Resistance defined by WHO

1
Resistance defined by WHO

• The ability in a strain of some organism to
  tolerate doses of a toxicant which would prove
  lethal majority of individuals in a normal
  population of the same species.

2
Resistance defined by A.W.A. Brown

• Any population, within a species normally
  susceptible to a given insecticide, that is no
  longer controlled by the pesticide in the area
  concerned

3
Tolerance

• Higher doses needed to effect species A vs. B
• Interspecies term

4
Cross-resistance

• Resistance to one compound following the
  development of resistance to another due to the
  presence of a mechanism that gives protection
  against both compounds.
• Compounds are usually "similar".

5
Negative Cross-resistance

• Increased susceptibility to one compound
  following the development of resistance to
  another compound

Multiple resistance(or multi-resistance)
A population with resistance to different
compounds due to individuals having two or more
mechanisms of resistance
6
Frequency of resistance genes prior to
insecticide selection
7
Hypothetical change in resistance gene frequency
following selection
8
How resistance evolves
Increasing insecticide selection
9
How resistance evolves
Increasing insecticide selection
10
Hypothetical changes in gene frequency from
prior to insecticide use (A), initial use (B),
moderate use (C) , heavy use (D) and long term
heavy use (E)
A
B
C
D
E
Increasing insecticide selection
11
Learn More!

• Pesticides, the Environment, and Human Health
  (Entom. 3070) Fall 2012.
• Insecticide Toxicology (Entom. 4900) Spring 2011.