Crops
Thrips
General
- Rather polyphagous insects distributed worldwide, present from tropical to polar regions depending on the species. They feed by sucking the contents of the cells of the epidermis, thus the damaged tissues quickly become necrotic.
- Classified in the order Thysanoptera, and the family Thripidae .
- Species* reported in tropical areas on vegetables:
- tabaci (tobacco thrips)
- Frankliniella occidentalis Pergande
- Thrips palmi Karny
- Heliothrips haemorrhoidalis (Corked)
- Caliothrips helini Hood
- Corynothrips stenopterus Williams (cassava thrips)
- Some are vectors of dreaded viruses, in particular the Tomato spotted wilt virus ( TSWV ).
- Observed in the open field and under shelters.
* The first two species are very polyphagous, developing on several hundred hosts, whether cultivated or not, while the others are present on a few botanical families.
- Sensitive botanical family (s) * :
| Caliothrips helini | Solanacées | Composed |
| Thrips tabaci | Cucurbits | Euphorbiaceae (o) |
| Brassicas | Legumes | |
| Alliaceae | ||
| Thrips palmi | Solanacées | Cucurbits |
| Vegetables | Alliaceae | |
| Frankliniella occidentalis | Vegetables | |
| Corynothrips stenopterus | Euphorbiaceae (x) | |
- Production area affected :
| Caliothrips helini | Mayotte | Reunion |
| Thrips tabaci | Reunion | New Caledonia |
| French Polynesia | ||
| Frankliniella occidentalis | Reunion | Guyana |
| New Caledonia | French Polynesia | |
| Thrips palmi | Reunion | Guyana |
| New Caledonia | French Polynesia | |
| Corynothrips stenopterus | Guyana | Guadeloupe and Martinique |
- Organs attacked
| Leaves | Fruits | Rod |
Symptoms, damage
- Symptoms :
- Numerous and tiny silvery lesions, even patches of irregular size and shape appear on the leaf blade (figure ); they gradually become necrotic and take on a beigeish tint.
- Presence of tiny black dots materializing the droppings of thrips.
- Affected leaves and leaflets tend to become chlorotic and dull.
- Whitish lesions on the flowers (figure ).
- Silvery or even suberized alterations, more or less extensive, developing on the fruits (figure ).
- Signs : Presence of tiny elongated insects on the affected plant organs (figures ).
- Possible confusion :
Biology
- Development cycle : comprising 6 stages: egg, two larval stages, two pronymph stages and adult; its duration varies according to the temperature and the host plant (for example, for F. occidentalis it fluctuates from 34 days at 15°C to 13 days at 30°C).
- Kidney-shaped eggs laid on aerial organs, especially leaves.
- Larvae, once formed, very mobile and feeding on the underside of the leaves. At the end of the second instar, they drop to the ground and pupate.
- The first pronymph stage is characterized by the appearance of wing outlines. The second pronymph stage, paler, also shows more consequent wing outlines and long and curved antennae towards the rear of the body.
- Adults with 2 pairs of well-developed wings.
- Larvae and adults, taking refuge in places with mild temperatures, ensure the survival of these insects. For this, they settle in plant debris, the frames of shelters; they sometimes bury themselves up to 8 centimeters deep. They may also hibernate on field crops, including various Alliums . ( to be contextualized to tropical areas )
- Fairly easily dispersed insects passively carried by air currents and/or actively by flying. Workers can contribute to their dispersal during cultivation operations; this is also the case for seedlings or plants of other parasitized species.
- The nature of the plant, the temperature, the hygrometry in the culture, influence in particular the development of thrips.
Protection
- Evacuate the farm if thrips populations are high.
- Wash with water and treat the walls of the shelters, the posts, the concrete paths.
- Disinfect the reused substrate or soil.
- Produce the seedlings in an nursery insect-proof .
- Check the sanitary quality of the plants before and during their introduction into the crop or shelter.
- Install canvases insect-proof at shelter openings when weather conditions allow.
- In cultivation under cover, detect the first pests using blue sticky panels placed above the crop as soon as the plants are introduced.
- Remove and destroy infested plant debris and crop residues.
- Favor natural enemies in field crops or under open shelters.
- Introduce auxiliaries into closed shelters if available.
- Reason chemical protection, especially if you use auxiliaries.
- Treat plants before uprooting in the presence of high pest populations so as not to contaminate nearby susceptible crops.
**: resistance to insecticides or acaricides is known in these pests.
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Figure 12
Figure 13
Figure 14
Figure 15
Figure 16
Figure 17
Figure 18
Figure 19
Figure 20
Figure 21
Figure 22
Figure 23
Figure 24
Figure 25
Figure 26
Figure 27
Figure 28
Figure 29
Figure 30
Figure 31
Figure 32