Bemisia tabaci , Trialeurodes vaporariorum , etc

Whiteflies or white flies

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 : 

Biologie

• Cycle de développement : comprend 3 phases de développement se déroulant à la face inférieure des feuilles des plantes attaquées : œuf, 4 stades larvaires et adulte. Seul le premier stade larvaire est mobile et le dernier en fin de développement est appelé nymphe ou puparium. La durée du cycle complet (figure 17) varie en fonction de la température, de la plante-hôte et des différentes espèces, et est d'environ 3 semaines en conditions tropicales. Dans les conditions tropicales, les cycles sont continus et tous les stades sont présents à un même moment.
• Ces insectes se maintiennent sur leurs plantes cultivées tant qu'elles perdurent, mais aussi sur diverses plantes adventices, qu'il conviendra donc d'éliminer soigneusement.
• Dispersion : Les adultes volent peu mais sont facilement emportés par le vent, et se dispersent rapidement dans les cultures. La diffusion de plants infestés contribue à la dispersion de ces insectes.
• Conditions favorables : les aleurodes se multiplient rapidement en conditions climatiques tropicales, et davantage dans les abris (absence de pluie et de vent, excès de fertilisation azotée).

Protection

• Faire un vide sanitaire sur l'exploitation si les populations d'aleurodes sont importantes.
• Produire les plants dans une pépinière insect-proof.
• Contrôler la qualité sanitaire des plants avant et durant leur introduction dans la culture ou l'abri.
• Installer des toiles insect-proof aux ouvertures des abris quand les conditions climatiques le permettent.
• En culture sous abris, détecter les premiers ravageurs grâce à des panneaux jaunes englués posés au-dessus de la culture dès l'introduction des plants.
• Favoriser les ennemis naturels en culture de plein champ ou sous les abris ouverts.
• Introduce auxiliaries into closed shelters if available.
• Reason for  chemical protection, in particular 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.