Delphastus pusillus is a small, shiny black beetle of 1.3-1.4 mm. It belongs to the ladybird family and originates from North-America. After copulation it takes about 3-5 days before the female lays her first eggs. She deposits them in the upper part of the plant and on the underside of the leaf, amongst whitefly eggs and larvae. Under laboratory conditions and with sufficient whitefly eggs as food available, a Delphastus can produce about 3 eggs per day, or a total of 183 in her whole life. In the greenhouse this can amount up to 6 eggs per day. The oviposition varies significantly from day to day, but is on average quite constant with age.

At 28°C (84.4°F) larvae hatch after 4 days. They have an elongated body and are pale yellow to white. Immediately after birth they start eating whitefly eggs and larvae around them. There are 4-5 larval stages in 11 days. Subsequently, the older larvae migrate to sheltered places (as the underside of the leaf) in the lower part of the plant to pupate in groups. The pupal stage takes about 6 days at 29°C (84.4°F).

The total development time at this temperature is about 21 days. An adult female lives for about 60 days, while an adult male stays alive for about 49 days. Larvae and adult Delphastus beetles probe the leaf surface with their mouth parts until they get in touch with a prey. They often walk past whiteflies if no actual contact occurs. Once they have found a whitefly egg, larva or pupa, they bite through its covering and extract the contents. For an adult Delphastus it takes no longer than half a minute to handle a whitefly egg. A larva eats about 1000 whitefly eggs (or less if it also eats whitefly larvae) during its entire development. An adult beetle devours daily up to 160 whitefly eggs, or 12 whitefly larvae of the 4th stage.

Only on a diet of whitefly larvae a female cannot deposit eggs. Therefore, she needs a daily consumption of at least 100 to 150 whitefly eggs. Delphastus predates both on greenhouse whitefly and on tobacco whitefly. Whitefly pupae parasitized by Encarsia are left untouched, but recently parasitized whitefly larvae are not recognized as such.

Delphastus pusillus is used to clean up whitefly colonies mainly in eggplant and gerbera. On tomato the beetle does not work well due to the glandular hairs on the leaf. Delphastus is to be introduced in increasing whitefly colonies. In dispersed whitefly populations it does not find its prey.

A good whitefly control therefore has to be combined with the parasitic wasps Encarsia formosa or Eretmocerus californicus. Delphastus rather has to be considered as a biological correction. The amount of beetles to be introduced depends on the infestation. Often about 100 Delphastus per 10 plants are released in the hot spots.

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