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Greenhouse Pests Insect & Mite Pests. David J. Shetlar, Ph.D. The “BugDoc”. The Ohio State University, OARDC & OSU Extension Columbus, OH. © November, 2003, D.J. Shetlar, all rights reserved. Greenhouse & Interiorscape Pest Management.

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Greenhouse Pests

Insect & Mite Pests

David J. Shetlar, Ph.D.

The “BugDoc”

The Ohio State University,

OARDC & OSU Extension

Columbus, OH

© November, 2003, D.J. Shetlar, all rights reserved


Greenhouse & Interiorscape

Pest Management

Managing insect and mite pests in greenhouses should be a simple task! If you believe in laws of thermodynamics (i.e., matter can be neither created nor destroyed), the biological corollary should be: living organisms must come from living organisms! In short, we know that pests can not spring forth from “primordial much” which was a common thought during the Dark Ages!

In short, if you start with a clean greenhouse and clean plants, then pests should not be a problem!


Greenhouse & Interiorscape

Pest Management (cont’d)

  • The most common sources of insect and mite pests in greenhouses are:
  • Preinfested Stock(Cuttings and seedlings often have pests when purchased. Start clean!)
  • “Typhoid Mary” Plants(Stock that is infested and isn’t removed before the next crop is begun. University greenhouses are notorious for this! Smaller greenhouse operations that grow a variety of crops continuously are also guilty!)
  • Fly-Ins (Greenhouse doors, cooling vents and air vents are not properly covered allow flying insects to enter)
major greenhouse pests
Major Greenhouse Pests
  • Whiteflies
  • Mealybugs & Scales
  • Mites (spider mites, broad mites, & etc.)
  • Thrips
  • Leafminers
  • Nuisance Pests (fungus gnats, shore flies, & etc.)

Greenhouse Whiteflies

  • Greenhouse (Trialeurodes vaporariorum)
  • Sweetpotato (Bemisia tabaci)
  • Silverleaf (Bemisia argentifolii)
  • Bandedwinged (Trialeurodes abutilonea)

Best site on Internet: The Whitefly Knowledgebase


Notes: The greenhouse whitefly has been the traditional whitefly found in greenhouses. In the mid 1980s, another whitefly which was slightly smaller, slimmer and had a more yellowish body became common in Florida and the Carolinas. This new whitefly was a major problem on certain greenhouse vegetables and flowers such as poinsettias, gerbera daises, and hibiscus. This whitefly was eventually identified as the sweetpotato whitefly – Strain B, but this pest was subsequently described in 1994 as the silverleaf whitefly. At present, the greenhouse and silverleaf whiteflies are the most common pests in greenhouses, but the sweetpotato and bandedwinged whiteflies are occasionally encountered.

It is important to identify each species since they have varying susceptibilities to biological and chemical controls.



Nymph I


Nymph II


Nymph III


Nymph IV (=“Pupa”)


Whitefly Life Cycles

At 70ºF, the greenhouse whitefly life cycle takes: 6-10 days for egg hatch, 3-4 days as a nymph I, 4-5 days as nymph II, 4-5 days as nymph III, 6-10 days for the pupa. Adults can live for 30 to 40 days.


Greenhouse whitefly pupa, note raised upper surface and long, glass-like spines.

Greenhouse whitefly adults hold the wings flatter over the body and they are more white in base color.


Greenhouse whiteflies: note wings held wider and more flat on body, and pupae with long spines.

Silverleaf & sweetpotato whiteflies: note wings held closer to sides of bodies, and pupae have no spines.


Other whitefly species can be found, especially in southern greenhouses. Fortunately, most are not significant problems in production settings.

Palm whitefly adult and “pupae.” Many whiteflies have such characteristic waxy fringes.

A giant whitefly and its nymphs plus an old pupal exoskeleton.


Whitefly Management

  • Monitoring – visual inspection of plants, upper leaves for adults, lower leaves for nymphs; yellow sticky cards.
  • Cultural Control – sanitation, resistant plants
  • Biological Controls – parasitoids & diseases
  • Chemical Controls – emphasis on insect growth regulators, rotating chemistries, etc.
  • Integrated Programs – combining cultural and biological controls with chemical controls selected to have minimum adverse action on biologicals.

Whitefly Monitoring

  • Yellow sticky cards
  • Visual Inspections – adults prefer to lay eggs on younger foliage; undisturbed females lay eggs in circles; various thresholds (e.g., whitefly nymphs and/or pupae per leaf) have been developed for certain crops.

Note rings of eggs that indicate that the females were undisturbed for a considerable time!


