Silverleaf whitefly
Encyclopedia
The silverleaf whitefly (Bemisia tabaci, which is informally referred to as Sweetpotato or Silverleaf whitefly strain B) is one of several whiteflies
Whitefly
The whiteflies, comprising only the family Aleyrodidae, are small hemipterans. More than 1550 species have been described. Whiteflies typically feed on the underside of plant leaves.-Agricultural threat:...
that are currently important agricultural
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
pests
Pest (animal)
A pest is an animal which is detrimental to humans or human concerns. It is a loosely defined term, often overlapping with the related terms vermin, weeds, parasites and pathogens...
. The Silverleaf Whitefly is classified in the family Aleyrodidae, and is included in the large sub-order of insects, Heteroptera
Heteroptera
Heteroptera is a group of about 40,000 species of insects in the Hemiptera. Sometimes called "true bugs", that name more commonly refers to Hemiptera as a whole, and "typical bugs" might be used as a more unequivocal alternative since among the Hemiptera the heteropterans are most consistently and...
. The Silverleaf whitefly was first found in the United States in poinsettia
Poinsettia
Euphorbia pulcherrima, commonly known as Zack Wood or noche buena, is a species of flowering plant indigenous to Mexico and Central America. The name "poinsettia" is after Joel Roberts Poinsett, the first United States Minister to Mexico, who introduced the plant into the US in 1825...
crops Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
during the mid-1980s. It was found to have moved to tomato
Tomato
The word "tomato" may refer to the plant or the edible, typically red, fruit which it bears. Originating in South America, the tomato was spread around the world following the Spanish colonization of the Americas, and its many varieties are now widely grown, often in greenhouses in cooler...
es, other fruit and vegetable crops less than a year later. Within five years, the Silverleaf whitefly had caused over $
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
100 million in damage to the Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
and California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
agriculture industries.
The whitefly thrives worldwide in tropical, subtropical, and less predominately in temperate habitats. Environments with cold temperature often lead to the mortality of both adult and larvae of the species. The whitefly can be confused with other insects in its species such as the common fruitfly
Drosophila melanogaster
Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...
but with close inspection, the whitefly is slightly smaller and has a distinct wing color that helps to differentiate it from other insects.
Anatomy and life cycle
During the adult stages of the silverleaf whitefly, the body expands up to 0.8mm in length and has a snow-white color, which is attributed by the secretion of wax across its wings and body. During feeding or resting stages the whitefly adult covers its body over with its wings. When depositing eggs, the females will lay 50 to 400 eggs ranging from 0.10mm-0.25mm on the under part of leaves. Female whiteflies are diploid and emerge from fertilized eggs whereas male whiteflies are haploid and emerge from unfertilized eggs. Eggs are laid in groups, being small in size with dimensions of 0.2 mm wide and .1mm in height. Eggs are initially whitish in color and change to a brown color towards the time of hatching within 5 to 7 days. After the egg stage, the whitefly hatchling develops through four instarInstar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
stages.
In the first instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
, commonly called the crawler, the nymph is 0.3mm in size and grows to be 0.6 mm till the fourth instar stage. During the first instar stage the body is greenish in color and flat in body structure. The mobile whitefly nymphs walks to find a suitable area on the leaf with adequate nutrients and molts
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
into four other instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
or nymphal stages over the span of 40–50 days until it reaches adulthood. During molting,the flies shed silver skins, which are left on the leaves. During the instar phases, the whitefly maintains an opaque
Opacity (optics)
Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shielding material, glass, etc...
white appearance and does not move from the feeding site the crawler originally chooses. At the feeding site the nymphs use parts of their mouth to stab into the plant and consume the plant’s juices. The stage following the nymph stages is the pupal stage
Pupa
A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...
where the eyes become a deep red color, body color is yellow and the body structure thickening in size. After development is completed, adult whiteflies are approximately four times the size of its egg with light yellow bodies and white wings.
