Other formats

    Adobe Portable Document Format file (facsimile images)   TEI XML file   ePub eBook file  

Connect

    mail icontwitter iconBlogspot iconrss icon

The Pamphlet Collection of Sir Robert Stout: Volume 14

The Corn Aphis. Siphonophora granaria. Kirby

page 5

The Corn Aphis. Siphonophora granaria. Kirby.

Fig. I.

Fig. I.

1, Winged aphis; 2, nat. length and wing-breadth; 3, wingless, mag.; 4, nat. size.; 5, Aphidius avenæ (parasite), mag.; 6, nat. length and wing-breadth; 7, Ephedrus plagiator (parasite), mag.; 8, nat. length and wing-breadth.

In some seasons this aphis is very injurious to wheat plants. It, with kindred species, is also found upon oats, barley, and rye, but the wheat plant is the chief object of its attack in this country. It is found upon the plants in the early spring, at this time usually in small numbers, wandering about restlessly and singly until the ear is formed, after which time, in favourable conditions, there is a rapid increase in its numbers. The ear, with the sweet juices destined for the support of the forming grains, is evidently its great attraction.

Upon an examination of ears infested with aphides, generations of all sizes, and in all stages—larvæ, pupæ, and perfect insects, commonly known as flies—will be seen actively engaged in sucking the juices from the stems within the ears and from the bases of the grain clusters.

Directly the plant begins to change for ripening and its tissues harden, the aphides cease because they are compelled to cease from active effect upon it, but their excrement and exuviæ page 6 mixed with "honey-dew"* hinder respiration, and in a degree affect the development, and tend to spoil the colour of the grains. Aphis affected ears of corn frequently have light and imperfectly shaped grains, and in bad and persistent attacks the sample is thin, shrivelled, and, especially in the case of white wheat, discoloured. In the last season (1885) wheat plants were attacked by aphides in many parts of the country, as were many other agricultural and horticultural crops, with forest and ornamental trees, and in not a few localities much damage was sustained from loss of weight and imperfect shape of the corn, because in the abnormally cold weather in August the plants changed for ripening most slowly, so that the aphides had an unusually protracted time for work.

The com aphis has been long known in this country. Curtis speaks of it as infesting wheat ears in 1797. Serious injury is also caused to wheat plants, as well as to oats, barley, and rye plants in America and Canada by aphides, which, according to the description of Fitch and Thomas, well-known American entomologists, and of Bethune, in Ontario, appear to belong to the same species as those in this country. A species of aphis is destructive to grain crops in Germany, described by Taschenberg as identical with the English corn aphis, minutely delineated, with an elaborate illustration, by Buckton in his Monograph of British Aphides. As in America and Germany, so in England, aphides are found upon various corn plants and in many kinds of grasses, among which may be mentioned cocks-foot, Dactylis glomerata; soft grass, Holcus lanatus; some of the Poas; rye grass, Lolium, and couch grass, Triticum repens.

* "Honey dew" is a glutinous sweet liquid secreted by many species of aphides, and ejected by them upon the plants they infest.

Pracktische Inseckten Kunde, von Prof. Dr. E. L. Taschenberg.