Local species-specific effect of trees and shrubs on the incidence of the millet head miner, Heliocheilus albipunctella (Lepidoptera, Noctuidae)

Understanding the interactions between crop pests, natural enemies, and
semi-natural habitats in agricultural landscapes is crucial for developing
ecology-based pest management in agroecosystems. In the present study, we
investigated the local-scale species-specific effect of tree and shrub
cover on the incidence and natural pest regulation of the millet head
miner (MHM), Heliocheilus albipunctella de Joannis, and subsequent grain
losses, in a tree-crop agroforestry system in Senegal. To this purpose, we
monitored a network of 60 millet fields with variable tree and shrub
species composition within a 50 m radius buffer around the center of the
millet fields. Baobabs (Adansonia digitata) and apple-ring acacias
(Faidherbia albida) increased pest incidence and associated grain loss,
likely by providing favorable microhabitats for MHM or limiting habitats
for natural enemies, respectively. In contrast, soapberry trees (Balanites
aegyptiaca) and, to a lesser extent, bushwillow shrubs (Combretum
micranthum) increased natural pest regulation, but not enough to disrupt
the relationship between crop colonization, pest incidence, and yield
loss. Furthermore, Shannon’s diversity index had no measurable influence
on pest dynamics, suggesting that species identity and functional traits
are more important than diversity per se. These findings underline the
importance of careful woody species selection in agroforestry design
strategy for optimizing the delivery of multiple ecosystem services by
these trees and shrubs. Integrating tree functional traits, seasonal
canopy dynamics, and spatial scale considerations is key to enhancing
ecosystem services such as biological control in agroecological
intensification.