Whitefly Cultural Controls

  • Start Clean! – start a crop with “clean” plant material and keep rooms separated.
  • Sanitation – keep weeds and other vegetation surrounding greenhouses mowed, or eliminated with herbicides or ground covers.
  • Exclusion – screen vents, air cooling pads, etc. with material with screens fine enough to exclued white flies. Doors should be under positive air flow (e.g., air flows out when opened).
  • Use Resistant Plants – some cultivars appear to be less able to support whitefly populations. Be sure to ask seed dealers about resistant cultivars.

Whitefly Biological Controls

  • Parasitoids – mainly Encarsia and Eretmocerus species, many usage techniques (e.g., mainly introductions or “banker” systems).
  • Predators – green lacewings are often helpful in field crops, lesser so in greenhouses.



Encarsia formosa, a commonly used parasitoid. Parasitized pupae turn black. Can you find the two adults?


Development Times for

Greenhouse Whitefly


Scheduling Short Residual, Contact Insecticides for Control of Greenhouse Whitefly

(assuming “pupae” are resistant)

At 85º:

Eggs=3 Nymphs=7 Pupae=7 Adult Preovi=1

Day: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

At 65ºF:

Eggs=11 Nymphs=17 Pupae=12 Adult Preovi=2

Day: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


Whitefly Chemical Controls

  • Soaps & Oils – best on foliage plants because of phytotoxicity potential; kills mainly eggs, crawlers and scale states by contact.
  • Contact Insecticides – most pyrethroids kill by contact and most have some residual action. Eggs and “pupae” may be resistant, so reapplications may be necessary to catch the crawlers or adults that may emerge after an application.
  • Systemic Insecticides – systemic insecticides are usually effective for actively feeding stages of whiteflies.
  • Insect Growth Regulators – have been very effective, especially as alternate chemistries.

Whitefly Chemical Controls


Whiteflies are notorious for developing resistance to pesticides. Their high reproductive potential and short generation time make them excellent at developing resistance. While there is considerable debate on resistance management, do not use the same pesticide again if satisfactory control was not achieved with a recent application. It is often recommended that managers alternate chemical groups on a regular basis if whiteflies need continual control. Without cultural and biological controls, chemical controls will eventually fail.



Mealybugs & Scales

  • Mealybugs (citrus, longtailed, Mexican, etc.)
  • Soft Scales (brown soft scale, hemispherical scale, black scale, nigra scale, etc.)
  • Armored Scales (oleander, fern, Boisduval, false Florida, cactus, etc.)

Sites on Internet:


Greenhouse Mealybugs

  • Citrus (Planococcus citri)
  • Longtailed (Pseudococcus longispinus)
  • Mexican (Phenacoccus gossypii)
  • “Unnamed” (Phenacoccus madeirensis)
  • Root Mealybugs (Rhizoecus spp.)

Citrus mealybugs, early ovisacs, and a couple of crawlers.

Longtailed mealybugs – crawlers, nymphs, and adults.


Phenacoccus madeirensis

All stages on chrysanthemum.

Ovisacs and crawlers.

A male.


Other mealybug species often occur in lath-house ornamentals in southern states.

Striped mealybugs

Pink hibiscus mealybugs being tended to by fire ants.


Mealybug Hosts

  • Citrus – 27 families of plants; begonia, coleus, amaryllis, cyclamen, and dahlia are most commonly attacked in greenhouses.
  • Longtailed – 26 families of plants; Dracaenia & ferns most commonly
  • Mexican – mainly chrysanthemum, English ivy, geranium, Gynura, hollyhock, Ixia, lantana, and poinsettia.
  • “Unnamed” – mainly chrysanthemum & poinsettia as well as foliage plants.
  • Root – numerous long-lived greenhouse plants but most damaging to African violets.

Mealybug Life Cycles

  • Citrus - males known but not obligatory; up to 600 eggs per ovisac; 10 days for egg hatch; 50-60 days per cycle.
  • Longtailed - males obligatory; up to 200 eggs per female, no ovisac, possibly live birth; two to three months per cycle.
  • Mexican – males known; up to 400 eggs per elongate ovisac; cycle can be completed in 47 days.
  • “Unnamed” – males known; up to 300 eggs per elongate ovisac; cycle can be completed in 30 days.
  • Root – not much known; several species that lay small numbers of eggs in compact ovisacs; slow developing.

