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Thrips are not imported, as was once thought. There are nearly forty different types of indigenous thrips affecting various flowers. In the rose thrips (Thrips imaginis) the young are orange, while the adults are brown and have two pairs of fringed wings (see Fig. 16). They are about one-twelfth of an inch long and very slender. Most of the insects hibernate as pupae in the soil, or as dormant adults in sheltered positions. As spring progresses and the days become warmer the pupae and dormant adults reawaken, greatly increasing the numbers of active thrips. A few active insects can be found on a sunny day even in midwinter. The numbers of early spring thrips depend upon the autumn numbers and the weather. They feed on grains, grasses, and legumes, moving to roses as the second generation appears; this coincides with the blooming flush in October and November. Lush growth of winter grasses followed by dry weather and hot winds from the inland favour heavy infestation. Rain greatly decreases the numbers and is always very welcome in late or mid October, even if thrips are not unusually prevalent. Active thrips are present throughout the year, but they are most numerous and most damaging to roses in the spring. After reaching the young unopened bud they insinuate themselves between the petals. In a well-developed bloom they are to be found in greatest numbers in the innermost parts, yet they do most damage to the edges of the petals, where, by sucking, they cause a browning, and, usually, some degree of gumming together of the petals. This results sometimes in the balling of the bloom. Unless preventive spraying is done, almost an entire spring crop of roses can be lost when thrips are in plague numbers. The damage is most serious in light-coloured flowers; markings on dark roses are less obvious. Thrips cause silvery markings on foliage, too.

There are several generations of thrips each season, but they usually become less noticeable and less damaging to roses after the first blooming. The second crop of flowers, which extends onwards from December, always has a lot of thrips, but the roses have fewer petals and open quickly, leaving little opportunity for damage.

All rubbish heaps must be avoided, and the soil should be kept well stirred. Systox, E605, Lindane, and DDT will all control thrips, and have removed all anxieties about our spring crop of roses. The first spraying should be done just before the sepals begin to reveal the tightly folded petals, and should be repeated at intervals of five to ten days for at least two weeks in spring. These same applications will, of course, control aphides and caterpillars as well, and, for that purpose, will have been used a few weeks earlier, and repeated. It is important not to use household sprays, for most of these will injure plants.