Geoscience Reference
In-Depth Information
Leatherjackets are the larvae of crane flies or daddy-long-legs. They occur in
grassland, sports turf and corn fields, and can represent a significant force of sub-
terranean grazers. The most frequent offender in farmland is
Tipula paludosa
which
lays up to several hundred eggs during May and June. The larvae feed through the
autumn, winter and spring, developing into the characteristic grey, wrinkled cylin-
ders nearly 40mm in length before pupating. Leatherjackets are much preyed upon by
rooks, starlings, gulls and lapwings which probe for them just below the surface of
the soil.
The most economically important soil-living Diptera in this country belong to
the genus
Delia.
The adults look like small house flies and the larvae are typical mag-
gots.
Delia coarctata
the wheat bulb fly,
D. radicans
the cabbage root fly,
D. antiqua
the onion fly,
D. planipalpis
the turnip fly and
D. platura
the bean seed fly are pests
of several important crops as their common names indicate. They share a large re-
sponsibility for the use of insecticidal sprays and seed dressings on agricultural land.
The wheat bulb fly lays its eggs on bare or sparsely covered ground in July,
but these do not hatch until February when the young larvae burrow through the soil
in search of young cereal plants, making use of root exudates to home in over the
last few millimetres. They then bore their way into the shoot killing or damaging the
young wheat plant. They are, or used to be, mainly a problem after potato crops were
followed by winter wheat. Fields that were harvested later did not attract egg-laying
flies, and those that were sown with spring wheat were unaffected because most lar-
vae perished before the crop germinated.
Beetles constitute by far the largest and most diverse group among the larger
soil-and ground-living arthropods. Despite their enormous variation in size and shape,
adult beetles are readily recognized in almost all cases by the horny wing cases or
elytra which conceal the delicate flight wings underneath. In the rove beetles the
elytra are greatly shortened, and in many ground beetles the second pair of wings has
atrophied, while the female glow-worm is neotenous in becoming sexually mature
while retaining a larval appearance without any wings. In picking out a few with a
vegetarian diet, one must recognize that these represent but a corner of the whole pic-
ture. The next section makes some redress by considering beetles as predators but this
still omits dung beetles, burying beetles, scavengers and others.
Weevils probably constitute the largest family of insects in the world. They all
feed on plants or plant products and are often highly specific to particular plants and
parts of plants. The great majority occur on aerial parts but some species have larvae
that feed on roots or other subterranean structures. The attractive, irridescent green
nettle weevil is a good example. Its adult life is confined to about a month while the