Greenhouse Soft Scales

  • Brown Soft Scale (Coccus hesperidum)
  • Hemispherical Scale (Saisseta hemisphaerica)
  • Black Scale (Saissetia olea)
  • Nigra Scale (Parasaisetia nigra)

Soft Scale Life Cycles

  • Brown Soft Scale – ovoviviparous, males uncommon; 60 days to mature.
  • Hemispherical Scale – parthenogenic; up to 1000 eggs per adult; 40 to 105 days to mature.
  • Black Scale – parthenogenic
  • Nigra Scale – parthenogenic; lays eggs over long period of time; 40 to 60 days to mature.

Greenhouse Armored Scales

  • Oleander (Ivy) Scale (Aspidiotus nerii)
  • Cactus Scale (Diaspis echinocacti )
  • Fern Scale (Pinnaspis aspidistrae)
  • Bifasciculate Scale (Chrysomphalus bifasciculatus)
  • Boisduval Scale (Diaspis boisduvalii)

Oleander scales are irregularly round in shape. Males are smaller and more oval in shape.

Cactus scales are sexually dimorphic, females being rounded and males being slender, elongate forms.


Fern scale females are generally brown and oystershell shaped. Males are white with a medial ridge running down the waxy cover.


Boisduval females are irregularly rounded and males are elongate, white and with a medial ridge in the waxy covering. Settled nymphs produce a patch of elongate waxy threads as they form their covers.


Armored Scale Hosts

  • Oleander Scale – numerous woody plants
  • Cactus Scale – various cacti & orchids
  • Fern Scale – ferns and Aspidistra
  • Bifasciculate Scale – palms, rubber plants, & figs
  • Boisduval Scale – palms, banana, cacti, & orchids

Armored Scale Life Cycles

  • Oleander Scale – males & females common; 90 eggs per female; 30-35 days to mature.
  • Cactus Scale
  • Fern Scale – males and females common; few eggs per female; ~30 days to mature.
  • Bifasciculate Scale
  • Boisduval Scale – males & females common; 200 eggs per female; 23 to 32 days to mature.

Mealybug & Scale Management

  • Monitoring – early detection of mealybugs and scales is important to achieve good control.
  • Cultural Control – sanitation/start clean, throw away severely infested plants!
  • Biological Controls – parasitoid wasps are common
  • Chemical Controls – emphasis on systemics, following spray schedules, etc.
  • Integrated Programs – combining cultural and biological controls with chemical controls selected to have minimum adverse action on biologicals.

Greenhouse Mites

  • Twospotted Spider Mite (Tetranychus urticae)
  • Lewis Mite (Eotetranychus lewisi)
  • Southern Red Mite (Oligonychus ilicus)
  • Broad Mite (Polyphagotarsonemus latus)
  • Cyclamen Mite (Phytonemus pallidus)
  • Bulb Mite (Rhizoglyphus echinopus)

Twospotted spider mites have typical spider mite life cycles. They have egg, six-legged larval, eight-legged nymph I & II, and adult stages. Between every molt, the mites settle down and don’t move for a day or more, depending on the temperature.


Typical twospotted spider mite population. The eggs are completely spherical. Most of these are adults. The male in the middle is “guarding” a female nymph II that is in the process of molting into an adult.


Larva (above); egg, nymph I & II in molt rest, cast skins (right); nymph II female and male guarding (below).


When monitoring for spider mites, the tell-tale stippling is easily spotted. The mites will be on the underside!

If left uncontrolled, twospotted spider mites will completely encase the foliage in their fine silk. Note that the mites use the webbing as a walkway. Plants this heavily infested should be thrown away!


If left uncontrolled, spider mites can eventually kill their host plants. When this is about to occur, the mites often cluster at the tops of the plants in order to balloon to other plants. This is one such ballooning cluster.

Remember that an unmated female that is blown to a new plant can start an entire colony. When unmated, she can only produce eggs that will develop into males. However, the female can live long enough to mate with one of her sons and then she can begin to produce eggs that will develop into females!


Development Times for

Twospotted Spider Mite


Longevity & Fecundity for

Twospotted Spider Mite


“Red Mites”

Greenhouse managers often talk about “red mites” or “red spiders” when they are referring to spider mites. This is unfortunate, since there is no such species such as a “red mite”!

Twospotted spider mites take on a red or orange hue when chilled in fall conditions (above)

Southern red mites and European red mites have conspicuous spines and a reddish color (right).


Spider Mite Management

  • Monitoring – early detection of spider mite activity is important to achieve good control, look for stippling.
  • Cultural Control – start clean; remove weeds surrounding greenhouse environment; regularly syringe with water.
  • Biological Controls – numerous predatory mites are available and useful.
  • Chemical Controls – soaps & oils work well by contact; new miticides often have ovicidal activity, etc.
  • Integrated Programs – combining cultural and biological controls with chemical controls.

