Photo 1. Curled, bunched tomato leaves, caused by feeding of the cotton mealybug, Phenacoccus solenopsis.
Photo 2. Waxy secretions on stems, leaves and fruit infested with the cotton mealybug, Phenacoccus solenopsis.
Photo 4. Single mealybug, Phenacoccus solenopsis, showing the dark marks on the back, and the waxy filaments at the edges.
Cotton mealybug, Solenopsis mealybug
Phenacoccus solenopsis. It is possible that different biotypes exist in the Americas compared to Asia.
Worldwide. Asia, Africa, North, South, Central America, the Caribbean, Europe, Oceania. It is recorded from Australia (Queensland), and Fiji.
Wide, over 200 hosts in more than 50 plant families are known hosts; it is especially a pest of cotton, okra, Hibiscus species, papaya, and also found on plants in the potato (Solanaceae) family, e.g., capsicum, eggplant, tobacco, tomato. It occurs on a number of weeds. Note, this mealybug is found on the roots of plants as well as above ground, on stems and leaves.
The nymphs and adults do the damage by sucking sap from roots, leaves and stems. Heavy infestations cause stunting and distorted leaves, which turn yellow and fall. Flowers and fruits, too, are damaged and fall from infestations. In addition, the mealybug produces large amounts of honeydew as it feeds. This falls onto leaves and stems and is colonised by sooty mould fungi so that surfaces become black.
Because of the honeydew, the mealybug has a strong beneficial relationship with ants, especially with the red imported fire ant, Solenopsis invicta (see Fact Sheet no. 363). It is said to gain more honeydew than other species. The ants tend the mealybugs for honeydew, and in return the mealybugs receive protection from parasitoids and predators.
There are both males and females. Females lay eggs (up to 500 in a life of 3 months) into an ovisac – made of cottony and sticky wax - attached to the end of the insect. Crawlers (tiny first nymphs) emerge from the eggs and disperse to leaves, stems and roots. On cotton, they are also found around the bolls.
The crawlers go through several moults, but adult females and males are quite different. The adult female is 2.5 mm long and covered in a powdery wax. The body has 18 pairs of waxy filaments at the margin, and there are characteristic spots on the top surface (Photos 3-5). The males start as crawlers but after two moults develop a white cylindrical silken cocoon and emerge as fly-like insects with wings and long antennae. They last 1-2 days, sufficient time to mate.
Spread is by crawlers and adults in rain and wind, and on clothing and machinery. Crawlers can spread on birds and even other insects. Long distance spread is associated with the movement of nursery stock, domestically and internationally.
The impact of this pest is due to its rapid multiplication rate, a waxy body protecting it from natural enemies and pesticides, a small size allowing it to hide in plant crevices, and an ability to feed on many plant species.
Major crop losses have occurred on cotton in Pakistan and India. In 2005, for instance, losses in these countries were put at 14%. In following years, high losses have also been reported in Bt cotton, forcing farmers to use insecticides, increasing costs and contaminating water supplies.
Look for the pale-yellow body of the adult female below the white powdery wax. Look for mealybugs and waxy secretions on clumped leaves, and on stems above-ground and just below the soil surface. Look for the dark spots on the back: two at the front and six behind. Look for the 18 pairs of waxy filaments around the margin. Slide-mounted stained preparations are needed for identification (Photo 6).
To monitor populations of the mealybugs, sticky traps can be placed in and around fields.
Several parasitoids species (e.g., Chalcaspos, Cheiloneurus, and Aprostocetus in the USA, and Aenasius and Paranathrix in India) have been investigated as biocontrols of this mealybug. Aenasius bambawalei is the most important in parts of India with parasitism reaching 70%. A related species, Aenasius arizonensis, has given satisfactory control in Israel.
Predators include ladybird beetles (e.g., Cryptolaemus montrouzieri, and Harmonia and Rodolia species) that attack eggs and crawlers, and lacewing larvae that feed on eggs.
Note, an integrated pest management program is needed to manage outbreaks of this mealybug. The IPM program needs to include control of ants. The close association of this mealybug and the red imported ant is mentioned above; in Fiji, the white-footed ant (Technomyrmex species) plays a similar role (see Fact Sheet no. 360).
Use horticultural oil (made from petroleum), white oil (made from vegetable oil), or soap solution on plants infested with mealybugs (see Fact Sheet no. 56).
AUTHOR Grahame Jackson & Mani Mua
Information from CABI Phenacoccus solenopsis (cotton mealybug) (2018) Crop Protection Compendium. (www.cabi.org/cpc); and Scalenet. Phenacoccus solenopsis Tinsley 1898 (Pseudococcidae: Phenacoccus. (http://scalenet.info/catalogue/Phenacoccus%20solenopsis/); and from Phenacoccus solenopsis Tinsley. Plant Pests of the Middle East. (http://www.agri.huji.ac.il/mepests/pest/Phenacoccus_solenopsis/). Photo 6 Buamas C (2010) Solenopsis mealybug (Phenacoccus solenopsis): PaDIL - (http://www.padil.gov.au).
Produced with support from the Australian Centre for International Agricultural Research under project HORT/2016/185: Responding to emerging pest and disease threats to horticulture in the Pacific islands, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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