The need for multiple applications has a lot to do with the flea’s biology and behavior. Fleas undergo complete metamorphosis, meaning they have four life stages: egg, larva, pupa and adult. During both the egg and the pupal stage, fleas are protected from hazardous environmental conditions by naturally produced shelters: the shell in the egg stage, and the cocoon in the pupal stage. Unfortunately for pest professionals, the egg shell and the cocoon can also shelter developing fleas from pesticides. Therefore, a single application can reduce larval and adult populations, but will have little effect on eggs and pupae.
Another reason why a flea job may require multiple applications is because fleas can remain in the cocoon as pre-emerged adults for up to 20 weeks. They wait for cues such as vibrations or an increase in temperature to signal that a host has arrived. This behavior explains why vacationing homeowners with a small flea problem can leave for a few weeks, and be greeted by large numbers of hungry fleas when they return. This also explains why follow-up applications may be necessary to reduce adult populations.
By: Pest World