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Quadraspidiotus perniciosus (Comstock)
Aspidiotus perniciosus, Diaspidiotus perniciosus

Insecta, Homoptera, Diaspididae .

San José scale, Pernicious scale, California scale

Description, Biology, Life Cycle, Damage, Common Names, Images

- Adult: female apterous, pear-shaped, flattened, fixed to the plant and hidden under a detachable scale; scale circular, dark grey, about 2 mm across (*) ; males provided with a pair of wings.
- Nymph: young nymph mobile, yellow, provided with 3 pairs of short legs; once fixed, secretes a white scale which becomes grey and then black.

- Host plant: the San José scale is very polyphagous and develops on more than 150 species of host, especially on apple, pear, plum, peach, cherry, currant, black currant.
- Nymphs overwinter during the 1st instar in a state of diapause. After moulting twice (in March and May), they emerge either as males or females. Females are viviparous and each produces 8-10 nymphs per day from late May onwards, the egg-laying period spreading over 6 weeks. The average number of nymphs produced on a favorable host plant is 400.
Nymphs are at first mobile and then settle down by inserting their stylets into plant cells. They produce encrustations on twigs (*) , branches and sometimes on leaves and fruits around the eye (*) .

[R]Life Cycle
There are 2-4 generations depending on the region. As soon as winter approaches, 1st-instar nymphs enter a state of diapause; very young and 2nd-generation nymphs as well as adults die.

- Feed by these insects, when they inject toxic saliva, leads to a distortion of plant tissue, the premature dropping of leaves and the discoloration of the fruits' epidermis (*) as well as the decline of affected twigs and branches.
- A specific parasite of the San José scale, Prospaltella perniciosi (*) , was introduced to fight against this scale insect (*) .

[R]Common Names
DE: San-José Schildlaus, Kalifornische Schildlaus ES: Cochinilla de San José FR: Pou de San-José IT: Aonidiella perniciosa, Cocciniglia di San José PT: Piolho de S. José GB: San José scale, California scale, Pernicious scale

[R] Images

  1. Quadraspidiotus ostraeiformis (Curtis) (Bénassy C. / INRA Antibes)
    Colony on rose Male scales are elongate whereas those of females are circular and also larger.
  2. Quadraspidiotus perniciosus (Comstock) (Duteil)
    Male and female individuals The scale of the female was turned upside down to show the colour of the body of the female. Young nymphs can be seen (arrowed).
  3. Quadraspidiotus perniciosus (Comstock) (Coutin R. / OPIE)
    Colony on apple The change in colour of the epidermis reveals the presence of scale insects.
  4. Quadraspidiotus perniciosus (Comstock) (Bénassy C. / INRA Antibes)
    Damage on pear The change in colour of the epidermis is due to the presence of scale insects.
  5. Quadraspidiotus perniciosus (Comstock) (Duteil)
    Specific parasite Female of Prospaltella perniciosi" (Hymenoptera) about to lay eggs in a nymph.
  6. Quadraspidiotus perniciosus (Comstock) (Duteil)
    Parasitized colony Exit holes of adults of
    Prospatella perniciosi (Hymenoptera) in male and female scales.

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