Evaluation of endotoxin Bacillus thuringiensis var. israelensis and pyrethroid cypermethrin in Chironomus calligraphus (Diptera: Chironomidae)

SIRI AUGUSTO; ARRIGHETTI FLORENCIA; RODRIGUES CAPÍTULO ALBERTO; LAVARÍAS SABRINA

Buenos Aires

Congreso; SETAC Latin America 11th Biennial Meeting; 2015

SETAC A Professional Society for Environmental Scientists and Engineers and Related Disciplines Concerned with Environmental Quality

Pesticides are extensively used for the control of agricultural pests and disease vectors but they also affect both humans and animals. Cypermethrin (CYP) is a pyrethroid widely used in the Pampean region. Bioinsecticides have received great attention as environmentally benign and desirable alternatives. Bacillus thuringiensis israelensis (Bti) is one of the most used bioinsecticides for the control of mosquitoes and agricultural activities. In ecotoxicology, Chironomus species are widely used as bioindicators of the effects of chemicals in aquatic ecosystems. In order to compare the toxicity of different pesticides, Chironomus calligraphus was selected, which is highly sensitive to heavy metals and pesticides. Due to its small size, short generation time and easy maintenance in laboratory conditions, this species could be useful as a potential bioindicator of the Pampean region. Third instar larvae were exposed to serial dilutions of CYP (0.0025-6.4 μg/L) and Bti (0.5-16 μg/L) to determine 96-h LC50 values. A control group without insecticide was included. After the 96 h assays, the entire larvae were fixed in Bouin solution and 4% formaldehyde, then dehydrated and embedded in plastic resin. Sections 3 um were stained with hematoxyline-eosine and observed under optical microscope. For the ultrastructural studies the larvae were fixed in 2.5% glutaraldehyde and ultrathin section were observed under electron microscope. The 96-h LC50 values were 1.506 μg/L and 0.045 μg/L for Bti and CYP respectively. We focus in the histological and ultrastructural alteration in the mid section of the digestive tract. The midgut of the control group showed a single layer of cubical cells with microvilli in the apical surface and a big central nucleus. At very low concentration of Bti (2 μg/L) no histological changes were observed, but at 4 ng/ml exposure some minor histopathological changes were observed as disruption of the microvilli. At Bti exposures of 7.5 μg/L, the midgut cells lost the contact with their basal membrane and started to be disorganized, while at 15 μg/L the epithelium is completely disorganized. Chironomus calligraphus was sensitive to Bti and CYP toxicity as other Chironomus species. It would be interesting to carry out studies in larvae collected from freshwater bodies with insecticides to confirm the relationship between the stress situations and the histopathological changes observed in this study.