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Urban herbicide use threatens a non-target butterfly (Hypolimnas misippus) through direct toxicity and host plant stress in Ghana

Year: 2026

Type: article

Abstract: Urban residential areas are increasingly managed using herbicides, yet the ecosystem-level consequences of this practice remain poorly understood, particularly in sub-Saharan Africa. This study examined urban weed management practices in Ghana and assessed how commonly used herbicides influence plant–insect interactions focusing on the butterfly, Hypolimnas misippus, and its larval host plant, Portulaca quadrifida . A household survey of 600 participants across twelve urban towns in Ghana’s Central Region showed that herbicides are the dominant method of weed control, with glyphosate- and paraquat-based formulations most frequently used. Laboratory no-choice bioassays were conducted to evaluate the effects of field-recommended concentrations of glyphosate, paraquat, and haloxyfop-methyl on butterfly eggs and larvae. In parallel, herbicide-induced physiological stress in P. quadrifida was quantified using laser-induced chlorophyll fluorescence (LICF) induction kinetics. Paraquat caused acute toxicity, resulting in complete larval mortality within 24 h and near-total egg mortality (96%). Haloxyfop-methyl substantially reduced survival and adult emergence, with mortality occurring across larval and pupal stages. Glyphosate did not significantly affect survival but, slightly prolonged development time. LICF measurements revealed pronounced reductions in leaf vitality indices ( Rfd-685 and Rfd-740 ) following paraquat and haloxyfop-methyl exposure, indicating impaired photosynthetic performance and host plant stress. Together, these results demonstrate that routine herbicide use in urban residential environments can disrupt plant–insect interactions through both direct toxicity and, plant-mediated effects. Such disruptions may compromise urban ecosystem functioning and biodiversity, underscoring the need to integrate ecological considerations into urban weed management strategies.

Source: PLOS Ecosystems

DOI: 10.1371/journal.pesy.0000020