Toxicity of microbial insecticides toward the non‐target freshwater insect Chironomus xanthus

BACKGROUND Commercial formulations based on Bacillus thuringiensis subs. kurstaki (Btk) and Beauveria bassiana (Bb) are commonly used microbial insecticides in Brazil and other tropical regions. However, and despite being considered environmentally friendly, their use generates concerns regarding po...

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Bibliographic Details
Published in:	Pest management science Vol. 76; no. 3; pp. 1164 - 1172
Main Authors:	Silvestre Pereira Dornelas, Aline, A Sarmento, Renato, C Rezende Silva, Laila, Souza Saraiva, Althiéris, J de Souza, Danival, D Bordalo, Maria, MVM Soares, Amadeu, LT Pestana, João
Format:	Journal Article
Language:	English
Published:	Chichester, UK John Wiley & Sons, Ltd 01-03-2020 Wiley Subscription Services, Inc
Subjects:	Animals Bacillus thuringiensis Beauveria bassiana benthic invertebrates bioinsecticides Body length Brazil Chironomidae Chironomus xanthus Ecological effects Ecosystem Ecosystem assessment Emergence Evaluation Exposure Formulations Fresh Water Freshwater ecology Freshwater ecosystems Hemocytes Hemolymph Immune response Immunology Insecticides Insects Laboratories Larvae Low concentrations Microorganisms Organic chemistry Sublethal effects Toxicity Tropical environment Tropical environments Water Pollutants, Chemical Water pollution effects Brazil Beauveria bassiana Bacillus thuringiensis bioinsecticides benthic invertebrates
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Summary:	BACKGROUND Commercial formulations based on Bacillus thuringiensis subs. kurstaki (Btk) and Beauveria bassiana (Bb) are commonly used microbial insecticides in Brazil and other tropical regions. However, and despite being considered environmentally friendly, their use generates concerns regarding possible adverse ecological effects in freshwater ecosystems. Here, we evaluate the effects of these bioinsecticides on the tropical aquatic dipteran Chironomus xanthus under laboratory conditions. RESULTS After laboratory exposures to these compounds 48‐h median lethal concentration (LC50) values of 1534 μg a.i./L for Btk and of 6.35 μg a.i./L for Bb were estimated. Chronic assays revealed different sublethal effects: Btk‐based bioinsecticide exposure reduced C. xanthus growth [lowest observed effect concentration (LOEC) was 126 μg a.i./L for head width], decreased emergence rate (LOEC = 8 μg a.i./L) and increased immunological response (LOEC = 50 μg a.i./L) measured as total hemocyte count in larvae hemolymph. Exposure to low concentrations of Bb‐based insecticide also reduced C. xanthus growth (LOEC = 0.07 μg a.i./L for larvae body length measurements), and emergence rate (LOEC = 0.28 μg a.i./L), despite no clear effects on the total hemocyte counts. CONCLUSION Our results suggest that low concentrations of Btk and Bb bioinsecticides are toxic to C. xanthus. Given their widespread use and occurrence in tropical freshwater systems, research is needed to evaluate the potential effects of these compounds concerning natural freshwater insect communities and ecosystem functioning. © 2019 Society of Chemical Industry Results from laboratory ecotoxicity assays indicate that microbial insecticides, used as alternatives to synthetic insecticides, are highly toxic to Chironomus xanthus, a tropical freshwater chironomid.
ISSN:	1526-498X 1526-4998
DOI:	10.1002/ps.5629