Density Dependence and Growth Rate: Evolutionary Effects on Resistance Development to Bt (Bacillus thuringiensis)

Area of Science:

• Ecology
• Entomology
• Pest Management

Background:

• Pesticide dose is traditionally central to insect resistance management (IRM).
• Transgenic traits like Bt (Bacillus thuringiensis) often have fixed doses below the 'high dose' threshold.
• Pest population dynamics are increasingly recognized as critical factors influencing pesticide durability.

Purpose of the Study:

• To investigate how pest population dynamics, specifically density dependence and growth rates, interact with pesticide traits to affect resistance durability.
• To explore the impact of timing and strength of density dependence on the effectiveness of IRM strategies.
• To propose a broader definition of 'high dose' that includes population-dynamic context.

Main Methods:

• Utilized a deterministic model of a generic arthropod pest.
• Examined the interaction between timing and strength of density dependence, population growth rate, and Bt mortality.
• Analyzed effects on the time to resistance development.

Main Results:

• Pesticide durability was minimized at intermediate doses, but high population growth rates negated high-dose benefits.
• The timing of density dependence influenced durability: simultaneous effects made it insensitive to strength, while post-selection effects showed increased durability with decreased strength.
• Density dependence strength affected single traits and pyramids, contingent on timing and refuge size.

Conclusions:

• A broader definition of 'high dose' is needed, incorporating population-dynamic factors.
• Maximum growth rates, timing, and strength of density-dependent mortality interactions are key determinants of durability.
• Ecologically integrated approaches are essential for advancing IRM research and practice.