• Sushmita Khadka

Syangja district, nestled in the picturesque mid-hills of Nepal, is renowned for its diverse agriculture supported by favorable climatic and soil conditions. Among the important horticultural crops grown here, orange trees (Citrus reticulata– Orange and Citrus sinensis–Sweet Orange) play a vital economic and nutritional role for local farmers.

Orange orchards in Syangja not only contribute to the livelihood of many rural households but also support regional markets with quality citrus fruits. However, orange trees do not grow in isolation. They coexist with a rich biodiversity of insects, especially beetles, which influence the orchard health in complex ways. While some beetle species provide significant ecological services like pest regulation and soil improvement, others act as damaging pests that reduce fruit quality and yield.

Understanding the diversity of beetle species associated with orange orchards, their beneficial and harmful roles, and their interactions with orange trees is critical. Such knowledge helps develop integrated pest management (IPM) strategies that balance the need for pest control with conservation of beneficial insects, ultimately supporting sustainable citrus production in Syangja. Overview of beetles in Agriculture and Citrus Ecosystems Beetles are among the largest and most diverse insect orders worldwide, with over 350,000 described species. They occupy nearly every habitat and perform numerous ecological functions. In agricultural systems, beetles can be broadly classified as:

Beneficial beetles: Predators, decomposers, pollinators, and soil health promotors.

Harmful beetles: Herbivores and wood borers that damage crops and trees.

In Orange orchards, including those in Syangja, both groups coexist. The presence of a healthy population of beneficial beetles help suppress pest populations and maintains soil quality. Conversely, unchecked harmful beetles can cause extensive damage to trees and fruits, leading to economic losses.

Beneficial beetles in Syangja orange Orchards

1) Dung Beetle (गोबर किरा) – They play indispensable role in soil ecosystems, even though they do not feed directly on orange trees. Common species like Onthophagus nepalensis and Copris spp. are active in orchard soils. They bury animal dung and organic matter into the soil, facilitating decomposition and nutrient return to the soil profile. This enriches the soil with nitrogen, phosphorus, and other essential nutrients needs by orange trees. By digging tunnels and burrows, dung beetles improve soil aeration and water infiltration, enhancing root growth and reducing soil compaction. The burial of dung also reduces breeding sites for pests like flies and parasitic worms. Orchards in active dung beetle populations typically exhibit better soil health and improved orange tree vigor, leading to enhanced fruit yield and quality.

2) Ladybird Beetles (लालीगुँदे किरा) – These beetles feed voraciously on aphids (फूसा), scale insects (पिलुआ), whiteflies, and mealybugs, which suck sap from orange leaves and shoots. By controlling these pests, ladybird beetles help prevent leaf curling, yellowing, stunted growth, and reduced photosynthesis. Their predation reduces the need for chemical insecticides, promoting environmentally friendly and sustainable citrus farming. Farmers can conserve ladybird beetles by minimizing pesticide use, maintaining diverse orchard flora that provides nectar and shelter, and avoiding practices that destroy beneficial insect habitats.

3. Ground Beetles (जमिन किरा) – They are mainly nocturnal predators inhabiting orchard floor litter and soil surface. They feed on eggs, larvae, pupae, and small insects that could become harmful pests, including soil-borne species. Their activity contributes significantly to natural pest suppression before insect’s reach damaging adult stages. Ground beetles also increase biodiversity and ecological resilience in orchard ecosystems. Ground beetle populations thrive in orchards with natural ground cover, organic mulch, and minimal soil disturbance. Preserving such habitats is beneficial for sustainable pest management.

Harmful Beetles Affecting Syangja Orange Orchards:

While beneficial beetles support orchard health, several beetle species negatively impact orange trees through direct feeding or wood boring, causing economic damage.

1. Ambrosia Beetles (काठ भित्र पस्ने किरा) – These beetles are small wood-boring beetles that tunnel into the stems and branches of orange trees, causing severe damage. Genus Xylosandrus is known to infest citrus trees. Ambrosia beetles excavate galleries within tree tissues and introduce symbiotic fungi that degrade the wood. This fungal infection leads to branch dieback, wilting and eventual decline of the tree. Infestation symptoms include yellowing leaves, branch drying, and holes with sawdust-like frass at entry points. Early detection is difficult due to small entry holes and concealed damage. Heavy infestations can lead to significant crop losses.

