Document Detail

Ultrastructural analysis of midgut cells from Culex quinquefasciatus (Diptera: Culicidae) larvae resistant to Bacillus sphaericus.
MedLine Citation:
PMID:  18346899     Owner:  NLM     Status:  MEDLINE    
The larvicidal action of the entomopathogen Bacillus sphaericus towards Culex quinquefasciatus is due to the binary (Bin) toxin present in crystals, which are produced during bacterial sporulation. The Bin toxin needs to recognize and bind specifically to a single class of receptors, named Cqm1, which are 60-kDa alpha-glucosidases attached to the apical membrane of midgut cells by a glycosylphosphatidylinositol anchor. C. quinquefasciatus resistance to B. sphaericus has been often associated with the absence of the alpha-glucosidase Cqm1 in larvae midgut microvilli. In this work, we aimed to investigate, at the ultrastructural level, the midgut cells from C. quinquefasciatus larvae whose resistance relies on the lack of the Cqm1 receptor. The morphological analysis showed that midgut columnar cells from the resistant larvae are characterized by a pronounced production of lipid inclusions, throughout the 4th instar. At the end of this stage, resistant larvae had an increased size and number of these inclusions in the midgut cells, while only a small number were observed in the cells from susceptible larvae. The morphological differences in the midgut cells of resistant larvae found in this work suggested that the lack of the Cqm1 receptor, which also has a physiological role as being an alpha-glucosidase, can be related to changes in the cell metabolism. The ultrastructural effects of Bin toxin on midgut epithelial cells from susceptible and resistant larvae were also investigated. The cytopathological alterations observed in susceptible larvae treated with a lethal concentration of toxin included breakdown of the endoplasmic reticulum, mitochondrial swelling, microvillar disruption and vacuolization. Some effects were observed in cells from resistant larvae, although those alterations did not lead to larval death, indicating that the receptor Cqm1 is essential to mediate the larvicidal action of the toxin. This is the first ultrastructural study to show differences in the cell morphology of resistant larvae and further investigation is needed to understand the impact of the lack of expression of midgut enzymes on the physiology of resistant insects.
Janaina Viana de Melo; Romero Henrique Teixeira Vasconcelos; André Freire Furtado; Christina Alves Peixoto; Maria Helena Neves Lobo Silva-Filha
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2008-02-09
Journal Detail:
Title:  Micron (Oxford, England : 1993)     Volume:  39     ISSN:  0968-4328     ISO Abbreviation:  Micron     Publication Date:  2008 Dec 
Date Detail:
Created Date:  2008-09-23     Completed Date:  2009-01-06     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9312850     Medline TA:  Micron     Country:  England    
Other Details:
Languages:  eng     Pagination:  1342-50     Citation Subset:  IM    
Department of Entomology, Centro de Pesquisas Aggeu Magalhães-Fundação Oswaldo Cruz, Recife, PE 50670-420, Brazil.
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MeSH Terms
Bacterial Toxins / pharmacology*
Culex / ultrastructure*
Insecticide Resistance
Larva / ultrastructure
Pest Control, Biological
Stomach / ultrastructure*
alpha-Glucosidases / analysis
Reg. No./Substance:
0/Bacterial Toxins; 0/binB protein, Bacillus sphaericus; EC

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