Greenhouse Pests

Question 1

Background information on Greenhouses and pests

Answer 1

~600,000 greenhouses worldwise in 2014
Production since 17th century but most expansion after 1945 (existence since 13th century)
~550,000 ha are plastic (polyethylene) covered, 50,000 ha glass
Vegetables are produced in 450,000ha, ornamentals in 150,000
2 most important greenhouse crops worldwide are tomatoes and cucumber
Others include: sweet pepper, watermelon, courgette, lettuce, beans, celery, cabbage, aubergine

Question 2

List the most important countries by area and crop

Answer 2

China - 360,000ha (cucumner, tomato)
Spain - 55,000 ha (melon, tomato)
Japan - 53,000 (tomato, melon)

Question 3

Why are crop yields higher in greenhouses and give an example

Answer 3

Environmental control in comparison to open field
- Netherlands only 0.5% of the area is used for food production comprises greenhouses. The area however produces nearly 20% of Dutch agricultural output value (>£20 million)

Question 4

What are the costs associated with greenhouse pest management?

Answer 4

Tomato pest management costs are ~2% of overall production costs
In ornamentals <1%
Therefore not an obvious target for reducing pesticide use given the small economic savings that might be realised

Question 5

Why is the greenhouse environment well protected from pest species?

Answer 5

Greenhouses can be cleaned/sterilised
Closed environment should prevent pest colonisation, if this does occur the pest complex should still be smaller than a field situation
Can use inert/sterile media for growing crops (hydroponics) so minimising disease/neamtodes
Neighbouring greenhouses can have individually tailored programmes (no cross contamination would occur)
Release of natural enemies can be accuratley timed
Fixed environmental conditions make population models of rates of development (pests and predators) a lot more accurate

Question 6

Name some key greenhouse pests

Answer 6

Whitefly (Bemisia tabaci)
Aphids (Myzus persicae)
Leafminers (Liriomyza trifolii)
Spider mites (Tetranychus urticae)
Thrips (Frankliniella occidentalis)

Question 7

Why are greenhouse pests so effective?

Answer 7

All named in key greenhouse pests are polyphagous, extremley fecund, damage plants both as adults and nymphs, grow quickly and can rapidly develop resistance to insecticides (r-selected pests)

Question 8

Describe the whitefly

Answer 8

Bemisia tabaci
Hemipterous pests related to aphids
Adults with wings covered in powdery secretion, juveniles look like scale insects, nymphs pupate after three nymphal instars
Development time is about a month and adults can live for about a month
Suck sap, produce honeydew (sooty molds) and vector pathogens

Question 9

Describe aphids

Answer 9

Myzis presicae
Hemipterous, feeds on sugar rich products of photosynthesis
Pest populations develop rapidly because of parthenogenesis
Damaged plants dry up and leaves curl
Vector disease and produce honeydew

Question 10

Describe leafminers

Answer 10

Liriomyza trifolii
Dipterous polyphagous pests in which juveniles damage crop plants
Juveniles create mines in leaves that disrupt translocation of nutrients
Larvae pupate in leaves and exit holes can serve a point of entry for pathogens
Life cycle takes about 20 days with larvae moulting 3 times
North American origin with global distribution

Question 11

Describe spider mites

Answer 11

Tetranychus urticae
Damage caused by feeding of both adults and juvenules
Extremely fecund and polyphagous
Extract sap from leaf epidermal cells - leaves may become dry and paper like
Cannot fly but easily transported by other organisms including humans

Question 12

Describe thrips

Answer 12

Frankiniella occidentalis
Native to USA now global distribution
Hemimetabolous insects in order Thsanoptera (also called thunderflies)
Extremely polyphagous with >500 host crops
Populations can reproduce parthenogenetically, life cycle 20 days adults live about 30 days
Adults pierce leaf cells to get sap and lay eggs

Question 13

How many companies use biocontrol in greenhouses and how is this cultured?

Answer 13

100 companies

tritrophic culturing

Question 14

Which pest management strategies are used in European greenhouse tomato production?

Answer 14

8 different natural enemies
Microbes (Verticillium, Bt)
Host plant resistance (for nematodes)
Climate control (for disease control)
Cultural techniques (hydroponics or steam sterilisation for soil control of soil diseases)
As a result of the above, insecticide use in most greenhouse tomato production has been eliminated

Question 15

What are the advantages of pest management in greenhouses without pesticides?

Answer 15

Reduced operator exposure to pesticides (particular problem in enclosed environment)
No residues in harvested product
No phytotoxic effects on young plants
Easy to release predators and can be finely tuned
Predators will be confined so get continuous control of pest species

Question 16

What are the latest developments in pest management?

Answer 16

Use of “banker plants” to support populations of predators. These plants supports pests but not pests of the crop under cultivation i.e. wheat plants with wheat aphids but generalist aphid predators
Plant breeders improving crops for predators i.e. cucumber plants with fewer trichomes improve searching efficiency of Encarsia
Use of cultivars that produce volatiles to attract predators