using economic thresholds, and implementing IPM practices effectively.
• Neighbouring rice field can coordinate their pest control efforts to prevent BPH from spreading across fields, reducing the likelihood of outbreaks. Community pest surveillance systems can also improve early detection and timely intervention.
Conclusion
In 2024, the brown planthopper continues to pose a significant threat to aman rice production in Bangladesh, with both direct and indirect damage mechanisms severely impacting yields and quality. With the combined challenges of pesticide resistance, environmental concerns, and food security pressures, there is an urgent need for sustainable BPH management strategies. Integrated pest management approaches that incorporate monitoring, cultural practices, and biological control can offer more effective, long-term solutions to mitigate BPH damage and safeguard Bangladesh's rice production.

The writer is a Principal Scientific Officer Crops Division, BARC, Bangladesh Ph.D (Ehime University, Japan)