Toxic effects of neonicotinoids on apis mellifera L. workers (Hymenoptara: Apidae)

Neonicotinoid insecticides are applied in the cultures of melon (Cucumis melo L.) to control pests of insects. However, insecticides can have indirect effects on bees, which are important pollinators of melon crops. The objective of this work was to evaluate the toxicity of neonicotinoids to the bee Apis mellifera, Linnaeus. The bioassays were carried out at the Entomology Laboratory of the Center for Agro-Food Science and Technology (CCTA), Federal University of Campina Grande (UFCG), and repeated measures were taken in the mortality time for thiamethoxam, imidacloprid and acetamiprid products (two formulations: Orpheus and Mospilan). Sprays of chemical solutions containing the highest and lowest doses recommended by the manufacturers were sprayed manually (500mL capacity and 0.58mL flow rate and average application rate 1.5 ± 0.5mL solution/cm2). The work consisted of 9 treatments with five replicates. In each plot, we used ten adults of worker bees with 48 hours (h) of age. After spraying, the bees were transferred to a wooden cage (11.0 in length x 11.0 cm wide x 7.0 in height) with a glass cap and kept in an air-conditioned room at 25 ± 2°C, UR 70 ± 10% and 12h of photophase, disposed of in completely randomized design. Observations of the dead insects were made in the hours one, two, three, six, 12, 24, 48, 72 and 96 hours. Regardless of dosage, all insecticides evaluated were toxic to A. mellifera workers. Thiamethoxam showed higher toxicity among the evaluated active ingredients, killing all bees within 1h after spraying, regardless of the dosage.