Aonidiella aurantii (Maskell)
Taxonomic placing: Insecta, Hemimetabola, Hemiptera, Sternorrhyncha, Coccomorpha, Diaspididae.
Common name: California red scale.
Geographical distribution: Outdoors in most tropical and subtropical regions of the world; within greenhouses in cooler areas. Commonwealth Institute of Entomology Map #2, 1996 (revised).
Host plants: Polyphagous; a pest mainly of citrus, sometimes of mango, rarely of roses.
Morphology: The dorsal macroducts are one-barred, slender, 5-6 on each side of the pygidium, none on the pre-pygidial segments. The body of the female is initially yellow, pear-shaped, later brown-red, round, almost square. After mating the fused prosoma and thorax become heavily sclerotized, strongly reniform, expanding around the pygidium. The entire body adheres to the shield and cannot be separated. The pygidium bears three large lobes, all externally notched, the fourth lobe appearing as a mere point. Four club-like processes (paraphyses) arise from the lobes on either side of the pygidium, and the anus is located halfway between the median lobes and the vagina. There are no perivulvar pores. The shield is about 2.0 mm in diameter, thin, almost transparent, brownish, round and slightly convex, the darker juvenile exuviae at center. The ventral exuvium (“velum”) is retained as a thin membrane. The winged males are pale-orange, their dark shields are oval and the exuvium of the 1st instar are placed near one end.
Life history: The California red scale is viviparous, giving birth to crawlers. Crawler emergence is affected by temperature and light, emerging mostly in the morning, as temperatures rise above 12°C, but not in the dark at low temperatures. Annually the pest raises four generations along the coastal plain of Israel, peaks in crawler production occurring in February, June, September and October. In warmer regions it may raise another 1-2 generations. The populations of the pest have two yearly peaks, attaining their maxima in autumn, dropping during winter and spring, increasing in mid-summer to decline in late summer, finally to peak in autumn. Crawler settlement sites are determined by a compromise between being phototactic and sensitivity to low relative humidity. Along the coastal plain, where humidity may be high, the scale prefers to settle on young citrus trees or on the outer rows of mature orchards, being rare within dense plantations. But in the inner, warmer and drier parts of Israel the scale is more abundant within trees, where humidity is somewhat higher. Crawlers prefer to settle on citrus species and varieties that have relatively few oil glands (sour orange, Citrus aurantium L.) as compared to those with abundant oil glands (mandarine, Citrus reticulata Blanco). The threshold of development was calculated to be at 11°C and 825 day degrees were required for one generation. Optimal conditions for development are around 24°C and air humidity of above 60%. Scale fecundity is affected by season and by host plant. An average of 220 offspring was produced on lemon fruit in the spring, 108 in the summer and only 38 on the same host in autumn. On citrus leaves average fecundity came to 20 progeny in the spring, 80 in the summer and 44 in the autumn.
The crawlers (and males) may be dispersed by winds to a distance of over 300 m, their numbers decreasing with increasing distances from the source. The wind-borne crawlers, which appear to be relatively tolerant to desiccation, then establish new colonies. Mature females may also be dispersed by winds. The California red scale females produce a sex pheromone that attracts the short-lived males. The pest can be mass-reared on green lemons, banana squash fruit or on potato tubers. Individual scales may be reared on disks of lemon leaves floating on water.
Economic importance: The California red scale, a major pest of citrus throughout the world, attacks all above-ground parts of the trees. On trunks of young trees the scale may form thick incrustations, and also infests the leaves and fruit. At feeding the pest injects toxins into the leaves, which causes them to yellow and drop. Heavy defoliation retards and stunts tree growth, affecting the yield; young trees are mostly at risk. Although scales that settle on young fruit in the early summer often die, but the pit that remains around them detracts from their market value. Large numbers of scales on the face of the fruit, which are difficult to remove even by descaling machines, further reduce the fruits’ value. On rose bushes that are more than three years old the scale settles on the wooden or even green branches, leading to their die back, general plant weakening and even death. Attack is more common on greenhouse roses.
