These three species of Diaspis are very similar in their appearance and damage symptoms. Here, the Boisduval scale is described in more detail, as it is the most important one. The Boisduval scale, Diaspis boisduvalii, occurs throughout the tropics, and in greenhouses in more temperate climates. It is very polyphagous and can be a pest of orchids, palms, pineapples, bananas and many other plants.
Life cycle and appearance of Boisduval scale
Females are white to light yellow, thin and semi-transparent, approximately 1.2-2.2 mm in diameter and circular or oval. The cast skins of the nymph form a light yellow spot near the centre of the scale called the exuvium.
Adult females can produce up to 200 eggs and live up to seven months. Eggs hatch within five to seven days under the scale and become crawlers. The crawlers move out to look for a suitable place to feed and become sessile usually after a few hours The development from egg to the adult stage takes on average 33 days for males, and 50 days for females.
The first sign of Boisduval scale is the presence of the scales on upper and lower leaf surfaces, fruits, and stems of plants. On palms, Boisduval scales are normally found on the leaves and stems. Toxic saliva injected while feeding causes necrosis of tissue at the feeding site. In orchids, this scale tends to prefer the leaf midrib and the portion of the petiole that is covered by the sheath. Small infestations on orchids cause extensive discolouration.