NAVMED P-5010-8 - Navy Medicine - U.S. Navy
NAVMED P-5010-8 - Navy Medicine - U.S. Navy
NAVMED P-5010-8 - Navy Medicine - U.S. Navy
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8-13 CHAPTER 8. NAVY ENTOMOLOGY AND PEST CONTROL TECHNOLOGY 8-13<br />
8-13. Resistance to Pesticides<br />
a. Definition of Pesticide Resistance.<br />
Resistance of pests to pesticides is defined as the<br />
ability of a given population to withstand a<br />
poison that was effectively lethal to earlier<br />
generations of the species.<br />
b. Development of Resistance. Most<br />
normal populations of animal species include<br />
individuals that vary in their susceptibility to<br />
pesticides. Consequently, candidate pesticides<br />
will kill some individuals of a species more<br />
readily than others. Individuals in a population<br />
that are less susceptible to a chemical are<br />
considered to be more resistant. Continued<br />
pesticide pressure upon a population will destroy<br />
the most susceptible individuals, permitting the<br />
more resistant individuals to survive and<br />
produce generations of increasingly resistant<br />
offspring. Thus, the species becomes<br />
increasingly difficult to control because of<br />
genetic factors transmissible to subsequent<br />
generations. Development of resistance in a pest<br />
population can be subtle or quite dramatic.<br />
Houseflies were found to develop resistance to<br />
DDT within a year after it was introduced into<br />
areas of Europe. For mosquito control, the use<br />
of the same insecticide as a larvicide and<br />
adulticide is thought to enhance the development<br />
of resistance. Resistance is not confined to<br />
insecticides, nor is it always rapid in<br />
development. Some Norway and roof rats and<br />
house mice have become resistant to<br />
anticoagulant rodenticides in Europe and the<br />
U.S. after 20 years of use. Pesticide resistance<br />
has been reported for more than 225 species of<br />
arthropods. All of the modern day insecticide<br />
groups that include organophosphates,<br />
organochlorines, and carbamates have examples<br />
of the development of resistance. Even crossresistance<br />
between these groups occurs. For<br />
example, chlordane (organochlorine) resistance<br />
may increase propoxur (carbamate) resistance in<br />
the German cockroach, Blatella germanica. This<br />
condition further complicates the situation for<br />
control work and necessitates reliance on specialists<br />
for recommending changes in methods,<br />
materials, and dosage rates. Not all field reports<br />
of resistance are valid. Other factors may be<br />
responsible for unsatisfactory control. Faulty<br />
techniques, chemical agents and equipment,<br />
inexperienced or incompetent operators, increased<br />
breeding rates, migration from outside the controlled<br />
area, and poor sanitation are a few of the<br />
more frequently observed reasons for ineffective<br />
control. It must be continually emphasized that<br />
change to another insecticide should be considered<br />
only when conclusive laboratory proof of resistance<br />
is obtained. The question of whether a<br />
resistant strain will revert to susceptibility when<br />
not exposed to the pesticide for a period of time<br />
has not been completely answered. The consensus<br />
among researchers is that while reversion will<br />
probably occur if there is no further exposure to<br />
the same or related pesticides, the time required<br />
would be dependent upon the degree of resistance<br />
developed. However, it has been experimentally<br />
demonstrated that once a resistant insect species<br />
has reverted back to susceptibility that resistance<br />
may quickly reappear with resumed use of the<br />
original insecticide.<br />
c. Prevention of Resistance. Selection<br />
of an insect population for insecticide resistance<br />
may be averted or delayed by rotating the different<br />
classes of insecticides available for control.<br />
For example, treating a German cockroach<br />
population repeatedly with an organophosphate<br />
insecticide may hasten the development of<br />
resistance to this class of insecticides. The use<br />
of integrated pest management techniques which<br />
include preventive, exclusion, biological, physical<br />
as well as chemical control methodologies<br />
together in a comprehensive pest control<br />
strategy will also help to slow or stop the<br />
development of resistance.<br />
9 Nov 2004<br />
8-13