Ethnobotanical Knowledge and the Distribution of Pesticidal Plants in Northern Tanzania: A Multi-Ethnic Perspective

Pesticidal plants are vital for pest management in sub-Saharan Africa, yet knowledge about them is culturally and geographically unevenly documented. This study examined ethnobotanical knowledge and the distribution of pesticidal plants among six ethnic groups (Maasai, Chagga, Iraqw, Pare, Nguu, Zigua) in northern Tanzania. Data related to ethnobotanical knowledge were collected from questionnaire surveys involving 266 participants, 24 focus group discussions, 26 key informant interviews, complemented by field verifications across the six ethnic groups. Pesticidal plant coordinates were accessed from herbarium voucher specimens from The National Herbarium of Tanzania. Chi-square tests of independence assessed associations between ethnic groups and knowledge transmission pathways. Penalized logistic regression analysis was conducted to assess the influence of demographic factors on reported knowledge of pesticidal plants. Spatial overlay was conducted to examine the distribution of pesticidal plant species occurrences across agroecological zones and rainfall gradients. The results revealed a significant association between ethnic group and the source of pesticidal plant knowledge. Across all ethnic groups, knowledge was predominantly acquired through family/community traditional sources, with the highest frequencies recorded among the Maasai, Iraqw, and Zigua. Knowledge is mainly transmitted orally, particularly among the Maasai, Iraqw, and Zigua. A total of one hundred and six distinct species were recorded across the six ethnic groups surveyed, with Tephrosia vogelii and Solanum incanum being the most frequently cited. Leaves were the most frequently used plant part across all ethnic groups, with notably high usage among the Chagga, Iraqw, and Maasai. Perceptions of the declining population of pesticidal plants were the highest among the Maasai. Spatial mapping revealed pesticidal plant hotspots in the Northern Rift and Volcanic Highlands agroecological zones, and they fall within zones receiving moderate to relatively high rainfall. The findings highlight that ethnobotanical knowledge of pesticidal plants in northern Tanzania is strongly shaped by ethnic affiliation, oral knowledge transmission, and localized ecological availability, with clear spatial hotspots aligned to specific agroecological zones and high-rainfall areas.