| The wheat-stem maggot Meromyza americana Fitch (Dipt. - Chloropidae) is a well known and widely distributed insect pest in North America injuring wheat, barley, rye and a great range of grasses.;In a date-variety-test in the greenhouse it was demonstrated that oviposition is also influenced by the growth stage of the host plants, since in three out of six varieties the more advanced plants got twice as many eggs as the later plants. It is suggested that the range of wavelength of the light reflected from the host plant and the stage of growth may act separately, or together, or in turn, probably with additional unknown factors to cause preference during oviposition.;The presence of inflated femora in the adults of M. americana would suggest a great leaping ability similar to that known in flea beetles. However, leaping only occurs over distances of a few millimeters. In flies, the wings of which were cut off, leaving does not occur. The swollen femora together with the curved tibiae were demonstrated to provide an efficient mechanism for cleaning and stretching the wings. The flight is strongly limited to temperatures above 13°C. The possibility of rearing M. americana in the greenhouse continuously over several generations is positively discussed. Attention is focused upon the question whether M. americana might transmit western wheat streak mosaic, since abundance of adults in early sown wheat and its activity, as for instance the feeding on honey-dew of aphids and on guttation water, makes it highly suspicious in this regard. (Abstract shortened by UMI.);In several oviposition tests is the greenhouse it could be proved that preference during oviposition was involved. The soft wheat variety Harvest Queen was repeatedly the least preferred variety, whereas the hard wheat varieties Ponca, Pawnee and Comanche were attractive and Red Chief and Cheyenne took an intermediate position. Balbo rye was not very attractive. The two barley varieties Reno and Dictoo carried only a few eggs. On the oat varieties Cherokee, Kanota and Mo.0--250 no oviposition could be observed at all. The range of preference in the wheat varieties mentioned above was changed when the flats were exposed to different light sources involving the colors yellow, red and blue. No evidence of adverse effects on the developing larvae could be demonstrated in the wheat varieties involved in the tests. |
