Insecticide use, farmers’ self-reported health status, and genetically modified cowpea in Nigeria: Findings from a clustered randomized controlled trial with causal

Mulubrhan Amare, Kwaw S. Andam, David J. Spielman, Temilolu Bamiwuye, Chibuzo Nwagboso, Patricia Zambrano and Judith A. Chambers

No 2388, IFPRI discussion papers from International Food Policy Research Institute (IFPRI)

Abstract: Excessive insecticide use in smallholder agriculture can threaten human health and the environment. We evaluate the effects of receiving a genetically modified cowpea variety that confers resistance to the legume pod borer (Maruca vitrata) using a clustered randomized controlled trial with an encouragement design in Nigeria. We find that farmers who received the pod borer-resistant (PBR) cowpea with complementary inputs significantly reduce insecticide volumes and report fewer days of insecticide-related illness compared to farmers who only received a conventional cowpea variety. Farmers receiving PBR cowpea alone experience smaller, mostly insignificant reductions. To explore heterogeneous responses, we combine ANCOVA (analysis of covariance) interactions with machine learning-based Causal Forest estimates of Conditional Average Treatment Effects (CATEs). Results reveal that smaller, less wealthy, and labor-constrained households experience the largest reductions in insecticide use and health improvements, whereas wealthier farmers or those with higher baseline spraying practices experience lower reductions. Women-managed plots exhibit modestly higher responsiveness. Our findings highlight the importance of moving beyond average effects and seed distribution toward targeted, context-specific interventions that account for behavioral and resource constraints in smallholder farming systems.

Keywords: insecticides; farmers; health; genetically modified foods; cowpeas; randomized controlled trials; machine learning; Nigeria; Western Africa (search for similar items in EconPapers)
Date: 2025-12-18
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