Bibio johannis L

Larvae of this species are sometimes damaging to cereals and other crops, infestations most

166 Pests of Agricultural and Horticultural Crops dSSSID

Fig. 243 Tip of the body of bibionid larvae: (a) Bibio: (b) Dilophus.

often being reported in fields of winter wheat in the late winter or early spring. Adults are small (wings 4.5-6.5mm long); both sexes are black-bodied but the legs of females are ochreous and those of males reddish with black femora. The flies occur from March to June and are often found resting on the leaves of cereal plants and grasses.

NOTE Morphological differences between larvae of the various species of Bibio are slight and specific determinations are not always reliable.

Dilophus febrilis (L.) Fever fly

This species is a minor pest of various crops, including cereals (notably spring barley and maize), potato and sugar beet, and infestations tend to occur on damp, heavily manured sites; damage is also reported on grassland and on various horticultural crops, including hop and strawberry. The soil-inhabiting larvae feed on the roots, tubers and stolons, and attacked plants often collapse and die. On cereals, the larvae

Fig. 244 Foreleg of fever fly, Dilophus febrilis.

often hollow out the seed; they also destroy the roots and lowermost parts of the shoots. On potato, the larvae burrow into the flesh of the tubers to form extensive galleries and cavities. Adults are useful pollinators of fruit trees.

BIOLOGY

Adults emerge from April onwards. Large numbers of males often congregate on low vegetation, including the tips of grasses and cereal plants. The flies frequently visit open flowers and, in the spring, are of some benefit as pollinators of fruit trees and other plants. After mating, females burrow a few centimetres into the soil, especially in the presence of rotting vegetation or organic manure. Each then forms a small cell in which a cluster of 200-300 eggs is laid. Eggs hatch about a month later. The larvae feed gregariously on the subterranean parts of plants and, in favourable situations, there may be several thousand individuals per square metre. Larvae pass through four instars and then pupate; adults appear a few weeks later. There are usually two or three generations annually, and adults tend to be most numerous in the spring and autumn.

DESCRIPTION

Adult mainly shiny black; pronotum with two transverse rows of backwardly directed spines; wings 4-7 mm long; fore tibiae each with an apical circlet of seven to nine stout spines (Fig. 244). Egg 0.55 mm long, sausage-shaped, white

Fig. 245 Larva of fever fly, Dilophus febrilis (x6).

when newly laid, becoming slightly darker at each end. Larva up to 12mm long, dull, light brown, more or less cylindrical; each body segment with several relatively short papillae (Fig. 245) (cf. Bibio, Fig. 85); head prominent, blackish-brown (cf. leatherjackets, e.g. Tipula spp., p. 164); posterior spiracles each with three pores (Fig. 243b). Pupa 7.5 mm long, whitish, darkening to brownish-grey; head with one (female) or three (male) pointed anterior processes (cf. Bibio, p. 165).

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