What drives reproductive divergence in aphid speciation, according to host adaptation studies?

Adaptation to a new host's unique chemistry or resistance mechanisms

A core mechanism driving the rapid evolution and speciation of aphids, particularly the formation of host races, is the necessity to overcome plant defenses. When an aphid lineage successfully colonizes a new host plant, the unique chemistry or resistance mechanisms inherent to that host impose intense selective pressure. This pressure acts as a powerful filter, exclusively favoring individuals within that lineage that possess the necessary tolerance or detoxification capabilities to survive on the new host. This process of adaptation to novel host environments serves as the catalyst that drives reproductive divergence, leading to the formation of specialized, reproductively isolated groups over relatively short time scales.