Age-dependent hypopharyngeal gland development and morphometric characteristics in the cross-bred lineage of honeybees reared for high royal jelly production

Abstract

Abstract We reared the cross-bred FD lineage (F♀ × D♂) from inbred lines in pursuit of high royal jelly (RJ)-producing honeybee traits. The present study compared the new crossbred FD line to a high RJ-producing colony (HRC) and a low RJ-producing colony (LRC) by investigating the production of RJ, morphological characteristics, and age-dependent hypopharyngeal gland (HPG) development of the honeybees. The HRC exhibited the highest RJ production (416.46 ± 71.49 mg/cup), followed by the FD (369.29 ± 80.89 mg/cup), and the LRC (284.79 ± 38.54 mg/cup) colonies, respectively. The 10-HDA content was highest in the FD colony (2.38%), followed by the LRC (2.06%) and the HRC (1.91%). Compared to newly emerged bees, the body weight, fresh head weight, and HPG development increased until 9 days, and then decreased thereafter. Moreover, the length of the acini of the HPG at 9 days-old was almost twice as long than those of the bees at first emergence in all colonies. The acini diameters of the HPG in the HRC were significantly larger at all age stages. Compared to the LRC line, the acini in the FD line were significantly longer until 9 days after hatching. The abdominal length and forewing length were longer in the HRC, while the corbicular area, and head, proboscis, and glossa lengths were longer in the FD. The discriminant function analysis revealed that 78.1% of the individuals were classified correctly. Further assessements of wing geometric morphometrics are needed to clarify the morphological characteristics of the new hybrid FD line with high RJ-producing traits.