ACW | 2012
Temporal patterns of the abundance of the cabbage root fly (Delia radicum, Diptera: Anthomyiidae)
Romana Schmon, Ute Vogler
Agroscope Changins-Wädenswil Research Station ACW, CH-8820 Wädenswil; www.agroscope.ch
What are the temporal patterns of the abundance of the cabbage root fly (Delia radicum) in the vegetable brassica crops - oilseed rape agroecosystem?
Fields with oilseed rape offer an undisturbed overwintering habitat for D. radicum with available host plants. At harvest, alternative host plants (vegetable brassica crops, self-seeding oilseed rape, weeds) are present and attractive for migration and oviposition.
Fields with vegetable brassica crops represent a disturbed overwintering habitat without available host plants, with crop rotation and tillage. During growing season, host plants are cultivated continuously and offer possibilities for oviposition.
Background
• The cabbage root fly Delia radicum is a main insect pest in cruciferous crops including vegetable brassica crops and agricultural brassica crops, e.g. oilseed rape Brassica napus (Brassicaceae)
• Cultivated area with oilseed rape increased in Switzerland from 14’606ha (1994) to 22’245ha (2011) whereas the cultivated area for vegetable brassica crops was stable
• Restricted choice and limited availability of insecticides for crop plant protection
Adult Eggs
Larva Pupa
Methods
Results and Conclusions
Figure 3: Location of the yellow water traps in oilseed rape (F1, F2, F3) and cauliflower (CF)
Monitoring Monitoring period:
• 26.03.2012 – on going Egg oviposition (Fig. 2A):
• Weekly observation of 10 randomly selected plants per field: 3 oilseed rape fields (F1, F2, F3), 1 cauliflower field (CF)
Flight activity (Fig. 2B):
• One yellow water trap per field, changed weekly
• Identification of D. radicum in the laboratory
Figure 2: Control of egg oviposition (A);
Control of flight activity using yellow water traps (B).
A
B
• Ruswil (LU), Switzerland
• Distance between traps ranged from 330 m to 1400 m (Fig. 3)
• Traps were placed in winter oilseed rape (F1, F2, F3) sown in August 2011, in a fallow field (broccoli cultivation in 2011), cauliflower (CF) cultivated in 2012, and in chinese cabbage (CC) cultivated in 2012 (not shown in Fig. 3)
Study site
Figure 1: Development of the cabbage root fly D. radicum
B
Figure 5: Results from the vegetable brassica crop fields during growing season 2012 (2011 = Fallow field with broccoli cultivation in 2011; CF = Field with cauliflower in 2012; CC = Field with chinese cabbage in 2012). D) Total number of D. radicum flies in yellow traps, representing flight activity. The trap was built up in the field with vegetable brassica crops cultivation in 2011 and changed to the cauliflower field (CF), as soon as cauliflower was planted. E) Total number of eggs representing oviposition of the cabbage root fly on 10 randomly selected plants in cauliflower. F) Plant development of cauliflower.
Flight activity (D), egg oviposition (E) and plant development (F) in vegetable brassica crops
C F
Oilseed rape
• Strong flight activity of the 1st generation for eight weeks and egg oviposition in oilseed rape
• Flight activity of the 2nd generation for four weeks and no egg oviposition in oilseed rape
→ Indication of migration to more attractive sites
Vegetable brassica crops
• Flight activity of the 1st generation for six weeks in field with cauliflower in the previous year 2011 and no egg deposition
• Strong flight activity of the 2nd generation for six weeks and egg oviposition in cauliflower
→ Indication of immigration from less attractive sites
Overwintering site and availability of host plants influences the initial population size in spring!
Flight activity (A), egg oviposition (B) and plant development (C) in oilseed rape
Figure 4: Results from the three oilseed rape fields (F1, F2, F3) during growing season 2012. A) Total number of D. radicum flies in yellow traps, representing flight activity. B) Total number of eggs, representing oviposition of the cabbage root fly on 10 randomly selected plants in oilseed rape. C) Plant development of oilseed rape.
B A
E D