Native/original community
Research indicates that the silverleaf whitefly likely came from India. Since the whitefly is predominately associated with areas exhibiting tropical/subtropical climates, the focus shifts to how these insects attained access to crops in habitats with temperateTemperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
climates. One hypothesis
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
suggests that the transfer of decorative plants from tropical regions may have aided in the spread of the silverleaf whiteflies to temperate environments. The adaptations of the whitefly to plants facilitate the spread of dangerous plant viruses, which these insects are notorious for transmitting. Plants which are affected by the whitefly include: tomato
Tomato
The word "tomato" may refer to the plant or the edible, typically red, fruit which it bears. Originating in South America, the tomato was spread around the world following the Spanish colonization of the Americas, and its many varieties are now widely grown, often in greenhouses in cooler...
es, squash, poinsettia
Poinsettia
Euphorbia pulcherrima, commonly known as Zack Wood or noche buena, is a species of flowering plant indigenous to Mexico and Central America. The name "poinsettia" is after Joel Roberts Poinsett, the first United States Minister to Mexico, who introduced the plant into the US in 1825...
, cucumber
Cucumber
The cucumber is a widely cultivated plant in the gourd family Cucurbitaceae, which includes squash, and in the same genus as the muskmelon. The plant is a creeping vine which bears cylindrical edible fruit when ripe. There are three main varieties of cucumber: "slicing", "pickling", and...
, eggplants, okra
Okra
Okra is a flowering plant in the mallow family. It is valued for its edible green seed pods. The geographical origin of okra is disputed, with supporters of South Asian, Ethiopian and West African origins...
, beans and cotton
Cotton
Cotton is a soft, fluffy staple fiber that grows in a boll, or protective capsule, around the seeds of cotton plants of the genus Gossypium. The fiber is almost pure cellulose. The botanical purpose of cotton fiber is to aid in seed dispersal....
. Other common plant damages of whitefly include: removing plant sap, breakdown of the leaves of the plant, and leaf shedding.
Ecological impact
The silverleaf whitefly is considered an invasive speciesInvasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
in all areas it inhabits in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
as well as Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and several European countries. It was classified as an agricultural pest in Greece
Greece
Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....
around 1889 and had a significant impact on tobacco crops there. The first whitefly found in the United States dates back to 1897, and was found on a crop of sweet potatoes.
This tiny insect wreaks havoc in two simple ways. First, the silverleaf whitefly, a parasite, feeds off of its host plants by piercing the phloem
Phloem
In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...
or lower leaf surfaces with its mouth and removing nutrients. Affected areas of the plant may develop chlorotic spots, whither, or lose leaves. Whiteflies also produce a sticky substance called honeydew
Honeydew (secretion)
Honeydew is a sugar-rich sticky liquid, secreted by aphids and some scale insects as they feed on plant sap. When their mouthpart penetrates the phloem, the sugary, high-pressure liquid is forced out of the gut's terminal opening. Honeydew is particularly common as a secretion in the Hemipteran...
, which is left behind on the host. Honeydew can induce the growth of sooty mold
Sooty mold
Sooty molds are Ascomycete fungi which grow on plant exudates and the sugary honeydew secreted by insects such as aphids, scales, the whitefly, and other insects which suck sap from their host plants. The name itself is descriptive, as sooty mold is a black, powdery coating adhering to the leaves...
s, which can then reduce the plants ability to absorb light. This results in less growth, lower yield, and poor quality plants. It also requires that crops be thoroughly washed after harvesting, which raises processing costs for the grower.
The second problem with the silverleaf whitefly is its notorious status as a vector for plant disease. It has been transmitting gemniviruses such as lettuce infectious yellow virus, tomato yellow leaf curl virus
Tomato yellow leaf curl virus
Tomato yellow leaf curl virus is a plant pathogenic virus of the family Geminiviridae.-External links:***...
, and African cassava mosaic virus
African cassava mosaic virus
African cassava mosaic virus is a plant pathogenic virus of the family Geminiviridae that may cause either a mosaic appearance to plant leaves, or chlorosis, a loss of chlorophyll. In Manihot esculenta , a highly valuable African food crop, the virus is the only known plant virus for cassava and...
for years and over many continents.
Bemisia tabacia became a serious issue in crops across the southwestern United States and Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
in the 1980s. Scientists speculate that this pest was introduced via infested ornamental plants brought into the United States at this time. Florida’s poinsettia greenhouses were crippled by the pest beginning in 1986, and by 1991, the whitefly infestation had spread through Georgia, Louisiana, Texas, New Mexico, and Arizona to plague crop growers in California. California, the state that produces approximately 90% of the United States’ winter vegetable crop, has incurred an estimated $500 million in crop damage due to silverleaf whitefly populations. Across the plant industry, this is thought to cost the state $774 million in private sector plant sales, 12,540 jobs, and $112.5 million in personal income. On a national scale, the United States has suffered crop and ornamental plant damages in excess of $1 billion.
