Repeated use of the same class of pesticides can cause undesirable changes in the gene pool of a pest, leading to another form of artificial selection—pesticide resistance.
Manage insecticide resistance
When a pesticide is first used, a small proportion of the pest population may survive exposure to the material due to their distinct genetic makeup.
These individuals pass along the genes for resistance to the next generation.
Subsequent uses of the pesticide increase the proportion of less-susceptible individuals in the population.
Through this process of selection, the population gradually develops resistance to the pesticide.
The speed with which resistance develops depends on several factors:
- How fast the insects reproduce
- Migration and host range of the pest, the availability of nearby susceptible populations
- Persistence and specificity of the crop protection product
- Rate, timing and number of applications made.
Resistance management recommendations
Recommendations for successful resistance management*:
•Consult a local agricultural advisor or extension services in the area for up-to-date recommendations and advice on IPM and IRM programs.
•Consider options for minimizing insecticide use by selecting early-maturing or pest tolerant varieties of crop plants.
•Include effective cultural and biological control practices that work in harmony with effective IRM programs.
Adopt all non-chemical techniques known to control or suppress pest populations, including biological sprays such as Bt’s, resistant varieties, within-ﬁeld refuges (untreated areas) and crop rotation.
•Where possible, select insecticides and other pest management tools that preserve beneﬁcial insects
•Use products at their full, recommended doses. Reduced (sub-lethal) doses quickly select populations with average levels of tolerance, whilst doses that are too high may impose excessive selection pressures.
•Appropriate, well-maintained equipment should be used to apply insecticides.
•Recommended water volumes, spray pressures and optimal temperatures should be used to obtain optimal coverage.
•Where larval stages are being controlled, target younger larval instars where possible because these are usually much more susceptible and therefore much more effectively controlled by insecticides than older ones.
•Use appropriate local economic thresholds and spray intervals.
*Modern Crop Protection Compounds, Wolfgang Kramer and Ulrich Schirmer
See this article in Tree Fruit June 2019