Many flea control problems are aggravated due to the lack of understanding and knowledge of the pupal stage of the flea. Even with advanced technologies in pest management, the flea pupae has proven to be the hardest to control of all stages of the flea life cycle. Many people believe that their flea control program is failing when in fact they just do not understand the tough nature of the flea pupae.

Life Cycle of Fleas Pupae Development Controlling Flea Pupae

Fleas develop through a life cycle known as complete metamorphosis. This is a basic four stage cycle that includes eggs, larvae, pupae and adult. (Although flea larvae cycle through three larval instars, the larvae is still considered only one of four stages.) Adult female fleas (after feeding and mating) are little insect machines whose life is consumed by three activities: laying eggs, gorging on the blood of her host and defecating undigested blood in small drops. These hardened drops of blood and her eggs are distributed as they fall of off the host animal. After a few days, the eggs hatch and the first instar of the flea larvae emerge. These larvae locate and feed on the hardened drops of blood that are scattered in the same areas as the flea eggs. After going through a series of molts or instars (flea larvae have a total of three of these instars) the larvae begin the process of building their cocoon which is known as the pupal casing. It is in this pupal stage that the flea larvae change, developing into a fully grown adult flea. At the correct time, the adult flea will emerge from its protected casing and begin anew the cycle of locating a host, feeding, mating and (in the case of the female) laying eggs.

Pupal Casing - Flea Pupae Development

Flea pupae development actually begins during the third and final instar of the larvae. Flea larvae spin their pupal case with a combination of materials collected in their immediate area, with the help of a special silk produced by the larvae. This silky material (produced by saliva of the larvae) helps bind together debris collected by the immature flea. In a home, these materials include pet and human hair, lint, dust and fabrics from carpets, furniture and upholstery. Using these materials, the larvae puts together a water-tight cocoon that is almost invisible - totally camouflaged by blending in with its surroundings.
The major change occurs inside of the pupal case: the legless, eyeless worm is changed into a highly developed insect that is engineered to detect warm blooded nesting animals, jump high enough and fast enough to latch on to the animal and feed voraciously from the animal's blood.
If you were to open a flea pupal casing you would either find a fully developed adult flea, a changing flea larvae or an undeveloped larvae that has been deformed by an insect growth regulator. An IGR (Archer, Precor) does not effect any fully developed flea pupae. A larva that has been deformed by an IGR can actually live long enough to pupate but it will never emerge from the pupae stage. IGR sprays only effect the eggs and larvae of fleas.
The pupal stage only lasts about a week or 10 days. Although the change is complete, the fully developed adult flea will not necessarily emerge at this time. Nature has a way of protecting creatures from starvation to the point of extinction. Immediately after emerging, the adult flea must have a blood meal to survive and mate. If the fleas emerge and there is not a suitable host in the immediate area, the fleas would not survive. Nature protects fleas by giving them the ability to remain in their cocoon (pupal casing) until there is a good chance that a host is close by. It is not unusual for the protected flea to remain dormant for several months at a time. Without sensing a possible meal, the flea remains dormant. Many people return home from vacation only to find thousands of fleas that they did not know existed before they went on their trip. The very act of walking around, shutting doors, etc., produces vibrations that cause thousands of fleas to hatch at the same time - hungry fleas that attack anything that moves, in search of a meal.
Animals produce vibrations felt by fleas; they also exhale carbon dioxide and give off heat from their bodies. All of these things are indicators or signals for fleas. When the flea feels vibrations from animal activity, detect body heat and also sense the warmth, humidity and carbon dioxide of the animal's breath, they know that their blood meal is close. The signals of a nearby animal prompt the emergence of the hungry adult flea. The same signals trigger the flea to jump, catching a ride on its intended host.

Controlling Flea Pupae

This is the most frustrating part of flea control and is the reason why an understanding of the dormant stage is so important from an integrated pest management point of view. Most people assume that as soon as a home or lawn has been sprayed or otherwise treated, they will not see any more fleas. This just is not the case. Pesticide sprays kill adult fleas that are exposed to the spray. Insect growth regulators effect only flea eggs and flea larvae, preventing them from becoming adults. Flea Stoppers kills flea eggs and flea larvae.
Pesticides, insect growth regulators and borate carpet treatments (Flea Stoppers) do not kill fleas that are in their protected pupal casing. The case or cocoon is water tight and not effected by sprays.
This means that control of flea pupae involves removing them mechanically (cleaning, vacuuming) and encouraging them to hatch.
Your vacuum cleaner is your best friend and most important tool for controlling flea pupae in your home. As mentioned in development of fleas inside pupae, there are only three possible creatures inside of the pupae: a fully developed flea, a maturing flea and a larvae deformed by an IGR that will not live. Once you have treated your home with a product for eggs and larvae, the next step is to get rid of as many pupae as possible.
Vacuuming carpets, rugs, floors and furniture accomplishes two important jobs:

Picks up pupae that can be disposed of in an outdoor garbage receptacle.
Entices adult fleas to hatch.

Unlike flea larvae, the pupae do not have the ability to move about or avoid being picked up by a vacuum cleaner. With the very real possibility of thousands of pupae laying around in your home, every one of them that you can remove mechanically represents another adult flea that you have to put up with or kill. Ridding infested areas of pupae will obviously reduce the numbers of hatching adult fleas.
As previously mentioned, larvae and adult fleas respond to warmth, carbon dioxide and vibrations. A fully developed flea that has yet to hatch will respond to nearby warm and vibrations. Your vacuum produces a small amount of heat and a great deal of vibration which will encourage developed fleas to hatch out of their pupal casing. If the developed fleas do not hatch, they cannot be killed by contact insecticides! This bears repeating: contact insecticides kill by contacting (touching) targeted insects. A flea inside the pupal casing cannot contact the insecticide - it must emerge (hatch) and come into contact with your insecticide.
When a flea touches a treated surface, do not expect it to die that very instant! The flea picks up a lethal dose of insecticide after moving through the treated surface. This lethal dose will take effect anytime between a few minutes to a day but usually within a couple of hours.
Insecticides that have enough residual power to kill ants and roaches for 28 days or more do not have the same residual for fleas. Your best killing power or knockdown for fleas is within a 2 week time frame after proper treatment.
For the reasons mentioned here, you can expect to see fleas hatching inside of your home for a few days or even as long as 8 weeks. You will see an increase in adult flea activity about 2 weeks after initial treatment. It is at this time that a follow-up treatment is often necessary.

To summarize control for flea pupae:

Vacuum thoroughly and on a regular basis.
Dispose of vacuumed fleas in a sealed container, outdoors.
Mechanically removing flea pupae is great pest control.
The vibrations of your vacuum cleaner will help remaining fleas hatch out of their casing.
Once they have hatched, adult fleas will be exposed to your insecticide treatment.

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