In particular, the whitefly is a devastating pest simply because it feeds on over 500 hosts. Included in its host domain are agricultural crops such as tomatoes, squash, broccoli, cauliflower, cabbage, melons, cotton, carrots, sweet potato, cucumber, and pumpkin, and ornamental plants such as poinsettia
Poinsettia
Euphorbia pulcherrima, commonly known as Zack Wood or noche buena, is a species of flowering plant indigenous to Mexico and Central America. The name "poinsettia" is after Joel Roberts Poinsett, the first United States Minister to Mexico, who introduced the plant into the US in 1825...
, crepe myrtle, rose bushes, lantana
Lantana
Lantana is a genus of about 150 species of perennial flowering plants in the verbena family, Verbenaceae. They are native to tropical regions of the Americas and Africa but exist as an introduced species in numerous areas, especially in the Australian-Pacific region. The genus includes both...
, and lilies. It can cause specific damage to certain host plants, like "silverleaf" on squash, irregular ripening of tomatoes, whitestalk in broccoli and cauliflower, white stem in poinsettia, and light root in carrots.
The whitefly has many natural predators including parasitoid
Parasitoid
A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism in a relationship that is in essence parasitic; unlike a true parasite, however, it ultimately sterilises or kills, and sometimes consumes, the host...
s and various arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s. More on this subject can be found below in the section titled natural enemies.
Integrated pest management
The silverleaf whitefly is a very costly and common pest to the agricultural world. It destroys crops and causes the transfer of a variety of viruses that affect agricultural plants in harmful ways such as the earlier ripening of tomatoes through the tomato yellow leaf curl virusTomato yellow leaf curl virus
Tomato yellow leaf curl virus is a plant pathogenic virus of the family Geminiviridae.-External links:***...
. As silverleaf whiteflies continue to destroy crops, scientists are trying to find ways to combat these agricultural pests. Some major controls for this pest have come from the development of oils from agricultural wastes, usage of natural enemies such as the four species of Eretmocerus (Eretmocerus sp, Eretmocerus mundus, Eretmocerus hayati, and Eretmocerus emiratus), employment of trap crops, release of insect growth regulators, and implementation of the Light-Emitting Diode Equipped CC trap (LED-CC).
Most of the control tools that have been created affect the plant and soil properties at a minimal level. Scientists are currently focusing on targeting the whitefly through safe mechanisms that do not cause pollution or contamination (i.e. insecticides). It is important to be able to reduce the number of B. tabaci individuals that settle on plants as to decrease plant damages such as those caused by viral transmissions. This pest can be hindered by reducing settling, decreasing oviposition
Oviposition
Oviposition is the process of laying eggs by oviparous animals.Some arthropods, for example, lay their eggs with an organ called the ovipositor.Fish , amphibians, reptiles, birds and monetremata also lay eggs....
, and abating its population development.
Biological controls
Classical biological control tends to be the only long-term sustainable solution to controlling exotic pests. One of the main key issues of this type of control is its lack of predictability of success and establishment of the controlling agents. The solution to this problem is finding a way to transition biological control as an empirical method to a more reliable, predictive science.Entomologists with the U.S. Arid-Land Agricultural Research Center identified the most common causes of death of the whitefly which included predatory insects, parasites, and weather induced dislodgement. They emphasize the importance of exploiting the use of natural predators and have identified predators by the use of enzyme-linked immune sorbent assay (ELISA). Through experimentation it was found that the use of the biological controls and insect growth regulators produces a higher predator-to-prey ratio. Therefore insect growth regulators, such as buprofezin and pyriproxyfen
Pyriproxyfen
Pyriproxyfen is a pyridine based pesticide which is found to be effective against a variety of arthropoda. It was introduced to the US in 1996 to protect cotton crops against whitefly...
, conserve natural predators as oppose to conventional insecticides, which can indiscriminately kill both predator and prey populations.
