Mealybugs

Mealybugs

Closely related to scale insects and aphids, the mealybugs are a large and diverse group of insects.  Many species are pests of horticultural crops and ornamental plants.  Their name is derived from the mealy secretion of waxy filaments they produce as a protective barrier.  They feed by inserting their mouthparts directly into the plant, sucking up nutrients from the sap. 

Mealybugs can build up in large numbers causing debilitation of the plant.  They also produce large quantities of a sticky secretion called ‘honeydew’.  This often allows the growth of unsightly fungi leading to a black coating called ‘sooty mould’. 

Citrus mealybug showing waxy filaments (mealy secretion)

Ants and mealybugs

Ants are often associated with mealybugs in a two-way relationship.  The ants benefit by feeding on the honeydew produced and in return they protect the mealybugs from predators and parasites.  Controlling or restricting access to ants can do a lot to reduce the  abundance of these difficult pests.

Chemical sprays

Mealybugs are very difficult to control chemically.  The reasons for this are manyfold and include:

• The mealy secretion and waxy covering they produce protects them from being wetted by chemical sprays.
• Their habit of hiding in tight, confined spaces such as under the calyx or in the navel end of an orange makes it extremely difficult to get the required coverage.
• Most pesticides that have any effect against mealybugs are extremely toxic and almost always cause greater harm to beneficial species leading to a resurgence of the pest in a very short time.
• Mealybugs are quick to develop resistance to synthetic pesticides.

Solenopsis mealybug on cotton

Biological control

Most mealybugs species (and there are very many of them) have effective biological control agents.  If these can be encouraged or strategically released they can do an impressive job.  Beneficial insects that help keep mealybug populations at low levels include various ladybird beetles, lacewings and specific wasp parasites.

The wasps can be extremely effective as they are highly mobile and efficient at seeking out their prey, but they are often very host specific.

The ladybird beetles can do a great job of ‘cleaning up’ a population of mealybugs but require a higher population of the pest to establish and flourish.  They may disappear when the levels drop below a certain level.

Lacewings are general predators and will feed readily on mealybugs as well as several other important pests such as aphids, thrips and young caterpillars.

Cryptolaemus adult and immature feeding on citrus mealybug

Other ways of managing mealybugs

If there are only a few mealybugs on valuable ornamental plants it may be possible to remove them physically by rubbing or washing.  A cotton bud dipped in alcohol does a great job.  Soap sprays and oil sprays can also help control mealybugs without the disruption that can be caused by toxic chemical sprays.

Root feeding mealybugs

There are mealybug species that spend most of their time in the soil where they may feed on plant roots.  These are a real challenge as most beneficial insects find it difficult to access them here.  Drenching with an insecticidal soap solution and keeping ants away are useful strategies in this case.

Pink wax scale

Pink wax scale (Ceroplastes rubens)

At this time of year we commonly get enquiries about pink wax scale.  This pest occurs on a variety of plants including fruit trees such as citrus, mango, avocado, custard apple as well as some garden plants including lillypilly and umbrella tree.

Adult pink wax scales with visible crawler (orange)
and 1st stage nymph  (small star like organism) 

In Queensland there are usually two generations per year.  Typically one of these occurs in late spring and the second in early autumn.  Like other scale insects, pink wax scale settles early in its life and never moves again.  The young stages (crawlers) emerge from under the body of the adult female to settle nearby.  They may also be carried easily on wind currents.  Very quickly they start to produce their characteristic protective waxy covering.

Wax scales generally do best in humid coastal districts where temperatures are more moderate.  They can produce large quantities of honeydew causing a black sooty mould which can downgrade fruit and, if severe will even limit photosynthesis.

Pink wax scale adults and nymphs on Grevillea leaf.
This is the time when oil sprays are likely to be most effective.

Biological control of pink wax scale

A range of predators and parasites will attack pink wax scale.  Of the predatory insects both lacewings and cryptolaemus ladybird beetles will feed on this pest.  The best agent however is a small wasp parasite called Anicetus beneficus.  Anicetus wasps deposit their eggs into the scale insect and the larval stage consumes it from within.  Unfortunately however the wasp is not commercially available.  

Anicetus beneficus wasp parasite of pink wax scale
(Photo: 'Best friends natural enemies' QDPI publication)

Oil sprays to control pink wax scale

An oil spray can help reduce numbers of pink wax scale but only if timed correctly and applied thoroughly.  This should be applied when crawlers are emerging and first stage nymphs are settling on the leaves of the host plant.  This is the only time the insects are sufficiently vulnerable for the spray to be effective.

Ant control

Ants can be a nuisance in our homes as well as our gardens and farms. In an orchard they can interfere with biological control agents and encourage pests such as mealybugs, aphids and scale insects.

It is important to remember that ants also play an important role in our environment by removing waste and recycling. There are very many species of ants and while some of them can be very troublesome the great majority of ants are benign and indeed can be very beneficial.

For these reasons we may want to manage nuisance ants without entirely eradicating all ants.

Chemical control of ants is not easy because of their complex social behaviour. They often have large colonies that may be some distance from the area where they are making a nuisance of themselves. Attempts at chemical control rarely last for any length of time.

