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Silverleaf whitefly

Article author: Erfan Vafaie
Most recently reviewed by: Pat Porter & David Kerns & Suhas Vyavhare (2018)

Common Name(s): Silverleaf Whitefly, Sweetpotato whitefly

Description

The silverleaf whitefly, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae), is a global pest of many economically important host plants (Simmons et al. 2008) such as eggplant, tomato, sweet potato, cucumber, garden bean (Tsai & Wang 1996), cotton, and poinsettias, to name a few. Similar to other sucking insect pests, silverleaf whiteflies reduce plant vigor, growth, and can even cause mortality by piercing plant tissue and feeding on plant phloem (Bryne & Miller 1990). Whiteflies excrete waste as a sugary solution, known as honeydew. Excessive honeydew can result in inoculation of a complex of fungi, resulting in a black layer or crust forming on the surface, commonly referred to as sooty mold. In addition to causing detrimental damage by feeding, B. tabaci has been recorded to vector more than 100 plant viruses (Jones 2003), which can result in rapid widespread crop loss. Some of these viruses in Texas include Cucurbit leaf curl virus (Brown et al. 2000) and cucurbit yellow stunting disorder virus (Kao et al. 2000).

Adult whiteflies resemble very small (1 mm or 3/64-in) white moths. When disturbed, adult whiteflies will often leap off the plant and fly a short distance before landing on a nearby surface. Whitefly nymphs, especially younger nymphs, can be hard to see with the naked eye. Whitefly nymphs often blend with the leaf due to their color and relatively flat shape. The final nymph instar is often referred to as a pupa, when they become darker yellow color and are more round, making them easier to distinguish on the leaf. Once they emerge as adults, their shed ‘skin’ stays on the leaf, known as an exuvia. The exuviae stay on the leaf and resemble a small empty shell.

Adult silverleaf whiteflies can be confused for other whiteflies that may occur in Texas, with two other common ones being the badedwing whitefly (Trialeurodes abutiloneus) and greenhouse whitefly (Trialeurodes vaporariorum).

Origin and Distribution

Silverleaf whiteflies are considered a global pest, however there are certain biotypes or species that are more prevalent in different parts of the world. Texas has populations of both MEAM1 (B biotype) and MED (Q biotype) whitefly.

Life Cycle

Whiteflies are closely related to mealybugs and scale insects. Female adult whiteflies lay eggs, often in a circular pattern as result of the female using her feeding proboscis as a pivot while laying eggs. Eggs are pear-shaped and approximately 0.2 mm long (CABI MEAM1). On cotton, eggs take between 5 to 22.5 days to emerge as crawlers when held at 16.7ºC (62F) or 32.5ºC (90.5) (Butler et al. 1983), respectively. After emerging from the eggs, a mobile stage known as “crawlers” find a place nearby to settle. Once settled, whitefly nymphs are considered rather immobile until after metamorphosis. Bemisia tabaci undergo four instar stages before pupation and becoming a winged adult. The total development time from egg to adult varies from 16.6 days at 30ºC (86F) to 65.1 days at 14.9ºC (59F) in cotton (Butler et al. 1983). Adult females lay approximately 72 – 81 eggs and survive an average of 8 to 10.4 days in controlled studies (Butler et al. 1983).

Management

If you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.

Silverleaf whitefly taxonomy is currently under revision, but it is generally agreed upon that there are specific groups of silverleaf whiteflies that exhibit different host plant preferences, reproductive rates, and resistance to insecticides. Originally, it was thought that silverleaf whiteflies were composed of several different ‘biotypes’, a couple well-known ones including the “B” (MEAM1) and “Q” (MED) biotypes, but now has been proposed to be made up of at least 34 morphologically indistinguishable species (Tay et al. 2012). The MEAM1 whiteflies have greater reproductive potential than the MED whiteflies, however the MED whiteflies are resistant to several different insecticides, such as pyriproxyfen and imidacloprid. Growers are encouraged to either use biological control to prevent further rise of resistance to insecticides, or rotate between insecticides that are known to be effective against both MEAM1 and MED whiteflies. See “Related Publications” below for more information.

Whitefly populations can be monitored using yellow sticky cards or searching the undersides of leaves for eggs, nymphs, pupae, exuviae, or adults. Look for other signs of infestation, such as honeydew, sooty mold, or chlorosis.