Natural enemies
Natural enemies are highly effective as biological controls. Parasitoids, predators, and pathogens species of the whitefly keep the population under control. The four Old World species of Eretmocerus (Eretmocerus mundus, Eretmocerus hayati and Eretmocerus emiratus) established in the Western United States are a group of genetic individuals of related taxa that are parasitoidParasitoid
A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism in a relationship that is in essence parasitic; unlike a true parasite, however, it ultimately sterilises or kills, and sometimes consumes, the host...
s of B. tabaci and serve as biological control agents. Scientists are considering the idea of releasing these parasites in order to be able to control their host’s population growth and save the destruction of important crops. Consequently, not all Eretmocerus can be successfully transplanted into areas where the whiteflies are present due to differences in climate preference. For example, the species Eretmocerus melanoscutus failed to establish in the western United States due to climate issues. Therefore one of the important factors that are involved in successfully implementing specialist parasitoids is the climate. Goolsby (2005) mentions that different species of Eretmocerus are matched with the climate they are able to survive in. The success of the species of Eretmocerus in the USA can be contributed to the smaller host range, better climatic adaptation, and higher attack rate. Other natural species of the B. tabaci include several species of wasps, bigeyed bugs, lacewing larvae, and lady beetle
Coccinellidae
Coccinellidae is a family of beetles, known variously as ladybirds , or ladybugs . Scientists increasingly prefer the names ladybird beetles or lady beetles as these insects are not true bugs...
larvae, which all prey on the nymphs of the whitefly.
There are eight different arthropod orders that attack B. tabaci. These include members of the families Phytoseiidae
Phytoseiidae
Phytoseiidae is a family of mites which feed on thrips and other mite species. They are often used as a biological control agent for managing mite pests.-Subfamilies:* Amblyseiinae Muma, 1961* Phytoseiinae Berlese, 1916* Typhlodrominae Scheuten, 1857...
, Coccinellidae
Coccinellidae
Coccinellidae is a family of beetles, known variously as ladybirds , or ladybugs . Scientists increasingly prefer the names ladybird beetles or lady beetles as these insects are not true bugs...
, Syrphidae, Anthocoridae
Anthocoridae
The Anthocoridae are a family of bugs, commonly called minute pirate bugs or flower bugs.-Name:The vernacular name probably stems from the notion that these very small animals can do much pain to humans, just like small pirate vessels can do so to big ships.The scientific name is a combination of...
, Nabidae
Nabidae
The insect family Nabidae contains the damsel bugs. The terms damsel bug and nabid are synonymous. There are over 400 species. They are soft-bodied, elongate, winged terrestrial predators. Many damsel bugs catch and hold prey with their forelegs, similar to mantids...
, and Miridae
Miridae
The large and diverse insect family Miridae contains the plant bugs, leaf bugs, and grass bugs, and may also be known as capsid bugs. It is the largest family of true bugs belonging to the suborder Heteroptera, with over 10,000 known species and new ones constantly being described...
, Chrysopidae
Chrysopidae
Green lacewings are insects in the large family Chrysopidae of the order Neuroptera. There are about 85 genera and 1,300–2,000 species in this widespread group...
and Coniopterygidae
Coniopterygidae
The dustywings, Coniopterygidae, are a family of Pterygota of the net-winged insect order . About 460 living species are known...
. There are currently four species that are commercially available; they include Delphastus pusillus
Delphastus pusillus
Delphastus pusillus is a small ladybird beetle which preys on all species and stages of whitefly, but prefers eggs and nymphs. The adults are small , shiny, black beetles. Newly-emerged adults are pale-brown to almost white. They eventually turn black with a brown head. The eggs are 0.2 mm...
, Macrolophus caliginosus, C. carnea, and Chrysoperla rufilabris. D. pusillus are a small, shiny black beetles species that suck-out the inside contents of the silverleaf whitefly by piercing its shell. Adults and larval stages of this beetle agent feed at all life stages of the pest. C. rufilabris is only able to feed on the immature stages or the larval stages of B. tabaci.
Another natural mechanism of controlling the population of B. tabaci is the use of fungal pathogens. The most commonly known pathogens to the whitefly pest are Paecilomyces fumosoroseus
Paecilomyces fumosoroseus
Paecilomyces fumosoroseus is a microscopic fungus that infects and kills insects. It shows promise as a biological pesticide with an extensive host range.-Life cycle:...
, Aschersonia aleyrodis, Verticillium lecanii, and Beauveria bassiana
Beauveria bassiana
Beauveria bassiana is a fungus that grows naturally in soils throughout the world and acts as a parasite on various arthropod species, causing white muscardine disease; it thus belongs to the entomopathogenic fungi. It is being used as a biological insecticide to control a number of pests such as...
