1. Factors that affect resistance expression
Physical Factors
Plant Nutrition
Biotic Factors
Plant factors
Pest factors
Biotype
Initial infestation level

2. HPR as a response by the pest
Antixenosis (non-preference) -- prevents pest from commencing attack. Two types
Chemical – Allelochemicals are chemicals produced by one species (plant) to affect another species (pest).
Morphological – can be very long lasting.
Antibiosis – Interferes with pest attack once it begins.
Pest has reduced survival, fecundity, reproduction, etc.
Two types
Primary metabolite missing
Toxin

3. HPR as a phenotype category
Constitutive – prepares defense as plant grows
Often associated with yield drag
Plants always commit a portion of photosynthate to defense
All target tissues must be defended
Several advantages:
Young plants can be screened
Easier to assay
More dependable
Induced – defense prepared when attack comes
Localized – Hypersensitivity mostly with pathogens
Systemically Acquired Resistance (SAR)
Both have time lags & can be overwhelmed by large initial pest population

4. Genetic Basis of HPR Better understood for pathogens
Fewer control options
Effect of races more pronounced
Closer genetic association between pathogens & plants
Horizontal vs. Vertical Resistance
Vertical – based on one gene, “gene for gene hypothesis”
Horizontal – based on >1 gene, “general resistance”

5. Vertical – “All or None”

6. Horizontal Resistance – Graded with Rank Order

7. Vertical vs. Horizontal Resistance in IPM
Vertical’s advantages over horizontal
Amenable to simple, qualitative scouting methods
Easier to develop & manipulate
Effectively resists initial attack vs. changing the rate of increase after attack
Vertical’s disadvantages relative to horiz.
May be too specific (single race)
May be overcome by pest more easily, this can happen quickly
From the pest’s perspective, these are phenotypes
Multiple vertical genes can be combined to give a synthetic horizontal cultivar: “Multi-lines”
A single trait that is polygenetically determined may be overcome as easily as a monogenetic one.

8. Sources of Resistant Genes
Wild plants – Most wild plants’ genetic systems are not well studied
Germplasm collections
Primitive (heirloom) cultivars – Developed in thousands of years of selection
Tissue culture – Captures somatal mutations
Induced mutations – Limited success
Microbial sources
Rapid and straightforward
Preserves other agronomic traits

9. Gene Deployment Strategies
Objective of GDS is to prevent pest from overcoming the HPR mechanism
Sequential Release (Replacement) – most common, least effective, several problems
Cultivar rotation
Geographic spacing – older technique
Mosaic planting (some fields planted in one variety, other fields in other varieties)
Multilines – Mixing cultivars in the same field
Pyramiding/Stacking – May be the best approach when applicable
Refugia

10. Special Case: Bt Crops Read this article for background Toxic Crystal
Phase contrast of Bacillus thuringiensis. The vegetative cells contain endospores (phase bright) and crystals of an insecticidal protein toxin (delta endotoxin). Most cells have lysed and released the spores and toxin crystals (the structures with a bipyramidal shape)

11. BT Mode of Action
Caterpillar consumes foliage with the protoxin and/or spore
Toxin activated by gut pH, binds to gut wall membrane, caterpillar stops feeding (minutes)
Gut wall breaks down, microflora invade body cavity, toxin disolves (hours)
Caterpillar dies from septicemia (1 – 2 days)

12. Different Bt strains produce different versions of protoxin
Group
Shape
Size (kDa)
Pest Controlled
Cry I
Bipyramidal
130 – 138
Lep larvae
Cry II
Cuboidal
69 – 71
Leps & Flies
Cry III
Flat Irregular
73 – 74
Beetles
Cry IV
73 – 134
Flies
Cry V-IX
Various
35 – 129

13. Special Case: Herbicide Resistant Crops

14. Bt and Herbicide Resistant Crop Prevalence in the US, 2000

15. Benefits/Concerns Over HRC
Simplifies weed management
Speeds adoption of reduced tillage systems
Overall reduction in pest losses
Concerns
Will eventually create herbicide-resistant weeds
Unknown pleiotropic effects
Regulatory/marketing issues
Over-reliance on them will prematurely end their usefulness

16. Using HPR in IPM As a stand-alone tactic Integrated with other tactics
Objective is to preserve the resistance; emphasis on deployment strategy
Integrated with other tactics
Crop rotation: if HRC’s are used, must rotate both for pest and herbicide type.
Pesticides: Emphasize measures to prevent pesticide resistance (lower doses, frequency)
Biological control: Conflicts do occur
Action Thresholds: Whenever there is significant, cultivar-specific variation in yield response to a pest, action thresholds should be re-examined

17. Behavioral Control Your Text Follows This Outline:
Vision-based tactics
Auditory-based tactics
Olfaction-based tactics
Food-based tactics
Lecture Will Follow This Outline
Behavior modifiers
Mating disruption
Genetic manipulations

18. Behavior Modifiers Most insect behavior modifiers are chemical
Semiochemicals – Facilitate communication between individuals
Pheromones: within a species
Allelochemicals: Between species
Allomones: Producer benefits, receiver does not
Kairomones: Receiver benefits, producer does not
See book discussion, pp: 379 – Pay particular attention to the pheromone types.

19. Pheromone Usage Sex pheromones most widely used in IPM
Relatively simple chemistry enables synthetic versions.
Three main uses in IPM:
Monitoring one sex
Mass trapping sexually active adults
Interfering with mating
A few “Anti-pheromones” are now available. Future use unknown. Here’s an example.

20. Pheromone Disperser Examples
Plastic Spiral
Card style
Cable/Twist Tie
Rubber septum (with holder)