Iflaviruses in arthropods: when small is mighty

Iflaviruses are arthropod-infecting viruses classified in the family Iflaviridae. The most well-studied iflaviruses are responsible for deleterious overt (symptomatic) infections in economically important insect species like honeybees and silkworms. The fact that iflaviruses are also found in mass reared insects such as crickets and flies, makes their study relevant for the food and feed industries and for biological control applications (e.g., mass reared insects for sterile insect techniques). In recent years it was found that iflaviruses are not restricted to insects, but are widely spread in many arthropod species, often causing covert (asymptomatic) infections. Fitness costs may be associated with these covert infections, as seen in a variety of host species. In this work we review the latest research on iflaviruses in respect to host range, viral genome organization, cycle of infection, tissue tropism, virus transmission strategies, fitness costs and pathogenic effects of both covert and overt infections, host immune responses to iflavirus infections, interactions between iflaviruses and other microorganisms, and the effect of iflavirus infections on host behavior.