. When spore solutions of V. lecanii are sprayed on eggs, first, second, and third instar nymphs of B. tabaci approximately 89% to 90% of these eggs are killed. There has been resistant traits developed in the whitefly to its fungal pathogens. For example, whitefly pests have grown resistant to infection by V. lecanii.
B. bassiana is only an effective biological control agent at a maximum temperature of 20°C and a humidity level greater than 96%. Not enough studies have been conducted to show the productiveness of fungal pathogen in the real world environment. Much of the success of this biological control on B. tabaci has been conducted in the laboratory. However, it can be concluded though that when the fungal pathogen is combined with an insecticide, the synergistic effect of the two will induce a higher mortality rate of the whitefly. P. fumosoroseus has a broad host range but can attack silverleaf whiteflies at a variety of life stages and these include eggs, nymphs, pupae, and adults stages. On the other hand, A. aleyrodis only infects and destroys nymphs and pupae.
Another natural enemy of the whitefly are parasitoids, which kill their host once their development has been completed. There are three hymenopterous families to which whitefly parasitoids are affiliated with. These families are Platygasteridae, Aphelinidae
Aphelinidae
Aphelinidae is a moderate-sized family of tiny parasitic wasps, with some 1160 described species in some 35 genera. These minute insects are challenging to study as they deteriorate rapidly after death unless extreme care is taken , making identification of most museum specimens difficult...
, and the Eulophidae
Eulophidae
Eulophidae is a large family of hymenopteran insects, with over 4,300 described species in some 300 genera . The family as presently defined also includes the genus Elasmus, which was previously treated as a separate family, "Elasmidae", and is now treated as a subfamily of Eulophidae...
. The best studied of these whitefly parasitoids are E. formosa and Eretmocerus eremicus, both of which are commercially available. The two most common and well studied parasitoids specific to the silverleaf whitefly include Encarsia formosa
Encarsia formosa
Encarsia formosa is a species of wasp and a well known parasitoid of greenhouse whitefly. The tiny females are black with a yellow abdomen and opalescent wings. There are many fewer males than females...
("Beltsville Strain") and Eretmocerus sp. E. formosa "Beltsville Strain" however, is unable to control B. tabaci biotype B in commercial greenhouses; it is only able to control the species in small experimental greenhouses. In an experiment done by the Hoddle laboratory, the release of three or more E. formosa on B. tabaci per week failed to control the pure population of the species on poinsettia plants because wasps that are reared in the B. tabaci are less fecund, have a slower development, and fail to allow immature parasitoids to survive and develop. The species E. formosa works much better at controlling the whitefly species T. vaporariorum rather than B. tabaci. On the other hand, Eretmocerus sp is much better at controlling species of silverleaf whitefly rather than E. formosa "Beltsville Strain." In an experiment done again by the Hoddle laboratory, the release of three female wasps of the species Eretmocerus sp. were able to effectively eliminate patches of the fly nymphs right after discovery. The parasitoid is faster at searching for patches of nymphs of its host species and is consistent with controlling the population. Eretmocerus sp. are bi-parental ecto-endoparasites meaning that parents lay their eggs on the outside of the fly, as the larvae grows it penetrates the fly and continues its growth and development inside the host. Plants growers today have been successfully able to control the population of B. tabaci by using the variable release strategy. In the variable release strategy, six female parasitoids are released per week for the first half of the growing season, while only one female is released per week for the remaining of the season. Thus, the effectiveness of the parasitoid can be improved by releasing varying amounts of the parasitoids per week so that search rate is low. If natural enemies are not able to control the pest population at low levels due to a significant increase in pest, an insecticide compatible with the biological control agent should be used to help keep the population at low levels again.
Natural oils
One of the important tools for controlling the silverleaf whitefly population is through the usage of natural oils. Currently, the most effective oil in the market is the ultra-fine oil, which is a paraffinParaffin
In chemistry, paraffin is a term that can be used synonymously with "alkane", indicating hydrocarbons with the general formula CnH2n+2. Paraffin wax refers to a mixture of alkanes that falls within the 20 ≤ n ≤ 40 range; they are found in the solid state at room temperature and begin to enter the...
ic oil product that reduces the settlement of the adult flies, decreases oviposition
Oviposition
Oviposition is the process of laying eggs by oviparous animals.Some arthropods, for example, lay their eggs with an organ called the ovipositor.Fish , amphibians, reptiles, birds and monetremata also lay eggs....
