TITIN Regulates Body Size via the JH–JHE Pathway in Honeybees (Apis mellifera)

Honeybees play a vital role in pollinating crops and wild plants, but their health and efficiency are strongly influenced by their body size. Large bees tend to have longer lifespans, stronger foraging abilities, and greater resistance to diseases. However, the molecular mechanisms that control honeybees’ body size are not fully understood. In this study, we focused on 3 to 5-day-old larvae of Apis mellifera ligustica and investigated the roles and interactions of juvenile hormone (JH), juvenile hormone esterase (JHE), and TITIN in regulating honeybees’ body size using RNAi, exogenous hormone treatment, and qRT-PCR. The results showed that suppression of Jhe expression caused JH accumulation in larvae, subsequently reducing Titin expression and ultimately increasing adult body size. Furthermore, exogenous application of JHIII also inhibited the expression of Titin. Suppression of Titin expression alone directly increased the body size of adult honeybees, but did not affect the JH titer, which indicates that JH negatively regulates Titin expression in a unidirectional manner, whereas Titin does not feedback-regulate JH titer. The study suggests a regulatory link between JH, Jhe, and Titin in body size control. The discovery of this pathway, when combined with traditional breeding methods, may provide insights for future breeding strategies in honeybees.