Understanding Spider Mites and Other High Tunnel Insects

Christopher PhilipsAssistant ProfessorFruit and Vegetable EntomologistUniversity of MinnesotaDepartment of EntomologyNorth Central Research & Outreach Center (NCROC)

Aphids

Whiteflies

Spider mites

Thrips

Insects in High Tunnels

High Tunnel IPMIPM programs use current, comprehensive information on the life cycles of pests and their interaction with the environment.

This information, in combination with a variety of techniques to reduce the risk of pest damage by the most economical means, and with the least possible hazard to people, property, and the environment.

IPM Implementation

• Step 1 – Identify the pest.

• Step 2 – Evaluate the pest infestation level

• (sampling, monitoring, amount of injury).

• Step 3 – Assess the tolerance level of the commodity to injury.

• Step 4 – Take an action (or no action!).

Insect identification

• Why do I need to identify it anyway?• Determines your management strategy

• Different problems require different solutions

• NOT ALL INSECTS ARE BAD

Why Do Insect Pest Problems Occur?

• Why are pest insects free from the control of natural enemies and diseases?

• How do modern agriculture and forestry practices contribute to problems?

• What effects have the movement of plants and insects had on pest problems?

Abiotic factors

Physical (environmental)

Climate

Space

Insecticides

MortalityDensity Independent Mortality

% mortality is not related to host density

Density dependent mortalityAs host population increases, % mortality increases -related relationship

Biotic FactorsIntraspecific competition (crowding)Dispersal/migrationDormancy/diapauseGenetic diversityInterspecificNatural enemiesCompetitorsFood organisms

Insect Life CyclesNumber of generations per year -Voltinism

Why Do Insect Pest Problems Occur?

Insect Growth and Development

Affected by two major factors, time and temperature

The amount of heat required by an organism to complete its development is known as physiological time.

• Minimum or lower developmental threshold is the temperature below which insect development is negligible.

• Maximum or upper developmental threshold is the temperature at which insect growth stops.

Insects in High Tunnels

• Multiple generations - up to 12-15 / year

• Limited natural enemies to reduce populations

• Almost unlimited food

• Improved environmental conditions

• Some life stages are not susceptible to treatment

• Major insecticide and miticide resistance

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TSSM GPA Melon GH WF BW-WF Silverleaf onion thrips WFT

Resistance to Pesticides

Aphids

Whiteflies

Spider mites

Thrips

Common Pests

Two-spotted Spider Mite

BiologyOverwinters in MN

FrequencyCommon pest in MN

E. Erbe, USDA-ARS

Favored by hot dry conditions

4-14 days development increases with temeratureF

7-10 generations a year

Adult females – 30 days ~100 eggs avg (up to 300)

Two-spotted Spider MiteLife Cycle

Feed on over 180 host plants, including over 100 cultivated species

Damage• Spider mites injure leaves by piercing cells

and sucking out cell contents. • This injury produces white or yellow spots

or "stippling" that is heaviest on the underside of the leaves

• As mite numbers increase, these white speckles will increase in number, the leaf will take on a bleached appearance and die.

Two-spotted Spider MiteHost and Damage

• Prevent spider mite outbreaks by scouting weekly and releasing natural enemies as needed.

• Look for the characteristic spotting on plant leaves.

• The two-spotted spider mite has two prominent spots on the upper surface of its body.

• Look for mites on the undersides of leaves. Also look for their silken webbing

D. Cappaert, Michigan State University, Bugwood.org #5371009

Two-spotted Spider MiteManagement

Control• Chemical control of spider mites generally involves pesticides that are specifically

developed for spider mite control• Few insecticides are effective for spider mites and many even aggravate problems.• Furthermore, strains of spider mites resistant to pesticides frequently develop,

making control difficult.

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Two-spotted Spider MiteManagement

Two-spotted Spider Mite Cultural and Mechanical

Sanitation • Disposing of old or infested plant material

Inspections

Avoid over-fertilization • Promotes succulent new growth which is more susceptible to two-

spotted mites.

Use of high-pressure water spray or overhead irrigation to dislodge spider mites

Two-spotted Spider Mite Biological control

• “the enemy of my enemy is my friend”

• e.g., predators, parasitoids, pathogens

• Biological control is a method of controlling pests using other living organisms.

