The White Plague of the Chumbos
The prickly pear cactus, opuntia species, or chumbo as it is
colloquially known is part of the landscape of Andalucía –
gaunt but in harmony, a weird Dali-esque signature on the
landscape. And yet they are not a native plant.
They were brought into Europe by the Spanish galleons after their
discovery of America some 500 years ago and, because of its
toughness, it was commonly planted as green fencing to deter
intruders – both 2-legged and 4.
Ask any campesino or person of a certain age about chumbos and
they will fill you with tales of this glorious plant.
During the civil war years, the years of hunger, the fruits of the chumbos were greatly valued and I´ve heard that the leaves were eaten too, either raw or roasted, as they do in Mexico – apparently they taste like asparagus or tender green beans.
So it´s very sad to see these proud warriors smothered and suffocated by the white blanket that is dactylopius coccus or the cochineal scale insect.
For a few years now this insect has been gaining ground and this year it is like a white plague – given a huge impulse by the exceptionally hot summer this year. Ironically, this insect was introduced to the plants and farmed for the natural cochineal dye that can be extracted. Spain had huge world-wide markets for the red dye; then chemical dyes entered the marketplace and, because they were cheaper, the nopal cactus farms, as they were known, fell into disuse. Even more ironically, now that there are millions of the insects swamping the cactus, there is only very small scale production
Many of you have written asking what´s to be done to save the prickly pears; make no mistake, a really severe attack can kill your cacti, literally sucking them dry. There can be little doubt, but if you want to positively identify the problem as cochineal insect, simply squash them, crushing the waxy protective coating and you will see the dark red liquid which is actually the body fluid of the insect.
The cochineal insect produces carminic acid to deter other insects. The females are about 5mm long and they cluster on the cactus pads, piercing the skin and feeding on its juices. After mating, she gives birth to tiny nymphs which are able to secrete a waxy substance to protect themselves from extreme weather and water loss. This is what gives the grey/white
appearance, though the insect will appear dark purple. Adult males, smaller than the females, can be identified because they have wings and once breeding has occurred, they die. The juveniles feed and produce long wax filaments, as they progress to the outer edge of the pad where the wind catches the wax threads and blows them to a new host. Typically, females will greatly outnumber males so population increase is rapid, a full cycle normally lasting 3 months but warm conditions can accelerate this.
As with many of our great plagues – the palm and agave weevils and processionary caterpillars – local authorities seem to be powerless and have, on the whole, left control to individuals. It´s a grave problem in Andalucía - where there is even talk of extinction - and, I believe, throughout half of the Spanish provinces but I´d be interested to hear from you on the spread of the problem.
The insects do have several natural enemies; ladybirds, lacewings, some parasitic wasps, some ants, birds, rodents (especially rats) and reptiles.
I´ve heard of large stands of prickly pear cactus that are infested by rats and this is because of the easy food source. You may prefer to use a pressure hose on your cacti, this will clean away a lot of the problem and then apply repeated doses of a soft soap insecticide which is able to penetrate the waxy coating.
A badly infested plant is a sad thing and it is well worth the effort to bring it back to its normal glory. And, don´t forget, next time you see a chumbo seller on the street, buy a few fruits – they are part of our recent history here and a dying trade that may not be seen by our children.