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Plantwise Technical Factsheet

turnip maggot (Delia floralis)

Host plants / species affected
Allium cepa (onion)
Allium porrum (leek)
Brassica napus var. napus (rape)
Brassica oleracea var. viridis (collards)
Brassica rapa subsp. oleifera (turnip rape)
Brassicaceae (cruciferous crops)
Raphanus sativus (radish)
Sinapis alba (white mustard)
Thlaspi arvense (field pennycress)
List of symptoms/signs
Roots  -  internal feeding
Stems  -  dead heart
Stems  -  internal feeding
Description
Larvae

Identification from immature stages is not generally practical although many Cyclorrhapan Diptera spp. have been described; see Ferrar (1987) for references. The following notes may help differentiate Anthomyiidae spp. from other Diptera: eggs are approximately 1-2 mm long, white; third (final)-instar larva up to 10 mm long with 5-16 (Delia) or 6-27 (Pegomya) lobes on each anterior spiracle; puparium brownish, up to 7 mm long (Ferrar, 1987).

Adults

Griffiths (1984, 1993) presented separate keys to males and females of Pegomya and Delia spp. found in North America. For European keys see Hennig (1966-1976).

Characteristics of the genus Delia are as follows: head; eyes bare (not covered in setulae); longest aristal hairs shorter than width of first flagellomere. Thorax: 3 pairs long post-sutural dorsocentral setae; katepisternal setae arranged 1 + 2 (not in an equilateral triangle); area of anepisternum just below anterior notopleural seta with fine setulae only; scutellum with setulae on the ventral surface; male surstylus not cleft; tibia brown to grey. Wing: setae on lower surface of costa (if present) closely spaced; vein A1 traceable to wing margin (Huckett, 1987).

D. radicum and D. floralis share the following features: wing length up to 6.0 mm; costa (vein C), lower surface extensively setose to beyond end of vein R1, in addition to a series of setulae on the dorsal and anterior surfaces of the vein. Prealar seta (first post-sutural supra-alar seta) longer than posterior notopleural seta. Male hind femur, antero-ventral surface densely setose basally and apically.

D. radicum and D. floralis cannot be separated without specialist help, examination of male gentialia and reference collections. There are differences in the male hind femora; D. radicum has a greater density of basal antero-ventral setae than D. floralis. Griffiths (1993) also reported differences in the female hind femora, but these are very difficult to interpret and masked by considerable intra-specific variation. The male fifth sternite processes have shorter outer lateral setae in D. radicum than in D. floralis. The male surstylus is somewhat more slender and elongate in D. floralis than in D. radicum (See Pictures for both species).
Prevention and control
Cultural Control

Cultural methods are very important. Grass mulches increase yield (Hellqvist, 1996) and tillage can decrease emergence (Dosdall et al., 1996b). Late sowing of rape (Brassica napus) can reduce infestations, but it may also reduce seed yield (Dosdall et al., 1996a). Intercropping (beans (Phaseoulus vulgaris) or weeds) can also significantly reduce attack (Hofsvang, 1991)

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:

Host-Plant Resistance

There has been some interest in selective breeding for resistant crop varieties, and a recent review of progress in kale and swede is provided by Baur et al. (1996).
Impact
D. floralis attack reduces the weight of leaves, stems and roots with the greatest effect on the latter. Hopkins et al. (1995) noted a 26-46% reduction in root weight of swede (Brassica napus var. napobrassica), rape (B. napus) and kale (B. oleracea var. acephela) after inoculation with 10 eggs per plant. Sugar content was also reduced in some of the rape and swede cultivars.
Related treatment support
 
External factsheets
Pennsylvania State University Insect Pest Fact Sheets, The Pennsylvania State University, 2010, English language
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