Impact of entomopathogenic nematodes on Africanized honey bees Apis mellifera L. (Hymenoptera: Apidae) workers

Abstract

Africanized honey bee populations (Apis mellifera L.) have been decreasing mainly due to the intense use of synthetic insecticides associated with pollution and climate change. To minimize these impacts on the environment and bee populations, the use of biological control agents has been intensified. These products are generally safer for non-target insects, such as bees, which are important pollinating insects. Thus, the objective of this study was to evaluate the impact of entomopathogenic nematodes on the longevity of the Africanized honey bee A. mellifera workers. Seven treatments were used: Heterorhabditis amazonensis, Heterorhabditis bacteriophora, Heterorhabditis indica, Steinernema carpocapsae, Steinernema feltiae, and Steinernema rarum, at a concentration of 40 infective juveniles per cm2 (IJs/cm2) and a control in which autoclaved distilled water was used. Two bioassays were performed: 1) spraying nematodes on the workers and 2) spraying nematodes on glass plates, in which the bees remained for two hours. Each treatment consisted of five replicates with 20 bees each. Bees were kept in cages of PVC (20 × 10 cm) covered with a voile fabric and provided pieces of cotton soaked in water and Candy paste. The cages were kept in a climatized room (27 ± 2 °C temperature, 60 ± 10% relative humidity, and 12 h photophase) and the mortality was evaluated from 12 to 240 hours. In bioassay 1, the three treatments with nematodes of the genus Steinernema reduced the longevity of the workers (103.9, 96.3, and 99.6 h) when compared to treatments with Heterorhabditis (149.7, 126.8, and 134.7 h), of which, only H. amazonensis (149.7 h) did not differ from the control (166.0 h). In bioassay 2, all treatments reduced the longevity of honey bees (155.4 to 93.9 h) in relation to the control (176.1 h). Entomopathogenic nematodes, especially Heterorhabditis, need to be tested using other methodologies and for different durations of exposure and application because in the laboratory, they were less selective to A. mellifera.