Parasites For Potato Moth

Press, Volume CVI, Issue 31079, 7 June 1966, Page 11

Parasites For Potato Moth

Three varieties of tiny insects have been introduced to New Zealand from South America in an attempt to control potato tuber moth.

Since January the insects—which as yet have no common name—have been liberated at Nelson, Christchurch and Oamaru, and there have also been liberations in the North Island.

The insects are parasites of the potato tuber moth and they were collected by staff of the Commonwealth Institute of Biological Control, one of whom is a New Zealander, Dr Lloyd. C.1.8.C. staff, studying the potato tuber moth and its natural enemies, select the most promising of these enemies for rearing and testing under quarantine condition to ensure that no unwanted organisms are present Sufficient stock are bred up for distribution to countries requiring them. The potato tuber moth, which originates with the potato in South America has a number of host plants including tomatoes, tobacco, and some solanaceous weeds, but the potato is the most seriously damaged. Laying Of Eggs

Eggs are laid on the undersides of leaves, and on exposed tubers, usually about the eyes. Caterpillas, hatching from eggs on leaves, produce blotch mines in the foliage, later tunnelling in the stems, sometimes even down into the tubers.

The caterpillars, when hatching from eggs laid on exposed tubers, burrow straight into the flesh and tunnel about, usually just below the surface. Mature caterpillars (up to fin long) pupate under dead leaves in the crop, or among tubers in store.

The emerging adult is a small greyish-brown moth, about half an inch long, which flies mainly at night. Tuber moth is distributed throughout New Zealand, but

prefers a warm dry climate, and may produce as many as five or six generation a year in favourable areas. Only in some districts is the insect an annual problem, but most localities experience occasional problem years, when considerable damage is done. Home gardeners are more regularly bothered with the pest than are commercial growers.

Using a small glasshouse, and a liberal supply of potatoes, Mr C. T. Jessep. a technician at the Crop Research Division, Lincoln, has been building up the population of the parasites for liberation in potato growing districts from time to time. No Common Names

As yet the introduced parasites have no common names. The first Is copidosoma koehleri, an efficient internal parasite less than one sixteenth of an inch long. The female parasite deposits its egg inside the moth egg. Both eggs hatch normally and host and parasite develop together. The parasitised larve matures, spins its cocoon, then succumbs to its internal parasites and becomes a mummified carcase from which the brood of copidosoma koehleri emerges.

This particular parasite is polyembryonic—the contents of one egg can divide and develop into up to 70 or more individuals. By this means several thousand individual parasites can emerge from less than one hundred eggs laid—an ideal adaptation fpr helping to keep pace with any population explosion of the pest Copidosoma koehler is the smallest of the three insect varieties, and Mr Jessep believes it holds out best prospects because it can reproduce so rapidly.

The other two insects are orgilus ap. and microchelonus curvimaculatus. They are internal parasites of the larval or caterpillar stage of the potato tuber moth. Eggs are laid in the caterpillars, with only one parasite per caterpillar. Main Liberation Oamaru has been selected as the main liberation point for the parasites because of

its annual incidence of potato tuber moth. It is hoped that the parasite population will increase naturally in these areas, and then spread to other infested areas throughout New Zealand by both natural and mechanical means. "This introduction is not regarded as the complete answer to the tuber moth problem, but is an additional cheap controlling factor,” Mr Jessep said.

With the aim of eventually reducing potato tuber moth to a minimum, Mr Jessep urges growers to adopt the following practices: Keep growing tubers well moulded at all times. Never leave freshly dug potatoes (bagged or otherwise) in the paddock overnight. Never cover freshly dug potatoes with the potato tops.