CHAP. VIII - Coleoptera

Summary

Order 19. Coleoptera. Beetles

An extensive group, the members varying in size from very small to very large. The first pair of wings are horny, forming wing covers or elytra, these meet over the back in a mid-dorsal line, the suture, giving the insect a wingless appearance; hind wings membranous, folded under the elytra, not always present; mouth parts biting; metamorphosis complete.

Family Cryptophagidae

Very small beetles, seldom exceeding 3-4 millimetres in length; more or less elongate in form; first abdominal segment longer than the others; usually yellowish or brown in colour; antennae clubbed.

Atomaria linearis Steph. Pigmy Mangold Beetle

DESCRIPTION. Adult. Colour variable from deep red to black: elongate, parallel-sided. Head finely punctate; antennae brown, the three apical segments dilated. Thorax rather long and broad, finely punctured, base marginated. Elytra with short pale pubescence. Legs reddish brown. Length 1-2 mm.

LIFE HISTORY. The winter is passed in the adult stage; in autumn large numbers of the adult beetles may be found under clods of earth or debris in fields and meadows. These hibernating individuals emerge in May or June when they attack young mangolds and sugar-beet, just below soil level. The larvae do not appear to have been described; they probably feed upon the roots of the same host plants. It is thought that there are two generations a year.

HOST PLANTS. Chiefly mangolds, but it is also recorded from sugar-beet, of which it is a severe pest on the continent.

SYMPTOMS OF ATTACK AND INJURY TO HOST PLANT. The beetle attacks the young seedling plant just below soil level, producing an injury somewhat similar to that attributed to springtails (p. 21) except that the latter is above soil level. Injury is also caused to the roots, and a certain amount of feeding takes place upon the epidermis of the leaves. The most serious damage, however, is that below ground, as seedlings so attacked are usually killed, often breaking off in the wind.

DISTRIBUTION. The following remarks on the incidence of this beetle are quoted from Fryer (report on insect pests of crops for 1925-7). “In 1925 considerable damage was done locally in an area extending from the East Coast, south of the Wash to Bristol and including the southern counties. By 1926 the outbreak had returned to normal proportions, except in the S.E. province.