In many regions of Europe and North America, silverleaf whiteflies in protected culture (i.e. greenhouses) are managed through regular releases of biological control agents. In the USA, commercially available biological control agents that have demonstrated potential management of silverleaf whiteflies include Eretmocerus eremicus (Hoddle and van Driesche) and Amblyseius swirskii (Calvo et al. 2010).

Insecticidal management of silverleaf whiteflies are highly dependent on commodity, location, setting, and thresholds. Some active ingredients that have demonstrated efficacy against both MEAM1 and MED silverleaf whiteflies include:

  • Abamectin
  • Abamectin + Bifenthrin
  • Acetamiprid
  • Beauvaria bassiana
  • Cyantraniliprole
  • Dinotefuran
  • Isaria fumosorosea
  • Horticultural Oil*
  • Insecticidal Soap*
  • Pyridaben
  • Pyrifluquinazon
  • Spiromesifen
  • Spirotetramat
  • Thiamethoxam

(Kumar et al. 2017)
*Beware of application in extreme heat and exposure to sun. Can cause leaf burn/phytotoxicity.

For more information, consult one of our related publications below for whitefly management specific to your situation.

Related Publications

CABI Bemisia tabaci (MEAM1) fact sheet: https://www.cabi.org/isc/datasheet/8925#8440C199-FEDE-40E6-AED0-E7C195DC4E5B

CABI Bemisia tabaci (MED) fact sheet: https://www.cabi.org/isc/datasheet/112682

Byrne, David N. (1991). Whitefly biology. Annual Review of Entomology, 36: 431 – 457.

Suhas et al. (2018). Managing Cotton Insects in Texas. Texas A&M AgriLife Extension. https://agrilife.org/extensionento/resources/management-guides/managing-cotton-insects-in-texas/other-pests/

Kumar et al. (2017). Whitefly (Bemisia tabaci) management program for ornamental plants. UF/IFAS Extension. https://mrec.ifas.ufl.edu/lso/bemisia/Documents/EDIS-Whitefly-Management-Program.pdf

Citations

Brown et al. (2000). Cucurbit leaf curl virus, a new whitefly transmitted geminivirus in Arizona, Texas, and Mexico. The American Phytopathological Society, 84(7): 809.

Butler et al. (1983). Bemisia tabaci (Homoptera: Aleyrodidae): Development, oviposition, and longevity in relation to temperature. Annals of the Entomological Society of America, 76: 310 – 313.

Byrne & Miller (1990). Carbohydrate and amino acid composition of phloem sap and honeydew produced by Bemisia tabaciJournal of Insect Physiology, 36: 433 – 439.

CABI Bemisia tabaci (MEAM1) fact sheet: https://www.cabi.org/isc/datasheet/8925#8440C199-FEDE-40E6-AED0-E7C195DC4E5B

Calvo et al. (2011). Control of Bemisia tabaci and Frankliniella occidentalis in cucumber by Amblyseius swirskii. 56(2): 185 – 192.

Hoddle, M. and van Driesche, R. G. (1999). Evaluation of inundative release of Eretmocerus eremicus and Encarsia formosa Beltsville strain in commercial greenhouses for control of Bemisia argentifolii (Hemiptera: Aleyrodidae) on poinsettia stock plants. Biology and Microbial Control, 92(4): 811 – 824.

Jones D (2003). Plant viruses transmitted by whiteflies. European Journal of Plant Pathology, 109: 197 – 221.

Kao et al. (2000). First report of Cucurbit yellow stunting disorder virus (genus Crinivirus) in North America. The American Phytopathological Society, 84(1): 101.

Kumar et al. (2017). Whitefly (Bemisia tabaci) management program for ornamental plants. UF/IFAS Extension. https://mrec.ifas.ufl.edu/lso/bemisia/Documents/EDIS-Whitefly-Management-Program.pdf

Simmons et al. (2008). Forty-nine new host plant species for Bemisia tabaci (Hemiptera: Aleyrodidae). Entomological Science, 11: 385 – 390.

Tay et al. (2012). Will the real Bemisia tabaci please stand up? PLoS ONE, 7(11): 7 – 11.

