Planococcus citri (Risso)
Common name: Citrus mealybug.
Geographical distribution: World-wide. Indoors the pest infests ornamentals, outdoors perennial crops in tropical and subtropical zones.and outdoors CABI map 43, 1999.
Host plants: This mealybug is highly polyphagous, attacking plants in 70 families. In the Middle East it reaches high densities on citrus, persimmon, banana and Annona, as well as on many understory weeds. In greenhousesThe pest occurs in large numbers, mainly on roses.
Morphology: The adult female is mobile, with extended legs. The antennae are eight-segmented, the body bears 18 pairs of cerarii, with the anal pair longest. The setae on the anal lobes are up to one quarter of the body’s length, but often break up. The ovoid body is 2-5 mm in length, depending on host plant, the feeding tissue and the infestation density, and is covered by a white-grayish wax produced through various pores. The female larvae and the two early instars of the male resemble the female, but are smaller.
Life history: In summer the mealybug requires 4-6 weeks to complete a generation, about 3 months in winter, during which the fertilized females hide in bark cracks. After emergence females emit a sex pheromone that may attract males from a distance of 50-100 m. Each male can mate with several females, which then deposit their eggs (300–600/female) in masses that are covered in fluffy, cottony layers of wax filaments (ovisacs). Most emerging larvae remain near their hatching site, thus forming aggregates. Others may wander for long distances and can easily become airborne. The developmental threshold is at 12-13°C, and about 500 day degrees are needed for the development of a generation. On persimmon and banana they usually infest the upper roots and the bases of the stems. Persimmon fruits are colonized in summer, whereas banana bunches are massively infested in the autumn. High mid-summer temperatures hinder the pest’s development, which resumes for a short period in the autumn, as temperatures drop. In Israel the pest raises 6 annual generations, of which 4 are during the warm season.
Economic importance: Damage to citrus begins in the spring at flower drop and during fruit set. Most damage is caused by the young nymphs, due to their infestation of small fruits, especially where they touch. They also settle under the sepals.The injury to young fruits results in corky scars. By mid-summer some infested fruits show blemishes and the pests’ honeydew and the covering sootymold. This damage affects photosynthesis, reduces the market value of the crop and bars such fruit from export. Growth is stunted and leaves and fruit drop. By mid-summer fruit moths Ectomyelois ceratoniae (Zeller) and Cryptoblabes gnidiella (Milliere) are attracted to the honeydew and/or the sooty mold on the fruit and lay eggs there. Their larvae add to mealybug injury by shallow tunneling in the sepal area, sometimes causing fruit drop. Economic losses to persimmons are compounded by the fungus Alternaria alternata (Fr.) Keissl, which develops on the feeding scars caused by the mealybug. Major damage in banana plantations is due the sootymold that contaminates the fruit. Injury to roses and young citrus saplings causes deterioration due to the dense scale populations on the roots stem bases. The pest affects ornamentals by reducing growth as well as flower buds, which eventually leads to plant wilt. In addition, the citrus mealybug is the vector of the grapevine leafroll-associated virus 3 (GLRaV-3), which causes leafroll, a serious grapevine disease that is widespread throughout the world.
Monitoring: Sticky traps baited with the sex pheromone, which may remain attractant for several months, may be used to capture males.
Plant resistance: Varieties and species of citrus differ in their susceptibility. The yellow species and varieties, e.g. Marsh grapefruit, red grapefruit, pummelo, Sweetie (Citrus paradisi X C. grandis), lemon, and the peeling orange varieties (e.g. C. sinesis) are mostly attacked In the Middle East.
Horticultural control: Clipping the branches of nearby trees so that their leaves do not touch, in order to slow mealybug spread. Cleaning farm equipment and other objects used in the field can help curtail its transport. Smearing an adhesive material around tree trunks to reduce mealybug migration from the roots to other tree parts. Plants that are preferred by the pest should not be grown near citrus groves.
