Sandy's Garden ... Spodoptera Exempta

“So Moses stretched out his staff over Egypt, and the Lord made an east wind blow across the land all that day and all that night. By morning the wind had brought the locusts; they invaded all Egypt and settled down in every area of the country in great numbers. Never before had there been such a plague of locusts, nor will there ever be again. They covered all the ground until it was black. They devoured all that was left after the hail—everything growing in the fields and the fruit on the trees. Nothing green remained on tree or plant in all the land of Egypt.”

But might these words be about to be proven wrong? “Never before had there been such a plague of locusts, nor will there ever be again.” Well, it’s not locusts which are advancing on Egypt; it’s a very nasty caterpillar called the African armyworm, a truly devastating crop pest which is spreading remorselessly through sub-Saharan Africa and which, the United Nation’s Food and Agriculture Organisation has warned, may well spread into Europe via the Mediterranean basin and Asia through the Middle East unless the insects advance can be contained. Like the infamous desert locust, the African armyworm has such a major impact because, in its adult stage as a moth, it is migratory and its movements are very difficult to predict. The adult moth is some 14-18 mm long … let’s say between ½ inch and ¾ inch in old money … with a wingspan of about twice these measurements. The female moths lay tiny eggs in batches of anything from 10 to 600, eggs which hatch into caterpillars which feed enthusiastically on the growing points and young stems of cereal crops like maize, wheat, sorghum, millet and rice. A severe infestation of these African armyworms … and they’re not called ‘armyworms’ without good reason … results in the total defoliation of the infected plants, which effectively kills them.

Mother Nature has a habit of arranging necessary coincidences; and the very time when the eggs of Spodoptera exempta … to give this pest its Sunday name … hatch corresponds with the time the farmers’ crops are starting to sprout. To add to the farmers’ problems, these caterpillars have no natural enemies in Africa, seemingly an unexpected natural oversight – until one learns that the moth is not native to the African continent but is an unwanted immigrant from the Americas. This absence of natural controls on the caterpillar population means that the farmers of sub-Saharan Africa must spray imported chemical pesticides if they are to prevent the loss of much of … and sometimes all of … their much-needed food crops. And … and you may well be ahead of me, gentle reader … since many of the subsistence farmers of sub-Saharan Africa cannot afford imported chemical pesticides, they have no option but to watch their intended food supply being eaten by these caterpillars.

Spodoptera exempta has spread rapidly, aided by drought and by climate change. The moths sometimes migrate over substantial distances and effective management of outbreaks requires international cooperation. Several national crop protection services, especially in eastern, central and southern Africa and the Yemen, have departments with special responsibility for control of migrant pests, including armyworm. But, since only the larval stage … the caterpillar … is accessible to control by insecticides, eggs are difficult to find, pupae are underground and moths fly at night, control is proving very difficult. But, as climate change brings the armyworm closer by the year, Egypt … and Europe … must hope that scientists soon find a surefire way to counter the threat posed by Spodoptera exempta!