Tsai & Wang (1996). Development and reproduction of Bemisia argentifolii (Homoptera: Aleyrodidae) on five host plants. Environmental Entomology, 25(4): 810 – 816.

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Grasshoppers

Article author: Pat Porter
Most recently reviewed by: Ed Bynum (2018)

Common Name(s): Differential Grasshopper, Grasshoppers, lubber grasshopper, migratory grasshopper, Packard grasshopper, red-legged grasshopper, two-striped grasshopper

Description

Grasshoppers undergo gradual metamorphosis as the nymphs (immature insects) molt to the next growth stage. This means that nymphs look very much like adults, except that the nymphs do not have fully developed wings. If a grasshopper’s wings are fully developed, then it is an adult. The long hind pair of legs is well adapted for jumping, and adults are good fliers over short distances.

There are many color variations according to species, and many species are well camouflaged and difficult to see unless they move. Other species are brightly colored.

All grasshoppers have mandibles (teeth) and damage plants by chewing chunks of tissue from leaves and other plant parts. The feeding usually begins on outside edges of leaves and the chewed area has ragged or irregular edges. This often looks quite different from the smoother, more even damage done by caterpillars.

 

Origin and Distribution

Grasshoppers are distributed worldwide and occasionally reach serious pest outbreak status causing major crop loss. Occasionally, large flights of grasshoppers are detected on radar.

Habitat & Hosts

Almost any type of plant including corn, alfalfa, Bermudagrass, cotton, millet, peanut, rice, ryegrass, sorghum, Sudangrass, soybean, sugarcane, vegetables, wheat, flowers and landscape plants.

Life Cycle

Grasshoppers deposit their eggs 1⁄2 to 2 inches below the soil surface in pod-like structures. Each egg pod consists of 20 to 120 elongated eggs cemented together. The whole mass is somewhat egg-shaped. Egg pods are very resistant to moisture and cold and easily survive the winter if the soil is not disturbed.

Eggs are deposited in fallow fields, ditches, fencerows, shelter belts and other weedy areas, as well as in crop fields, hay fields and alfalfa. Eggs begin hatching in late April or early May. Hatching peaks about mid-June and usually ends by late June. If spring weather is cool and extremely dry, hatching may be delayed and continue into July.

Young grasshoppers are called nymphs, and they undergo simple metamorphosis. They look like adults, but are smaller and have wing pads instead of wings. Nymphs go through five or six developmental stages and become adults in 40 to 60 days, depending on weather and food supplies. The adults of grasshopper species that damage crops become numerous in mid-July and deposit eggs from late July through fall. Usually only one generation of grasshoppers is produced each year.

Grasshoppers have a high reproductive capacity. The female lays an average of 200 eggs per season, and sometimes as many as 400 eggs. If favorable weather increases the number of eggs, the grasshopper population may be dramatically larger the following year. Grasshoppers cause some damage every year, but they become very destructive during outbreaks. The main factor affecting grasshopper populations is weather. Outbreaks, or exceptionally large populations, are usually preceded by several years of hot, dry summers and warm autumns. Dry weather increases the survival of nymphs and adults. Warm autumns allow grasshoppers more time to feed and lay eggs.

Management

If you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.

Nosema locustae is a protozoan that can be purchased commercially to treat large areas. Its spores have been incorporated with bran to make insecticide baits such as Semaspore®, Nolo Bait® or Grasshopper Attack®. These baits kill some nymphs but almost no adults, though infected adults lay fewer eggs. Baits act too slowly and kill too few grasshoppers to be useful for immediate control.

When grasshoppers are at low numbers, handpicking them is an option. However, when at high numbers control becomes very difficult and insecticides are warranted.

Home garden control options include:

  • Carbaryl (Sevin)
  • Neem
  • Pyrethrins
  • Synthetic pyrethroids

Related Publications

 

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Cotton aphid/Melon aphid

Article author: David Kerns
Most recently reviewed by: Pat Porter (2018)

Common Name(s): Cotton Aphid, Melon Aphid

Pest Location

Row Crop, Vegetable and Fruit

Description

Cotton or melon aphids, Aphis gossypii, are highly variable in size and color, varying from light yellow to dark green or almost black. Although size can vary based on environmental conditions, adult aphids tend to be about 1/16th inch in length, are soft bodied and pear shaped. Aphids have piercing-sucking mouthparts and have two protrusions on their rear tips called cornicles. Aphid adults can be winged (alate) or wingless (apterous). The formation of winged types is usually in response to overcrowding or poor host quality. The immatures or nymphs of the aphid are similar in appearance to the adult but smaller.