, and abates the transmission of the tomato yellow leaf curl virus
Tomato yellow leaf curl virus
Tomato yellow leaf curl virus is a plant pathogenic virus of the family Geminiviridae.-External links:***...
. Ultra-fine oil’s effect can be strengthened through the combination with oils such as limonene
Limonene
Limonene is a colourless liquid hydrocarbon classified as a cyclic terpene. The more common D isomer possesses a strong smell of oranges. It is used in chemical synthesis as a precursor to carvone and as a renewably-based solvent in cleaning products....
or citronellal
Citronellal
Citronellal or rhodinal or 3,7-dimethyloct-6-en-1-al is a monoterpenoid, the main component in the mixture of terpenoid chemical compounds that give citronella oil its distinctive lemon scent....
. On the other hand, olive oil is highly effective in controlling the number of flies that infect the leaves of their host plants and virus transfer. Other oils such as cottonseed, castor, peanut, soybean, and sunflower can also be used to reduce the settling and oviposition of B. tabaci adults. Out of this group of oil, peanut was the most effective in reducing the population. All of these oils cause direct mortality to all immature life stages of the silverleaf whitefly once the life stages come into contact with the oils that have been sprayed on the leaves. The oil extracted from the seeds of sugar apple is as effective against the whitefly as the use of insecticides. The seed oil causes the silverleaf whitefly nymph to shrink in size and therefore detach from the tomato plant leading to starvation, as nymphs require close contact to the leaf to properly feed. In addition, the fourth nymphal stage is the most vulnerable to predation. Spraying a strong concentration on possible areas of nymph habitation can make oil a high-quality treatment. Sugar apple seed oil is not phytotoxic to tomato plants of any concentrations and reduces the survival rate of the pest. Spraying oil on leaves that have been infested or can be potentially infested will help reduce the number of silverleaf whiteflies that will reach the adult stage. The reduction of settling through various mechanisms can also help limit the amount of plants that become infected with viruses transmitted by these pests.
Insect growth regulators
Insecticides are known to be costly, and there is also an increasing resistance of the whitefly to insecticides. In a study of the silverleaf whitefly, a pest of other curcurbits family plants including zucchini squash, cucumber, and pumpkin was examined. In particular squash is infected with Squash silverleaf, which is a serious physiological disorder that involves silvering of the surface of leaves, reduction in chlorophyllChlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
concentrations and higher reflectance. To combat this disease, insect growth regulator
Insect growth regulator
An insect growth regulator is a substance that inhibits the life cycle of an insect. IGRs are typically used to control populations of harmful pests, such as cockroaches or fleas.- Advantages :...
(IGR), pyriproxyfen
Pyriproxyfen
Pyriproxyfen is a pyridine based pesticide which is found to be effective against a variety of arthropoda. It was introduced to the US in 1996 to protect cotton crops against whitefly...
has been used. This hormone is a juvenile hormone analogue, which affects hormonal balance and chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
in premature insects, which causes deformation and death during molting and pupation stages. Therefore making pyriproxyfen effective in reducing the whitefly populations. It reduces the fruit damages, and increases the size, weight, and quality of fruit. Effectively, IGR does not kill adult whiteflies, but instead sterilizes the eggs of those adults that are treated. It is also a potent inhibitor of embryogenesis
Embryogenesis
Embryogenesis is the process by which the embryo is formed and develops, until it develops into a fetus.Embryogenesis starts with the fertilization of the ovum by sperm. The fertilized ovum is referred to as a zygote...
, adult formation and metamorphosis
Metamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...
. It kills larva and keeps adults from completing the last nymphal stage. The IGR has low toxicity to mammals, fish, birds and bumblebees.
Man-made traps and covers
In addition, the Light-Emitting Diode Equipped CC trap (LED-CC) was developed by plant physiologist Chang-Chi Chu and Thomas Henneberry. Originally, the trap was used to monitor population of silverleaf whitefly populations, but as the trap improved in its effectiveness it was used in control programs to limit whitefly pest populations. The trap itself includes a green LED light that attracts and traps the whiteflies. The LED device works best at night,and is inexpensive and durable. In addition, the LED is parasite friendly and therefore does not harm predators of the whitefly. The trap also does not utilize pesticides.Another technique used to reduce virus damage include the use of FRC known as floating row covers, which are covers used to keep plants from exposure from pests. Field studies have been conducted in Australia and have shown that the use of FRCs and IGR increase the yield of harvested fruit and quality. The row covers have been known to reduce virus damage to cucurbits.
