The Corn Saw-Fly. Cephus pygmæus. Curtis.

Fig. IV.

1. The fly, mag.; 2. Length and breadth across wings; 3. Corn stem with larva in situ; 4 and 5. Larva nat. size and mag.; 6. Its parasite, Pachymerus calcitrator, mag.; 7. Length and breadth across wings.

This is one of the very numerous species of the family of Tenthredinidæ, or saw-flies, of the order Hymenoptera. Many of these species are most destructive to farm crops-corn, turnips, grasses, fruit trees,-and to forest trees. This species, Cephus pygmæus, or rather its larva, lives within the stems of wheat, and other corn plants more rarely, and sometimes gives rise to considerable mischief. It is said by Curtis that it occasionally attacks rye plants very seriously. French and German entomologists report that this Cephus is destructive both to rye and wheat plants, not unfrequently causing the loss of a fiftieth, or even a sixtieth, part of the crop.

Grave complaints of injuries were made to me from Gloucestershire, Cheshire, and Worcestershire in 1883 and 1884. It was mentioned that in several wheat fields from twenty to thirty per cent. of the stems had become yellow, not yellow as of ripening straw, but a pale sickly yellow, while the other plants had not begun to change, and would not in the natural course change colour for some time. Several stems were sent for examination. The ears of these had no signs of grains in them. Upon cutting down these stems it was discovered that the knots or joints had all been bored or pierced through, and the inner membranous substance of the page 18 stem had plainly been eaten away, which had made the stem prematurely blanched or etiolated. Near the foot stalks legless, or apparently legless, maggots were found nearly white, but in some cases rather inclining to cream colour. Later on more specimens of affected corn stems were sent; in these it was seen that the stem had been cut round just above the ground, and the farmers who forwarded them said that much of the straw had broken off at the base of the stalk and was lying upon the ground, and that the fields looked as if a flock of sheep or other animals had been driven through them, because so much of the straw was broken and lying on the ground. Various accounts of similar damage have been sent from time to time. Fortunately the injuries of this insect have not hitherto been very generally extensive.