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United States Department of Agriculture

Agricultural Research Service

Research Project: Sustainable Pest Management Strategies for Arid-land Crops

Location: Pest Management and Biocontrol Research

Title: A population genetic model of evolution of host-mate attraction and nonhost repulsion in a bark beetle Pityogenes bidentatus

Author
item Byers, John

Submitted to: Psyche
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 14, 2012
Publication Date: February 15, 2012
Citation: Byers, J.A. 2012. A population genetic model of evolution of host-mate attraction and nonhost repulsion in a bark beetle Pityogenes bidentatus. Psyche. 2012:1-9.

Interpretive Summary: Insecticide resistance in insects develops after a genetic mutation that renders the toxin ineffective and the resulting gene is then selected during reproduction due to enhanced survival of this genotype. Population genetic models can show how pest insects can develop insecticide resistance and how resistance can remain hidden for many generations before rapidly becoming apparent. The bark beetle Pityogenes bidentatus (Coleoptera, Curculionidae, Scolytinae), while orienting to aggregation pheromone, avoids odors of nonhost trees (Norway spruce, birch, and oak) and even healthy host Scotch pine. A population genetic model of two behavioral genes was hypothesized where AA, Aa, and aa were allele combinations regulating orientation to aggregation pheromone, and BB, Bb, and bb were combinations allowing avoidance of nonhost and unsuitable host odors. The nine possible genotypes were assigned different survival factors that remained constant during simulation. The initial proportion of aabb genotype (little aggregation/host response and little avoidance of nonhosts) was ~1.0 when a mutation was hypothesized that caused better orientation to host/beetle odors (Aabb) and another mutation causing more efficient avoidance of nonhosts (aaBb). After these initial mutations, the model used indiscriminate mating of genotypic proportions and subsequent survival as input for each successive generation. The results indicate that AABB eventually becomes 100% in the populations in some scenarios, while AABB and other genotypes reach stable equilibriums much less than 100% in other models depending on genotypic survival values that are supported by ecologically-sound assumptions. The hypothetical mutations in bark beetles above are similar to that expected in the development of insect resistance to insecticides or formerly resistant host plants.

Technical Abstract: Studies have shown that the bark beetle Pityogenes bidentatus (Coleoptera, Curculionidae, Scolytinae) avoids volatiles of nonhost trees (Norway spruce, birch, and oak) and healthy host Scotch pine when orienting to aggregation pheromone. A population genetic model of two behavioral genes was hypothesized where AA, Aa, and aa were allele combinations regulating orientation to aggregation pheromone, and BB, Bb, and bb were combinations allowing avoidance of nonhost and unsuitable host odors. The nine possible genotypes were assigned different survival factors that remained constant during simulation. The initial proportion of aabb genotype (little aggregation/host response and little avoidance of nonhosts) was ~1.0 when a mutation was hypothesized that caused better orientation to host/beetle odors (Aabb) and another mutation causing more efficient avoidance of nonhosts (aaBb). After these initial mutations, the model used indiscriminate mating of genotypic proportions and subsequent survival as input for each successive generation. The results indicate that AABB eventually fixates in the populations in some scenarios, while AABB and other genotypes reach stable equilibriums in other models depending on genotypic survival values supported by ecologically-sound assumptions. The models indicate how development of insecticide resistance in pest insects may proceed.

Last Modified: 11/1/2014
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