Research Article

Pest Regulation and Natural Enemy Support in Agroforestry Systems: Evidence from Grevillea robusta with Tomato-Based Alley Cropping in Nyagatare District, Rwanda

Gaspard R. Ntabakirabose¹, Jean de Dieu Buregeya², Julienne Uwitonze³, Festus Maniriho⁴, Mbabazi Mbabazize⁵, and Charles Halerimana⁶

¹Forest Research Department, Rwanda Forestry Authority, Huye, Rwanda

²Department of Transforming the Eastern Province through Adaptation to Climate Change, Rwanda Forestry Authority, Huye, Rwanda

³Environmental Economics and Natural Resources, Management; University of Lay Adventist of Kigali, Rwanda

⁴Forest Investment Program, Rwanda Forestry Authority, Huye, Rwanda

⁵Faculty of Business and Commerce, ISBAT University, Kampala, Uganda

⁶Department of Crop Science and Horticulture, Makerere University, Uganda

*Corresponding author e-mail: gmutago@gmail.com

(Received: 10/06/2025; Revised: 16/04/2026; Accepted: 16/06/2026; Published: 20/06/2026)

ABSTRACT

Tomato (Solanum lycopersicum L.) is an important vegetable crop in Rwanda, but its production is constrained by severe insect pest infestations and excessive pesticide use. This study evaluated the effectiveness of Grevillea robusta–tomato alley cropping in suppressing sap-sucking pests, enhancing natural enemy populations, and improving tomato productivity in Nyagatare District, Eastern Rwanda. A field experiment was conducted using a randomized complete block design with two treatments: alley cropping and sole tomato cropping. Pest and natural enemy populations were monitored throughout the cropping season, while growth, yield, and pest damage parameters were assessed. Results revealed that alley cropping reduced major sap-sucking pest populations by 53.7–57.8% compared with sole cropping. The abundance and diversity of natural enemies, including lady beetles, lacewings, spiders, and parasitoid wasps, increased significantly, leading to greater biological control activity. Consequently, marketable tomato yield increased by 29%, while pest damage declined by over 50%. The findings highlight alley cropping as a sustainable pest management strategy for smallholder tomato production in Rwanda.

Keywords: Pest, Natural enemy, Agroforestry, Tomato, Alley cropping

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