A Population Genetic Model of Evolution of Host-Mate Attraction and Nonhost Repulsion in a Bark BeetlePityogenes bidentatus

Studies have shown that the bark beetlePityogenes 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 host tree and pheromone odors, 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.

Female Spider Wasps, Anoplius splendens Driesbach (Hymenoptera: Pompilidae), Learn to Associate the Odor of Host Feces With the Presence of the Host

Laboratory studies were conducted to determine whether or not adult female wasps, Anoplius splendens (Dreisbach), can learn a chemical stimulus (host feces) associated with host microhabitats. In a two-choice, static-air olfactometer, wasps previously exposed to hosts only in association with one stimulus (filter paper conditioned with odors from feces of the host spider, Drassodes auriculoides Barrows) exhibited a greater tendency to visit exclusively, and spend more time in, chambers containing a source of that stimulus as compared to control wasps exposed to paper with no host odors. The capacity for learning olfactory cues based on previous encounters with hosts should enhance the ability of wasps to accurately identify microhabitats where suitable hosts are most likely to be located.