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Italian: Dorifora della patata
English: Colorado Beetle
Tincture prepared by covering the crushed live beetles with alcohol.
Animalia; Insecta (Hexapoda) - Insects; Rhynchota / Hemiptera; Coleoptera - Beetles; Chrysomelidae
Allen: Cyclopoedia, V. 4. Hering: Guid. Symptoms, V. 5. Macfarlan: High Pot. Provings.
Description of the substance
This insect was an innocuous feeder on native plants of the nightshade or potato family along the Missouri River until the middle of the last century, when it exhibited a strong preference for the Irish or white potato which was becoming increasingly available in the garden patches of emigrants to the Northwest. It has now spread to all potato-growing sections in our region, except those in California, and since 1922 has established itself in Europe.
- Adult: Oval body, very convex, 10 to 11 mm long. The prothorax of a brown red coloration, as is the head, bears several black spots. The yellow elytra are decorated with 10 characteristic black longitudinal bands.
- Eggs: orangy yellow, ovoid, 1.5 mm in length, they are fixed in clusters of 10 to 30 on the underside of the leaves.
- Larva: after hatching, it is orangy red and measures 1.5 to 2.0 mm in length. Once development is complete it measures 11 to 12 mm in length, it is soft and plump, of a more or less dark red colour. The head and legs are black as well as 2 rows of obvious plates on the side of the body.
- Pupa: in the ground, pinkish, 1 cm long.
- Host plants: exclusively Solanaceae, especially potato; otherwise, egg-plant, tomato and wild Solanaceae: black nightshade (Solanum nigrum), woody nightshade (Solanum dulcamara).
- Adult: hibernates in the ground at a depth of between 25 and 40 cm. It emerges out in spring after rain and once the ground temperature reaches 14 °C at its hibernation depth. It then feeds on the young potato leaves. After mating, the female immediately starts to lay eggs.
Fecundity: 700 to 800 eggs.
Lifespan: 1 to 2 years.
- Egg: embryonic development lasts 4 to 10 days.
- Larva: feeds on foliage, moults 3 times and completes its development in 15 days. It then buries itself in the ground at a depth of between 2 and 20 cm to pupate.
- Pupa: development lasts 8 to 15 days.
- 1 generation, a second generation sometimes incomplete in temperate and meridional zones. The total length of the cycle is about 5 to 6 weeks.
- The adults appear at regular intervals from April onwards; the first generation adults appear in July and feed abundantly. Some of them reproduce, the other bury themselves in the ground and enter diapause.
- As a result of the adult lifespan, the annual generations superimpose themselves and all the instars can be simultaneously observed in the fields.
- End of August beginning of September, the surviving adults bury themselves in the ground to hibernate.
The adults and the larvae destroy partially or totally the foliage of potato or other host Solanaceae. In the event of a major invasion, the harvest is greatly reduced.
Originating from America, this pest was introduced to France in 1922 in the Bordeaux region, before it invaded all France and Europe mainland from 1940 onwards.