Insecta, Diptera, Muscidae .
Description, Biology, Life Cycle, Damage, Common Names, Images
- Host plants: beet, Chenopodiaceae.
Fluctuations in population level are enormous and vary according to climatic conditions and biotic agents. If May is cold and rainy, the fly does little harm. Drought and high temperatures are limiting factors during the summer, being lethal to both larvae and eggs.
- The insect overwinters in the soil as a pupa.
- Adult: feeds on nectar and sap dripping from wounds.
- Total fecundity: 70 to 80 eggs.
- Eggs: time until hatching, 4 to 6 days (4 at 16°C). Hatching en masse as soon as temperature rises.
- Larva: 15 days; 3 instars.
- 3 generations per year.
- The 1st-generation adult appears from mid-April to late May. It will fly under hot, dry conditions but shelters beneath leaves when wet and cold. Mating and egg-laying occur from early May to late June. The female lays eggs in groups of 3 to 8 every 8 to 10 days.
- On hatching, the larva bites through the chorion and penetrates the leaf at the point of contact. It digs a narrow mine between the upper and lower epidermal layers. The mines of larvae from the same group of eggs fuse with one another.
- Pupation occurs in the soil at varying depths according to humidity.
- The 2nd-generation adult appears towards the end of June or beginning of July. Large numbers of eggs are laid from 5th to 25th July in the Paris region.
- Pupation occurs towards mid-August.
- The 3rd-generation lays eggs from early August to late September.
- The larvae migrate to the soil from mid-August onwards.
- The pupa enters diapause in September.
The worst damage is done by the 1st-generation larvae. Translucent marks appear where the tissue is damaged, becoming browner as they dry out (*) . Seedlings die and fully developed plants are weakened, especially when growing conditions are unsatisfactory. Once the host root has passed stage 6 (real leaves), it becomes distinctly less susceptible and insecticide treatments are unnecessary.
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