What environmental cues trigger the shift from rapid asexual reproduction to sexual reproduction?

Shortening daylight hours or temperature drops signaling impending hardship

The switch from the highly efficient asexual reproduction mode (parthenogenesis and viviparity) to the sexual reproduction mode is a carefully timed evolutionary response to impending adversity. The primary environmental signals that trigger this shift are external cues indicating that favorable conditions are ending, specifically shortening daylight hours or noticeable drops in temperature. When these cues signal impending hardship, such as the onset of winter, the reproductive strategy pivots. This carefully timed change ensures that while populations explode asexually when resources are abundant, the species survives the harsh period by producing the genetically diverse and robust eggs resulting from sexual recombination, which are far more resistant to freezing than live nymphs or adults.