Predators of MitesPredators are very important in regulating spider mite populations and should be protected whenever possible. Important predators include:

the predatory mites,• Phytoseiulus persimilis,• Mesoseiulus longipes,• Neoseiulus californicus,• Neoseiulus fallicus• Galendromus occidentalis

The lady beetle, Stethorus;

The minute pirate bugs, Orius;

Predatory MitesAcari: Phytoseiidae

67 genera, 2,000 species Neoseiulus fallacis

Galendromus occidentalisMesoseiulus longipes

Phytoseiulus persimilis

Neoseiulus californicus

Can consume 20 eggs or five adults daily.

Phytoseiulus persimilishighly specialized - preys only on the two-spotted spider mite

Neoseiulus (Amblyseius) californicus. where high temperatures and/or relative humidity variations

Predatory Midge: Feltiella acarisuga

Should be used in conjunction with a predatory mite. The gall midge larva feeds on spider mite eggs.

Each female lays an average of 30 shiny yellow eggs near mite colonies

They can consume over 300 mite eggs as they complete their development in about a week

They then spin fluffy white cocoons on the underside of leaves, usually along a leaf vein,

Native to North America and is found throughout the mid-Atlantic region and also in the Midwest

Stethorus punctum is strictly a predator of plant-feeding mites, particularly the spider mites such as the European red mite and the twospotted spider mite, and especially the eggs.

S. punctum consume up to 100 mites per day

Lady BeetlesColeoptera: Coccinellidae

Stethorus punctum

Photo: D.Asquith

Application• Start early to control spider mite populations since spider mites reproduce

quickly at high temperatures and low humidity.• If used on a curative basis, introduce multiple mite species to clean up hot spots.• Always use the predatory midge in conjunction with a predatory mites.• Concentrate predator introductions at spider mite hot spots..• Monitor predator activity by checking spider mite colonies weekly. Additional

biological controls should be added as needed.

Management Challenges• New Pests

• Resistance

• Timing

• Biology and ecology of natural enemies

• Unintended consequences of other management

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Spotted wing Drosophila (SWD)

• Drosophila suzukii

• native to Asia

• lays eggs into healthy, ripening soft fruits, using a saw-like ovipositor

SWD non-SWD Photo credits: N. Gompel (top); M. Hauser (bottom)

Timing

Biological control agents must be released before two-spotted spider mite populations reach damaging levels. • The population growth of predatory mites

depends on the density and distribution of two-spotted spider mite populations as well as temperature and RH.

Biology and ecology of natural enemies

• Most of the natural enemies require specific temperature and RH

• found that in high tunnels the temperature and humidity fluctuated too widely to support this species except for several weeks in spring and summer

WeedsSoilDiseasesInsects

• Organophosphates (malathion), • Pyrethroids (bifenthrin, cyfluthrin, and permethrin)

• Neonicotinoids (Acetamiprid, Clothianidin, Dinotefuran, Imidacloprid, Thiamethoxam)

Unintended consequences

Thrips

(A) Flower thrips, Frankliniella tritici

(B) Western flower thrips, Frankliniella occidentalis

(C) Tobacco thrips, Frankliniella fusca

(D) Soybean thrips, Neohydatothrips variabilis

Scale bars represent 0.5 mm.

Onion thrips, Thrips tabaci

Thrips>7,000 species described worldwide

most are not pests

Biologymigrate into MN

FrequencyA recent survey of Midwest greenhouse operators identified WFT as the most difficult greenhouse pest to manage

Thrips like dry conditions, so keep plants well watered and relative humidity high.

Damage• Have piercing-sucking, multi-purpose

mouthparts. • The mouthparts are used to pierce leaves,

flowers, seeds, pollen grains, and fruit, as well as to drink open liquids such as nectar, water, or insect secretions;

• Transmit pathogens

ThripsHosts and Damage

Extremely wide host range

Thrips feeding damage on cucumber fruit.

Thrips feeding damage on cucumber leaves

Thrips Damage

Oviposition scars and feeding damage on sweet pepper.

Thrips egg-laying scars on tomato

Thrips feeding damage on pepper leaves.

A very important aspect of thrips is the transmission of virus diseases.

Tomato spotted wilt virus, transmitted by the • western flower thrips, • tobacco thrips, and • onion thrips.

