BioEd Online

Experts are warning that swarms of locusts munching their way across Africa may yet reach plague proportions - while Australia is bracing itself for the onslaught of another species of the voracious insect.

African desert locusts (Schistocerca gregaria), bunch together into flying swarms that can strip fields of crops overnight. Since late last year, rainy weather has encouraged them to breed in north-western Africa and numbers have gradually climbed.

This week, the Food and Agriculture Organization warned that swarms are escalating in Mauritania, Mali and Niger and are spreading east into Chad. The pace of breeding is unprecedented, says Clive Elliott, part of the FAO's locust-forecasting group in Rome. "The number of swarms is larger than anybody expected."

Experts are concerned that the locusts will spread as far as Sudan and the Middle East, at which point the situation would be classified as a plague. The swarms could also survive for several years. Elliott says that the situation already looks worse than an equivalent period during the most recent plague, between 1986 and 1989.

Driving force

Rainy weather has been the main driver behind the locusts' spread, as it provides them with green vegetation to feed on and damp sandy soil in which to lay eggs. Each time the insects spawn a new generation, which they have done at least four times since last October, their numbers swell by a factor of about 20.

Elliott says that financial support is now coming from the international community. But exactly how the situation pans out will depend on the impact of control efforts and weather conditions. Part of the reason that the previous plague ended in 1989 was simply because freak winds gusted swarms out into the Atlantic.

In the midst of the locust battle, the FAO is pushing for studies into new ways to control the insects besides conventional organophosphate pesticides sprayed from planes. It hopes to test a chemical that stops the insects manufacturing a protein called chitin in their hard outer skeleton. The chemical could be laid down to form barriers in the desert, killing juvenile locusts by preventing them from growing a new coat after moulting.

Down under

In Australia, meanwhile, experts warned this week of an imminent attack on crops by the Australian plague locust (Chortoicetes terminifera). The current wet weather means that the insects' could conceivably reach plague levels, as they last did in 1987."

The insects developed after heavy rains in parts of southern Queensland and northern New South Wales in January, and laid eggs that are expected to hatch shortly. Although the exact scale of the expected population boom is difficult to predict, Laury McCulloch, director of the Australian Plague Locust Commission in Canberra, expects a serious outbreak that will affect areas otherwise clear of locusts for 25 years.

But the Australian infestation will not rival that in Africa, McCulloch says. There, "there is a high risk that a worst-case scenario may be unfolding," he says.