Middle East DVEP - Armed Forces Pest Management Board

Appendix CPesticide-Resistant Arthropods in the Middle EastVector-borne diseases are an increasing cause of death and suffering in many areas of theworld. Efforts to control these diseases have been founded on the use of chemicalpesticides. However, the spread of resistance among arthropods has rendered manypesticides ineffective, while few substitute pesticides are being developed.Resistance is formally defined by the WHO as "the development of an ability in a strain ofsome organism to tolerate doses of a toxicant that would prove fatal to a majority ofindividuals in a normal population of the same species." Resistance has a genetic basis andarises from a change in the genetic composition of a population, which is a direct result ofthe selection effects of the pesticide.Early detection and monitoring are vital to resistance management. Historically,standardized methods, test kits, and insecticides were provided by the WHO. The simplestmethod of detecting resistance is the diagnostic dose test. The diagnostic dose is apredetermined insecticide dose known to be lethal to a high proportion of susceptibleindividuals, but that a high proportion of resistant individuals can tolerate. A list ofrecommended diagnostic doses of many insecticides for a number of arthropod vectors isavailable from the WHO. For terrestrial and/or adult stages, the insecticide is eitherapplied topically or insects are exposed to a surface treated with insecticide. For aquaticstages, insecticide is added to water at given concentrations.New approaches use biochemical tests to detect resistance and determine resistancemechanisms. These methods permit rapid multiple assays of a single specimen.Worldwide application of biochemical assays will require production of standardized kitssimilar to the insecticide bioassay kits supplied by the WHO. The choice of method to testfor resistance is of great importance in order to determine resistance mechanisms. ConsultTG 189, Procedures for the Diagnostic Dose Resistance Test Kits for Mosquitoes, BodyLice, and Beetle Pests of Stored Products. To obtain test kits and additionalrecommendations for resistance testing contact :USACHPPM/Entomology Science Programs5158 Blackhawk RoadAberdeen Proving Ground, MD 21010-5422Tel: (410) 436-3613DSN: 584-3613, FAX: (410) 346-2037Pesticide resistance can be classified into two broad categories: physiological andbehavioral. There are many mechanisms of physiological resistance, including reducedpenetration of insecticides through the cuticle, presence of enzymes that detoxify theinsecticide, and reduced sensitivity of the target site of the insecticide. Physiologicalresistance can confer cross-resistance to structurally related insecticides of the samechemical class or related classes. Some vector populations have acquired severalresistance mechanisms providing multiple resistance to a variety of insecticide classes.Many vector control programs have reached a stage where resistance is so great that fewchemical alternatives are available.186