Toxicidade aguda do inseticida fipronil para apis mellifera africanizada e scaptotrigona bipunctata

Abstract

Bees are an important group of pollinators, necessary for the maintenance of biodiversity. Their populations are declining due to human actions, mainly due to the use of chemicals formulated in agricultural crops. Currently, fipronil is among the most commercialized insecticides in the world, with 61 formulations registered in Brazil and authorized for use in several crops, such as soybeans. The foliar application of fipronil in plantations can expose foraging bees to residues of these pesticides, generating harmful effects to these non-target insects, including the death of individuals and entire colonies. The widespread use of fipronil in agricultural crops and its association, in recent years, in cases of loss of bee colonies in Brazil has warned of the need for research to support measures to protect pollinating insects. Considering that the sensitivity to pesticides is different in species of bees and that Brazil has a high diversity of bees, it is necessary to include native species in risk analysis of pesticides. In this context, the present study aimed to evaluate the acute toxicity of fipronil, in Africanized Apis mellifera and Scaptotrigona bipunctata (representative of the Brazilian fauna), in order to determine the median concentration and lethal dose (LC50 and LD50), respectively, in oral exposure and topical forage bees. The tests were performed based on acute oral (OECD 213) and topical (OECD 214) toxicity protocols for honey bees. For this purpose, five dilutions were established based on the field rate used for soybeans (32g a.i. of fipronil / 100L of syrup). The commercial fipronil product used was Nortox® 800WG: 80% active ingredient (a.i.). In oral exposure, concentrations for A. mellifera comprised a range of 0.0016 to 0.32 ng a.i./μL of diet and for S. bipunctata from 0.0008 to 0.032 ng a.i./μL of diet. On topical exposure, concentrations were limited to the range of 0.08 to 1.6 ng a.i./bee for A. mellifera and 0.016 to 0.32 ng a.i./bee for S. bipunctata. Data analysis was performed using the R program, the mortality rate was calculated using the “drc” package. For food consumption, ANOVA or Kruskal-Wallis (whether parametric or non-parametric) was adopted. The results of the acute oral toxicity test determined the LC50 (in 72 hours): 0.0204 ng a.i./μL of diet to A. mellifera and 0.0031 ng a.i./μL of diet to S. bipunctata. The consumption of food by the bees did not differ between the control and the concentrations tested with fipronil, for both species, indicating that the product did not cause repellency (P> 0.05). In the acute topical toxicity test, the LD50 values in 72 hours were 0.3096 ng a.i./bee to A. mellifera and 0.0938 ng a.i./bee to S. bipunctata. These data reveal that the concentration of fipronil indicated for use in soybean crops in Brazil is highly toxic to bees. In addition, it should be noted that the native bee evaluated in this study is more susceptible than the exotic bee. Studies carried out with other Brazilian species also show that native bees are less tolerant to the insecticide fipronil than A. mellifera. The authors emphasize the urgency of including native bees in pesticide risk analysis, and of putting public policies and measures in place to protect pollinators.