Phalaenopsis Mite is a relatively common mite pest of orchids. The mites are very flat and reddish-orange in color. Their feeding often causes white pitting of the orchid surface.

Unless the orchid is rare, disposal is the simple solution. Otherwise repeated applications of soaps or oils often work.


Cyclamen mites are small mites that often concentrate their feeding around leaf and flower buds. This causes stunting and distortion. Often heavy infestations cause the new leaves to die, making them look like they have died from Botrytus fungus.

The little white spot at the end of the arrow is a mature cyclamen mite!


Thrips in Greenhouses

  • Flower Thrips (Frankliniella tritici)
  • Western Flower Thrips (Frankliniella occidentalis)
  • Greenhouse Thrips (Heliothrips haemorrhoidalis)
  • Banded Greenhouse Thrips (Hercinothrips femoralis)
  • Gladiolus Thrips (Physothrips simplex)


The flower, greenhouse, and banded greenhouse thrips have been the most common thrips, traditionally, in greenhouses. These thrips cause damage to various greenhouse crops (floral, foliage and vegetable). Their damage was usually noted to be foliar discoloration (blanching of leaf tissues or streaking of flower petals) and damage to floral parts necessary for seed production.

In the 1980s, the western flower thrips (WFT) increased in importance when it was discovered that this thrips transmitted Tomato Spotted Wilt Virus (TSWV). Subsequent to this discovery, WFT was also found to be a vector of Impatiens Necrotic Spot Virus (INSV). Since these viruses can infect a wide range of greenhouse plants and infected plants can not be treated but have to be destroyed, considerable research has been undertaken to develop more intensive management programs for control of thrips.

The gladiolus thrips and some similar species are common pests of greenhouse grown glads and other floral crops.


Thrips feed by rasping into cells and removing their contents. This causes “blanching” of the feeding area. Thrips also produce small “tar spot” type of excrement.

Adult thrips have bladelike wings with a long hair fringe.


Western flower thrips nymphs feeding on leaf. Note typical “blanched” areas on leaf and tarspots.

Greenhouse thrips adults are black, but the nymphs are light colored. Note the greasy tarspots on this leaf.


Thrips Life Cycles

(using gladiolus thrips)


nymph I

nymph II

nymph III

nymph IV


“larva” 1

“larva” 2



Entomologists that work with thrips often call the first two nymphal instars “larvae,” the non-active third instar nymph a “prepupa,” and the fourth instar nymph a “pupa.”



Most thrips have four nymphal instars, but the third and fourth instars do not feed and are usually sluggish (= the third instar) or immobile (= the fourth instar). Because of this inactivity during the process of transforming from a non-winged nymph to the fully winged adults, many thrips experts call these instars the “prepupa” and “pupal” stages, respectively.

Depending on the species of thrips, the “prepupae” and “pupae” usually find protected places on host plants to undergo their molting processes, or they may even drop from the plant and undergo these instars in the soil or potting mixes.

Most thrips insert their eggs into plant tissues. Therefore, when managing thrips, one has to keep in mind that the eggs, “prepupae,” and “pupae” are usually in protected areas that will not be reached by pesticides. This usually require adoption of spray schedules (e.g., spraying every few days for a set period of time) in order to knock out hatching nymphs and newly emerging adults.


Western Flower Thrips

First instar nymph (upper left), second instar (above) and adult (left).


Development Times for Western Flower Thrips

  • Eggs – about 3 days at 80-85ºF
  • “Larvae” (1st & 2nd instar nymphs) – 3-4 days
  • “Prepupa” & “Pupa” (3rd & 4th instar nymphs) – 3-4 days
  • Adults – average 28 days longevity at 85ºF and 57 days at 68ºF
  • Fecundity – 125 to 250 eggs per female, mating is not necessary.

Thrips in Greenhouses - Diagnostics

  • Visual Inspection – look for blanched areas and tiny tar spots
  • Sticky Cards – western flower thrips shows a preference for blue sticky cards, but yellow cards are fine for general monitoring

Thrips Management in Greenhouses

  • Monitoring – sticky cards are generally recommended, early detection and number of adults per card per day is used.
  • Cultural Control – screening is available to prohibit entry of thrips from outside; eliminate surrounding vegetation.
  • Biological Controls – several predatory mites are available and useful.
  • Chemical Controls – rotation of chemistry is highly recommended as well as following strict spray schedules.
  • Integrated Programs – combining cultural and biological controls with chemical controls.

Special Factors for Managing Western Flower Thrips in Greenhouses

In viral disease transmission, only the feeding nymphs (“larvae”) can pick up the viral bodies from infected plants. The resulting infected adults can then transmit the virus to other plants and since they are highly mobile, spread of the virus can be very rapid.