Whiteflies

Silverleaf and sweetpotato whiteflies(Bemisia argentifolii and B. tabaci)

Greenhouse whitefly(Trialeurodes vaporariorum)

Bandedwinged whitefly(Trialeurodes abutilonea)

BiologyDo not overwinter in MNcontinue from year to year in greenhouses

FrequencyCommon pest in MN

ControlThere is really no easy way to control whiteflies

Whiteflies

AphidsMelon/cotton aphid, Aphis gossypiiGreen peach aphid, Myzus persicae

BiologyCabbage aphid overwinters as eggs in MNGreen Peach aphid migrates into MN

FrequencyCommon pest in MN

ControlUsually not necessary; biological control

Aphids and WhitefliesHosts and Damage Numerous Host

Damage• Piercing/sucking mouthparts,

• plant distortion and discoloration, • leaf chlorosis, • leaf withering and premature leaf drop plant• death;

• Excrete honeydew, promotes the growth of sooty mold

Aphids and Whiteflies Damage

rich sooty

induce

Tomato yellow leaf curl virus

Vector taxa Vector group Total plant viruses

Hemiptera Aphids 197

Whiteflies 128

Melon aphids are known to transmit 44 plant viruses, while green peach aphids are known to transmit more than 100 plant viruses

Management Challenges

• All of these pests thrive under tunnel conditions.

• The dry foliage, stems, and fruit grown under intense irrigation and fertigation are ideal environments for these pests to flourish.

• Unintended consequences of other management

• Organophosphates (malathion),

• Pyrethroids (bifenthrin, cyfluthrin, and permethrin)

• Neonicotinoids (Acetamiprid, Clothianidin, Dinotefuran, Imidacloprid, Thiamethoxam)

Smith and Clement, Annu. Rev. Entomol. 2012. 57:309–28

Unintended consequences

• Suppress expression of important plant defense genes, • Alter levels of phytohormones involved in plant defense,• Decrease plant resistance to unsusceptible herbivores, spider

mites Tetranychus urticae (Acari: Tetranychidae), in multiple, distantly related crop plants.

Unintended consequences

Mites reared on treated foliage were extremely toxic to predators, eliciting sharp reductions in feeding, locomotion, and longevity

Stethorus punctum

Unintended consequences

Sanitation

• Remove weeds in and around high tunnels

Limit the use of quick-release fertilizer

Aphid, Whitefly, and ThripsCultural and Mechanical

Photo credit: Galen Weston,

Biological control

• “the enemy of my enemy is my friend”

• e.g., predators, parasitoids, pathogens

• Biological control is a method of controlling pests using other living organisms.

Types of Biological Control

Classical

Augmentation

inundative releases and

inoculative releases

Conservation

Getting Started

• Start small and start early

• Pesticide Residues and when needed use soft pesticides

• Good Sanitation

• Weed management is critical

• Clean Transplants

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Questions?

Christopher PhilipsAssistant ProfessorFruit and Vegetable Entomologist

University of MinnesotaNorth Central Research & Outreach Center (NCROC)

cphilips@umn.edu

Questions?

Biology, ecology, and management of invasive species

Questions?

ThripsBiological Control

Amblyseius cucumerisAmblyseius cucumeris prefers a diet of thrips but is considereda generalist because it can survive on pollen and spider mitesin the absence of thrips.A. cucumeris will work best at a temperature of 70˚F or aboveand RH > 65%.

Orius insidiosusOrius insidiosus (minute pirate bug) is a common generalist predatorfound naturally in many field-grown crops. It preys on thrips, whiteflies,spider mites, aphids and many other pests. It can survive on pollen inthe absence of prey. The minute pirate bug will work best at atemperature of 70 to 90 degrees F and a day length of 11 hours ormore.

Biological control of Aphids: Parastitoids

Aphidius colemaniWorks best at a temperature of 50 to 76˚F and tolerates cool temperatures.

Aphidius erviThis small, black wasp parasitizes all types of large aphids. It prefers an air temperature of 86˚F.

Biological Control of Whiteflies: Parasitoids

Encarsia formosa

(Hymenoptera: Aphelinidae)

8-10 eggs per day

Primary Prey: whiteflies and aphids

Key Characters: parasitized hosts turn black

Vegetable crops: release needed

Eretmocerus eremicusE. formosa prefers an average temperature above 64˚F, and RH >70%

Intrinsic capacity of Oriusinsidiosus to reduce flower

thrips populations

Predator-Prey Ratios1 : 217 = population suppression

1 : 51 = rapid local extinction

From: Sabelis & Van Rijn (1997) Thrips as Crop Pests. (Lewis, ed.) CAB International, UK

Thrips Predation

Photo Joe Funderburk