Chemical control: The cryptic habits and waxy body cover of mealybugs hinders chemical control and requires nonselective pesticides like the organophosphate chlorpyrifos, or summer oil, applied in citrus groves late in the spring. Soil treatments with organophosphates control the root-infecting citrus mealybugs. Ants, which transport mealybugs within and between trees and disrupt the activities of the natural enemies, should be eliminated by dusting or spraying the understory ground around tree bases.
Biological control: The encyrtid Anagyrus pseudococci is the principal parasitoid of P. citri in the Mediterranean region. Its effect is sometimes reduced due to encapsulation by the pest. Common predators in the Middle East include larvae of Dicrodiplosis spp. (Cecidomyiidae) and several Coccinellidae, such as Cryptolaemus, Nephus and Scymnus. The brown lacewing, Sympherobius sanctus Tjeder, (Hemerobiidae) commonly occurs in Warmer regions. However, the biological control of this pest remains tenuous, as the natural enemies can seldom reduce the damage. They cannot prevent the spring pest infestations of young fruits, which reach large numbers only by mid-summer, when injury is already pronounced. On crops where the mealybug is not a major pest, and fruit moths do not occur, natural enemy activity can reduce the damage. Introductions of exotic natural enemies have so far failed to solve the citrus mealybug problem in many citrus growing regions. The usefulness of mass releasing natural enemies in citrus in Israel had no effect on the level of damage. Insect growth regulator treatments against other citrus pests may kill the predators and result in P. citri outbreaks. The application of entomopathogenic nematodes to control the pest is conditional on conditions of high humidity.
Ahmed, N.H. and Abd-Rabou, S.M. 2010. Host plants, geographical distribution, natural enemies and biological studies of the citrus mealybug, Planococcus citri (Risso) (Hemiptera: Pseudococcidae). Egyptian Academic Journal of Biological Science 38: 39-47.
Blumberg, D., Klein, M. and Mendel, Z. 1995. Response by encapsulation of four mealybug species (Homoptera: Pseudococcidae) to parasitization by Anagyrus pseudococci. Phytoparasitica 23: 157-163.
Cid, M., Pereira, S., Cabaleiro, C., Faoro, F. and Segura, A. 2007. Presence of grapevine leafroll-associated virus 3 in primary salivary glands of the mealybug vector Planococcus citri suggests a circulative transmission Mechanism. European Journal of Plant Pathology 118: 23–30.
Mendel, Z., Gross, S., Steinberg, S., Cohen, M. and Blumberg, D. 1999. Trials for the control of the citrus mealybug in citrus orchards by augmentative release of two encyrtid parasitoids. Entomologica 33: 251-266.
Michelakis, S. and Hamid, H.A. 1995. Integrated control methods of the citrus mealybug, Planococcus citri (Risso) in Crete, Greece. Israel Journal of Entomology 29: 277-284.
Satar, G., Ateş, H.F. and Satar, S.2013. Effects of different insecticides on life stages of Planococcus citri Risso (Hemiptera: Pseudococcidae) IOBC-WPRS Bulletin 95: 183-190.
Tingle, C.C.D. and Copland, M. J. W. 1988. Effects of temperatures and host-plant on regulation of glasshouse mealybug (Hemiptera: Pseudococcidae) populations by introduced parasitoids (Hymenoptera: Encyrtidae). Bulletin of Entomological Research 78:135-142.
van Niekerk, S. and Malan, A.P. 2012. Potential of South African entomopathogenic nematodes (Heterorhabditidae and Steinernematidae) for control of the citrus mealybug, Planococcus citri (Pseudococcidae). Journal of Invertebrate Pathology 111: 166-74.
Zada, A., Dunkelblum, E., Harel, M., Assael, F., Gross, S. and Mendel, Z. 2004. Sex pheromone of the citrus mealybug Planococcus citri: Synthesis and optimization of trap parameters. Journal of Economic Entomology 97: 361-68.