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

SIRI, AUGUSTO; ARRIGHETTI, FLORENCIA; RODRIGUES CAPÍTULO, ALBERTO; LAVARIAS, SABRINA MARÍA LUISA

Buenos Aires

Congreso; XI Biennial Meeting SETAC Latinoamérica; 2015

Sociedad de Toxicología y Química Ambiental

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 Argentina. On the other hand, 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 indicators of the effects of chemicals in aquatic ecosystems. In order to compare the toxicity of different pesticides, Chironomus calligraphus was selected because is very sensitive to some toxicants. Due to 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, some entire larvae were fixed in Bouin solution and others in 4% formaldehyde, then dehydrated and embedded in plastic resin. Sections 3 µm 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 Bti exposures of 2 µg/L no histological changes were observed, but at 4 µg/L 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. Larvae exposed to CYP showed similar histopathological changes like Bti. C. calligraphus was sensitive to Bti and CYP toxicity as other Chironomus species. Future studies in larvae collected in freshwater bodies polluted with these insecticides could help to understand the relationship between the effects of these insecticides and the histopathological changes observed in the present study.