VL 8

Question 1

Pathogen

Answer 1

any infectious agent (microorganism) that can cause a disease in its host

includes viruses, bacteria, parasites, fungi, protozoa, some worms

Question 2

Disease

Answer 2

an abnormal medical condition associated with specific symptoms

Question 3

Vector

Answer 3

a living agent that acquires, carries and transmits an infectious pathogen between hosts

Question 4

How do insects vector disease?

Answer 4

Mechanical transmission

Biological transmission
- acquire: uninfected insect bites infected host
- maintain: pathogen matures inside the insect
- transmit: infected insect bites an uninfected host

Question 5

what makes an insect vector efficient?

Answer 5

Vector must have an overlapping host range with the pathogen

Vectorial capacity takes into account daily biting rate, probability of transmission per bite, incubation period and mortality rate

Specialists may be more efficient at transmission, but generalists can transmit between species (eg. West Nile Virus)

Question 6

Life cycle of Triatomine

Answer 6

Hemimetabolous

Eggs - First nymphal instar - second nymphal instar - thrid nymphal instar - fourth nymphal instar - fifth nymphal instar - adult

Question 7

Mosquito life cycle

Answer 7

Eggs - Larva - Pupa - Adult

Question 8

Aphid - dispersal

Answer 8

Offspring become winged morph when host plants become crowded

50% aphid flights go at least 90m, and 10% go further than 1 km

Distance of dispersal is important for pathogen spread

Question 9

Why are aphids good vectors?

Answer 9

See page 16 and internet

Mouthparts and saliva make it possible to efficiently enter plant

Stylets
Proboscis
Saliva
Cbyrial pump
Salivary sheath

Probing, penetration, ingestion

Question 10

Control methods - trapping

Answer 10

Control of human disease vectors
Most vectors use sight and smell to find hosts
Traps reduce vector density / redirect them / target a specific portion of the population
Particularly useful for monitoring

Example: Tsetse flies, vector of trypanosomiasis / nagana are attracted to the contrast of blue and black, and to the odour of bovine urine

Question 11

Trapping - Crop pest management

Answer 11

Sex pheromone attracts large numbers of males to be collected and killed

In theory reduces likelihood of female mating - mating disruption

Usually more useful as a monitoring technique, to ascertain when to start control measures

Question 12

Insecticides - crop pests

Answer 12

Over the last 70 years, pesticides applied wether or not pest populations at damaging levels - applying heavy selection pressure

Effects of other organisms: Neonicotinoids are harmful to bees. High toxicity and sublethal effects that cause disorientation and affect the immune system, learning and memory, egg laying and fertility

Question 13

Insecticides - human disease vectors

Answer 13

Indoor / outdoor spraying
Indoor residual spraying kills off any vectors inside buildings and remains persistent. Good for mosquito species that rest inside on walls during the day

Insecticide treated bednets
- protect against night biting species which vector malaria in Africa, such as Anopheles gambiae
- Behavioural resistance developing

Question 14

Biological control - Human disease vectors (malaria)

Answer 14

Spray with pathogens, such as fungi shorten lifespan below incubation period of malaria

Question 15

Biological control - Crop pests

Answer 15

viruses
Baculoviridae are arthropod viruses with no vertebrate associations. They can be targeted against specific species, not impacting beneficial insects
However: slow kill time, limited host range, complex to prepare

Question 16

Biological / environmental control - human idseas vectors

Answer 16

use of predatory organisms
Modification of environment

Question 17

Biological control - human disease vectors (Wolbachia / Sterile insect technique / GM insects)

Answer 17

Wolbachia are bacteria that manipulate insect reproduction. Cross strains can interfere with pathogen growth or be lethal

Rearing and release of irradiated sterile males - particularly effective in species where female only mate once - used to eradicate tsetse flies from Zanzibar

Can also release insects genetically modified to create sterile offspring / reduced lifespan

The biggest challenges are large populations and immigration / reinvasion

Question 18

Biological control - Crop pests (GM plants)

Answer 18

Plants modified to produce aphid alarm pheromone (E)-beta-farnesene

this pheromone normally causes aphids to disperse from the plant and engage in avoidance behaviours

But increased constitutive emission from the plants did not repel aphids in field trials

Question 19

Biological control in crop pests - 4 strategies to manipulate natural enemy population

Answer 19

Classical: introduce a natural enemy from original habitat (eg. ladybugs and cotton cushiony scale)

Introduced exotic: introducing an exotic natural enemy to control a native pest which is not controlled by native natural enemies

Conservation: encouraging movement to and retention of natural enemies in crop systems by providing suitable habitats of hosts for them (part of the push-pull system)

Augmentation: release additional individuals to augment an already present population of natural enemies

Question 20

Push-pull

Answer 20

A cropping system in which different companion plants repel insect pests from the main crop and attract them away from the main crop