Longtailed mealybug - Natural enemies and diseases

Longtailed 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. They all (see below) attack the longtailed mealybug. None of these parasitoids 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, longtailed mealybug was attacked by most of the natural enemy species found, including six of the encyrtids and C. gurneyi. These parasitoids, in various combinations and with predators, have provided good biological control of longtailed mealybugs in other parts of the world. This indicates that there is little justification for further introductions of natural enemies against longtailed 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) which has been critical in the control of longtailed mealybugs in some overseas countries.

Diseases of mealybugs have been little studied. The known species are all fungi and only about five species have been confirmed as pathogenic. Longtailed mealybug has been reported to be infected by Cladosporium sp. in laboratory trials.

The known and possible natural enemies in New Zealand are:

Alamella mira Noyes (encyrtid wasp). This species is known only from the Auckland region where it was reared from longtailed mealybugs feeding on citrus. However, it may be more widespread. It is an accidental import to New Zealand and was first recorded in 1981.

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 longtailed mealybugs but only from the Auckland region, where it appeared to be well established. It originates from Australia and is another accidental introduction. Now that it has been discovered in Auckland, spread to other regions could assist biological control of longtailed 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 longtailed 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. It is common in populations of longtailed mealybug. 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.

Gyranusoidea advena Beardsley (encyrtid wasp) is closely related and very similar to A. fusciventris. During a survey of the natural enemies of mealybugs from 1990-92, this species was reared exclusively from longtailed mealybugs on citrus crops, but was widespread from Northland to Gisborne. All the adult wasps emerged from second- or third-stage (instar) mealybugs. This parasitoid may yet prove to be present on other crops. This wasp is native to Hawaii and was first recorded in New Zealand in 1962.

Hover fly, Melanostoma fasciatum (Macquart). Larvae of this native species have been observed as voracious predators of second and third stage longtailed mealybugs in Auckland vineyards. However, this species is widespread throughout New Zealand and may be feeding on mealybugs in a variety of crops in other regions.

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, Coccinella undecimpunctata L., eleven spotted ladybird. This ladybird feeds on a wide variety of prey and occurs among colonies of longtailed mealybugs.

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 longtailed 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 mealybugs on apples and grapes from Auckland to Hawkes Bay. It has been easily reared on longtailed mealybugs, suggesting that this species is likely among its range of prey. M. pygmaeus is similar in appearance and size to Scymnus 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 longtailed 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 longtailed mealybugs on grapevines in Auckland and on other mealybug species in apples (Hawkes Bay). 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, Ophelosia charlesii Berry and Ophelosia keatsi Girault. The first two of these Australian pteromalid wasps are primary parasitoids of mealybugs and predators within the egg sacs. The feeding habits of O. keatsi are unknown. 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 'mummified' longtailed mealybugs in the North Island during a survey of the natural enemies of mealybugs in 1990-92. They have also been recorded from other mealybug species on apples in Hawkes Bay and Nelson. O. bifasciata was first recorded in New Zealand in 1966, O. charlesi in 1925, and O. keatsi in 1963. O. charlesi has been reared in the laboratory at ambient temperatures and took about 52 days to complete development (from pairing to offspring adult emergence). An adult female has been recorded to survive 56 days in these conditions. A native pteromalid wasp, Aphobetus nana, has also been reared from longtailed mealybug.

Parectromoides varipes (Girault) (encyrtid wasp). This species was reared only from longtailed mealybugs during a survey of the natural enemies of mealybugs in 1990-92. It occurred on citrus and persimmon crops from Northland to Gisborne but was not found in Hawkes Bay. Further research is needed to determine if it occurs on mealybugs in pipfruit.

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 usually attacked citrophilus mealybugs but it was also occasionally reared from longtailed mealybugs.

Tetracnemoidea peregrina (CompËre) (encyrtid wasp) is well established in New Zealand and considered common in Auckland. It is principally a parasitoid of longtailed mealybugs (although it reproduces readily on citrophilus mealybug). It was recovered only on citrus crops in a 1990-92 survey of mealybug natural enemies. 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.

Tetracnemoidea sydneyensis (Timberlake) (encyrtid wasp) appears to be a recent and accidental introduction and was first recorded in New Zealand in 1962. It originates from Australia. In a survey of mealybug natural enemies from 1990-92, this species was recorded in all regions surveyed, from Northland to Hawkes Bay, but always from longtailed mealybugs. It was present on citrus, persimmon, and grapes, and may be expected also to occur on longtailed mealybugs attacking pipfruit.