Quadraspidiotus perniciosus

Quadraspidiotus perniciosus (Comstock)

(Sometimes placed in the genus Diaspidiotus).

Taxonomic placing: Insecta, Hemimetabola, Hemiptera, Sternorrhyncha, Coccomorpha, Coccoidea, Diaspididae.

Common name: San Jose scale.

Geographical distribution: Almost cosmopolitan. In the Middle East (Turkey) since the 1960s and is now widely prevalent there. CIE Map #7, 1986 (revised).

Host plants: The San José scale has been collected from ca 250 plant species around the world, mostly rosaceous fruit trees.

Morphology: The dorsal macroducts are one-barred. The body of the female is yellow, about 1.0 mm long, pear-shaped, pygidium with two convergent lobes, both with an external notch; the third lobe is only a small round projection. One pair of club-like processes (paraphyses) arises between the median and second lobes, another near the reduced third lobe. With 2-3 broad, fimbriate plates placed beyond the third lobe. The anus is located between the median lobes and the vulva. There are no Perivulvar pores. The shield of the female is slightly convex, rounded, grey, about 1.5 mm in diameter. The exuviae of the juveniles are darker, almost black, slightly off-center. The shield of the male is grey, longated, bearing at one end the darker shield of the crawler.

Life cycle: The San Jose scale is viviparous, each female producing about 100-200 crawlers. They often settle near their mother, preferring shaded sites. The pest overwinters on tree bark; most of its population being in the first larval stage (“black cap stage”), with a minority of mated females. Development resumes as temperatures rise in the spring. The pest raises 3-4 annual generations. The threshold of development is at 7-10.5°C, according to the geographical area, lower in coler regions. Dispersal is via winds, insects, birds and infested nursery stock. In the laboratory the pest may be mass-reared on potato tubers, on which its fecundity is lower than on rosaceous hosts.

Economic importance: San Jose scale is a major pest of rosaceous fruit trees, especially almond, apple, peach, pear and plum. It infests mainly the bark and branches, occurring also on the fruit, which it discolors. A red halo-like spot (due to secreted toxins) appears on tender peach twigs within 24 hours of crawler settlement, the spot growing along with the pest. Infested tissues may crack and exude gum, followed by desiccation and die-back. Wounded, weakened branches may be attacked by wood-boring insects. Heavy infestations cause death of branches and even that of entire trees within a few years. The scale raises very large populations on the wooden parts of the trees (especially on the trunk), and as the dead insects do not drop off, this results in thick shield layers on the trunks and main branches.

Management

Monitoring: Pheromone traps are used to monitor male flights and thus crawler appearance.

Mechanical control: Pruning of heavily infested branches removes some overwintering scales, reduces the crawlers’ settling sites (due to their tendency to avoid direct sunlight), and improves the coverage of pesticide sprays.

Post-harvest control: Maintenance of infested apples for 10 hours at 46°C killed all pest stages without harming the fruit.

Chemical control: San Jose scale may be controlled by organophosphates, insect growth regulators or by white oil sprays applied either during winter (“dormant sprays”) or according to catches of males. In the latter case the recommended spraying date is at 600-700 day-degrees after the initial catch of males in pheromone traps. An alternate method is at 200-300 day-degrees after the beginning of crawler emergence. Sticky barrier traps can also be used for male trapping.

Biological control: The pest is attacked by predatory insects and by aphelinid parasitoids. The important predator is the coccinellid Chilocorus bipustulatus. The parasitoids are several species of Aphytis and Encarsia perniciosis (Tower).

References

Angerilli, N.P.D. and Logan, D.M. 1986. The use of pheromone and barrier traps to monitor San Jose scale (Homoptera: Diaspididae) phenology in the Okanagan Valley of British Columbia. Canadian Entomologist 118: 767-774.

Bayoumi, M.H. 2011. Functional response of the aphelinid parasitoid, Aphytis diaspidis: Effect of host scale species, Diaspidiotus perniciosus and Hemiberlesia latania. Acta Phytopathologica et Entomologica Hungarica 46: 101-113.

Gentile, A.G. and Summers, F.M. 1958. The biology of San Jose scale on peaches with special reference to the behavior of males and juveniles. Hilgardia 27: 269-285.

Kozar, F., Jasnosh, V.A. and Konstantinova, G.M. 1982. Comparative evaluation of the distribution of scale-insects (Hom. Coccoidea) and their parasites in Georgia (USSR) and in Turkey. Zeitschrift fur angewandte Entomologie 93: 333-338.

Kozar, F. et al. 1979. Distribution and density of scale insects (Homoptera: Coccoidea) on fruit trees in Turkey in 1976. Acta Phytopathologica Academiae cientiarum Hungaricae 14: 535-542.

Lurie, S., Fallik, E., Klein, J.D., Kozar, F. and Kovacs. K. 1998. Postharvest heat treatment of apples to control San Jose scale (Quadraspidiotus perniciosus Comstock) and blue mold (Pencillium expansum Link) and maintain fruit firmness. Journal of the American Society for Horticultural Sciences 123: 110-114.

Moursi, K.S., Mesbah, H.A., Mourad, A.K. and Abdel-Razak, S.I. 2008. Ecological studies on San José scale, Diaspidiotus perniciosus (Comstock) (Homoptera: Diaspididae) as a new insect pest on pear trees in Burg El-Arab area, Alexandria, Egypt. Communications in Agricutural and Applied Biological Sciences 73: 439-450.

Rice, R.E. and Jones, R.A. 1988. Timing post-bloom sprays for peach twig borer (Lepidoptera: Gelichiidae) and San Jose scale (Homoptera: Diaspididae). Journal of Economic Entomology 81: 293-299.

Sazo, L., Araya, J.E. and Esparza, S. 2008. Control of San Jose scale nymphs, Diaspidiotus perniciosus (Comstock), on almond and apple orchards with pyriproxyfen, phenoxycarb, chlorpyrifos, and mineral oil. Chilean Journal of Agriculture Research 68: 284–289.

Websites: https://www.google.co.il/search?q=quadraspidiotus+perniciosus&biw=1280&bih=687&tbm=isch&tbo=u&source=univ&sa=X&ved=0CBoQsARqFQoTCPjWk9a358gCFYFwGgodBTYHGg http://www.inra.fr/Internet/Produits/HYPPZ/RAVAGEUR/6quaper.htm

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