Search

Nosema ceranae is a microsporidium that infects Apis mellifera, causing diverse physiological and behavioral alterations. Given the existence of individual and social mechanisms to reduce infection and fungal spread in the colony, bees may respond differently to infection depending on their rearing conditions. In this study, we investigated the effect of N. ceranae in honey bee foragers naturally infected with different fungal loads in a tropical region. In addition, we explored the effects of N. ceranae artificially infected young bees placed in a healthy colony under field conditions. Honey bees naturally infected with higher loads of N. ceranae showed downregulation of genes from Toll and IMD immune pathways and antimicrobial peptide (AMP) genes, but hemolymph total protein amount and Vitellogenin (Vg) titers were not affected. Artificially infected bees spread N. ceranae to the controls in the colony, but fungal loads were generally lower than those observed in cages, probably because of social immunity. Although no significant changes in mRNA levels of AMP-encoding were observed, N. ceranae artificially infected bees showed downregulation of miR-989 (an immune-related microRNA), lower vitellogenin gene expression, and decreased hemolymph Vg titers. Our results demonstrate for the first time that natural infection by N. ceranae suppresses the immune system of honey bee foragers in the field. This parasite is detrimental to the immune system of young and old bees, and disease spread, mitigation and containment will depend on the colony environment., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

In social insects, juvenile hormone (JH) has acquired novel functions related to caste determination and division of labor among workers, and this is best evidenced in the honey bee. In contrast to honey bees, stingless bees are a much more diverse group of highly eusocial bees, and the genus Melipona has long called special attention due to a proposed genetic mechanism of caste determination. Here, we examined methyl farnesoate epoxidase (mfe) gene expression, encoding an enzyme relevant for the final step in JH biosynthesis, and measured the hemolymph JH titers for all life cycle stages of Melipona scutellaris queens and workers. We confirmed that mfe is exclusively expressed in the corpora allata. The JH titer is high in the second larval instar, drops in the third, and rises again as the larvae enter metamorphosis. During the pupal stage, mfe expression is initialy elevated, but then gradually drops to low levels before adult emergence. No variation was, however, seen in the JH titer. In adult virgin queens, mfe expression and the JH titer are significantly elevated, possibly associated with their reproductive potential. For workers we found that JH titers are lower in foragers than in nurse bees, while mfe expression did not differ. Stingless bees are, thus, distinct from honey bee workers, suggesting that they have maintained the ancestral gonadotropic function for JH. Hence, the physiological circuitries underlying a highly eusocial life style may be variable, even within a monophyletic clade such as the corbiculate bees., (Copyright © 2017 Elsevier Ltd. All rights reserved.)