Biological Control of Mealybugs

8/10/2019 Biological Control of Mealybugs

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Due to flood damage this organism will unavailable

for some time

Leptomastix

Citrus mealybug parasite

Leptomastix wasp with citrus mealybugDan Smith

Leptomastix dactylopii

Leptomastix is a highly specialised wasp parasite of the citrus mealybug Planococcus citri- a very

common pest of citrus, custard apples, persimmons and a wide range of ornamental plants in the sub-

tropics and greenhouse environments. It is a very efficient parasitoid and particularly good at seeking

out mealybugs in their natural hiding places. Because of this trait, leptomastix are able to control

mealybugs in low-density infestations. Leptomastix is a small brown wasp about 3mm long with

distinctive antennae. The adult female wasp can lay up to 80 eggs. These are deposited individually into

3rd instar and adult mealybugs. The larvae of leptomastix develop fully within the mealybug, emerging2-3 weeks later as adult wasps, ready to mate and continue the cycle.

Leptomastix life cycleChris Lambkin

Target pests

Citrus mealybug Planococcus citri

Citrus mealybug is a serious pest of citrus, custard apples, persimmons and many indoor and glasshouse

grown ornamental plants. Leptomastix will not control longtailed mealybug or citrophilous mealybug.

Mealybugs thrive in protected areas such as in the navel end and under the calyx of citrus fruit, in the

growing tips of many ornamental plants, and in flower buds. Mealybugs feed by sucking the sap from the

host plant. They produce large quantities of honeydew which encourages the growth of sooty moulds.

The citrus mealybug takes about 4 weeks to reach maturity in summer and can lay up to 500 eggs in a

white woolly egg mass.
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Mealybugs are difficult to control with pesticides. This is largely due to their waxy covering, their habit of

feeding in sheltered areas, and the difficulty of achieving effective coverage. Mealybugs are also quick to

develop resistance to pesticides.

Adult male leptomastixDan Papacek

Suitable crops/environments

Leptomastix is suitable for controlling citrus mealybug in a range of crops and environments. They

perform best at temperatures of 25C and above. Sunshine and warmth will keep them active.

Leptomastix are specific parasitoids of the citrus mealybug Planococcus citriand will only attack this

species. Where other mealybug species occur, cryptolaemus beetles are the preferred biological control

agent. Like other wasp parasites, leptomastix prefers healthy, well-foliaged trees and plants that provide

shelter from the extremes of heat and low humidity. Dust is harmful to most beneficial species and

effective biological control may be difficult in dusty areas such as alongside roadways.

Before release

Leptomastix should be released into areas where evidence of mealybugs exists and into areas with a

history of mealybug infestation. It is best to commence releases before mealybug populations have

reached high levels.

In orchards, releases should commence in spring when temperatures are starting to rise and when

mealybugs first become evident.

In greenhouses and indoor plantscapes, leptomastix releases can be made throughout the year as long

as temperatures are warm and mealybugs are present.

Healthy crops with good foliage development will provide the best environment for establishment of the

wasps.

Avoid the use of toxic pesticides for at least two weeks before release (longer for indoor situations).

At release

Leptomastix are supplied in tubes of 100 adult wasps. Release by opening tubes near mealybug

infestations. The wasps will soon seek out suitable mealybugs into which to lay their eggs.
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Recommended release rates

Orchards: Aim for 7,500 wasps per hectare as three releases of 2,500 per hectare at intervals of two

weeks.

Greenhouses and plantscapes: Aim for 10-15 wasps per square metre. For low mealybug populations and

to prevent mealybug build up, lower release rates of 5 wasps per square metre at intervals of two to

three weeks should suffice.

After release

It is difficult to detect the adult wasps after release because they spend most of their life cycle

developing within and feeding on mealybugs. Regular monitoring by an experienced scout is

recommended to check that the leptomastix have established. The presence of characteristic tanned,

leathery pupal cases will indicate successful establishment. As a guide, continue releasing until

leptomastix pupal cases can be found at 30% of mealybug-infested sites.

Leptomastix wasp with characteristic pupal casesDan Smith

Cultural practices to aid establishment

Farm practices that reduce wind, increase humidity and minimise dust in orchards will aid the

establishment of leptomastix. Windbreaks and overhead irrigation can help. Weeds and cover crops

between rows help to increase humidity and further reduce dust within the orchard. Some weeds can be

useful as a supply of nectar for adult leptomastix to feed on.

High populations of ants may interfere with parasites and reduce their performance. In these situations

ants should be controlled or excluded from the crop.

Chemical use

Like most beneficial insects, toxic pesticides may cause them great harm and hinder establishment. Most

nutritional sprays and many commonly applied fungicides are quite safe to leptomastix.

No synthetic pyrethroids should ever be used. Organophosphate and carbamate insecticides are toxic

and must also be avoided. If the latter are applied, at least four weeks should elapse before the release

of parasites. Drift of pesticides from neighbouring blocks should also be avoided. If a spray treatment is

deemed necessary call us to discuss your options.
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Additional information

Leptomastix are usually despatched by express post and should be received within one or two days.

Honey is provided as a food for the adult wasps while in transit.

On arrival, leptomastix should be released as soon as possible. In the event of adverse weather such as

extreme heat or high rainfall, they may be stored if necessary for several days before release in a

darkened room at about 17C. They should never be refrigerated. Extra honey should be provided as

food for the wasps if the original supply has already been consumed.

Other natural enemies of mealybugs

Parasitic wasp Leptomastidea abnormis

Parasitic waspAnagyrus spp.

Mealybug ladybird Cryptolaemus montrouzieri

Green lacewings Mallada signatus

Predatory fly Diadiplosis koebelei
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Biological Control of Mealybugs