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.

Zélé et al. Full dataset Ecol Evol (Tab delimited text)

Complete dataset with the survival of females from 12 different populations (“population” column), belonging to different spider-mite species (“species” column with Te: T. evansi, Tl: T. ludeni, Tu: green form of T. urticae, and Tc: red form of T. urticae), and sprayed with B. bassiana, M. brunneum, or with Tween 20 only as control (“treatment” column with BB, MB and C, respectively). The “daydeath” column indicates the day of death of each female (i.e. the number of days after being sprayed), and the column “censor” indicates whether each female died accidentally (drowned in the wet cotton; 0) or ‘naturally’ (1). The “disc” column indicates the identity of the bean leaf disc on which each female was placed (20 females were placed together on each leaf disc; a total of 12 independent leaf discs, numbered from 1 to 12, were used per treatment and per population), and the column “block” indicates the temporal block.