Whiteflies are small hemipterans that typically feed on the undersides of
plant leaves. They comprise the family Aleyrodidae, the only member of the
superfamily Aleyrodoidea. More than 1550 species have been described.
Agricultural threat The ability of whiteflies to carry and
spread disease is the widest impact they have had on global food production. In
the tropics and subtropics, whiteflies have become one of the most serious crop
protection problems. Economic losses are estimated in the hundreds of millions of
dollars. While several species of whitefly cause
crop losses through direct feeding, a species complex, or group of whiteflies
in the genus Bemisia are important in the transmission of plant diseases.
Bemisia tabaci and B. argentifolii, transmit African cassava mosaic, bean
golden mosaic, bean dwarf mosaic, bean calico mosaic, tomato yellow leaf curl,
tomato mottle, and other Begomoviruses, in the family Geminiviridae. The
worldwide spread of emerging biotypes, such as B. tabaci biotype B, also known
as, 'B. argentifolii', and a new biotype Q, continue to cause severe crop losses
which will likely continue to increase, resulting in higher pesticide use on
many crops. Efforts to develop environmentally friendly integrated pest
management systems, with the goal of reducing insecticide use aim to
re-establish the ecological equilibrium of predators, parasitoids, and microbial
controls that were once in place. New crop varieties are also being developed
with increased tolerance to whiteflies, and to the plant diseases carried by
them. A major problem is the fact that whiteflies and the viruses they carry
can infect many host plants, including agricultural crops, palms, and weeds.
This is complicated by the difficulty in classifying and detecting new whitefly
biotypes and Begomoviruses. Proper diagnosis of plant diseases depends on
using sophisticated molecular techniques to detect and characterize the viruses
and whiteflies which are present in a crop. A team of researchers, extension
agents and growers working together are needed to follow disease development,
using dynamic modeling, to understand the incidence of disease spread.
In 1997, tomato yellow leaf-curl begomovirus was discovered in Florida,
USA. This is the worst viral disease transmitted by the whitefly, Bemisia
argentifolii. The whitefly has also been shown to transmit almost 60 other viral
plant diseases. = Whitefly damage by feeding =
Whiteflies feed by tapping into the phloem of plants, introducing toxic
saliva and decreasing the plants' overall turgor pressure. Since
whiteflies congregate in large numbers, susceptible plants can be quickly
overwhelmed. Further harm is done by mold growth encouraged by the honeydew
whiteflies secrete. This may also seriously impede the ability of farms to
process cotton harvests. Whiteflies share a modified form of
hemimetabolous metamorphosis, in that the immature stages begin life as mobile
individuals, but soon attach to host plants. The stage before the adult is
called a pupa, though it shares little in common with the pupal stage of
holometabolous insects. = Control =
Whitefly control is difficult and complex, as whiteflies rapidly gain
resistance to chemical pesticides. The USDA recommends "an integrated program
that focuses on prevention and relies on cultural and biological control methods
when possible." While an initial pesticide application may be necessary
to control heavy infestations, repeated applications may lead to strains of
whiteflies that are resistant to pesticides, so only use of selective
insecticides is advised. Specific insecticide information and guidance for
the fig whitefly is available from the University of Florida. Care should be
taken to ensure that the insecticide used will not kill the natural predators
of whiteflies. For effective use of biological method after application of
pesticide, plant washing is advised prior to release of predators or
parasitoids. Pesticides used for whitefly control
usually contain neonicotinoid compounds as active ingredients: clothianidin,
dinotefuran, imidacloprid and thiamethoxam. Neonicotinoids can be
harmful if ingested. Rotation of insecticides from different families may
be effective at preventing the building of tolerance to the product.
Clothianidin and dinotefuran are of the same family. Spraying the leaves using
insecticidal soap is another, environmentally friendly, option.
= Nonchemical means = Biological methods have also been
proposed to control whitefly infestation, and may be paired with
chemical methods. Washing the plant, especially the undersides of leaves, may
help reduce the number of the pests on the plants and make their management by
other methods more effective. Whiteflies are also attracted by the color yellow,
so yellow sticky paper can serve as traps to monitor infestations. Dead
leaves or leaves that have been mostly eaten by whiteflies can be removed and
burned or carefully placed in closed bins to avoid reinfestation and
spreading of the disease. Early detection in combination with
hosing or vacuuming of diseased portions as well as removal of any section that
is heavily infested. Pesticide use is not ideal in the case of controlling
whitefly and widespread contamination can be costly; it is best to avoid this
problem with aggressive preventive measures.
Several predators and parasitoids may be effective in controlling whitefly
infestations, including green lacewings, ladybirds, minute pirate bugs, big-eyed
bugs, and damsel bugs. Integrated management of whiteflies can
as well be done using biopesticides based on microbials such as Beauveria
bassiana or Isaria fumosorosea. Green lacewing larvae have voracious
appetites, so will attack whiteflies, as well as other pests, including aphids,
mealybugs, spider mites, leafhopper nymphs, moth eggs, scales, and thrips.
They also can attack other insects, including caterpillars. They are
available as eggs from commercial insectaries, and will stay in a larval
stage after they hatch for one to three weeks. The adult insects can fly and
will feed only on pollen, honey, and nectar to reproduce. Repeated
application may be necessary and the eggs could be eaten before they hatch by
their natural predators, such as ants or mature green lacewings.
Ladybirds are also used. They eat mostly insect eggs, but will also feed on
beetle larvae, aphids, scale insects, and young caterpillars. Adults are often
collected when in a dormant state in the wild and shipped for use in pest
control; however, they may not stay in the location where they are released.
They do live for about a year and will continuously lay eggs and reproduce.
Spraying the bugs' wings with a sticky substance before release may hinder
their ability to fly. Companion plants
A number of plants can be intercropped with vegetables, in a garden setting,
serving as companion plants to protect against whiteflies.
For example, nasturtiums are thought to provide a defense to gooseberries or
tomatoes. They provide root chemicals that deter whiteflies.
Zinnias, conversely, attract predators that consume whiteflies, including
hummingbirds and predatory wasps and flies. Other plants with a similar
function include the hummingbird bush, pineapple sage, and bee balm. Each of
these plants also conceals the scent of nearby plants, making their detection by
some pest insects more difficult, as do most other mints.
Selected species The greenhouse whitefly, Trialeurodes
vaporariorum, is a major pest of many fruit, vegetable, and ornamental crops,
frequently being found in glasshouses. The citrus blackfly, Aleurocanthus
woglumi, is a whitefly which attacks citrus crops, and the silverleaf
whitefly, Bemisia argentifolii, is a pest of a number of agricultural and
ornamental crops. The cabbage whitefly, Aleyrodes
proletella is a pest of various Brassica species.
References External links
USDA Whitefly Knowledgebase on the UF / IFAS Featured Creatures
Website Aleurocanthus spiniferus, orange spiny
whitefly Aleurocanthus woglumi, citrus blackfly
Dialeurodes citri, citrus whitefly Metaleurodicus cardini, Cardin's
whitefly Parabemisia myricae, bayberry whitefly
Singhiella citrifolii, cloudywinged whitefly
Siphoninus phillyreae, ash whitefly CISR: Center for Invasive Species
Research, Ash Whitefly CISR: Center for Invasive Species
Research, Giant Whitefly CISR: Center for Invasive Species
Research, Silverleaf Whitefly The White-Files: a taxonomic checklist
of the world’s whiteflies by D. Ouvrard & J.H. Martin
http:www.whiteflyresearch.org