Microbial Pest Control

Question 1

What is the bacterium that controls the market in regards to pest control?

Answer 1

Bacillus thuringiensis

Controls Coleoptera, Diptera and Lepidoptera but not Hemiptera

Question 2

How does B.thuringiensis work?

Answer 2

During sporulation bacterium produces a parasporal crystal that is toxic to pests
When swallowed gut is damaged and septicaemia develops
Feeding stops within hours and death is around 1-3 days after ingestion

Question 3

What is the toxic crystal called that is given off by B.thuringiensis after sporulation?

Answer 3

Delta-endotoxin

Question 4

Advantages of bacteria as pest control agents?

Answer 4

High specificity
Easy to produce
Good shelf lives of commercial formulations
Fast rate of discovery of new proteins and cheap development costs
Zero toxicity to mammals and many other non target species
Secondary disease cycling may occur

Question 5

Disadvantages of bacteria as a pest control agent?

Answer 5

No systemic activity
Toxins sensitive to sunlight
Not toxic to Hemiptera
Although feeding stops in hours death may take days so kill is not rapid
Resistance has been documented in heavily exposed field populations
High specificity means pest complexes cannot be controlled

Question 6

Characteristics of fungi as pest control agents?

Answer 6

Approx 1000 pathogenic fungi have now been described
10-15 developed commercially
Formulations comprise freeze-dried spore mixtures designed for dilution with water

Question 7

Examples of fungal pest control agents?

Answer 7

Beauvaria bassiana

Verticillium lecanii

Question 8

Mode of action of fungi?

Answer 8

Spores come into contact with pests and germinate on the cuticle
Mechanical and enzymatic processes attack the exoskeleton and hyphae spread throughout the target
Can take 3-10 days for death to occur

Question 9

Advantages of fungi as pest control agents?

Answer 9

Not toxic to mammals and many other non target species
Simple to produce by fermentation
Effective against Hemiptera
Secondary disease cycling can occur

Question 10

Disadvantages of fungi as pest control agents?

Answer 10

Susceptibility to environmental conditions
Spores may be inactivated by UV light
Shelf lives usually less than a year and particular conditions for storage may be required

Question 11

Characteristics of nematodes as pest control agents?

Answer 11

> 3000 nematode-insect relationships described
Commercial formulations (approx 20) all derived from 2 families Steinermatidae and Heterorhabitidae
First used in 1970s
Mostly used where high RH exists
Easy to mass produce
Available as freeze dried formulations

Question 12

Mode of action of nematodes?

Answer 12

Infective juveniles penetrate mouth, anus, spiracles
Symbiotic gut bacteria is released in nosy by nematode
Bacteria cause lethal septicaemia that kills host in 1-2 days

Question 13

Advantages of nematodes as pest control agents?

Answer 13

Rapid kill
Can seek out and locate hosts
Production is easy
Registration requirements have been eased
No mammalian toxicity or effect on other non target species

Question 14

Disadvantages of nematodes as pest control agents?

Answer 14

Require a high RH
Sensitive to temperature changes
Also sensitive to UV
Have poor shelf live (months)

Question 15

Characteristics or Protozoa as pest control agents?

Answer 15

Around 60,000 species worldwide divided into 7 phyla
4 phyla are know to parasitise invertebrates
Only microsporidia have been investigated for pest control

Question 16

Example of Protozoa used to control pests?

Answer 16

Nosema locustae

Question 17

What type of culturing is used in protozoa?

Answer 17

Tritrophic culturing

Question 18

Mode of action of Protozoa?

Answer 18

Grasshoppers consume spores sprayed onto vegetation
Spores terminate in host
Time scale to death is weeks/months
Cause chronic rather than acute illness

Question 19

Advantages of Protozoa as pest control agents?

Answer 19

Complete safety to mammals and other non targets

Question 20

Disadvantages of Protozoa as a pest control agent?

Answer 20

Problems with production and rate of kill

Question 21

Characteristics of viruses as pest control agents?

Answer 21

7 viral families that cause disease in arthropods
All commercial formulations are derived from Baculoviridae as it cannot reproduce in vertebrate cells
49 species identified to date
20 formulations available, all control lepidopterous pests
Tri tropic culturing

Question 22

Mode of action of viruses?

Answer 22

Viral particles ingested
Invade cells lining gut wall
Multiply and kill host
Day to weeks for death to occur

Question 23

Advantages of viruses in pest control?

Answer 23

Very specific

No toxicity to mammals

Question 24

Disadvantages of viruses in pest control?

Answer 24

Specificity is a problem
Difficult to produce
Work slowly
Sensitive to sunlight

Question 25

What are the microbial methods of pest control?

Answer 25

Bacteria
Fungi
Virus
Nematodes
Protozoa