Trap crops
Another important control is the use of other crops as a source of trap crops. Squashes can act as trap crops for the silverleaf whitefly due to the flies’ attractiveness to these crops. Silverleaf whiteflies are actually more attracted to the squash crop than they are to the tomato plant. When squash serves as a trap crop, the tomato yellow curl leaf virus can be controlled and limited. Scientific experiments show in the fields that growing squash crops around the areas where tomato plants can be found is a useful manipulation in regulating the silverleaf whitefly population as well as the transmission of TYLCV. Other plants that can serve as trap crops include cantaloupe and cucumber.Cultural controls
Through a cultural control method, different planting areas can limit the amount of B. tabaci infected plants. Planting different host crops away from each other will decrease the number of plants the flies will be able to infect. Thus, the best control is to maximize the distance and time interval between host crops. Good sanitation in winter and spring crops is also required for the maintenance and control of the fly population. Weeds and host crop residues must be removed immediately to avoid infestation. Silver/aluminum cover mulches can repel the adult silverleaf whitefly. Thus, when planting seeds, placing a reflective polyethylene mulch on planting beds will significantly reduce the rate of colonization.Cultural controls are very important to crops such as vegetables and fruit. For example, in the family of Cucurbitaceae family, vegetables such as watermelon and squash contract squash vein yellowing virus (SqVYV) by the silverleaf whitefly. The SqVYV virus discovered by plant pathologist Benny Bruton and Shaker Kousik is essentially a crippling disease of the watermelon, which leads to the vine of the watermelon to collapse, causing the death of the watermelon before harvest. Kousik and pathologist Scott Adkins
Scott Adkins
Scott Adkins is an English actor and martial artist who is perhaps best known for playing Yuri Boyka in Undisputed II: Last Man Standing and Undisputed III: Redemption and Bradley Hume in Holby City and Ed Russell in Mile High...
at ARS Subtropical Plant Pathology Research Unit worked together in screening the watermelon germplasm for resistance to SqVYV as to search for potential sources of resistance in wild-type watermelon. Kousik examined different combinations of insecticides and silver plastic mulch that could be used to reduce the whitefly populations.
Summary
Under the integrated pest management plan, there are several different ways to control and manage the pest population of B. tabaci. The mechanical control used to control the species population is through the use of natural oils such as sugar apple and the more common type of insecticides. From experimentation, scientists have seen that the sugar apple oil (and other natural oils) has the same strength as insecticides but with the benefit of not causing pollution. Through cultural control methods, the flies are regulated through the process of trap crops and man-made traps, such as the Light-emitting diode. The most important and pollution free method of controlling the amount of damage down by the silverleaf whitefly annually is the usage of natural enemies (i.e. pathogens, parasites, and predators). There are a variety of predators and several different pathogens and parasites that can effectively keep the pest population under a minimal level. The most common parasitoid of the silverleaf is Eretmocerus, a wasp species that finishes its development inside the host, killing the host once it reaches adulthood. Most of the predators of B. tabaci tend to just eat out the insides of the pest, while pathogens transfer deadly viruses.External links
- silverleaf whitefly on the University of FloridaUniversity of FloridaThe University of Florida is an American public land-grant, sea-grant, and space-grant research university located on a campus in Gainesville, Florida. The university traces its historical origins to 1853, and has operated continuously on its present Gainesville campus since September 1906...
/ Institute of Food and Agricultural SciencesInstitute of Food and Agricultural SciencesThe University of Florida’s Institute of Food and Agricultural Sciences is a federal-state-county partnership dedicated to developing knowledge in agriculture, human and natural resources, and the life sciences, and enhancing and sustaining the quality of human life by making that information...
Featured Creatures - USDA Whitefly Knowledgebase
- CISR – Silverleaf Whitefly Center for Invasive Species Research summary on Silverleaf Whitefly
- Species Profile – Silverleaf Whitefly (Bemisia argentifolii), National Invasive Species Information Center, United States National Agricultural LibraryUnited States National Agricultural LibraryThe United States National Agricultural Library is one of the world's largest agricultural research libraries, and serves as a National Library of the United States and as the library of the United States Department of Agriculture...
. Lists general information and resources for Silverleaf Whitefly.