Israeli scientists appear to be winning the war — or at least holding the fort — against an insect that has been decimating the iconic prickly pear cactus in northern Israel.
A team working under entomologist Prof. Zvika Mendel at the Volcani Center Agricultural Research Organization has been dispatching armies of predatory beetles and flies to devour a destructive scale insect, Dactylopius opuntiae.
The Indian fig prickly pear (botanical name Opuntia ficus-indica, Arabic name sabr, Hebrew name sabra) has been adopted by Israelis as the symbol of the typical local persona of the Jewish tribe — tough on the outside, but sweet inside.
For Palestinians, rows of sabras with their huge spiny pads, bright flowers and succulent fruits, formerly used as fences, mark and bear silent witness to the villages from which their families were displaced.
Ironically, this plant, whose identity is claimed by Jews and Arabs in one of many such metaphorical tugs of war, is native neither to Israel nor even to the Mediterranean, but to the Americas. It was probably first domesticated in Mexico around 8,000 years ago.
In its natural habitat, the cactus provides a home to a species of scale insect called Dactylopius coccus, which produces carminic acid to deters its predators. This acid is the key ingredient in the production of the natural red dye, cochineal. It was for this pigment — worth the weight of gold until the advent of artificial dyes — that Aztecs and Mayans in North and Central America farmed the insect and its prickly pear plant home. (Cochineal is still used today as a food and lipstick colorant, and is being commercially produced again, with Peru the biggest exporter, as public worries grow about the dangers of artificial food additives).
It was because of the value of cochineal that the prickly pear was transported to different parts of the world. It reached the Mediterranean in the 16th century and the eastern part of the basin not long afterwards. But the Dactylopius coccus insect was unable to survive in this environment. Locals grasped onto the plant’s potential and used it as a deterrent, drought-resistant form of fencing for animal enclosures and fields.
For centuries, the Indian fig prickly pear appears to have thrived unhindered in Israel, ignored by the Mediterranean fruit fly, the most common fruit pest locally.
That was until several years ago, when a bright spark from Lebanon apparently had the idea of producing cochineal and, instead of importing Dactylopius coccus, purchased Dactylopius opuntiae, a related species of scale insect which also lives on the prickly pear but is far more aggressive and damaging.
They live in the pads of the prickly pear, sucking juices and nutrients out of the plant’s tissue. The nymphs cover their bodies in a white, waxy substance to protect against water loss and the sun’s harmful rays, making them look white or grey. Nymphs are blown to new hosts by the wind and can be transferred significant distances by birds which like to hide in the prickly pear. Infested pads turn yellow before collapsing.
Nature knows no borders, and in 2013, Dactylopius opuntiae was spotted in the Hula Valley in the upper Galilee. By last year, the flat, oval-shaped, soft-bodied creature had spread to the entire Galilee, much of the Golan Heights and the northern coastal plain, where it infested and killed prickly pears with devastating effect.
Prof. Mendel and his team initially tried to curb the spread of the pest by spraying unaffected stands with insecticide. Last year, aerial spraying was carried out with the help of the KKL-JNF but was abandoned for fear that people might gather fruit from treated hedges.
The first attempt at biological control — using a predatory insect to devour a pest — was to release massive numbers of a species of mealybug-guzzling Australian lady beetle (Cryptolaemus montrouzieri) into the eastern Galilee and the western slopes of the Golan Heights. Originally brought to Israel to fight bugs in citrus and later avocado groves, these lady beetles have become naturalized and readily adapted to feeding and breeding on Dactylopius opuntiae along the Galilee coast, but not further inland.
Prof. Mendel and his team then turned to Mexico from where they imported two insect predators known to feed exclusively on the damaging bug — trident lady beetles (Hyperaspis trifurcata) and aphid flies (Leucopis bellula). The beetles and flies were brought to Israel, quarantined, bred and tested on both the target and other insects before being dispatched into the wild.
Thousands of trident lady beetles were released in summer 2017 in the eastern Galilee, followed 18 months later, in different areas, by swarms of aphid flies.
The main area of infestation has been north of a line from southern Acre on the northern Mediterranean coast to Beit Shean in the northern Jordan Valley, Prof. Mendel told The Times of Israel, with one infested island near Ben Gurion Airport, between Tel Aviv and Jerusalem, to which the pest was possibly transported by birds.
The predatory insect project is “already succeeding,” he said. “There are lots of places where a new balance has been established without creating damage. We are in the middle of the process so it’s a bit chaotic, but there is cause for hope.”
At an organic farm in Rakefet, a northern Israeli community settlement where the Volcani Center is chalking up success, farmers from nearby are “queuing up” to take prickly pads rich in the predatory insects to their own holdings and in so doing are helping the natural enemies of the pest to spread, he added.
In their natural environment, trident lady beetles and aphid flies are attacked by parasitoids — typically wasps whose larvae hatch inside the body of the insect and live as parasites, eventually killing their hosts. As these parasitoids do not exist in Israel, the predatory beetles and flies are especially effective.
The Indian fig prickly pear — economically the most important cactus species worldwide — thrives in Mediterranean and subtropical climates on all continents bar Antarctica. It is cultivated as a commercial fruit and as a fodder crop that is healthy, needs little water and grows well in harsh conditions, particularly in areas of Asia and Africa where alternative crops will not grow. With global warming, it is likely to become even more popular. In Israel, commercial production is small but developing.
Dactylopius opuntiae is currently wreaking havoc in parts of the Mediterranean such as southern Spain, as well as in Morocco, where countless jobs depend on the 1,200,000 dunams that are under prickly pear cultivation. The insect has been reported in Lebanon, Syria and Jordan, according to Prof. Mendel, who has sent information in Arabic to Palestinians and Jordanians in the hope that they will take measures as quickly as possible and pass the knowledge on.
“It’s in our interest that our neighbors also deal with the problem,” Mendel said, adding that one Lebanese publication had blamed what it called “northern Palestine” [Israel] for the outbreak.