Bemisia tabaci , Trialeurodes vaporariorum , etc

Whiteflies

General

• Rather polyphagous insects widely distributed in the world, and particularly damaging in tropical areas. Certain species are vectors of numerous and formidable viruses. They belong to the order Hemiptera and the family Aleyrodidae.
• The adults resemble almost entirely white midges, about 1 to 3 mm long depending on the species, and are mostly found on young leaves. The larvae, flattened, have an oval shape and are whitish or dark in color, covered or not with white waxy secretions depending on the species, which allows them to be recognized. However, the color of the larvae can change if they are parasitized by microhymenoptera. These larvae can be confused with mealybugs, but these are rare on vegetable crops and we will not observe "white flies" in this case.
• Many species found in tropical areas: 
  • The tobacco whitefly Bemisia tabaci Gennadius, mainly biotype B - synonymous with Bemisia argentifolii (Bellows & Perring) - (Figures 1 to 4)
  • The greenhouse whitefly Trialeurodes vaporariorum (Westwood) (Figure 5), found in cool climates or at high elevations
  • Solanaceae whitefly Aleurotrachelus trachoides (Back) (Figures 6 to 8)
  • Cabbage whitefly Aleyrodes proletella (L.) (Figure 9)
  • The spiral-laying aloe Aleurodicus dispersus Russel (Figures 10 and 11)
  • Cassava whitefly Aleurotrachelus socialis Bondar present in Guyana
• These insects are observed in the open field and in crops under cover.

Sensitive botanical family (s):

the first two species are highly polyphagous, developing on several hundred hosts, whether cultivated or not, while the others are present in a few botanical families.

Affected production areas :  

Organs attacked

Damage 

• Symptoms :
  • Numerous bites and sap sucks causing a slowdown in plant development and sometimes leaf chlorosis.
  • Honeydew produced in large quantities by these insects. This substrate is subsequently colonized by opportunistic fungi responsible for sooty mold (figures 12 and 13). The mold produced covers the surface of the aerial organs of plants, soiling them, sometimes making the fruit unsuitable for marketing, and decreases photosynthesis.
  • The bites of larvae of biotype Bemisia tabaci cause physiological disorders in certain crops (silvering of zucchini (figure 14) and other Cucurbita , poor ripening of tomato (figure 15).
  • Many viruses such as TYLCV (figure 16) and PYMV can be transmitted by eventually Bemisia tabaci, in particular on Solanaceae, leading to the death of the plant. Trialeurodes vaporariorum can sometimes transmit viruses.

• Signs : Presence of larvae and adults on affected organs (Figures 2, 10 to 15). From the sooty mold (sooty mold) (Figure 12) is often associated with the presence of whiteflies. Remember that the latter leads to a reduction in photosynthesis and leaf respiration and makes the productions non-marketable.
• Confusions possibles : 

Biology

• Development cycle : includes 3 development phases taking place on the underside of the leaves of attacked plants: egg, 4 larval stages and adult. Only the first instar larvae are motile and the last in late development is called a pupa or puparium. The duration of the complete cycle (figure 17) varies according to the temperature, the host plant and the different species, and is about 3 weeks in tropical conditions. Under tropical conditions, the cycles are continuous and all stages are present at the same time.
• These insects remain on their cultivated plants as long as they last, but also on various weeds, which should therefore be carefully eliminated.
• Dispersal : Adults fly little but are easily blown away, and disperse quickly in crops. The spread of infested plants contributes to the dispersal of these insects.
• Favorable conditions : whiteflies multiply rapidly in tropical climatic conditions, and more in shelters (lack of rain and wind, excess nitrogen fertilization).

Protection

• Evacuate . the farm if whitefly populations are high
• Produce the seedlings in an insect-proof nursery.
• Control the sanitary quality of the plants before and during their introduction into the culture or shelter.
• Install  canvases  insect-proof at shelter openings when weather conditions permit.
• In cultivation under cover, detect the first pests using yellow sticky panels placed above the crop as soon as the plants are introduced.
• Favor natural enemies in open field cultivation or under open shelters.
• Introduce auxiliaries in closed shelters if available.
• Consider  chemical protection, especially if you use auxiliaries or biopesticides , especially since most insecticides are not very effective on whiteflies.
• Treat plants before uprooting in the presence of high pest populations so as not to contaminate nearby host crops.