Mealybugs in citrus

Page last updated: Thursday, 23 July 2020 - 8:23am

Mealybugs (family Pseudococcidae) are oval-shaped, segmented, soft-bodied insects covered with white, mealy wax. They are often found between touching fruit, under the calyx or in the 'navels' of oranges, producing honeydew on which sooty mould can grow. Four species of mealybug have been recorded from citrus in Western Australia.

Damage

  • Mealybugs have piercing or sucking mouthparts that they insert into the plant to feed.
  • Feeding weakens and stunts plants, causes leaf distortion and with spherical mealybug, shoots may twist if the infestation is heavy.
  • Large quantities of honeydew are produced by mealybug, which can turn black with the growth of sooty mould fungus.
  • Mealybugs can also hide under the calyx of the fruit, which can cause export problems.

Life cycle

  • All mealybug species have a similar life cycle.
  • Eggs are laid into an ovisac, an envelope made of silk enclosing the eggs or egg mass. The longtailed mealybug gives birth to live young.
  • The young are free of wax, but appear similar to the adult female.
  • Males have an additional pupal stage from which they emerge as delicate winged insects with long tail filaments. Seldom-observed, the adult male is a very weak flier and does not have a mouth to feed, dying within a few days of emerging.

Control

  • In Western Australia, mealybugs were highly damaging to citrus in the early 1900s. Following the introduction of predatory beetles such as Cryptolaemus montrouzieri, populations have declined.
  • Mealybugs are primarily managed by conserving their natural enemies and reducing ant populations.
  • Treatment is rarely required and horticultural oil sprays are effective on young stages only. Mealybugs are less sensitive to petroleum spray oils than other citrus pests.
  • Insecticides are also registered for mealybug control in citrus. As these recommendations can change, consult your nearest chemical reseller or the Australian Pesticides Veterinary Medicines Authority (APVMA) for more information.

Biological

Leptomastix (mealybug parasite)
Leptomastix wasp (mealybug parasite)

Parasites

Citrus mealybug
  • Wasp parasites of citrus mealybug in Australia include Leptomastix dactylopii Howard, Anagyrus sp. (parasitises third instar), Leptomastidea abnormis (Girault) on second instar and Coccidoxenoides peregrina (Timberlake) on first instar. None is available commercially.
  • Of these, Leptomastix dactylopii is considered to be the most useful mealybug parasite for control of citrus mealybug. The wasp (honey-coloured, 3mm long) parasitises third instar and young adult stages.
  • It was released into Queensland from Brazil in 1980 and 1987, became established in Queensland and may occur in WA. It is not commercially available.
Longtailed and spherical mealybug
  • In Australia, the wasp Anagyrus fusciventris (Girault) parasitises longtailed mealybug while spherical mealybugs are attacked by Anagyrus agraensis Saraswat. None of these species is commercially available.

Predators

Cryptolaemus larva - mealybug predators
Cryptolaemus larva are mealybug predators often mistaken for mealybugs
  • Naturally occuring predators include lady beetles, lacewings and hoverfly larvae (Syrphids).
  • An efficient predator of all three mealybug species is the mealybug ladybird, C. montrouzieri (pictured). Introduced from NSW to Western Australia in 1902, the adult and larvae feed on both larval and adult stages.
  • Adults are black with a tan front end, 4mm long. Larvae grow to 1.3cm long and are covered with white waxy curls making it difficult to see their legs. The larvae resemble a mealybug, but are generally much larger. The wax can be scraped off to reveal the alligator-shaped beetle larva.
  • C. montrouzieri eggs are yellow and are laid among the cottony egg sacks of mealybugs. Pupation occurs in sheltered places on stems or other substrate.
  • Cryptolaemus can be purchased from a commercial insectary in early spring and released in orchards where citrus mealybugs were a problem the previous year. Release rates are around 1000 to 2000 beetles per hectare.

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