Ultrastructural Changes in the Midgut of Brazilian Native Stingless Bee Melipona scutellaris Exposed to Fungicide Pyraclostrobin

Author:

Domingues Caio E. C.12ORCID,Inoue Lais V. B.2ORCID,Gregorc Aleš1ORCID,Ansaloni Leticia S.1,Malaspina Osmar2,Mathias da Silva Elaine C.3

Affiliation:

1. Faculty of Agriculture and Life Sciences, University of Maribor, Pivola 10, 2311 Hoče, Slovenia

2. Centro de Estudos de Insetos Sociais (CEIS), Departamento de Biologia Geral e Aplicada, Instituto de Biociências (IB), Universidade Estadual Paulista (UNESP)—“Júlio de Mesquita Filho”, Rio Claro 13506-900, SP, Brazil

3. Laboratório de Ecotoxicologia e Análise de Integridade Ambiental (LEIA), Departamento de Biologia (DBio), Universidade Federal de São Carlos (UFSCar), Sorocaba 18052-780, SP, Brazil

Abstract

Melipona scutellaris is a Brazilian stingless bee that is important for pollinating wild flora and agriculture crops. Fungicides have been widely used in agriculture, and floral residues can affect forager bees. The goal of our study was to evaluate the effects of sublethal concentrations of pyraclostrobin on the midgut ultrastructure of M. scutellaris forager workers. The bees were collected from three non-parental colonies and kept under laboratory conditions. The bees were orally exposed continuously for five days to pyraclostrobin in syrup at concentrations of 0.125 ng a.i./µL (FG1) and 0.005 ng a.i./µL (FG2). The control bees (CTL) were fed a no-fungicide sucrose solution, and the acetone solvent control bees (CAC) received a sucrose solution containing acetone. At the end of the exposure, the midguts were sampled, fixed in Karnovsky solution, and routinely processed for transmission electron microscopy. Ultrastructural analysis demonstrated that both the fungicide concentrations altered the midgut, such as cytoplasmic vacuolization (more intense in FG1), the presence of an atypical nuclear morphology, and slightly dilated mitochondrial cristae in the bees from the FG1 and FG2 groups (both more intense in FG1). Additionally, there was an alteration in the ultrastructure of the spherocrystals (FG1), which could be the result of cellular metabolism impairment and the excretion of toxic metabolites in the digestive cells as a response to fungicide exposure. The results indicate that ingested pyraclostrobin induced cytotoxic effects in the midgut of native stingless bees. These cellular ultrastructural responses of the midgut are a prelude to a reduced survival rate, as observed in previous studies.

Funder

São Paulo Research Foundation

Brazilian National Council for Scientific and Technological Development

Slovenian Research and Innovation Agency

research for the improvement of safe food and health

Public Agency for Research Activity of the Republic of Slovenia

Publisher

MDPI AG

Subject

Chemical Health and Safety,Health, Toxicology and Mutagenesis,Toxicology

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