by Christopher Philips, Assistant Professor | Department of Entomology, University of Minnesota Presented at the 2015 Minnesota Statewide High Tunnel Conference.

1. Understanding Spider Mites and Other
High Tunnel Insects
Christopher Philips
Assistant Professor
Fruit and Vegetable Entomologist
University of Minnesota
Department of Entomology
North Central Research & Outreach Center (NCROC)

2. Aphids
Whiteflies
Spider mites
Thrips
Insects in High Tunnels

3. High Tunnel IPM
IPM 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.

4. 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!).

5. Insect identification
• Why do I need to identify it anyway?
• Determines your management strategy
• Different problems require different solutions
• NOT ALL INSECTS ARE BAD

6. 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?

8. Abiotic factors
Physical (environmental)
Climate
Space
Insecticides
Mortality
Density Independent Mortality
% mortality is not related to host
density
Density dependent mortality
As host population increases, %
mortality increases -related
relationship
Biotic Factors
Intraspecific competition (crowding)
Dispersal/migration
Dormancy/diapause
Genetic diversity
Interspecific
Natural enemies
Competitors
Food organisms
Insect Life Cycles
Number of generations per year -
Voltinism
Why Do Insect Pest Problems Occur?

9. 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.

10. 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

12. Aphids
Whiteflies
Spider mites
Thrips
Common Pests

13. Two-spotted Spider Mite
Biology
Overwinters in MN
Frequency
Common pest in MN
E. Erbe, USDA-ARS

14. 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 Mite
Life Cycle

15. 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 Mite
Host and Damage

16. • 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 Mite
Management

17. 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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TSSM
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Two-spotted Spider Mite
Management

18. 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

19. 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.

20. Predators of Mites
Predators 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;

21. Predatory Mites
Acari: Phytoseiidae
67 genera, 2,000 species Neoseiulus fallacis
Galendromus occidentalisMesoseiulus longipes
Phytoseiulus persimilis
Neoseiulus californicus
Can consume 20 eggs or five adults daily.
Phytoseiulus persimilis
highly specialized - preys only on the two-spotted
spider mite
Neoseiulus (Amblyseius) californicus.
where high temperatures and/or relative humidity
variations

22. 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,

23. 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 Beetles
Coleoptera: Coccinellidae
Stethorus punctum
Photo: D.Asquith

24. 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.

25. Management Challenges
• New Pests
• Resistance
• Timing
• Biology and ecology of natural enemies
• Unintended consequences of other management
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26. 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)

27. 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.

28. 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

29. Weeds
Soil
Diseases
Insects
• Organophosphates (malathion),
• Pyrethroids (bifenthrin, cyfluthrin, and permethrin)
• Neonicotinoids (Acetamiprid, Clothianidin,
Dinotefuran, Imidacloprid, Thiamethoxam)
Unintended consequences

30. 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

31. Thrips
>7,000 species described worldwide
most are not pests
Biology
migrate into MN
Frequency
A 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.

32. 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
Thrips
Hosts and Damage
Extremely wide host range

33. 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.

34. Whiteflies
Silverleaf and sweetpotato whiteflies
(Bemisia argentifolii and B. tabaci)
Greenhouse whitefly
(Trialeurodes vaporariorum)
Bandedwinged whitefly
(Trialeurodes abutilonea)

35. Biology
Do not overwinter in MN
continue from year to year in greenhouses
Frequency
Common pest in MN
Control
There is really no easy way to control
whiteflies
Whiteflies

36. Aphids
Melon/cotton aphid, Aphis gossypii
Green peach aphid, Myzus persicae
Biology
Cabbage aphid overwinters as eggs in MN
Green Peach aphid migrates into MN
Frequency
Common pest in MN
Control
Usually not necessary; biological control

37. Aphids and Whiteflies
Hosts 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

38. Aphids and Whiteflies
Damage
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

39. 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)

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

41. • 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

42. Mites reared on treated foliage were
extremely toxic to predators, eliciting sharp
reductions in feeding, locomotion, and
longevity
Stethorus punctum
Unintended consequences

43. Sanitation
• Remove weeds in and around high tunnels
Limit the use of quick-release fertilizer
Aphid, Whitefly, and Thrips
Cultural and Mechanical
Photo credit: Galen Weston,

44. 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

45. Getting Started
• Start small and start early
• Pesticide Residues and when needed use soft pesticides
• Good Sanitation
• Weed management is critical
• Clean Transplants
+

47. Questions?
Christopher Philips
Assistant Professor
Fruit and Vegetable Entomologist
University of Minnesota
North Central Research & Outreach
Center (NCROC)
cphilips@umn.edu

48. Questions?

49. Biology, ecology, and management of invasive species

50. Questions?

51. Thrips
Biological Control
Amblyseius cucumeris
Amblyseius cucumeris prefers a diet of thrips but is considered
a generalist because it can survive on pollen and spider mites
in the absence of thrips.
A. cucumeris will work best at a temperature of 70˚F or above
and RH > 65%.
Orius insidiosus
Orius insidiosus (minute pirate bug) is a common generalist predator
found naturally in many field-grown crops. It preys on thrips, whiteflies,
spider mites, aphids and many other pests. It can survive on pollen in
the absence of prey. The minute pirate bug will work best at a
temperature of 70 to 90 degrees F and a day length of 11 hours or
more.

52. Biological control of Aphids:
Parastitoids
Aphidius colemani
Works best at a temperature of 50 to 76˚F and tolerates
cool temperatures.
Aphidius ervi
This small, black wasp parasitizes all types of large aphids.
It prefers an air temperature of 86˚F.

53. 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 eremicus
E. formosa prefers an average temperature above 64˚F,
and RH >70%

54. Intrinsic capacity of Orius
insidiosus to reduce flower
thrips populations
Predator-Prey Ratios
1 : 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