INSECT’S HABITS

Gisborne Herald, Volume LXXIV, Issue 22242, 30 January 1947, Page 4

INSECT’S HABITS

RED-LEGGED MITE FIRST NOTED IN 1942 ERADICATION UNLIKELY “The occurrence of the red-legged mite at Gisborne and Wairoa, in addition to the already large area at Napier, makes it unlikely that complete eradication can be achieved, as the mite probably occurs, as yet undetected, in other localities. As the mite cannot fly, its spread under its own locomotion is probably slow, but it may be accidentally transported with soil or on flowing water.”

Thus states an article by Mr. L. J. Dumbleton, Entomology Division, Department of Scientific and Industrial Research, 'in the January issue of the Journal of Agriculture, on the redlegged earth mite, Halotydeus destructpr Tucker, first observed in New Zealand in 1942. The mite first received attention in New Zealand in 1943, when specimens were sent in from West Shore, Napier, by Mr. D. Cunnold who had observed their depredations on vegetables in 1942 It is likely that the mite was present for several years before that. There is no evidence of the method by which il gained entry into the Napier area

Mr. Dumbleton describes the difference between the red-legged mite and the Blue Oat mite. The latter can be distinguished by a reddish streak in the middle of the back towards the tail. This streak is sometimes visible to the naked eye, but more often requires magnification. It is slower in movement than the red-legged mite and seldom occurs in large numbers, though it is recorded as damaging oat crops on the east coast of .the South Island.

Reports of red-legged earth mites in new areas should not be accepted until specimens have been identified. Egg Stage in Summer

In an area with low rainfall and high soil temperatures in summer the red mite is present only in the egg stage during summer. The active stages of the mite die off with the approach of hot, dry conditions in spring or early summer, which in most years in the Napier area is probably in late November unless the ' mites are sheltered by a heavy growth of crop or pasture. The eggs hatch in the autumn —probably late March in most years—when the autumn rains begin and the temperatures are lower. They will not hatch during .the high temperatures of mid-summer even if heavy rains occur. The mites which hatch from the eggs in autumn mature and lay their eggs in about 60 days. These eggs give rise to a second generation which lays its eggs after a similar period. The mites hatching from this last lot of eggs mature, but do not lay their eggs. With the approach of hot, dry weather .the eggs are accumulated inside the body and remain there after the death of the mite; in. that manner they pass the summer on or in the soil. Each mite may lay 50 to 100 eggs, and those produced by the first two broods of mites are laid on the undersides of leaves and hatch in one or two weeks, depending on the temperature. The largest number of the mite tend to occur in spring, during September and October.

The mites live on a liquid diet, which they obtain by piercing the leaves or stems of soft, succulent plants and sucking the sap or cell contents. The feeding places of the mite on a green leaf are marked by a white spot caused by the death of' the damaged plant cells. When a heavy infestation is present the whole leaf may be blotched with white patches or completely silvered. Such leaves on soft plants will wilt and die. On soft young transplants and germinating seedlings severe damage will cause the permanent wilting and death of the plant. Mite in Australia Much of the damage .to subterranean clover in Western Australia is done to germinating seedlings in the autumn, especially if the initial autumn rains are followed by dry weather. Young shoots coming through the ground are retarded, stunted, or even killed by heavy mite attack. The mite attacks a very wide range of plants, including both weeds and cultivated plants. Many weeds, such as Scotch thistle, wild turnip and stagweed seem to be preferred as food plants. Of the cultivated plants, damage seems .to be confined to the herbaceous, succulent, broad-leafed plants; little damage is done to grasses and cereals, and apparently none to woody plants. Many plants in the flower garden are attacked. Among the vegetables, tomatoes, French beans, broad beans, peas, potatoes, asparagus, silver beet, and marrows have been damaged in New Zealand. Melons, turnips, tobacco, plants, and lettuce are also reported to be damaged in Australia. Many pasture legumes, such as burr clover, subterranean . clover, Melilotus, and lucerne, are attacked and the white piottling on the leaves is quite evident in spring. Leaf damage to established plants, particularly perennials, in spring would seem unlikely to affect the carrying capacity or the vigour and reseeding of the plants very seriously. Autumn-sown crops such as peas and broad beans seem to suffer little damage during the winter. Broad beans, with their tall growth and erect habit, are little damaged in spring, but peas may be seriously damaged and the pods blemished. The principal damage so far observed in New Zealand is to plants such as French beans germinating in the spring, and to tomatoes immediately after planting out. Potatoes coming through the ground may be stunted and blackened, but once growth starts they seem to throw off the effects of the mite damage. Not Critical Factor

There is some evidence that the initial week or two after germination or planting is critical. Once the plant is established it appears to harden or become unpalatable to the mite. It appears that the mite will be controllable at a reasonale cost, and .the experience of market gardeners in Australia does not indicate that this pest will be a critical factor in production. There seems to be little or no prospect of controlling the mite by parasites or predators, as no effective organisms of this nature are known. There is a fungus disease, but it appears to be relatively unimportant. In flower gardens, vegetable gardens, and market gardens it is desirable to reduce to a minimum the areas of waste ground such as headlands, fence lines, and ditches, especially if they carry rough and weedy growth which provides the mite with both shelter and food. Wherever possible the vegetation should be cleared off such areas. Where that is difficult, or where infested pasture adjoins the garden area, it will be necessary to rely on a barrier strip treated with materials such as diesel oil, creosote. D.D.T., or gammexane dusts or sprays. The cost and efficacy of these materials have not yet been investigated. On the garden area freedom from weeds during the period when no crops are in the ground will help to keep the mite down, and cultivation at any time after the hatching of the eggs in autumn should serve the same purpose. It is very important that germinating plants in infested ground should be given a protective dust or spray as soon as they appear above ground. Some damage may be done by tiie mites penetrating to the shoots of French beans and potatoes through cracks in the soil before they appear above ground. Similarly, plants such as tomatoes should be treated immediately they are planted out, as very severe damage may be done in the first few days. ' It may be necessary to dust or spray the whole area of crops such as peas, aiming to kill the mites on the ground rather than on the plants. As the spray or dust deposit on the ground around the plant is probably an important factor in protection, it should be disturbed as little as possible during the first one or two weeks alter application. Mr, Durable ton makes a statement on