 Viruses cannot actively target their hosts and must wait to encounter them.The higher probability of collision may explain why cyanophages of the "Myoviridae" family primarily infect one of the most abundant cyanobacteria, "Synechoccocus".Evidence of seasonal co-variation between the phages and hosts, in addition to an increase in cyanophages above a threshold of 103 to 104 "Synechococcus" mL−1, may suggest a “kill-the-winner” dynamic.