Search

Two species of bean seed fly (Delia platura (Meigen) and Delia florilega (Zetterstedt)) occur in Britain. Their maggots can cause severe damage to dwarf French and runner beans (Phaseolus species) (Fig. 45.1), onions, particularly those sown in late summer, and field-grown cucurbits. Other crops affected include broad bean, pea, cauliflower and other brassicas, lettuce, spinach, radish, beet, cereals (maize, rye, oats and wheat), clover, freesia and gladiolus. Onion is also attacked by maggots of the closely related onion fly (see page 294). Most species of Delia, including the bean seed flies, are general scavengers on organic matter in the soil; they are often numerous in the debris of cereal crops. Open image in new window Fig.45.1 Two runner bean seeds cut open to show surface feeding and tunnelling by maggots of bean seed fly

Millepedes and centipedes are allied to insects but differ from them in many characters, the most obvious being the presence of legs on almost all of the many body segments.

Scale insects are widely distributed in Britain, living on the bark of many kinds of woody plants such as fruit trees and bushes, ornamental trees and shrubs, and forest trees. Most are small, similar in colour to the bark of the host plant and not easily noticed unless they occur in abundance. Others are quite conspicuous, either because their colour contrasts with that of the bark or because a white woolly mass is produced by the female when eggs are laid.

Several species of capsid bug occur on fruit. The majority are beneficial and prey on pests such as spider mites, apple sucker and leafhoppers, but the two species described here are plant feeders and cause injury to many kinds of fruit and ornamental plants. The apple capsid (Plesiocoris rugicollis (Fallen)), formerly a major pest of apple in England, was eradicated from commercial orchards soon after DDT came into general use in the late 1940s; it is now only an occasional pest of this crop in gardens and unsprayed orchards. The common green capsid (Lygocoris pabulinus (L.)) is a much more common species and attacks cane and bush fruits, occasionally strawberry, a wide range of shrubs and herbaceous plants and, to a lesser extent, apple, pear and other tree fruits.

The rounded galls of the turnip gall weevil (Ceutorhynchus pleurostigma (Marsham)) occur on the roots or stem-bases of cruciferous crops throughout Britain, but they are most common in west Cornwall. Turnip, swede, cabbage, savoy, winter cauliflower, Brussels sprout, kohlrabi, charlock, mustard and rape are all attacked, but damage is most pronounced in late-sown brassica crops which are small at the time of attack.

Stem nematode (Ditylenchus dipsaci (Kuhn) Filipjev) is a destructive pest of many different plants. It occurs as ‘races’ or ‘strains’ which differ in the range of host plants that they attack. One or more races infesting oats can also attack rye, sugar beet, fodder beet, man-gel, field bean, pea, vetch and, occasionally, potato among agricultural crops. Certain horticultural crops, such as onion, broad bean, runner and dwarf French beans, parsnip, carrot, rhubarb and strawberry can also be attacked (see pages 458 and 413). Different races of stem nematode infest clovers and lucerne.

Two species of spider mite, namely the two-spotted spider mite (Tetranychus urticae Koch) and the carmine spider mite (Tetranychus cinnabarinus (Boisduval)), are serious pests of plants grown under glass or polythene. Plants damaged include cucumber, dwarf French bean, pepper, strawberry, tomato, carnation, chrysanthemum and rose; also arum lily, hydrangea, orchids and many pot plants as well as stone fruits and vines.

The beet leaf miner is the maggot of the sugar beet and spinach in northern Europe. mangold (or mangel) fly (Pegomya hyoscyami (Panzer)) and is a well-known pest of mangel, sugar beet and spinach in northern Europe. The adult is a true fly and should not be confused with the mangold flea beetle (see page 174), which is also sometimes called ‘fly’.

Several species of nematode are known to attack potato crops in Britain. The most important are the potato cyst nematodes (see page 422), which are serious and widespread pests attacking the roots. Potato tuber nematode (Ditylenchus destructor Thorne) is much less serious and attacks only the tubers; it is less common now than in the past.

