Mealybugs in grapevines and deciduous fruit tree crops

Page last updated: Friday, 4 May 2018 - 8:32am

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Two mealybug species, the longtailed mealybug (Pseudococcus longispinus), and obscure mealybug (Pseudococcus viburni) occur in grapevines and deciduous fruit tree crops in Western Australia.

They are cosmetic pests in table grapes and deciduous fruit tree crops, but in wine grapes can affect fruit quality and yield, resulting in rejection by winemakers.

Mealybugs are a vector for virus diseases in grapevines.

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Longtailed mealybug adult female. This species is characterised by the spines on the end of the body being longer than the body
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Obscure mealybug adult female. This species is characterised by the spines on the end of the body being shorter than the body

The longtailed mealybug Pseudococcus longispinus and obscure mealybug Pd. viburni are pests in grape and deciduous fruit tree crops in Western Australia. The origin of longtailed mealybug is thought to be eastern Australia, whilst the origin of obscure mealybug is not known.

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Citrophilus mealybug adults and nymphs have red body fluid (Photo courtesy of: Bugwood website)

Another mealybug species, citrophilus mealybug (Pd. calceolariae) occurs as a pest of grapevines in eastern Australia and is not known to occur in WA. This mealybug can be distinguished from other species by the red body contents when individuals are prodded compared with clear to yellow fluid for species that occur in WA. For more information refer to Citrophilus mealybug: pest data sheet.

In other countries, vine mealybug (Planococcus ficus) and grape mealybug (Pd. maritimus) are important mealybug pests in grapevines but have not been recorded in Australia.

While the appearance, damage and insecticides for the control of the two species are similar, their biology, habits and possibly natural control agents are sufficiently different to justify confirming their identification.

In Western Australia, because mealybugs prefer reasonably high humidity, they are not pests in inland drier areas. For example, they are not pests in the winegrape vineyards of the Frankland wine region, but are important pests in vineyards adjacent to the coast.

Description and life cycle stages

Adults

Mealybugs are oval, soft bodied insects covered in white powder like waxy material and the edge of the body bears a series of spines. There are four longer spines on the rear of the body - the central two of these are much longer than the insect body for longtailed mealybug but shorter than the body in obscure mealybug. Adult female mealybugs are 3-4mm long.

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Male mealybug adult – microscope photo image

Mealybug adult males are frail, winged insects about half the length of adult females. They do not feed and live for less than a week. Because of their size they are rarely seen. Females of both species of mealybugs must mate to produce viable offspring. The females produce a pheromone to attract the winged males.

Immature stages

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Obscure mealybug adults lay yellow to brown oval shaped eggs into an egg sac consisting of white fibrous material

Obscure mealybug adults lay yellow to brown oval shaped eggs into an egg sac consisting of white fibrous material. The eggs hatch into the mobile crawler stage which disperse from the egg sac.

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Longtailed mealybug adults produce live young or crawlers which remain under the female’s body before dispersing

Longtailed mealybug adults produce live young in groups. These batches of crawlers remain under the female’s body for a short time before dispersing.

Crawlers are less than 1mm long. They seek a feeding site such as the underside of leaves, a grape bunch or the stem end of some fruits such as apples, plums and persimmons as well as the calyx end of fruit such as apples and pears.

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Immature mealybugs go through a series of moults as they increase in size before becoming adults

Immature mealybugs that become adult females undergo three moults as they increase in size. Mealybugs that become adult males moult twice and then form a cocoon before the final moult to become a winged adult.

Seasonal patterns

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Late stage nymphs and adults of mealybugs overwinter under bark on grapevines and deciduous fruit tree crops

In deciduous crops, mealybugs overwinter under bark. They may also be present on the root system, especially obscure mealybug.

Crawlers disperse from the overwintering sites to infest new growth in spring. In grapevines, foliage is infested whilst in deciduous fruit tree crops, the stem end of fruit may be infested quite early in the season - especially for apples where the stalk end of fruit is infested in preference to leaves.

As the insects develop and adults are formed and reproduce, the population increases and disperses. Mealybugs prefer more sheltered locations such as bunches in grapevines, the stalk end of apples, plums and persimmons, and the calyx end of apples and pears. Sometimes no mealybugs can be seen on leaves yet fruit is infested.

During the growing season, some mealybugs can be found under the bark of trunks and branches or cordons. From here they continue to produce crawlers to invade the canopy. It is likey these adults are feeding eventhough the substrate is woody.

After harvest, mealybugs in grapevines continue to breed on foliage up to leaf fall, which increases the infestation level of mealybugs on the wood ready to produce crawlers to invade the canopy next season.

In deciduous fruit tree crops where breeding on leaves is less common, the overwintering population is thought to consist of those insects that have left infested fruit to move to overwintering sites before harvest.

There may be up to five generations of mealybugs during the growing season.

Pest status

Mealybugs are pests in crops because of their presence, the unsightly black sooty mould produced by fungus that grows on honey dew - the sugary mealybug excretions – or the level of leaf loss associated with heavy infestation especially in vineyards.

They are also vectors for virus diseases in vineyards.

Direct damage

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The presence of mealybugs in grape bunches can lead to their rejection
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The presence of mealybugs at the stalk end of apples can lead to production of sooty mould causing fruit to require cleaning or is rejected
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The presence of mealybugs at the stalk end of plums can lead to the production of sooty mould causing fruit to require cleaning or is rejected
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The presence of mealybugs at the calyx end of pears is a cause for rejection of fruit and sooty mould if produced would also cause rejection of fruit
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The presence of mealybugs under the sepals of persimmon fruit is a cause for rejection of fruit and sooty mould if produced would also cause rejection of fruit

Mealybugs feed on the sap of plants and excrete excess fluid as honey dew. When present in large numbers, the honey dew supports the growth of sooty mould. Both the presence of mealybugs and sooty mould can lead to cosmetic damage resulting in rejection of fruit at market - table grapes, apples, plums, pears and persimmons.

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Leaf loss around the fruiting zone in winegrape vineyards exposes fruit to sunburn and may affect fruit maturation

In winegrape vineyards, leaf loss associated with heavy infestations of mealybugs exposes fruit to sunburn, The canopy of late maturing red varieties may be so depleted that fruit cannot be ripened sufficiently. Fruit that is heavily infested with mealybugs and has excessive sooty mould is rejected by wine makers.

Virus transmission

As sap suckers, mealybugs are capable of acquiring and transmitting virus diseases such as leafroll virus in grapevines.

To limit virus infection in vineyards, material should be tested for virus (especially grapevine leafroll associated virus 1 and 3 - GLRaV-1 and GLRaV-3) prior to planting or obtained from a reliable source such as the Western Australian Vine Improvement Association.

If virus is present within a vineyard block, the rate of transmission of the virus across a block can be restricted by controlling mealybugs present there.

When high virus levels occur across a block such that yield declines resulting in the block being uneconomic, the only control option is to remove the vines and replant the block after a suitable ley period to ensure no live vines or mealybugs remain.