Ants in citrus tree. They will aggressively attack parasites and predators.

This, in turn encourages many important pests such as aphids and mealybugs.

Some tips with ant management:

In the home

Ensure all food scraps, no matter how small, are cleaned up quickly and thoroughly. This is vital as depriving them of access to food quickly discourages them. Ants are not in the business of visiting your home for the fun of it. They are there to get the essentials of food, water and possibly shelter. All food should be kept in well sealed containers to deny access to these unwanted intruders.

In the farm or orchard

Again ants will only expend energy climbing onto trees, vines or other plants if there is some reward. To some extent this can be a ‘chicken and egg’ situation. Are the ants there because of the mealybugs or vice versa?

Ant baits

A variety of ant baits are available. The simplest of these is an old but well tested bait which incorporates borax as the toxicant. Small quantities of this relatively innocuous compound are taken back to the nest by an army of ant workers. It takes some time but eventually this action can reduce in size or kill out the colony. The important thing about an ant bait is that it should not be so toxic as to kill individual ants quickly before they have had a chance to return to the nest to transfer the toxicant to the colony at large.

A simple recipe for an ant bait is 3 cups of water + 1 cup of sugar with 4 teaspoons of borax. Some ant species prefer more or less sugar or may respond to protein (crushed dry dog food formula can work here).

Some commercial ant baits are available and these can be more or less effective. It is important to understand the habit of the ant species that is causing your problems before choosing your ant management strategy.

Ant barriers

Because ants do not have wings (other than when swarming) we can exclude them if plants or other valued items are kept on elevated benches. The use of sticky barriers can be an effective tool. In this case it is important that there are not alternative access points that the ants can use. There are several sticky compounds available for this purpose and Stikem Special is one of these. It may be necessary to re-work the material or apply a fresh band from time to time as dust and leaves can reduce the effectiveness of the barrier allowing ants across.

A simple water barrier can also be a great way to stop ants. 
Here preventing access to a tidy bin in the kitchen.

Bugs on TV

Channel 7 News recently ran a story about moves to cleaner and greener cotton production. Featured was Renee Anderson, a strong advocate for IPM in her cotton farm near Emerald in Central Queensland.  New technologies in cotton production have led to a significant reduction in need for toxic pesticides.  This in turn has improved the environment in the crop so that beneficial insects can survive and thrive.  Both naturally occurring and mass reared biological control agents contribute to a better pest management outcome.
Below is a link to the story that shows some of our bugs at work doing what they do best.

Link to:   Channel 7 News article 'Bumper Crop'

The Channel 7 crew on site at Kerry Downs, Emerald

Trichogramma wasps emerging ready to attack heliothis eggs

Fruit Fly Control

Queensland citrus growers are reminded that this is the time of year when they need to be especially vigilant about fruit fly.  Protein bait sprays are very effective and work best as part of an integrated approach which includes the use of MAT cups and a regular monitoring program.
In the Central Burnett district the varieties that are most at risk right now are imperial mandarin, grapefruit, navel orange and lemons.  The use of keltrol thickener is recommended during periods of showery weather of if fruit fly pressure is particularly high.  Some links that may provide more detail are:

Fruit fly information

Protein bait sprays

Fruit fly traps

Fruit fly thickener

Male Annihilation Technique (MAT)

Naturalure - for organic growers

Queensland Fruit Fly (Bactrocera tryoni) on banana

Photo: Dan Papacek

Californicus predatory mites

Bugs for Bugs have a new species of predatory mite to help growers in the war agains spider mites.  Neoseiulus californicus are very aggressive and extremely hardy with the flexibility to be able to survive well even at low prey densities.  This is largely due to their ability to take advantage of alternate food sources including other mite species and pollen.

The new mass rearing system developed in the Bugs for Bugs R&D department by our entomologist Alberto Guanilo represents a real step forward.  The ability to rear these important predators without the need for a host plant means we can make them available to growers in greater numbers at less cost.

More information is available about californicus mites at: http://www.bugsforbugs.com.au/product/Californicus-spider-mite-predator

Two spotted spider mite adult and eggs on bean leaf

Neoseiulus californicus adult and immature with spider mite eggs visible

Alberto becomes an 'Aussie'

After 3 years working at Bugs for Bugs Alberto Guanilo has achieved permanent residency status in Australia.  He came to us from his home country of Peru where he studied entomology.  After completing his masters at University of Saõ Paulo in Brazil he moved to Australia to gain work experience at Bugs for Bugs.

Alberto has worked in our insectary on several important insect cultures including our fly parasites (Spalangia) and some new predatory mite species.  Most recently he has developed a mass rearing method for the important predatory mite Neoseuilus californicus.  This represents a real breakthrough in biological control options for growers with spider mite problems.  Alberto is also an accomplished taxonomist with a special interest in the Phytoseiid mites.

During his stay with us Alberto has endeared himself to the staff at Bugs for Bugs.  We are all thrilled that he is now an 'Aussie'.

Dan congratulates Alberto on becoming an 'Aussie'.