| Prey specialization has multiple implications for the ecology and evolution of predators; it is a major issue in biological control and in speciation. My study focused on phenological and life-history traits that underlie the evolution of prey specificity, and on mechanisms of reproductive isolation that maintain it. I used a comparative approach with sibling species that have markedly different feeding habits: Chrysopa quadripunctata Burmeister, a generalist, and C. slossonae Banks, a specialist on the woolly alder aphid.;The two species showed disparate developmental and reproductive responses to each other's usual prey. On a diet of woolly alder aphids, C. quadripunctata hatchlings suffered high mortality and significant decreases in developmental and oviposition rates; however, the size of adults and eggs increased. Conversely, a diet of the generalist's prey did not influence the survival or development of C. slossonae immatures, but it detrimentally affected the adults' life-history traits.;Under semi-natural conditions, C. quadripunctata produced two or three generations per year as opposed to C. slossonae's single or a partial second generation. The disparity was related to differences in ecophysiological responses underlying the species' dormancy, especially photoperiodic induction of diapause, diapause intensity, and thermal requirements for postdiapause development. Different emergence periods produced partially asynchronous mating.;An asymmetrical pattern of hybridization resulted when individuals from four geographic populations of C. quadripunctata were paired with C. slossonae. C. quadripunctata females from populations that overlap with C. slossonae interbred at a lower rate than females from allopatric populations; most reciprocal crosses were fertile. Unsuccessful hybridization was associated with lack of sperm transfer from the bursa copulatrix to the spermatheca. Hybrids originating from sympatric populations were viable but they had reduced fertility.;The findings indicate that dietary specialization in Chrysopa is highly evolved and stable. First, a suite of life-history and phenological traits underlie the evolution of prey specificity. Second, a combination of mechanisms, such as seasonal and gametic isolation and hybrid infertility, keeps the specialist and generalist reproductively separated; thus, the species-specific prey associations are maintained. The study illustrates that a comparative phylogenetic approach can reliably evaluate the stability of predator-prey associations, thus strengthening the criteria for using predators in biological control programs. |
