Pesticide Usage

April 9, 2007

Pesticide Resistance

Dr. Donald E. Mullins

Department of Entomology

Reading assignment = Ware and Whiacre: Chapter 20.

A PowerPoint version of this lecture is available Click here

Rate of insecticide resistance development:

• Frequency of resistant genes
• Nature of resistance genes
• Intensity of selection pressure
• Reproduction rate
• Size and relation of populations
  • "Refugia"

Evolution: Adaptations

• "biological warfare among organisms"
• physical forces structures
  • thorns on bushes
  • tropical trees
• chemical forces
  • hard chapparal

Evolution: adaptations in the insect world

• Deception
• Camouflage
• Alarm
• Intimidation
• Predation

Allelochemistry / Allelochemics

• Allelopathy to herbivores
  • tobacco insects
  • growth & development of insects
    • juvenile hormone mimics
    • precocenes (anti-JH)
    • "phoney amino acids"
  • pyrethrins
• Defense
  • alarm
  • chemical
  • sequestration

Critical Cases of Insecticide Resistance

• Diamondback moth
• Whitefly
• Green peach aphid
• Leaf miner
• Budworms
• Colorado Potato beetle
• Twospotted spider mite
• European red mite
• Malaria mosquitoes
• House fly
• German cockroach
• Black fly

Insecticide Resistance: History

• 1907-1908 California red scale
  • hydrogen cyanide HCN
• 1908 San Jose scale
  • lime sulfur
• 1928 Codling moth
  • lead arsenate
• 1937 Ticks
  • arsenicals

Insecticide Resistance Types

• Natural Resistance
  • Mexican bean beetles ( DDT )
• Behavioral Resistance
  • grain beetles: fumigants
  • houseflies: treated surfaces
  • cockroaches: treated surfaces; baits
  • green peach aphid: feeding selectivity = avoid the xylem
• Biochemical or Physiological Resistance
  • Enzymatic:
    • Houseflies = DDT dehydrochlorinase
    • Houseflies = Malathion resistance
  • Excretion
    • Tobacco hornworms
  • Altered site of action :
    • Bacillus thuringiensis
      • Indian meal moth
      • Houseflies
      • mosquitoes
  • Nervous system changes :
    • axonic changes
      • cyclodiene/avermectins
      • kdr knockdown resistance
      • DDT, pyrethrins = sodium channels
    • acetylcholine esterase changes
      • green rice hopper
  • Decreased absorption:

Synergists:

• The role of synergists in combating the development of resistance

Cross resistance

Multiple resistance:

• Reflects history of insecticide selection
• Precludes the return to previous utility
• see handout reference materials

Persistence of resistant genes

 

• Resistance to other pest management tactics:
  • Insect growth regulators
  • Microbial insecticides
  • Resistance to parasites
  • Virulence to resistant plants
  • Crop rotations (extended diapause)
  • Sterile-male releases
  • Resistance to pheromones… not yet!

 

• Conditions that promote insecticide resistance: (Pedigo 2002)
  • Prolonged exposure to a single insecticide, or the insecticide is used in a slow release form
  • Every generation of the insect is selected
  • Insecticide selection pressure is high (mortality is great)
  • No functional refugia exists
  • A large geographical area is covered all populations in a given area are likely to have been treated
  • Selection occurs prior to mating
  • The insecticide is closely related to one used earlier (cross resistance potential)
  • A low population threshold (economic threshold) is recommended for application of the insecticide
  • The insecticide is inherently irritating and/or repellent

 

• Biological factors that promote resistance (Pedigo 2002)
  • No (or little) migration occurs between populations
  • The species has a monophagous habit
  • The species has a relatively short generation time
  • Numerous offspring per generation are produced
  • The species is highly mobile, increasing the possibility of exposure

 

• Management by moderation (Pedigo 2002)
  • Use low dosages, sparing a proportion of susceptible genotypes
  • Use less frequent applications
  • Use chemicals of brief environmental persistence
  • Avoid slow-release formulations
  • Apply selection against adults after reproduction, allowing susceptible genes to be passed on
  • Make local, rather than area wide applications. The use of trap crops fits here
  • Leave some generations or population segments untreated.
  • Preserve refugia (untreated pockets for population segments). This relates to point 7 and is accomplished by treating only "hot spots" in a field or directing nozzles toward only a part of a plant canopy. Site-specific farming fits here.
  • Utilize higher economic thresholds for insecticide application. This relates to point 2 because it should result in fewer applications

 

• Management by Saturation: (Pedigo 2002)
  • Saturate insect defense mechanisms by using dosages that can overcome resistance
  • High value crops/medical pests
  • Possible adverse impact on the environment
  • Computer models…Recessive genes are targeted
  • Suppress detoxification mechanisms..i.e. synergists

 

• Management by multiple attack: (Pedigo 2002)
  • Reduce selection pressure by imposing several independently acting forces
  • High value/medical pests
  • Possible adverse environmental effects; may adversely affect beneficial insect

   

Reference:

• Pedigo, L. P. (2002) Entomology and Pest Management, Prentice Hall, Upper Saddle River, NJ. 457pp.