A micronucleus assay detects genotoxic effects of herbicide exposure in a protected butterfly species

Michela Audisio,Alfredo Santovito,Simona Bonelli

doi:10.1007/s10646-020-02276-3

Abstract

Lycaena dispar Hawort (Lepidoptera: Lycaenidae), a protected butterfly, is declining in Europe, but it thrives in rice fields in northern Italy. Here, agrochemical usage could threaten its long-term survival. We investigated, by micronucleus (MN) assay, the genotoxic effect of glyphosate, a common herbicide, on L. dispar larvae. Micronuclei (MNi) are DNA fragments separated from the main nucleus and represent the result of genomic damage that has been transmitted to daughter cells. In a control/treatment experiment, we extracted epithelial cells from last-instar larvae fed with Rumex spp. plants sprayed with a solution containing 3.6 g/L of glyphosate, and from larvae fed with unsprayed plants. MNi and other chromosomal aberrations—nuclear buds (NBUDs) and bi-nucleated cells—were then scored in 1000 cells/subject. Significant differences were found between glyphosate-exposed and control groups in terms of MNi and total genomic damage, but not in terms of NBUDs or bi-nucleated cells. We reported a possible genomic damage induced by glyphosate on larvae of L. dispar. For the first time, a MN assay was used in order to evaluate the genomic damage on a phytophagous invertebrate at the larval stage. Increased levels of MNi reflect a condition of genomic instability that can result in reduced vitality and in an increased risk of local extinction. Therefore, farmland management compatible with wildlife conservation is needed.

Highlights

In the last decades, the expansion of intensive agriculture has triggered serious ecological problems, in terms of loss of habitats and biodiversity
Only about 200 cells were scored for six subjects, we decided to include them in the analyzed sample
We have shown that sublethal exposure to glyphosate-based herbicide Roundup® is able to induce, in L. dispar larvae, a significantly increased level of genomic damage, in terms of a higher frequency of MNi

Summary

Introduction

The expansion of intensive agriculture has triggered serious ecological problems, in terms of loss of habitats and biodiversity. This is principally due to the excessive use of pesticides, which control populations of targeted pests, and reduce the fitness of non-target species (Siroski et al 2016). The use of insecticides and herbicides, for instance, was found to negatively impact butterfly abundance and species richness (for a review see Braak et al 2018). The EU Pollinators Initiative named pesticide use as one of the main causes of the loss of managed bee colonies and the decline of wild bees and other insect pollinators (EU 2019). The drivers of this phenomenon are not well understood, there is increasing evidence of negative effects of pesticides on wild and managed bees (Sánchez-Bayo et al 2016), bumblebees (Stanley et al 2016) and butterflies (Forister et al 2016)

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