The cyclamen mite (Phytonemus pallidus palli-dus Banks) is a species of tarsonemid mite which causes considerable damage to a wide range of glasshouse plants. These include Amaranthus, antirrhinum, Aphelandra, Aralia, azalea, begonia, chrysanthemum, Cissus, Columnea, Crassula, cyclamen, delphinium, Fatshedera, Ficus, fuchsia, geranium, Gerbera, gloxinia, Hedera, Impatiens, Kalanchoe, Nertera, pelargonium, Saintpaulia and verbena. Damage is particularly severe on azalea, begonia, cyclamen (Figs 66.1 and 66.3), gloxinia, Hedera (Fig. 66.2) and Saintpaulia. Open image in new window Fig.66.1 Cyclamen with petals showing distortion, flecking and discoloration caused by cyclamen mite

Slugs are perhaps the most widely known of all the pests that attack cultivated plants. They cause serious damage on farms, in gardens and on allotments. Although few crops escape attack, autumn-sown cereals and maincrop potatoes are the worst affected. Other farm crops often severely damaged are peas, clover, reseeded ryegrass, and root crops, especially in the seedling stages. Many kinds of vegetables and flowers are also damaged.

The black bean aphid (Aphis fabae Scopoli) or blackfly is a common and widespread pest of field and broad beans, dwarf French and runner beans, sugar beet, mangel, fodder beet, spinach beet and spinach. It also occurs on fat-hen, poppy and dock. Very similar black aphids occur on other cultivated plants and weeds including rhubarb, dahlia, nasturtium, dock and thistle.

Potato cyst nematodes, well known as pests of potato (see page 422), are also serious pests of tomato. For many years they have been established in the main tomato-growing areas of England and Wales. Intensive growing of tomatoes in soil, either under glass or outdoors, can easily lead to nematode populations building up to a damaging level unless regular control measures are taken.

Described here are six species of moth whose caterpillars feed in the trunks, branches, stems or canes of fruit trees, shrubs or bushes.

The cabbage root fly (Delia radicum (L.)) is a destructive pest of cruciferous crops throughout Europe and North America. In Britain it is most serious on cauliflowers and cabbage, particularly summer and autumn cauliflowers and summer cabbage, but it also damages Brussels sprouts, calabrese, Chinese cabbage, radish, swede, turnip, garden stocks and wallflower. The pest can also live on many cruciferous weeds.

The raspberry leaf and bud mite (Phyllocoptes gracilis (Nalepa)) occurs throughout Britain on cultivated and wild raspberry, hybrid berries and blackberry. Where infestations are severe, vigour, yield and fruit quality are reduced. Damage is more prevalent on raspberries growing in sheltered situations.

The small insects known as thrips, or thunderflies, are abundant in Britain and some of them can cause considerable damage to cultivated plants.Different species breed on grasses and cereals and on fruit, vegetable and flower crops. Two species that attack peas are described here.

Two-spotted spider mite (Tetranychus urticae Koch), also known as red spider mite, is prima­rily a pest of protected crops (see page 361), but it can damage several crops outdoors, particularly in hot, dry summers. It has a wide host range and may spread from crop to crop by way of weeds or hedgerow plants. Strawber­ries, hops, beans (especially dwarf French and runner beans), black currants, cane fruits, wall-trained fruit trees (particularly apricot, nectarine and peach) and many ornamentals are frequently attacked.

The pea and bean weevil (Sitona lineatus (L.))and the clover weevils (Sitona hispidulus (Fabricius) and Sitona sulcifrons (Thunberg)) are common and widespread insects found on leguminous crops. The adult weevils feed on the leaves, whereas the grubs (larvae) feed on the roots or root nodules. As their names indicate, the different species have distinct host preferences, but all of them live on several different crop plants.

Attacks of stem nematode (Ditylenchus dipsaci (Kuhn) Filipjev) on narcissus have been recorded since the beginning of the century but it was not until 1943 that infested tulips were discovered in England. During the following 10 years tulip stem nematode (tulip eelworm) spread quickly in the important bulbgrowing areas of south Lincolnshire and became one of the most serious problems of the tulip industry. Much progress has been made in its control, but it remains a potential problem requiring strict attention.

