Effectiveness of eriophyid mites for biological control of weedy plants and challenges for future research

Eriophyid mites have been considered to have a high potential for use as classical biological control agents of weeds. However, in the past 20 years few species have been authorized for introduction, and few have significantly reduced the target plant's population. Natural enemies, resistant plant genotypes, and adverse abiotic conditions may all reduce the ability of eriophyid mites to control weeds. Furthermore, host specificity experiments conducted under laboratory conditions sometimes indicate a wider host range than that observed in the field, which results in failure to obtain approval for release. We need to know more about the natural behavior, life history and evolutionary stability of eriophyid mites. This is critical for designing and interpreting experiments to measure host plant specificity and potential impact on target and nontarget plants, which must be known before they can be released.