Abstract
Previous studies have shown that exposing young worker bees (Apis mellifera) to queen mandibular pheromone (QMP) reduces their aversive learning performance, while enhancing their attraction to QMP. As QMP has been found to reduce the rate of juvenile hormone (JH) synthesis in worker bees, we examined whether aversive learning in 2-day old workers exposed to QMP from the time of adult emergence could be improved by injecting JH (10 µg in a 2 µl volume) into the haemolymph. We examined in addition, the effects of JH treatment on worker attraction to QMP, and on the levels of expression of amine receptor genes in the antennae, as well as in the mushroom bodies of the brain. We found that memory acquisition and 1-hour memory recall were enhanced by JH. In contrast, JH treatment reduced the bees’ attraction towards a synthetic strip impregnated with QMP (Bee Boost). Levels of expression of the dopamine receptor gene Amdop1 were significantly lower in the mushroom bodies of JH-treated bees than in bees treated with vehicle alone (acetone diluted with bee ringer). Expression of the octopamine receptor gene, Amoa1, in this brain region was also affected by JH treatment, and in the antennae, Amoa1 transcript levels were significantly lower in JH-treated bees compared to controls. The results of this study suggest that QMP’s effects on JH synthesis may contribute to reducing aversive learning performance and enhancing attraction to QMP in young worker bees.
Highlights
In a honey bee colony, the queen bee advertises her presence using chemical signals known as pheromones [1,2]
We demonstrate that juvenile hormone (JH) alters the behaviour of young bees and the mushroom bodies (MBs) and antennal expression of amine receptor genes, suggesting that queen mandibular pheromone (QMP)-induced changes in circulating JH titres are likely to contribute to the effects of this pheromone upon both learning behaviour and attraction of young bees to QMP
JH treatment Using 2-day old bees exposed to QMP from the time of adult emergence, we examined the effects of JH treatment upon aversive learning performance, worker attraction towards QMP, and amine receptor gene expression in the antennae and MBs of the brain
Summary
In a honey bee colony, the queen bee advertises her presence using chemical signals known as pheromones [1,2]. QMP exposure has been shown to alter amine receptor gene expression, including a reduction in the brain and antennal expression of the dopamine receptor gene Amdop1 [5,6], and reduced expression of the putative dopamine/ecdysone receptor gene Amgpcr in the mushroom bodies (MBs) of the brain [4]. Exposure to this pheromone increases the likelihood that young bees will show attraction towards QMP [6]. We investigate the possibility that this pheromone-induced behavioural plasticity may involve QMPinduced modulation of juvenile hormone (JH) titres in the bee
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