Data were collected to estimate transmission efficiency, infectivity and net transmission rates, latent and retention periods, and retention and efficiency indexes of the strawberry crinkle virus (SCV) transmitted by apterae of Chaetosiphon fragaefolii (Cockerell) and C. jacobi (Hille Ris Lambers) infected by injection. The infectious extracts of (SCV) were prepared from virus-infected donor aphids. Data also were collected on the longevity and larviposition of SCV-infected as well as comparable apterae that were injected with similar extracts prepared from SCVfree aphids. Additional trials were done to assess the probability of transovarial passage (TOP). The effect of infection was monitored by serially transferring individual aphids to healthy Alpine strawberry test seedlings at 24-hr intervals at constant temperature (25°C) and continuous light until all aphids had died. The data on the comparative biology supported the following conclusions: 1. Injection with SCV resulted in reduced longevity of both vectors, with no significant evidence that the effect was different between the species. 2. Infection tended to reduce the number of larvae produced by C. fragaefolii, but not by C. jacobi. 3. The net reproductive rate of both infected and healthy C. jacobi tended to be lower than that of healthy C. fragaefolii. 4. Infection tended to reduce the generation time and to increase the intrinsic rate of population increase more for C. fragaefolii than for C. jacobi, but neither parameter appeared to be significantly affected by SCV infection. Continued inside back cover.