North West Weeds 
          Your local guide to local noxious weed control (NSW, Australia)

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Origin│ Which species? │ Description │ When to use │ How to distribute │Tips │More information │ Acknowledgements │ Disclaimer

Biological control of prickly pear has been one of Australia's success stories when it comes to weed control.  And, biological control continues to play a very significant role in controlling prickly pear species in New South Wales, particularly in the drier, warmer areas.

The two most important biological control agents are COCHINEAL (left) and CACTOBLASTIS (right).  The two are entirely different:  Cochineal (Dactylopius spp.) attaches to the outside of the plant and (like a mosquito) literally sucks all of the moisture out of the plant. On the other hand,  Cactoblastis (Cactoblastis cactorum) is a black and yellow striped "grub" that tunnels into and devours the inside of the plant.  (Click on photos for a larger view.)

Most people associate "cactoblastis" with "prickly pear", because of the spectacular impact it had on major prickly pear infestations in Queensland and New South Wales during the 1920's and 30's. (please see Prickly Pear History for more information on this story).

But, cochineal has also done incredible work in the control of various prickly pear species.  It is still doing an exceptional job, particularly in the dry, warmer areas of the State, and even more so with some basic assistance from the property owners.

Cochineal has had a long history in Australia.  The original cochineal insects were brought to Australia with Captain Arthur's First Fleet, to start a cochineal (red) dye Industries.  Please see Prickly Pear History for more information on the origins of cochineal in Australia.

There are four species of cochineal insects (and one mealy bug) of importance in the biological control of the main prickly pear (cactus) species found in Australia.  The four species of cochineal insects look the same, but they're not.   Dactylopius opuntiae cochineal feed on both common pear and velvety tree pear.  D. ceylonicus cochineal feed on Riverina and smooth tree pear,  D. austrinus feeds on tiger pear (photo, right) and D. tomentosus is specific to rope pear.

DESCRIPTION OF COCHINEAL INSECTS
The adult female cochineal is a soft, shapeless sac hidden beneath a white, silky covering.  The female grows to about the size of a "match head".  Once the female attaches itself to the plant, it sheds its "legs" and cannot leave.  The male is a small two-winged insect with mobility to visit the females as poor males have to do...

According to Dr John Hosking, entomologist with NSW DPI (Tamworth), one female can produce up to 2,000 offspring under ideal conditions.  Rate of development depends on temperature.  A generation may be completed in less that two months.  A cochineal population can actually double its number every five days under right conditions (i.e. dry, and a consistent around 26-28°C)!

Cochineal have their enemies.  A combination of wet and cold weather can wipe out cochineal insects in their thousands. Rain washes away their (white) protective covering, exposing them to the cold.  Ants sometimes take a special interest in cochineal, carrying away their hapless victims.  Another common, natural predator is the cryptolamus insect.  Please click on photo, right, to see one of these insects amongst a colony of cochineal on velvety tree pear.

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WHERE AND WHEN TO USE COCHINEAL?
"Where" relates to how much pear there is.  If you only have a small patch, if you want to keep your property really clean, or if you want to run special animals eg stud cattle or horses in the paddock, don't rely on insects.  On the other hand, if you have pear over a large and/or inaccessible area, biological control is an excellent, cost-effective and long-term option.

"When" to use cochineal relates to climatic conditions.  In north-western New South Wales, cochineal insects are at their peak from November to May. They are delicate little critters and are easily wiped out by a combination of wet and cold weather.   

MEANS OF DISTRIBUTION
The eggs hatch into tiny "crawlers" within a few hours. The crawlers' natural instinct is to move off to find a new food source.  They have four (4) different means of travel:

1)  They can crawl over smooth ground for up to 10 metres in search of new plants.  But, they're not so good on rough ground (eg they can disappear forever into a crack in black soil).

2)  Cochineal insects can be blown long distances by the wind. The sketch, right, (courtesy VC Moran & BS Cobby, 1979, Rhodes University, Grahamstown, South Africa) shows the insects' hairs which act as sails in the wind.

3) By being carried on the actual prickly pear plant material.  Pieces of pear are spread by (a) floodwaters, (b) by being attached to a passing animal or (c) by being attached to tyres of passing motor vehicles or farm machinery.

4) By being manually transferred from an infected plant to a new, non-infected plant - as demonstrated in the photo, right.

As you can imagine, distribution methods 1, 2 and 3 are very haphazard - especially where plants are very scattered.  Manual distribution of cochineal insects (as in method 4) is the most reliable for new areas. And, one person can carry out a lot of insect distribution in a short time.  Even a  few hours, every now and then, will make a huge difference. (Photo, right, shows simple method of distributing infected plant material into new areas. A bucket and a pair tongs.  Easy, and environmentally acceptable).

Tips to help the cochineal? 

• The basic thing to remember is that cochineal insects are very delicate.  They are just like us: they don’t like cold and wet weather (or extremes of heat).  When you put insects into a new plant (especially in the approach to winter) give them some protection from the elements.  Cover the infected segments with parts of the plant, or branches, bark, cow pads etc.
   

• Covering newly-infected plants with cardboard, plywood or even a bit of old corrugated iron will offer the cochineal insects maximum protection from the weather.  This photograph on the left demonstrates the point: cochineal thrived under the cardboard (Bingara 16 Oct 02) after what had been a long and cold winter.
  
  CAUTION: snakes may also take up residence under these protective coverings.
   

• Another trick is to breed the insects indoors, in readiness for release in early summer, the optimum time for release.  Store infected plant material in cardboard boxes in a dry, warm area.  Over a period of 6 to 8 weeks, generally, you’ll have good supplies to put out when the weather warms up.

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USE THE RIGHT COCHINEAL…  Tiger pear, common pear, tree pear and rope pear cochineal all look the same.  But, they’re each specific to their host plants.  Please take notice of the chart at the top of this page.  The only way to be sure that you're using the right insect is by collecting the correct host plant material which is already infected with cochineal.

MORE INFORMATION

Cactoblastis.htm to learn about that other famous prickly pear insect.  Also, information on individual prickly pear species is included in this website.  Please return to Weeds List to access rope pear, harrisia, velvety tree pear, prickly pear history etc.

ACKNOWLEDGMENTS:

Dr John R Hosking (NSW DPI, Tamworth) for providing the original technical information on the description and breeding of cochineal insects.

DISCLAIMER:   The information contained in this web site is based on knowledge and understanding at the time of writing. However, because of advances in knowledge, users are reminded of the need to ensure that information upon which they rely is up to date and to check currency of the information with the appropriate officer of North West Weeds or the user’s independent adviser.
LRT 9/11.2003

Send mail to lestanner@aapt.net.au with questions or comments about this web site.
Copyright © 2007-2008 Last modified: 25/11/07 - L R Tanner