Citrophilus mealybug - Natural enemies and diseases

Citrophilus mealybug is attacked by a range of natural enemies, including both parasitoid wasps and predators. The most effective mealybug natural enemies are usually considered to be small wasps of the family Encyrtidae, and seven species parasitise the major mealybug pests of pipfruit in New Zealand. Four of these species have been reported from citrophilus mealybug (see below). None were deliberately introduced. The only species of parasitoid wasp which was deliberately introduced was Coccophagus gurneyi (Aphelinidae) in 1933. The predator complex includes a variety of ladybird species, lacewings, a hover fly, and a predatory midge (Cecidomyiidae). The only species of mealybug predator deliberately introduced to New Zealand is the ladybird Cryptolaemus montrouzieri which is restricted to the north of the North Island. In a survey of mealybug natural enemies from 1990-92, citrophilus mealybug was predominantly attacked by Tetracnemoidea brevicornis, Coccophagus gurneyi, Tetracnemoidea peregrina, and Anagyrus fusciventris, and especially the first two. These parasitoids, in various combinations and with predators, have provided good biological control of citrophilus mealybugs in other parts of the world. This indicates that there is little justification for further introductions of natural enemies against citrophilus mealybug, but there may be a need to redistribute the existing species throughout the range of this pest. This could be especially valuable for A. fusciventris (see below).

Diseases of mealybugs have been little studied and few species are known. These are all fungi. Citrophilus mealybug has been reported to be infected by Aspergillus spp., Coniobolus sp., and Isaria (Hirsutella?) sp.

The known and possible natural enemies in New Zealand are:

Anagyrus fusciventris (Girault) (encyrtid wasp) was first recorded in New Zealand in 1992 during a survey of the natural enemies of mealybugs. It was reared from adult citrophilus mealybugs but only from the Auckland region, where it appeared to be well established. It originates from Australia and is an accidental introduction. Now that it has been discovered in Auckland, spread of this wasp to other regions could assist biological control of citrophilus mealybug.

Brown or Tasmanian lacewing, Micromus tasmaniae (Walker). This Australian species eats a wide variety of insects and is common in pipfruit orchards practising organic or integrated fruit production. It has been reported feeding on mealybugs in Australia, and as early as 1945 feeding on mealybugs in New Zealand. However, more recent records of predation are lacking. This lacewing was first reported in New Zealand in 1869.

Coccophagus gurneyi Compére (aphelinid wasp) was introduced to New Zealand in 1933 and is now widespread. It parasitises a number of mealybug species (polyphagous) but is reported to prefer citrophilus mealybug > longtailed mealybug > obscure mealybug. It has been found attacking all three species in New Zealand on a range of crops, including pipfruit. In California, this parasitoid is reported to be more effective in winter than summer, and there is similar evidence in New Zealand. Ants may interfere with its effectiveness as a parasitoid during their 'farming' (collecting) of honeydew from the mealybugs.

Hover fly, Melanostoma fasciatum (Macquart). Larvae of this native species have been observed feeding on longtailed mealybugs and may also be a predator of the citrophilus mealybug.

Lacewing, Cryptoscenea australiensis (Enderlein). This Australian species arrived in New Zealand accidentally and was first recorded in 1927. The larvae and adults are commonly found feeding on mealybugs, including in apple trees in Nelson and Hawkes Bay. They feed on all the major pest species and appear to be widespread from Nelson northwards.

Ladybird, Cryptolaemus montrouzieri Mulsant. This species is from Australia and has been introduced to a number of countries for mealybug control, including New Zealand in 1897, and again in the 1920s. It established well in Auckland and Northland and was thought to be confined to those regions because of its requirement for warm conditions, including a mild winter. It has now also been recorded attacking mealybugs in Bay of Plenty and Gisborne. Both adults and larvae are predatory and their prey includes citrophilus mealybugs on a variety of crops. The larvae are superficially similar in appearance to mealybugs. This predator can be easily reared and is a candidate species for mass production and inundative release for mealybug control.

Ladybird, Midus pygmaeus Blackburn was first reported in New Zealand in 1974, an accidental introduction. It has been recorded as an occasional predator of citrophilus mealybugs on apples and grapes from Auckland to Hawkes Bay. It is similar in appearance and size to S. loewi, and the larvae resemble mealybugs due to their white waxy secretions.

Ladybird, Rhyzobius sp. An unknown species of Rhyzobius ladybird was recorded feeding on mealybugs on citrus in Northland during a survey of mealybug natural enemies in 1990-92. This predator may be present in other regions and crops.

Ladybird, Scymnus loewi Mulsant, originates in North and Central America. It was accidentally introduced to New Zealand and was first recorded at Auckland in 1941. Adults and larvae have been found feeding on citrophilus mealybugs on apple trees in Hawkes Bay, and on other crops further north. The larvae appear very similar to mealybugs, and are covered with a dense white waxy secretion, similar to that of the larger C. montrouzieri.

Ophelosia bifasciata Girault and Ophelosia charlesii Berry. These Australian pteromalid wasps are primary parasitoids of mealybugs and predators within the egg sacs. O. bifasciata has been recorded once as a hyperparasite (i.e. parasites of other wasp parasitoids). There are commonly three or four Ophelosia larvae (up to six may develop) in each mealybug egg sac. Both species of Ophelosia were reared from citrophilus mealybugs in the North Island during a survey of the natural enemies of mealybugs in 1990-92, including from apples in Hawkes Bay. Wasps of this genus have also been recorded from mealybugs in Nelson. O. bifasciata was first recorded in New Zealand in 1966, and O. charlesi in 1925. O. charlesi has been reared in the laboratory at ambient temperatures and took about 52 days to complete development (from pairing to offspring emergence). An adult female has been recorded to survive 56 days in these conditions.

Predatory midge, Diadiplosis koebelei (Koebele). The predatory larvae of this midge were found to be the most widely distributed of the mealybug predators during a survey of their natural enemies from 1990-92. They attacked all the major pest species on all the crops surveyed, including pipfruit. The pupae were found in spun silken cells alongside the mealybug cadavers. Early imports of this predator to New Zealand in 1927-28 were not released and it is thought to have arrived accidentally on mealybug-infested produce.

Tetracnemoidea brevicornis (Girault) (encyrtid wasp) is widespread from Auckland to Southland. It is not known when it became established in New Zealand but the first record was in 1924. During a survey of mealybug natural enemies from 1990-92, this wasp was usually reared from citrophilus mealybugs.

Tetracnemoidea brounii (Timberlake) (encyrtid wasp) is widespread in New Zealand in habitats ranging from native forest through srcub and tussock to domestic and commercial gardens. It has been recorded from citrophilus mealybug but most of the known host records are of unidentified mealybugs collected from native plants.

Tetracnemoidea peregrina (CompËre) (encyrtid wasp) is considered common in Auckland and small numbers have been reared from citrophilus mealybug in a number of regions of the North Island. It was recovered from mealybugs only on citrus crops in the 1990-92 survey. The origin of this parasitoid is South America but it is now known from U.S.A., Italy, and France. It was first recorded in New Zealand in 1961.