Résumé
Spider mites are severe pests of several annual and perennial crops
worldwide, often causing important economic damages. As rapid evolution of
pesticide resistance in this group hampers the efficiency of chemical
control, alternative control strategies, such as the use of
entomopathogenic fungi, are being developed. However, while several
studies have focused on the evaluation of the control potential of
different fungal species and/or isolates as well as
their compatibility with other control methods (e.g.
predators or chemical pesticides), knowledge on the extent of inter- and
intraspecific variation in spider mite susceptibility to fungal infection
is as yet incipient. Here, we measured the mortality induced
by two generalist
fungi, Beauveria bassiana and Metarhizium brunneum, in 12 spider mite populations belonging to different Tetranychus species: T. evansi, T. ludeni, the green form of T. urticae and the red form of T. urticae, within a full factorial experiment. We found that spider mite species differed in their susceptibility to infection by both fungal species. Moreover, we also found important intraspecific variation for this trait. These results draw caution on the development of single strains as biocontrol agents. Indeed, the high level of intraspecific variation suggests that (a) the one-size-fits-all strategy may fail to control spider-mite populations and (b) hosts resistance to infection may evolve at a rapid pace. Finally, we propose future directions to better understand this system and improve the long-term success of spider mite control strategies based on entomopathogenic fungi.