Management
Monitoring: The sex pheromone has been synthesized and, impregnated onto yellow cards, was used for monitoring the periods of mass male flights and hence of subsequent crawler emergence.
Mechanical control: The pest, unless unfesting fruits in very high numbers, can be removed with high-pressure descaling machines that dislodge the scales.
Mating disruption: Placing dispensers that release the sex pheromone in Spanish citrus orchards, before the second male flight (established by monitoring), effectively reduced fruit infestions.
Chemical control: On citrus the pest can be controlled with white white oils. Organophosphates, applied in spring against the susceptible crawlers were applied till the pest developed widespread resistance to such pesticides. An application of an insect growth regulator may control the pest for two years, whereas in Turkey one or two (in the spring and in the fall) oil treatments suffice. If windbreak trees (e.g. cypress) are also infested, they too should be sprayed. On roses organophosphates, applied four times at monthly intervals during winter, provided full pest control.
Biological control: Unless disrupted by pesticides, the pest is controlled by a suite of aphelinids ectoparasitoids. In mild and humid regions these include Aphytis chrysomphali (Mercet) and Aphytis lingnanensis Compere, whereas in more arid areas Aphytis melinus DeBach (the dominant species in Turkey) and Aphytis coheni DeBach may be found. Another important aphelinid endoparasitoid is Encarsia perniciosi (Tower). The encyrtid endoparasitoid Comperiella bifasciata Howard has recently been introduced into and became established in Cyprus. The coccinellid Chilocorus bipustulatus (L.) is a major predator.
Integrated management: Due to the current cosmetic thresholds in citrus fresh fruit in some markets, the combined activities of natural enemies may not suffice. An integrated approach is therefore implemented, combining mating disruption with the natural enemies.
References:
Eliahu, M., Blumberg, D., Horowiz, R. and Ishaaya, I. 2007. Effect of pyriproxyfen on developing stages and embryogenesis of California red scale (CRS), Aonidiella aurantii. Pest Management Science 63: 743–746.
Kehat, M. and Greenberg, S. 1968. Trials in the control of Aonidiella aurantii Mask. On greenhouse roses. Israel Journal of Agricultural Research 18: 25-30.
Levitin, E. and Cohen, E. 1998. The involvement of acetylcholinesterase in resistance of the California red scale Aonidiella aurantii to organophosphorus pesticides. Entomologia Experimentalis et Applicata 88: 115-121.
Orphanides, G.M. 1996. Establishment of Comperiella bifasciata (Hym: Encyrtidae) on Aonidiella aurantii (Hom: Diaspididae) in Cyprus. Entomophaga 41: 53-57.
Sorribas, J. and Garcia-Marí, F. 2010. Comparative efficacy of different combinations of natural enemies for the biological control of California red scale in citrus groves. Biological Control 55: 42–48
Uygun, N., Karaca, I. and Sekeroglu, E. 1995. Population dynamics of Aonidiella aurantii (Maskell) (Homoptera: Diaspididae) and its natural enemies on citrus in the Mediterranean region of Turkey from 1976 to 1993. Israel Journal of Entomology 29: 239-246.
Vacas, S., Alfaro, C., Primo, J. and Navarro-Llopis, V. 2015. Deployment of mating disruption dispensers before and after first seasonal male flights for the control of Aonidiella aurantii in citrus. Journal of Pest Science 88: 321-329.
Willard, J.R. 1972. The rhythm of emergence of crawlers of California red scale, Aonidiella aurantii (Mask.), (Homoptera: Diaspididae). Australian Journal of Zoology 20: 49-65.
Willard, J.R. 1974. Horizontal and vertical distribution of California red scale, Aonidiella aurantii (Mask.), (Homoptera: Diaspididae) in the field. Australian Journal of Zoology 22, 531-548.
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