Maconellicoccus hirsutus (Green)
Common name: Pink hibiscus mealybug, hibiscus mealybug.
Morphology: Females grey-pink, bodies 2.5-4 mm long, elongate, slightly flattened, with many long dorsal setae. It is covered by sparse white wax which extends to the ovisac. Antennae with 9 segments, body with several pairs of cerarii and oral rim ducts that are scattered all over the body except the legs. The eggs and crawlers are pink. Males have a single pair of wings, long antennae and with white posterior wax filaments.
Distribution: This scale, of South Asian origin, invaded the Americas in the 1990’s and now occurs in most tropical and subtropical regions. CABI Maps of Plant Pests, #187 (4th revision), Wallingford.
Host plants: Polyphagous, infesting over 330 species, especially those of the families Fabaceae, Malvaceae and Moraceae.
Life history: A life cycle takes 3-4 weeks. The calculated threshold of developmental is at 14.5°C and about 350°C are needed for completing a generational. A female may lay up to 500-600 eggs, depending on the host-plant. There are 12-15 annual generations in warm areas and population increase can be very rapid. In the absence of males reproduction may be by parthenogenesis. Dispersal is by walking, adhering to animals or being wind-borne as well by transferred infested plant parts.
Economic importance: Maconellicoccus hirsutus is on the Global Invasive Species Database (2017), at website http://www.iucngisd.org/gisd/species.php?sc=1580. This mealybug is a major pest of many commercial plants in tropical and subtropical regions, having invaded the New World in the early 1990’s. Damage is due to sucking plant constituents, injecting toxic saliva and to excreting honeydew which is colonized by sootymold. The pest prefers to feed on growing plant parts and on young stems, flowers, and fruits. Feeding on the young growth results in leaf crinkling and the premature senescence of flowers and foliage, in buds failing to develop and in shoot stunting (“bunchy top” or curly top). Fruits become contaminated by the honeydew and the sootymold and by the white wax, and may drop. Or they remain on the trees in a dried and shriveled condition, of little value. The entire plant may be stunted; very large mealybug populations can kill plants. When the pest invades without its natural enemies it can rapidly produce large, very damaging populations.
Monitoring: Looking for crinkled or twisted leaves and distorted shoots, unopened or shriveled flowers, deformed fruits, white wax and pinkish eggs, and for sootymold. Attention should also be paid to the presence of ants which are attracted by the honeydew. Sticky cards baited with the scale’s sex pheromone, which attract the males, can be used detect the pest in areas where its occurrence is not clearly evident.
Chemical control: Most pesticides are of little value against M. hirsutus due to the protecting wax that surrounds the scale. Systemics, insect growth regulators, pyrethrins and oils may be of some value in nurseries. However, pesticides should be avoided because they kill the natural enemies which usually control the pest.
Biological control: The encyrtids parasitoids Anagyrus kamali and Gyranusoidea indica Shafee often control the pest In the Middle East, often assisted by Cryptolaemus montrouziei. Other natural enemies, such as various Coccinellidae, including Scymnus spp., Neuroptera and Cecidomyiidae are active in other regions. However, biological control may be hindered by honeydew gathering ants or due to parasitoid encapsulation by the scale.
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