Verified and potential pathogens of predatory mites (Acari: Phytoseiidae)

Several species of phytoseiid mites (Acari: Phytoseiidae), including species of the genera Amblyseius, Galendromus, Metaseiulus, Neoseiulus, Phytoseiulus and Typhlodromus, are currently reared for biological control of various crop pests and/or as model organisms for the study of predator¿prey interactions. Pathogen-free phytoseiid mites are important to obtain high efficacy in biological pest control and to get reliable data in mite research, as pathogens may affect the performance of their host or alter their reproduction and behaviour. Potential and verified pathogens have been reported for phytoseiid mites during the past 25 years. The present review provides an overview, including potential pathogens with unknown host effects (17 reports), endosymbiotic Wolbachia (seven reports), other bacteria (including Cardinium and Spiroplasma) (four reports), cases of unidentified diseases (three reports) and cases of verified pathogens (six reports). From the latter group four reports refer to Microsporidia, one to a fungus and one to a bacterium. Only five entities have been studied in detail, including Wolbachia infecting seven predatory mite species, other endosymbiotic bacteria infecting Metaseiulus (Galendromus, Typhlodromus) occidentalis (Nesbitt), the bacterium Acaricomes phytoseiuli infecting Phytoseiulus persimilis Athias-Henriot, the microsporidium Microsporidium phytoseiuli infecting P. persimilis and the microsporidium Oligosproridium occidentalis infecting M. occidentalis. In four cases (Wolbachia, A. phytoseiuli, M. phytoseiuli and O. occidentalis) an infection may be connected with fitness costs of the host. Moreover, infection is not always readily visible as no obvious gross symptoms are present. Monitoring of these entities on a routine and continuous basis should therefore get more attention, especially in commercial mass-production. Special attention should be paid to field-collected mites before introduction into the laboratory or mass rearing, and to mites that are exchanged among rearing facilities. However, at present general pathogen monitoring is not yet practical as effects of many entities are unknown. More research effort is needed concerning verified and potential pathogens of commercially reared arthropods and those used as model organisms in research

Heritable symbionts in a world of varying temperature

Heritable microbes represent an important component of the biology, ecology and evolution of many plants, animals and fungi, acting as both parasites and partners. In this review, we examine how heritable symbiont–host interactions may alter host thermal tolerance, and how the dynamics of these interactions may more generally be altered by thermal environment. Obligate symbionts, those required by their host, are considered to represent a thermally sensitive weak point for their host, associated with accumulation of deleterious mutations. As such, these symbionts may represent an important determinant of host thermal envelope and spatial distribution. We then examine the varied relationship between thermal environment and the frequency of facultative symbionts that provide ecologically contingent benefits or act as parasites. We note that some facultative symbionts directly alter host thermotolerance. We outline how thermal environment will alter the benefits/costs of infection more widely, and additionally modulate vertical transmission efficiency. Multiple patterns are observed, with symbionts being cold sensitive in some species and heat sensitive in others, with varying and non-coincident thresholds at which phenotype and transmission are ablated. Nevertheless, it is clear that studies aiming to predict ecological and evolutionary dynamics of symbiont–host interactions need to examine the interaction across a range of thermal environments. Finally, we discuss the importance of thermal sensitivity in predicting the success/failure of symbionts to spread into novel species following natural/engineered introduction