Final- Entomology

Question 1

Transgenic arthropod resistance - how does it make the plant function

Answer 1

Basically makes an insecticidal plant that produces a toxin to kill the insect (bt corn or cotton)

Question 2

Mode of action of Bt

Answer 2

on the villa of the insect gut

within an hour of introduction, the insect gut is getting holes and disintegration

Question 3

Bt Resistance (virulence)

Answer 3

Mutation in the receptor on the membrane (brush border)

For Cry

Question 4

Cry toxin mode of action (product of Bt)

Answer 4

• Cadherin is principal receptor making this happen*
  1. Protoxin binding to cadherin receptors on the brush border
  2. Cell death from toxin olgomers
  3. Toxin olgomers bind to enzymes, and insert into basement membrane
  4. Pore forms, gut bacteria enter the body cavity, gut cell dies

Question 5

Inheritance of Bt resistance (virulence)

Answer 5

The insect gut is able to mutate rapidly and change the hertibility mechanism

Inherited as nonrecessive, incomplete dominant, recessive in different insects

Question 6

Transgene Bt Release Strategies:
Single Bt release / Moderate Bt toxin Expression
What, why, Pro/Con

Answer 6

Allows some susceptible insects to survive and dilute expression of virulence through intermating

Allows survival of benefical insects
bad = variable efficacy

Question 7

Transgene Bt Release Strategies:
Mixed release / Mixture of different toxins Expression
What, why, Pro/Con

Answer 7

Kill different susceptible homozygotes for each toxin to slow virulence
good = assumed no cross-resistance, no linked virulence
bad = with cross resistance and linkage the mixture would last just as long as a single toxin release

Question 8

Durability of Bt relies on

Answer 8

Refuge seed

Question 9

Idea behind refuge seed

Answer 9

Get a higher biomass of susceptible survivors from the non bt plants, than resistant survivors from the bt plants.
They intermate, and the level of virulence will be diluted and remain controlled.

Question 10

Refuge % vary by

Answer 10

crop and pest

Question 11

Where does the Bt gene come from?

Answer 11

Soil bacterium Bacillus thuringiensis (Bt) that produces endotoxins

Question 12

Advantages of molecular vs phenotypic markers

Answer 12

• Unaffected by environment
• More economical
• Track multiple genes

Question 13

Markers tell us

Answer 13

The location on the chromosome is linked in some way to the resistance gene

Question 14

For Molecular Assisted Selection for insect resistance to work the resistance gene locus must be ___

Answer 14

Linked in close proximity during crossover and co-segregate.

Question 15

Linkage possibilities between R genes and markers

Answer 15

could get complete linkage. Marker and gene always linked from one gen to another
incomplete- crossing over occurs differently for marker and allele,
none when the marker and allele are on different chromosomes or very far apart

Question 16

cM

• what
• how to interpret

Answer 16

Centi-morgans.

A statistical estimate of probability of linkage. Smaller number, tighter the potential linkage

Question 17

Recombination frequency of 0% and linkage

Answer 17

0% = completely linked

50% - entirely unlinked

Question 18

What types of R genes have successfully been identified with markers
-what crops

Answer 18

Dominant, single genes for resistance to insects

rice, soybean, sugar beet, wheat

Question 19

Major gene segregation

Answer 19

Discrete classes, easy to tease apart

Question 20

Minor gene segregation

Answer 20

A continuum, harder to tease apart

Question 21

Genotyping by Sequence and Association mapping benefits

Answer 21

GBS- good for plants where we don’t know the entire genome

AM- Use thousands of markers to screen for R-genes, lots of work not widely used

Question 22

For insect plant co-evolution this must happen

Answer 22

First- Need insect movement to the plant
Second-insect selects nutritive host or oviposition host based on volatiles, visual or contact ques.
If this happens enough, we get co-evolution. If it dead ends enough, insect selects another host, no co-evolution

Question 23

Bound to be found - hypothesis of plant cost/benefit of defense

Answer 23

• Perennials are bound to be found by insects due to longer life cycles, so have more broad defenses.
• Put more protection on their seed to protect future progeny
• Put more protection in areas that are susceptible to feeding

Question 24

Carbon/Nitrogen ratios influencing plant defensives

Answer 24

Plants living in high carbon environements have carbon based defenses (high silica & lignin)
Plants living in high nitrogen low carbon environments have nitrogen (toxin) based defenses

Question 25

Resource availability influencing plant defenses

Answer 25

Available resources determine plant growth, defense production increases when growth decreases

Question 26

Growth-Differentiation Balance influencing plant defenses

Answer 26

tradeoffs between growth & defense over a resource availability gradient
too Cloudy, partly cloudy (ideal), too sunny

Question 27

maysin (glycoside) QTL

Answer 27

Corn – corn earworm

Question 28

Why do some seed companies now breed for only drought tolerance.
-how does this relate to co-evolution

Answer 28

because an insect sucking the nutrients out the plant requires a similar resistance as drought tolerance. so they just breed for drought tolerance
-Drought stress accelerates coevolution by selecting of insect defenses with lower metabolic costs because of resource costs related to drought
stress.

Question 29

How do temp flucations influence co-evolution

Answer 29

Increased temperature fluctuations eliminate insect populations adapted
to heat or cold, reducing selection pressure for insect resistance & decelerating coevolution.

Question 30

How do increased CO2 levels influence co-evolution

Answer 30

Increased CO2 concentrations shift C/N ratios to C-based defenses, force
directional selection & accelerate co-evolution.

Question 31

Why are some insects more prone to developing biotypes

Answer 31

High number of biotypes because they move large distances and can reproduce rapidly
-There are major genes (sometimes many) exerting antibiosis effects on them. So survivors are forming new biotypes

Question 32

Factors Affecting Biotype Occurrence

Answer 32

Genetic diversity of pest, adaptive ability on different hosts and to
different ecological conditions
• Number of resistance genes
• Resistance category
• Percent of crop in resistant cultivars
• Integrated pest management program efficacy

Question 33

Biotype avoidance via combined antibiosis and antixenosis

Answer 33

combining antibiosi and antixenosis extend the time you can produce a crop without virulence take you from 2 to 8. Keeps virulence frequency low, so it develops slowly over time. Will be a yield hit

Year 1 Refuge - 1:1 ratio (Bt cotton currently the recommendation), Year two- use back selection and plant only susceptible