Effects of Neonicotinoid and Anthranilic Diamide Insecticides on the Metamorphosis of the Common Toad Rhinella Arenarum Individually and in Pairwise Combinations

FONSECA PEÑA, SHIRLEY VIVIAN DANIELA; BRODEUR, JULIE CÉLINE; NATALE, GUILLERMO SEBASTIÁN

Montevideo

Congreso; SETAC Latin America 15th Biennial Meeting; 2023

Society of Environmental Toxicology and Chemistry

In the agricultural region of the Argentine Pampas, the neonicotinoids (NEO) and anthranilic diamides (AD) insecticide families are widely used on crops such as soybeans and corn. NEO act by binding to acetylcholine receptors in target organisms, causing a nervous disorder that can cause paralysis or death. AD are the latest generation of insecticides that act by binding to ryanodine receptors (RyR), altering calcium release and disrupting coordinated muscle contraction in target organisms. Both insecticides are relatively persistent and mobile in the environment, reaching aquatic environments by lixiviation and runoff. The objective of the present study was to evaluate the impact of pairwise combinations of the NEOs, thiamethoxam (THIA) and imidacloprid (IMI) and the AD, chlorantraniliprole (CHLO), in their commercial formulations actara 25%, confidor 20% and coragen 20%, respectively, on the metamorphosis of the common toad Rhinella arenarum. Tadpoles at stages 34-37 (E34-37) (according to Gosner 1960) were exposed to the nominal concentration of 50 µg/L of THIA, IMI and CHLO, individually and pairwise combinations of 25 ug/L of each pesticides : THIA-IMI, THIA-CHLO, and IMI-CHLO, until completion of metamorphosis in a semistatic system. The effect on metamorphosis development was determined by evaluating the time required for 50% of individuals to reach stage 39 (S39), stage 42 (S42) or to complete metamorphosis (MET) and the proportion of individuals reaching each stage. Body weight and length, as well as the jumping ability of the individuals that reached the end of development were also evaluated. The effects observed occurred principally between S39 and S42. All insecticide exposures, individually and in pairwise combinations, caused a similar delay in development and a decrease in metamorphic success without affecting the weight and length of the metamorphs. The exception was the exposure to a mixture TIA-IMI, where metamorphic success where similar to controls but metamorphs had significantly lower weights. Evaluation of the jumping ability of the metamorphs revealed that individual exposures to CHLO and THIA and those exposed to the pairwise combinations of THIA-IMI and CHLO-THIA significantly reduced jumping ability compared to the control group and the group exposed to IMI.