RNAi-mediated knockdown of juvenile hormone acid methyltransferase depresses reproductive performance in female Aethina tumida

Abstract

Small hive beetles, Aethina tumide, are free-flying parasites of social bee colonies where they feed and reproduce. In case of mass infestation, A. tumida can cause significant economic losses. There is an urgent need to explore novel green molecular approaches for sustainable control of A. tumida. It has been confirmed that juvenile hormone acid methyl transferase (JHAMT) plays a crucial role in regulating the synthesis of juvenile hormone (JH). However, its impact on female reproduction of A. tumida remains unclear. In the present study, a novel JHAMT gene was identified from A. tumida with an open reading frame of 978 bp, encoding a polypeptide of 325 amino acids containing a Methyltransferase domain. The deduced amino acid sequence of AtJHAMT shared 60 % and 33 % identity with homologs from Brassicogethes aeneus and Apis mellifera, respectively. The expression profile indicates that the transcription level of AtJHAMT increases in the adult stages, reaching its peak in 5-day-old female adults. AtJHAMT exhibits the highest expression levels in the ovaries, and fluorescence in situ hybridization (FISH) demonstrates that this gene shows a significant number of positive signals in the ovarian ducts and the head region. Furthermore, we investigated the function of AtJHAMT through RNA interference and methoprene rescue experiments. We also investigeted the off-target effects of the dsJHAMT. The results showed that silencing AtJHAMT through oral dsRNA delivery (feeding dsRNA-SPc mix) affected ovarian development and significantly reduced JH titers, female fecundity, female fertility, and egg hatchability. The application of methoprene partially rescued the negative effect of silencing AtJHAMT on reproduction. Several genes associated with ovarian development were significantly downregulated following interference with AtJHAMT, but their expression levels were restored after complementation experiments. Additionally, the off-target effects experiment showed that dsJHAMT from A. tumida had no adverse effects on ovaries development in honey bee queens. Overall, this study illustrates the functions of the JHAMT in A. tumida, which can serve as a potential target for controlling the reproduction of the most deleterious bee parasites, A. tumida.

Keywords: Aethina tumida; Juvenile hormone acid O-methyltransferase (JHAMT); Ovary; Queen; RNA interference; Small hive beetle.