1. Whiteflies Biology and control
Spain
MODULE C15

2. Index Taxonomy 2. Importance as pests
3. Distribution: pests and viruses
4. Life cycle
5. Plant damage
6. Monitoring
7. Control
8. IPM based on Biological Control

3. Taxonomy Order Hemiptera. Family Aleyrodidae Trialeurodes vaporariorum
Bemisia tabaci
Whiteflies (Trialeurodes vaporariorum and Bemisia tabaci) are important worldwide pests of vegetable, cotton and ornamental crops, although they can also develop on a wide range of cultivated and wild plants
Whiteflies belong to the Ordre Hemiptera. The members of the family Aleyrodidae are known as whiteflies, and they mainly attack plant leaves. The two main species of whiteflies in Europe are shown in this slide.

4. Whitefly species identification
Eggs
Nymphs
Adults
T. vaporariorum
Differentiating the two species is important firstly because Bemisia is a very good vector of some important viruses. Secondly, whether using natural enemies or insecticides for control, knowledge of the species present in the crop will help us to choose the best options.
The main differences that we observe in the field are:
(1) Size and shape of adults: Bemisia adults are smaller and narrower because their wings are folded over their body, while those of Trialeurodes are larger and more triangular. Distribution of adults on the plant: Bemisia adults are distributed almost uniformly throughout the plant while those of Trialeurodes are concentrated on the 3 upper leaves.
(2) Colour of eggs: Newly laid eggs are white for both species but once mature they are yellow in the case of Bemisia and blackish in the case of Trialeurodes.
(3) Morphology of larvae: Bemisia larvae are flatter than those of Trialeurodes that are more voluminous and present a side wall shaped like a fence perpendicular to the surface of the leaf.
B. tabaci
Adaptadoed from
New York State Integrated Pest Management Program Online publications

5. B. tabaci as plant virus vector
IOBC "Integrated Control in Protected Crops, Temperate Climate. Turku, Finland April, 2005
B. tabaci is a very efficient vector
TYLCV
CVYV
CYSDV
High economic losses
Early infections
Very low spray threshold
Overuse of insecticides
On B. tabaci the most important damage, is due to its ability to transmit some viruses, such as the one producing Tomato Yellow Leaf Curl Disease (TYLCD), which can cause significant loss of productivity, even when Bemisia populations are low. It can also cause abnormalities in fruit ripening.
Besides crops, several weeds can serve as hosts for Bemisia. However, the largest populations are found in vegetable and ornamental crops so it is important to focus on management of these crops, especially when there is heavy infestation.

6. Attack high value crops (protected vegetables and ornamentals)
Importance as pests
Attack high value crops (protected vegetables and ornamentals)
Plant virus transmission specially B. tabaci
Introduced pests in many regions
(by man)
Quarantine species
Whiteflies and whitefly-transmitted viruses are some of the major constraints on European tomato production. Tomato crops are particularly susceptible to viruses causing Tomato yellow leaf curl disease (TYLCD).

7. Whitefly species distribution
Distribution of whitefly species in tomato
Single populations of T. vaporariorum are usually found in northern Europe, and mixed infestations of the two whitefly species are common in most of the tomato growing areas. Bemisia tabaci is widely distributed in Europe and single infestations are reported from Israel, and some regions of Spain, Greece, Morocco and Turkey.

8. Bemisia transmitted viruses on tomato
Geographical distribution of the virus: TYLCV and TYLCSV
Canary
Islands
Reunion
Island
Israel
Morocco ß
Algeria
Tunisia
Egypt
Lebanon
TYLCV & TYLCSV
Bemisia-transmitted viruses include some of the most damaging viruses, e.g. the group of species responsible for Tomato yellow leaf curl disease (TYLCD). Wherever the pressure of B. tabaci was high, TYLCD was classified as important or very important. TYLCV and TYLCSV, which produce a severe reduction of yield, mainly in tomato crops, are the most widespread Bemisia transmitted viruses in Europe and MPC-12 countries. According to tomato CS survey, TYLCV also produces damage to bean crops in some areas of Greece, to peppers in Reunion and to ornamentals in Israel and mainland Italy.

9. Whitefly life cycle Adults Eggs Nymphs Bemisia tabaci
Trialeurodes vaporariorum
The Bemisia female lays eggs mostly underneath the leaf (abaxial surface) of the host plant. From these eggs tiny mobile larvae hatch, these look for a suitable place to feed and develop. Larvae attach themselves to the leaf blade by the stylet, which they use to feed on the plant. They go through 3 more larval stages, during which they increase in size and undergo several morphological changes before reaching the pupa stage. From the pupa emerges a new adult that starts the cycle anew .
The duration of their development, and therefore, the speed at which populations grow, is determined primarily by 2 factors: the host plant and temperature.
Curs de Formadors de Producció Intregrada. Lleida, 22 de novembre de 2002

10. Whitefly damage Damage Weakening of the plant Black mould
Virus transmission
When whitefly populations are high, they produce weakening of the plant, abundance of molasses and sooty mold. Whitefly-transmitted viruses are some of the major constraints on tomato production

11. Monitoring for decision making
Chemical control mainly based on calendar treatments
IPM strategies mainly based on monitoring
Whitefly species always identified
Sampling neither associated to the IPM control strategy nor to the growing cycle but to the production area.
Most of insecticides sprays in the chemical managed crops are calendar based. Whereas, IPM strategies are mainly based on monitoring. Whitefly species always identified. Sampling neither associated to the IPM control strategy nor to the growing cycle but to the production area.

