O farnesol tópico altera parâmetros comportamentais, morfológicos e moleculares de operárias jovens de abelhas Apis mellifera

Abstract

Living organisms intertwine in daily contact with calls that are released into the environment, both by animals and plants, in an action known as environmental chemical interaction. This interaction can eventually cause changes in the physiology, morphology and behavior of organisms. Some plants, for example, the species Baccharis dracunculifolia, popularly known as alecrim-do-campo, contain farnesol in its resin. This sesquiterpene is an important precursor of the juvenile hormone (JH) synthesis pathway, a substance that governs several aspects of insect life. We hypothesize that, during foraging, Apis mellifera bee workers come into contact with significant amounts of JH precursors that, once inside the body, can be modified and converted into JH. Previous studies by our group showed that young workers who consume farnesol supplied in the diet ingest more food, are more aggressive, have larger corpora allata (CA, site of JH synthesis) glands, including the diameter of cell nuclei, and show alterations in the transcription profiles of genes encoding enzymes in the HJ synthesis and degradation pathway. Here we provide topical farnesol in young adult workers of A. mellifera to analyze its influence on biology, uncoupling its possible indirect effect on the rate of ingestion of these insects. For this, we carried out a series of experiments using two groups of newly emerged worker bees (24 hours): (Group I) 50 bees received the farnesol solution directly in the thorax (we tested 3 different concentrations: 10 μg, 2 μg and 0.2 μg); and (Group II) 50 bees that received acetone (control). The bees were kept in an oven for 72 hours at 36°C and 80% relative humidity. To assess the effects of farnesol on the morphology of the AKs, they were dissected and processed through historesin histology. To estimate the effects of farnesol on the synthesis/degradation pathway and response to JH, we determined (using qPCR) the level of coding genes for the enzymes methyl farnesoate epoxidase (mfe), methyltransferase (mt), and juvenile hormone esterase (jhe), Krüppel homologue (Kr h1), Metoprene-Tolerant (Met and TAI). Our results show that topical farnesol does not change feed intake in young bees. However, at high doses (10 μg), it is toxic, causing an increase in mortality in the treated group. We also observed that topical farnesol influences the behavior of young bees (increase in movement), especially in the first 48 hours after treatment, and promotes changes in the morphometric parameters of CA in treated bees, as they have a larger size (area and volume) of these structures in relation to the control group. Transcription level analyzes showed that the mfe and mt genes, representatives of the juvenile hormone (JH) synthesis pathway, and the HJ response genes (Jhe, homologous Krüppel - Kr h1, Metoprene-Tolerant - Met and TAI), were more expressed in the farnesol-treated groups compared to the control groups. Therefore, we conclude that farnesol promotes behavioral, morphological and physiological changes in young Apis mellifera bees, possibly when used as a precursor for the synthesis of JH or through a similar action to JH itself. The morphological alterations of the CA and the alterations in the expression levels of genes of the HJ synthesis pathway in bees treated with farnesol support the first explanation.