Analysis of the effects of the fungicide pyraclostrobin and the insecticide acetamiprid on eussocial bees (Hymenoptera: Apidae)

Author(s)

Caio Eduardo da Costa Domingues

• Document type: Doctoral Thesis
• Press: Rio Claro. 2021-03-17.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Rio Claro
• Defense date: 2021-03-03
• Advisor: Osmar Malaspina; Elaine Cristina Mathias da Silva Zacarin

Abstract

Bees are essential in the preservation of ecosystems and important in agriculture, considering the relevance of the ecosystem services of pollination provided by these insects. Apis mellifera is the main pollinator in crops, providing benefits in the quality and quantity of the production of many species used in human food. In contrast, the stingless native species Melipona scutellaris is vital for the maintenance of native flora. However, the use of pesticides associated with habitat fragmentation and intensive agriculture are a threat to the populations of these bee species. Keeping this in view, the present study aimed to evaluate the biological effects of fungicide pyraclostrobin, on an individual and subindividual scale, of larvae, newly emerged bees, and foragers of Africanized A. mellifera and foragers of M. scutellaris, as well as to evaluate the development of A. mellifera iberiensis colonies before and after exposure to the insecticide acetamiprid in eucalyptus plantations in Portugal. In the first part of the research, conducted in the laboratory, Africanized A. mellifera larvae were given an artificial diet, in vitro, containing three concentrations of pyraclostrobin [911,25 ng/mL; 94,06 ng/mL and 30,25 ng/mL], from the third to the sixth day of feeding. After exposure, fifth instar larvae and newly emerged bees were dissected, processed histologically for immunohistochemical evaluation through the diagnosis of cell death in the intestine epithelium and chitin marking in the peritrophic matrix. Harmful effects on post-embryonic development were not observed. However, higher concentrations of pyraclostrobin induced lesions in the intestine, such as cell death, and increased intensity of chitin marking in the peritrophic matrix of larvae and newly emerged bees. In the second part of the laboratory research, newly emerged bees, and foragers of Africanized A. mellifera and M. scutellaris were subjected to oral exposure for five days to three residual concentrations of pyraclostrobin [0.125 ng a.i./mL; 0.025 ng a.i./mL and 0.005 ng a.i./mL]. The parameters observed were survival rate, morphological, qualitative and semi-quantitative analyses, and histochemicals. The results showed a reduction in longevity, an increase in the total lesions index and a decrease in the labeling intensity of macromolecules such as proteins, neutral polysaccharides and glycoconjugates, in the midgut of foragers of A. mellifera and M. scutellaris. The newly emerged workers of A. mellifera did not present reduction of survival and lesions in the midgut, however, there was a reduction of labeling intensity for neutral polysaccharides and glycoconjugates. As a consequence of exposure to pyraclostrobin, the individual health of both species has been affected and this can compromise and harm the maintenance of the health of the colony. In this sense, studies with residual concentrations of fungicides present in food and their effects on different bee species are relevant to estimate interspecific sensitivity and to subsidize future programs of risk assessment of bees. Regarding the research conducted in Portugal, two areas were selected in landscapes dominated by eucalyptus. In the center of each location was installed an apiary, in which were defined as a control apiary and apiary with a punctual application of acetamiprid. The monitoring was carried out over six months, where the health and development of the colonies, as well as the foraging ranges, presence of pesticide residues and the use of resources in the landscapes were evaluated. The results showed that there was no difference in the development of the colonies, observed through the adult population, nest cells and honey production between the sites, before and after exposure to the insecticide. The foraging ranges of the apiary application colonies indicated that less than 4% came in contact with the radius of the point application. The collection of resources by the colonies proved to be more intense before the application of acetamiprid, with emphasis on species of shrub and subarbustive vegetation. Nevertheless, acetamiprid residues were detected in pollen and bee bread samples. Therefore, the period of application of the insecticide was not harmful to the colonies, however, the results apply to the specific conditions of the site studied. In this way, the parameters used in the monitoring of the colonies offered important information that can contribute to a lower exposure of the bees in the different landscapes where the pesticides are used. (AU)

• FAPESP's process: 16/15743-7 - Analysis of effects of strobilurin fungicide pyraclostrobin in midgut of Africanized Apis mellifera Linnaeus, 1758 (Hymenoptera: Apidae) and Melipona scutellaris Latreille, 1811 (Hymenoptera: Apidae)
• Grantee: Caio Eduardo da Costa Domingues
• Support Opportunities: Scholarships in Brazil - Doctorate