ABSTRACT. The stingless bee Tetragonisca angustula is an important pollinator of different agricultural and native crops. This study evaluated changes in the relative activity of esterases and critical electrolyte concentration in brain cells after exposure to pesticides malathion and thiamethoxam. Lethal concentration 50% showed greater toxicity of thiamethoxam in relation to malathion. Esterases EST-3 and EST-4 (carboxylesterase) were partially inhibited after contamination by contact and ingestion of malathion and contamination by contact with thiamethoxam, suggesting participation of these esterases in the metabolization of these compounds. The lowest critical electrolyte concentration (CEC) was found after contamination by malathion ingestion (0.15 M), indicating changes in gene expression. The alterations observed in the intensity of EST-3 and EST-4 and the chromatin structure indicate that pesticides can act in gene expression and be used as biomarkers of contaminant residues. Furthermore, knowing the susceptibility of T. angustula bees to pesticides, it would be possible to use this species for biomonitoring environmental quality in preserved areas and agroecosystems. ABSTRACT crops 50 EST3 EST 3 EST- EST4 4 carboxylesterase (carboxylesterase compounds CEC (CEC 0.15 015 0 15 (0.1 M, M , M) residues Furthermore T agroecosystems 5 0.1 01 1 (0. 0. (0 (

We determined the genome size of the Brazilian sciarid flies Bradysia hygida, Rhynchosciara americana and Trichosia pubescens (Diptera: Sciaridae) using absorbance measurements of Feulgen-stained nuclei belonging to these species (and chicken erythrocytes as a standard) to calculate the amount of DNA in picograms (pg) and the number of base pairs (bp), or C-value, for each of these species. The C-values were: 3 x 10(8) bp (0.31 pg) for B. hygida; 3.6 x 10(8) bp (0.37 pg) for R. americana; and 1 x 10(9) bp (1.03 pg) for T. pubescens. The sciarids investigated in this work had considerably higher C-values than the average for previously described dipteran species, including D. melanogaster.