SCIENTIFIC NAME: Diaspis boisduvalii Signoret
CLASS: Insecta
ORDER: Hemiptera
FAMILY: Diaspididae
Description
Adult Females
Cover of the adult female boisduval scale is circular or oval, thin, flat, white to light yellow, semitransparent, and 1.2 to 2.25 millimeters in diameter. Exuviae central to subcentral in position.
Adult Males
The male cover is somewhat rectangular in shape, elongate, about 1 millimeter in length, and snow white with three ridges down the back.
Eggs
Boisduval scale eggs are oval and pale yellow to pale orange.
Nymphs
Newly settled nymphs are pale orange.
Biology
Host Plants
Cattleya and Cymbidium orchids are the most common hosts, but this scale insect thrives on the leaves and bark of other orchids, palms, banana, and cacti.
Damage
New growth is frequently attacked prior to opening, and leaves may be killed if the infestation is dense. Lighter infestations produce irregular chlorotic spots that mark feeding sites and spoil the appearance of the leaves.
Life Cycle
Under greenhouse conditions, boisduval scale can complete its life cycle in about 50 days. Females may produce up to 200 eggs in a lifetime. Eggs hatch in 5 to 7 days and most of the crawlers settle to feed within 24 hours after hatching. The first stage lasts about 10 days, the second about 8 to 10 days for females and 15 for males. After mating, females retain their eggs for a short period, then oviposit. Because females produce eggs over a long period, generations overlap, and usually all stages can be found at an one time. Crawlers can settle anywhere on the leaf, but seem to prefer the midrib and major veins.
Management Strategies
Try to purchase plants from a supplier who does not have a scale infestation.
Pesticides
When scales are encountered, horticultural oils give adequate control without excessive phtotoxicity. Two thorough treatments, 2 weeks apart should give good control. Boisduval scale crawlers often establish themselves near the base of the plant and in leaf sheaths making control difficult. Also, both upper and lower leaf surfaces are attacked, so thorough coverage of any treatment is essential. For specific control recommendations, consult the Extension Service.