Spinosad in the native stingless bee Melipona quadrifasciata: Regrettable non-target toxicity of a bioinsecticide

- Imidacloprid and spinosad are highly toxic to adult stingless bee workers.
- The bioinsecticide spinosad was more toxic to the bee workers than imidacloprid.
- Imidacloprid impaired worker respiration, overall group activity and flight.
- Spinosad impaired flight, but not respiration and overall group activity.
- Both insecticides were highly hazardous to the stingless bee Melipona quadrifasciata.

The risks imposed by novel insecticides, mainly bioinsecticides, are largely unknown despite their increased use and their perceived environmental safety, which is based on their natural origin. Furthermore, unlike honeybees, native pollinator species have received little attention. In the present study, the lethal and sublethal effects of the neonicotinoid imidacloprid and the bioinsecticide spinosad were assessed in the stingless bee species Melipona quadrifasciata, an important native pollinator in the Neotropical region. The adult stingless bee workers exhibited high oral insecticide susceptibility, with LD50s of 23.54 and 12.07 ng a.i./bee for imidacloprid and spinosad, respectively. Imidacloprid also impaired worker respiration and overall group activity and flight, while spinosad significantly impaired only worker flight despite exhibiting higher oral toxicity to adult workers than imidacloprid. These findings indicate the hazardous nature not only of imidacloprid but also the bioinsecticide spinosad to adult workers of the native pollinator M. quadrifasciata. Therefore, bioinsecticides should not be exempted from risk assessment analysis due to their lethal and sublethal components.