Leaf structures affect predatory mites (Acari: Phytoseiidae) and biological control: a review

Because of their size, small arthropods can be highly affected by characteristics of the leaf surface. Leaf surfaces have various structures, such as trichomes and domatia, which add to the complexity of the microenvironment experienced by arthropods. Plant structure can affect the retention and performance of predators and parasitoids and it has been proposed that phylloplane characteristics be modified to improve the utility of these organisms as biological control agents. Phytoseiids have a long history as biological control agents of pest mite species in agricultural systems. In the past 30 years, extensive research has shown that trichomes and domatia influence phytoseiid populations and performance. Various reasons have been proposed to explain this relationship, including increased pollen capture for use as a food source, escape from predation, avoidance of adverse abiotic conditions, and increased/decreased ease of prey capture. There is potential for the manipulation of crops to improve biological control by phytoseiids, but incorporating beneficial traits into plants is likely to have lower priority than other breeding characteristics. The objectives of this review are to summarize the evidence for the relationship between phytoseiids and leaf surface structures, discuss possible hypotheses to explain this relationship, examine the potential of altering current crop varieties for the purpose of increasing phytoseiid populations or performance, and conduct a meta-analysis to quantify the effects of plant surface structures on phytoseiid and phytophagous mite densities.