  • Exclusion – since infected thrips adults can come from outside the greenhouse, special screens are commonly installed in areas where this thrips can overwinter.
  • Plant Resistance – new cultivars of plants have been developed that are resistant to the virus or the thrips. This greatly reduces the risk of viral problems.
  • Sanitation – if one plant is discovered with virus, then the entire crops is usually destroyed!



Greenhouse Leafminers

  • “American Serpentine” Leafminer (Liriomyza trifolii)
  • Serpentine Leafminer (Liriomyza brassicae)
  • Vegetable Leafminer (Liriomyza sativae)
  • Pea Leafminer (Liriomyza huidobrensis)
  • Chrysanthemum leafminer (Chromatomyia syngenesiae)


In the past, several types of leafminers (mainly dipterous and lepidopterous) were occasional pests in greenhouse crops. In the late 1970s and early 1980s, dipterous leafminers in the Agromyzidae became significant and wide spread pests of greenhouse floricultural and vegetable crops.

At first, L. trifolii, was identified as the main pest and this was often called the “chrysanthemum” leafminer because this was the crop most affected. Soon, it was learned that a very similar fly, L. sativae, was also involved. Both flies are yellow with black markings and you have to closely inspect the head markings to differentiate between the two.

The vegetable and pea leafminers are significant pests of greenhouse vegetable production.

These species have adult females that produce the typical “pin holes” which are called “stings” in the greenhouse industry. These are places where the female flies have punctured the leaf tissues to expose the juices so that the fly can lap them up.

The larvae usually make winding mines that gradually widen as the larvae mature.


Agromyzid leafminer adults are about the size of a common fruit fly. Most are yellow with black markings, but some can be almost entirely black.

The serpentine, American serpentine, and vegetable leafminers are mainly yellow with black markings like the fly above.

The pea leafminer is mainly black with some yellow markings like the fly to the right.


Serpentine leafminer damage to a Schefflera leaflets.

Extensive pinhole damage to young Schefflera leaf. In greenhouses, these spots are commonly called “stings” or “stipples.”


Greenhouse Dipterous Leafminer

Life Cycles

  • Complete Life Cycles – egg, larvae (three instars), pupa and adult stages.
  • Overwinter as pupae in soil in southern states, continuous activity in greenhouses.
  • Eggs – are inserted into leaf or petiole tissues, take 2-8 days to hatch.
  • Larvae – three instars take 12 to 20 days to mature.
  • Pupae – may be formed in mine or the last instar larva can drop to the soil or potting mix.
  • Adults – females often live for 3 to 4 weeks, males survive for shorter periods.

Leafminer Control in Greenhouses

  • Monitoring – watch for pinholes and early signs of mines.
  • Cultural Control – screen to keep out adult flies; eliminate surrounding vegetation.
  • Biological Controls – several parasitoids are useful.
  • Chemical Controls – select systemic products for larval control, though adults can be killed with stomach poisons.
  • Integrated Programs – combining cultural and biological controls with chemical controls.



Greenhouse Nuisance Pests

  • Fungus Gnats(several species of Sciaridae, often Bradysia spp.)
  • Shore Fly (Scatella stagnalis)
  • Springtails
  • Millipedes & Isopods
  • Snails & Slugs

Fungus gnat adults have long legs and antennae. They often “dance” around on leaves and flowers, rapidly flying and running over the surfaces. Adults cause no damage.

Fungus gnat larvae are nearly transparent, except for the white fat bodies visible through the exoskeleton. They have distinctive black head capsules. The larvae may feed on root hairs and roots of plants.


Fungus Gnat Control in Greenhouses

  • Monitoring – adults are easily monitored using yellow sticky cards.
  • Cultural Control – peat mixes seem to be very attractive to adults; keep soil mix on dry side.
  • Biological Controls – several parasitoids are useful as well as insect parasitic nematodes.
  • Chemical Controls – not normally needed but some drenches are useful if populations become excessive.
  • Integrated Programs – combining cultural and biological controls with chemical controls.


Shore flies are about the size of fruit flies and they have the same features – short antennae and legs. The larvae feed on blue-green algae and the adults appear to feed on similar materials.

These flies become numerous where potting mixes are kept constantly moist, especially where capillary mats are used (fiber mats that hold water under greenhouse pots).

Neither the adults or larvae cause any plant problems, but the adults produces numerous “fly specks” which are fecal and regurgitation spots. These appear as tiny white to black, round spots on pots and plant foliage.

Probably the best way to manage these flies is to conserve water so that blue-green algal growth is kept to a minimum.