Origin and Distribution

Cotton aphid is nearly cosmopolitan, having a world-wide distribution. However, host specificity does vary depending on geographic origin.

Habitat & Hosts

Cotton aphids are extremely polyphagous and can feed on a large range of host plants covering 25 plant families. Among many others, notable hosts include asparagus, beans, begonia, catalpa, citrus, clover, cucurbits, cotton, eggplant, ground ivy, gardenia, hops, hibiscus, hydrangea, okra, peppers, potato, spinach, strawberries, tomatoes and violet. Crops typically most affected by cotton aphids include citrus, cotton and hibiscus.

Cotton aphids will initially be found feeding on the underside of new leaves, the plant terminal and flower buds, but as the population grows will infest the under side of older leaves.

Cotton aphids feed using sucking-piercing mouthparts which they use to pierce leaves and ingest copious amounts of plant sap from the phloem. Feeding robs the plant of energy that would otherwise be utilized for growth or fruit production. Heavy and prolonged infestations can cause leaves to curl downward, older leaves to turn yellow and shed, plant fruit may also shed or suffer reduction in size.

Cotton aphids excrete wastes in the form of a syrup-like substance called honeydew. Honeydew will accumulate on the leaves (and other plant structures) giving them a shiny, sticky appearance. A black sooty mold will often grow on the honeydew covering the leaf which may partially inhibit photosynthesis. More importantly, the honeydew may accumulate on the lint of open cotton bolls rendering the lint undesirable for milling.

Cotton aphid is also an important vectors of over 50 plant viruses including cucumber mosaic virus, watermelon mosaic virus 2, and zucchini yellow mosaic virus. These viruses are non-persistent viruses and may be transmitted from aphid to plant in a little as 15 seconds.

Cotton aphids are often attended by ants, which collect an feed upon their honeydew.

Life Cycle

With exception of northern latitudes, cotton aphids in the United States are all females, reproduce asexually (parthenogenically), giving birth to live young without mating. Aphids have a tremendous reproductive capacity and nymphs are born with developing embryos already present; essentially aphids are born pregnant. One female may produce as many as 80 offspring that mature within 8 to 10 days. Thus, it is possible for cotton aphids to have as many as 50 generations per year. These generations also occur as frequently as every 5 to 7 days under optimum conditions. In northern latitudes cotton aphid is capable of producing sexual forms and laying eggs on catalpa and rose of sharon for overwintering purposes.

Wingless adults overwinter in protected areas on catalpa, hibiscus, and a number of weed hosts. In the greenhouse, they can be active year-round. In spring winged females fly to suitable host plants and can disperse great distances via wind and weather fronts.

Management

If you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.

Predators such as lady beetles, lacewings and syrphid flies, along with parasitoids and aphid-killing fungi are often the most effective means of managing an cotton aphids. These beneficial organisms can effectively prevent aphids from reaching the damaging levels. Aphid tending ants will often protect aphids from predators. Soil and seed applied insecticides offer protection during early plant growth, but foliarly applied insecticides are often necessary on more mature plants. Standard and organically certified insecticides are available, but cotton aphid is notorious for developing resistance to commonly used insecticides so adequate control is not certain.

Related Publications

Citations

Blackman, R.L. and V. F. Eastop. 2000. Aphids on the worlds crops: an identification and information guide 2nd edition. Chichester, UK: John Wiley & Sons Ltd.

Kerns, D.L., J.A. Yates and B.A Baugh. 2015. Economic threshold for cotton aphid (Hemiptera: Aphididae) on Cotton in the Southwestern United States. J. Econ. Entomol.108: 1795-1803.

Suhas, V., D. Kerns, C. Allen, R. Bowling, M. Brewer and M. Parajulee. 2017. Managing cotton insects in Texas. ENTO-075, 38 pp. http://www.agrilifebookstore.org/Managing-Cotton-Insects-in-Texas-p/ento-075.htm.

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