Transactions of RHASS Volume 1940 - Page 060
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| Year | 1940 |
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108 INSECT AND OTHER PESTS or 1939. emerge from the pupae in the galls during the early part of the morning, and the female, after pairing, lays all her eggs, amounting to 80-150, within a few hours after emergence. The egg is minute, reddish-orange in colour. In length it is only slightly more than a quarter of a millimetre, which is just too small to be readily visible to the naked eye. The places which are especially favoured by the females for egg- laying are near the growing ends of the shoots. Here the eggs are found in groups on the hairs of developing leaves or in the interstices between the petioles of the unexpanded leaves of the terminal buds. The eggs are said to hatch in four to twelve days, producing minute whitish or yellowish maggots. The larva, or maggot, is a legless oval, plump grub, rounded at either end, and measures about 1 mm. when full grown. Soon after hatching it burrows into the host plant, which responds by laying down a tubular gall around each grub. Inside the gall the grub completes its growth in three to four weeks or longer according to the season, and changes to a pupa within the gall. In ten days to several weeks the flies escape from the pupal skins. Whilst breeding proceeds continuously through- out the year there are two periods of maximum activity; the first when cuttings are being taken and rooted in the spring, and the second when the flowers are ready for marketing in the autumn. During winter and summer development is retarded. Barnes (loc. cit.) recently obtained five generations of the midge in one year under unheated glass-house conditions, and eight generations in similar time under laboratory conditions. Controls—As soon as the Chrysanthemum Midge has been found to have been introduced into a nursery steps should be taken to secure its eradication. The longer the insect is allowed to remain the greater the expense and trouble in dealing with it. A grower who suspects the presence of the pest in his glass houses or out-of—doors should notify the Department of Agriculture for Scotland, which has powers to deal with outbreaks under the Destructive Insects and Pests (Scotland) Order of 1933. Where the affected nurSery is a small one growing only common commercial varieties the owner would find it most economical to destroy the whole of his stock, and, after a specified interval, to restock with new cuttings from a source known to be free from the pest. Otherwise the measures which the Order enforces are :— 1. All plants not required for the purposes of propagation must be destroyed by fire immediately after the flowers have been cut. 2. All growth above ground must be completely removed from all plants required for propagation and must be burned. INSECT ANI) OTHER PESTS or 1939. 109 The stools so treated must- be assembled in a house which has not contained any chrysanthemum plants ‘or cuttings for a, period of at least fourteen days before the introduction of the stools. 3. All subsequent young growth on the plants so treated must be sprayed twice weekly with a nicotine solution con- sisting of 2 fluid oz. nicotine (95 per cent) and 1 lb. soft soap to each 10 gallon water, and all stools must be burned after cuttings have been taken. . 4. All cuttings must be dipped in the nicotine solution and must be rooted in a separate house in which again no chrysantheniums have been present for at least fourteen 'days. Spraying of the cuttings Inust then be carried out flaw in each week. THE CHRYSANTHEMUM LEAF MINER (Phytomyza atricornis). The discovery of the Chrysanthemum Midge in Scotland has served to stimulate the interest of chrysanthemum growers in the pests which attack this plant. Judging from. the inquiries which have come to hand there would appear to have been some doubt concerning recognition of the damage done by the Chrysanthemum Midge, and some growers appear to have mistaken the work of the Chrysanthemum Leaf Miner for that of the midge. Actually the damage caused by the two insects is quite distinct, and there should be no reaSon for confusing mines that ramify in the substance of the leaf for galls that project from the leaf— and stem- surfaces. Damage.—Thc Chrysanthemum Leaf Miner is the maggot of a small fly which also attacks cinerarias and other cultivated composites. The work of the miner is readily recognised by the pale, winding galleries (Fig. 8) which meander here and there through the leaves. Their beginnings are slender, but as the burrowing maggot increases in size so do the passages increase in breadth. In cases of severe attack, where there may be a dozen or more maggots per leaf, the whole of the green tissue may be excavated, so that the various galleries coalesce into a single large blotch affecting the whole leaf. Such leaves shrivel and die, and where several leaves. are similarly attacked the plants are so weakened that they either fail to produce flowers or a few small late ones. Young plants are frequently destroyed by the miner. Life-history.—The flies are small, dark-grey, with a single pair of wings. In length they measure about 7,1,, inch. Their activities are limited to short, jerky flights among the foliage |
| Title | Transactions of RHASS Volume 1940 - Page 060 |
