Older mothers produce offspring with improved development and growth efficiency.

Maternal age and diet can influence offspring development and fitness via maternal effects, but empirical evidence for their interactive effects remains limited. We examined how maternal age at oviposition and maternal dietary conditions influence offspring developmental responses to resource availability in the thelytokous predatory mite Amblyseius herbicolus. Mothers received either a restricted or abundant prey diet, and their offspring were exposed to varying prey availability and monitored for hatching success, survival to adulthood, developmental duration, size at maturity, and prey consumption. We asked how maternal age influences offspring development and whether maternal diet modifies these age-related effects. Offspring of older mothers had higher survival to adulthood, developed for longer, attained a larger size at maturity, and consumed fewer prey during development. Maternal age also interacted with offspring prey availability to influence survival, while maternal diet modified age-related effects on developmental duration, offspring size, and prey consumption. These findings demonstrate that maternal age and nutritional condition jointly shape offspring development and responses to resource availability, highlighting the importance of considering maternal age and environment when examining maternal effects and developmental plasticity.