Grass and clover seed crops are attacked by a wide range of pests, although relatively few cause serious loss of yield. Described here are (i) those pests which affect seedling establish-ment, (ii) pests of the leaf and stem, and (iii) pests of the flower head and seed. Pest situations in reseeded grassland are not dealt with.

Stem nematode (Ditylenchus dipsaci (Kuhn) Filipjev) is a destructive pest of many different plants. Within this species many races or strains have been recognized according to the range of plants attacked, but the races are plants difficult to define clearly and some seem able to adapt to new hosts. Onion is the most seriously and widely affected vegetable crop, but carrots, parsnips, beans, peas and rhubarb are also affected. At least some of these crops are attacked by a race which also attacks strawberries (see page 413), oats and some other crops (see page 440).

Caterpillars of some moths feed gregariously, for at least part of their lives, in communal silken webs or ‘tents’ which they spin on their food plants. Some species which have this habit and are economically important in Britain are described here. These species are the small ermine moths (Yponomeutaspp.), the lackey moth (Malacosoma neustria (L.)) and the brown-tail moth (Euproctis chrysorrhoea (L.)). The vapourer moth (Orgyia antiqua (L.)), whose caterpillars occur together in large numbers though not feeding within webs, is also included.

Four species of gall midge are known as pests of apple or pear in Britain, but nowadays they occur infrequently in commercial orchards. Three of them are probably more important as pests of nursery trees than of fruiting plantations. Damage is caused by the feeding of the larvae; the part of the tree attacked varies with the species.

The saddle gall midge (Haplodiplosis marginata (von Roser)) is associated with frequent cereal growing on heavy land. It is widely distributed in most European at Alford, Lincolnshire, in 1889. Sub-economic levels are now common throughout the Midlands and in eastern England from Yorkshire to Kent. Heavy localized attacks have resulted in yield losses of winter wheat and spring barley in most of these areas.

Cereal cyst nematode (Heterodera avenae Wollenweber) is a widely distributed pest of cereal crops, occurring in Britain, Ireland, various other northern European countries, Israel, India, Australia and N. America. In Britain it is more damaging to oats than to other cereals and is prevalent mainly on light-textured soils. For many years crop losses occurred chiefly on sandy soils in the West Midland counties and adjoining areas of Wales. After the Second World War damage became more widespread, especially on the thin chalk soils of Wiltshire and Hampshire, following wartime ploughing of large areas of downland. With the subse­quent decline in the growing of oats, this pest became less important. However, it still reduces yields of barley and wheat, espe­cially on light and inherently lower yielding soils; it is seldom important on heavy-textured soils.

Caterpillars of several species of tortrix moth can cause damage to strawberry. By far the most important in Britain are the strawberry tortrix (Acleris comariana (Lienig & Zeller)), the straw-coloured tortrix (Clepsis spectrana (Treitschke)) and the dark strawberry tortrix (Olethreutes lacunana (Denis & Schiffermuller)), but damage is also caused locally by other species including the carnation tortrix (Cacoecimorpha pronubana) (Hubner)) and the flax tortrix (Cnephasia asseclana (Denis & Schiffermuller)).

The wheat bulb fly (Delia coarctata (Fallen)) is probably the most serious insect pest of winter wheat in Britain. Damage is caused by the maggots feeding within the shoots. There is considerable annual variation in the intensity of the attacks but occasionally these are severe. Wheat bulb fly is particularly prevalent in the eastern half of Britain as far north as the Angus District of Tayside Region, but even within this area it is rather local.

Root-knot nematodes (Meloidogyne spp.) cause galls to be formed on the roots of tomato (Fig. 86.1), cucumber, and sometimes lettuce, dwarf French bean, chrysanthemum and various ornamental plants grown under protection. These swellings, which vary from the size of a pin-head to that of a walnut, are the plant’s reaction to feeding by the nematodes in the root tissues. The galls often merge with one another, resulting in completely deformed root-systems that have few active fibrous roots. With improved methods of crop protection, attacks occur much less frequently than in the past.