12. Control strategies: cultural measures
use plant material free from pests
remove weeds and remains from the previous crop
keep the area surrounding the greenhouse clean
keep cover material and enclosures in good conditions
be careful with neighboring crops highly infested
do not leave abandoned crops in the field.
Cultural measures: these are very important to keep the initial pest density low and delay its arrival in the crop. These measures include the following: use plant material free from pests; remove weeds and plant debris from the previous crop, In early crops it is important to keep the area surrounding the greenhouse clean; keep cover material and enclosures in good conditions; be careful when neighbouring crops highly infested with Bemisia are pulled up; and finally, do not abandone crops in the field.
Biological control: It is effective in controlling populations of this pest. The most commonly used natural enemies are: Eretmocerus mundus, a specific parasitoid of Bemisia and Macrolophus caliginosus a polyphagous predator that feeds on both Bemisia and Trialeurodes.

13. Control strategies 2 IPM-based on the rational use of insecticides
IPM-based on biological control (BC)
Chemical control, based only on the use of insecticides
Organic production (insecticide-free approaches
On protected environments, effective whitefly control is principally achieved through Integrated Pest Management (IPM) strategies
Bemisia tabaci is one of the principal insect pests driving insecticide use, primarily due to the threat of TYLCD and the resulting low tolerance thresholds that it imposes. Insecticide resistance has been reported for both whiteflies, especially for B. tabaci.
The number of insecticide applications per month is higher in IPM-Insecticide than in IPM-BC.
Not only insecticide applications but also active ingredients (a.i.) are saved with the use of IPM strategies:
IPM-Insecticide uses 18 % less a.i./application than the chemical strategy and 17 % more a.i./application than IPM-BC. Bemisia tabaci is one of the principal insect pests driving insecticide use, primarily due to the threat of TYLCD and the resulting low tolerance thresholds that it imposes. Insecticide resistance has been reported for both whiteflies, especially for B. tabaci, to all the pesticide compounds used

14. Control Strategies 1
Chemical Control: rotated insecticide a.i. to delay the appearance of resistant biotypes of Bemisia
Biological control: conservation and augmentative releases of polyphagous predators and parasitoids..
Chemical Control: To achieve effective chemical control chemical groups should be rotated correctly in order to delay the appearance of resistant biotypes of Bemisia. Biological control: It is effective in controlling populations of this pest.

15. Control strategies: Biological Control
▲: Eretmocerus mundus
▲: Eretmocerus eremicus
● : Encarsia formosa
* : Macrolophus caliginosus
: Nesidiocoris tenuis
: Typhlodromips swirskii
: Dicyphus hesperus
Canary Islands
Reunion Island
Israel
Morocco ▲ * ●  
Natural enemies used to control whiteflies
Natural enemies used in biological control of whiteflies in the different countries. Symbols in red are used for non-European native beneficials. The most commonly used natural enemies are: Eretmocerus mundus, a specific parasitoid of Bemisia and Macrolophus caliginosus a polyphagous predator that feeds on both Bemisia and Trialeurodes.

16. Control strategies: Biological Control
Use by country
(N=9)
% surveys by positive use (N=24)
Eretmocerus mundus
9/9 92
Macrolophus caliginosus
7/9 58
Typhlodromips swirskii 54
Eretmocerus eremicus
4/9 42
Nesidiocoris tenuis 29
Dicyphus hesperus
2/9 17
Biological control of whiteflies is mainly based on inoculative releases of the parasitoids Eretmocerus mundus and Encarsia formosa and/or the polyphagous predators Macrolophus pygmaeus (commercially labelled as M. caliginosus) and Nesidiocoris tenuis. Biological control is applied mainly within the framework of IPM and selective pesticides are applied for pests lacking biological solutions or when biological control failed to control the target pest. Natural enemies are also used in organic production but the acreage of tomatoes under this production system is limited

17. Natural enemies: release rates (indv./m2)
predators
parasitoids
Germany A
1.5 -
4-8 C
7.5-9
South France 4
25-55 3 10
North Spain 1
2-3
3-9 B 2
North Spain 2
South Spain
0.75 1 
Macrolophus
caliginosus
Nesidiocoris
tenuis
Eretmocerus
mundus
Encarsia
formosa
Area
Cycle
IPM based on BC is used in all the 4 tomato growing areas surveyed, the largest acreage being in the South of Spain.
Biological control of whiteflies is mainly based on inoculative releases of 2 polyphagous predators M. caliginosus and N. tenuis and 2 parasitoids E. mundus and E. formosa. Only in the North of Spain, a program based on the conservation of native populations of M. caliginosus is also used and, in that area release rates are related to predator natural populations abundance
In the other growing areas, predators are released on a calendar base due to their difficult availability and slow installation. In contrast, parasitoid releases are decided according to whitefly adult thresholds ( 1 to 2 adult whiteflies/plant). The parasitoid species are tightly correlated to the whitefly species present. Eretmocerus mundus only parasites B. tabaci and it is widely used in the Mediterranean basin in the tomato growing cycles when this whitefly is the predominant species. Encarsia formosa is used in Germany and the South of France, for T. vaporariorum control.
Release rates of both predators and parasitoids are very variable and often are decided according to advisors experience.