2. Longhorn Beetles (सिङ्गला किरा / लामो सिङ्ग किरा) – Longhorn beetles, called सिङ्गला किरा in Nepali, are large wood borers whose larvae tunnel extensively into orange tree wood. Anoplophora spp. are major longhorn beetles affecting citrus in Asia. Larval boring damages the cambium and sapwood, disrupting nutrient and water flow, weakening branches and trunks, and increasing breakage risk. Entry wounds also provide entry points for secondary pathogens. Though less reported in Nepal, the presence of suitable hosts and favorable climate in Syangja poses a risk of infestation.

3. Fruit Piercing Beetles (फल च्यात्ने किरा) – Fruit piercing beetles feed on ripe orange fruits by piercing the skin and sucking juice. Their feeding causes wounds that facilitate infection by fungi and bacteria, leading to fruit rot. Physical damage reduces the aesthetic quality and shelf life of fruits, lowering market prices. Premature fruit drop is another common consequence. These beetles are particularly active during the fruit ripening period when oranges are most vulnerable.

4. Leaf Beetles (पात चपाउने किरा) – Leaf beetles, or पात चपाउने किरा, feed on orange tree foliage. Heavy infestations cause significant leaf loss, reducing the tree’s ability to photosynthesize and produce energy. Weakened trees become more susceptible to other pests and diseases, further affecting yield. Leaf beetles are usually less damaging than wood borers or fruit feeders but can cause localized issues.

Ecological Balance: Importance of Beetle Diversity in Orange Orchards

The beetle community within Syangja’s orange orchards forms a complex ecological network where species interact with each other and the environment. Beneficial beetles maintain ecological balance by controlling pest populations and improving soil conditions, enhancing orchard resilience Harmful beetles, if uncontrolled, disrupt this balance and threaten productivity.

Factors affecting beetle diversity and populations include

 Excessive or indiscriminate pesticide use can harm beneficial beetles, leading to pest outbreaks. Orchards with diverse vegetation, organic mulch, and minimal disturbance support richer beetle communities. Seasonal monsoon rains, temperature, and humidity affect beetle breeding and activity cycles. Conserving beneficial beetles while managing pests is essential for sustainable orchard management in Syangja.

Integrated Pest Management (IPM) Strategies for Beetles in Syangja Orange Orchards

Conduct weekly inspections of trees for symptoms like boreholes, wilting, frass, and fruit damage. Employ traps such as pheromone or light traps to detect pest beetle activity early and accurately. Use scouting records to identify pest thresholds and inform control decisions. Prune and destroy infested branches and twigs to eliminate breeding sites. Maintain orchard sanitation by removing fallen fruits, debris, and pruning waste. Preserve natural vegetation around orchards to provide habitat for beneficial insects. Reduce pesticide use to conserve predatory beetles like ladybird and ground beetles. Introduce or encourage flowering plants that support beneficial insect populations. Educate farmers on recognizing and protecting beneficial beetles. Apply insecticides only when monitoring indicates pest populations above economic thresholds. Use selective or bio insecticides that minimize harm to non-target beneficial species. Rotate chemical classes to prevent resistance development.

Challenges and Opportunities in Syangja Citrus Beetle Management

Challenges

Limited local research on beetle species diversity, ecology, and effective control methods specific to Syangja’s conditions. Farmers’ knowledge gaps regarding the identification of beneficial versus harmful beetles. Resource constraints for implementing advanced monitoring and biological control techniques. Environmental concerns related to pesticide overuse affecting beneficial insect populations and ecosystem health.

Opportunities

Extension services and training can enhance farmer awareness and adoption of IPM practices. Participatory research involving local farmers can generate context-specific knowledge on beetle ecology and management. Promotion of organic and eco-friendly farming can support beneficial insect conservation. Collaboration with entomologists and agricultural agencies can lead to improved pest identification and control resources.

Conclusion

Beetles in Syangja’s orange orchards play dual and complex roles: some species support soil health and naturally suppress pests, while others pose serious threats through direct damage to trees and fruits. A nuanced understanding of these roles, combined with practical management strategies, is vital for sustainable citrus production. Integrating monitoring, habitat conservation, biological control, and judicious chemical use provides a pathway for Syangja’s farmers to enhance orange yields while preserving ecological balance. Investing in local research, farmer education, and support systems will further empower the community to manage beetle populations effectively and sustainably. Sustained efforts in this direction will ensure that Syangja continues to thrive as a prominent citrus-producing region, benefiting farmers, consumers, and the environment alike.

References & Further Reading

Research papers on beetle biodiversity in Nepalese agroecosystems.

Agricultural extension manuals on integrated pest management in citrus.

Local government and NGO publications on sustainable horticulture practices in Syangja.

Global literature on beetle roles in citrus orchards and biological pest control.