It is hard to imagine the Israeli landscape without sabra cactus bushes. And for many people, the thought of spending summertime in Israel without the prickly, sweet sabra fruit is tantamount to catastrophic. However, an invasive biological pest is now threatening the future of the plant that has become a symbol of modern Israel, for Jews and Arabs alike.
Two months ago, researchers in the Department of Entomology at the Volcani Center in Beit Dagan and personnel from the Jewish National Fund (Keren Kayemeth LeIsrael) began receiving reports from residents of the Hula Valley in northern Israel, concerning severe damage sustained by local sabra cactus bushes. When the Volcani and JNF personnel reached the area and began their investigation, they discovered the sabra plants were being attacked by an aphid capable of inflicting lethal damage on the bushes.
“We are talking about an aphid that secretes toxins into the tissues of the plant in order to make it easier for it to suck its food from the plant,” explains Prof. Zvi Mendel from the Volcani Center. “The aphid damages those parts of the plant which are vital for food supply and, in the end, the plant dies.” The aphid’s official Latin name is dactylopius opuntiae.
In the countries of Central America, which is the source of the sabra cactus plant, the aphid’s natural enemies limit the extent of damage that the aphid can inflict. However, these natural enemies are not present in the Israeli landscape. Consequently, the aphid - which has recently been discovered in Israel - is causing extensive damage. In effect, the insect is working against its own best interests because, if all the sabra cactus plants die, it will ultimately lose its food supply.
The sabra cactus plant was brought to Palestine a number of centuries ago. One of the reasons for its introduction was the desire to develop a dye industry based on the secretions of another aphid that lives off the sabra cactus plant without destroying it.
At this stage, the spread of the dactylopius opuntiae aphid is limited solely to the Hula Valley region, but it could spread to other parts of Israel. Indeed, there are fears that the pest could eventually destroy Israel’s entire sabra cactus population – both the plants that are principally used for decorative purposes and those found in open spaces. The greater the pest expansion to wider areas, the lesser the likelihood of stopping it.
It is still unclear how the insect was introduced into Israel. One hypothesis is that an Israeli tourist returning from Central America brought back a number of plants infested with the aphid, which then began to spread throughout parts of Israel. “We consider this plant [the sabra cactus plant] an important part of Israel’s open spaces, and we will make use of all our knowledge and resources in order to protect it,” said David Brand, from the Department of Forestry and Development at the Jewish National Fund. According to Brand, nearly half of the pests in Israel’s forests today are members of invasive species.
The aphid can be stopped initially through the use of pesticides. A more complex mode of treatment is to introduce the pest’s natural enemies into Israel, to promote their reproduction and disseminate them throughout the country. Mendel pointed out that Israel has successfully employed biological enemies against pests in the past.
The responsibility for authorizing and supervising the war against the dactylopius opuntiae aphid belongs to the Agriculture Ministry’s Plant Protection and Inspection Services division. The ministry has stated that the possibility of “importing” the pest’s natural enemies is currently being investigated. Furthermore, the ministry notes, a thorough investigation of this option is essential, since any imported new species might reproduce to such an extent that it itself could cause damage to Israel’s flora and fauna. The new species could become a threat once it creates a “population that consumes but is not consumed.” Such insects, adds the ministry, are liable to inflict damage on different species of flora and fauna and to have a serious, negative and irreversible ecological effect.
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