Neozygites tanajoae sp. nov., a pathogen of the cassava green mite

Brazilian fungal diversity represented by DNA markers generated over 20 years

Molecular techniques using fungal DNA barcoding (ITS) and other markers have been key to identifying the biodiversity of different geographic areas, mainly in megadiverse countries. Here, we provide an overview of the fungal diversity in Brazil based on DNA markers of phylogenetic importance generated since 1996. We retrieved fungal sequences of ITS, LSU, SSU, tef1-α, β-tubulin, rpb1, rpb2, actin, chitin synthase, and ATP6 from GenBank using different field keywords that indicated their origin in Brazil. A total of 19,440 sequences were recovered. ITS is the most representative marker (11,209 sequences), with 70.1% belonging to Ascomycota, 18.6% Basidiomycota, 10.2% unidentified, 1.1% Mucoromycota, two sequences of Olpidium bornovanus (Fungi incertae sedis), one sequence of Blastocladiomycota (Allomyces arbusculus), and one sequence of Chytridiomycota (Batrachochytrium dendrobatidis). Considering the sequences of all selected markers, only the phyla Cryptomycota and Entorrhizomycota were not represented. Based on ITS, using a cutoff of 98%, all sequences comprise 3047 OTUs, with the majority being Ascomycota (2088 OTUs) and Basidiomycota (681 OTUs). Previous numbers based mainly on morphological and bibliographical data revealed 5264 fungal species from Brazil, with a predominance of Basidiomycota (2741 spp.) and Ascomycota (1881 spp.). The unidentified ITS sequences not assigned to a higher taxonomic level represent 1.61% of all ITS sequences sampled and correspond to 38 unknown class-level lineages (75% cutoff). A maximum likelihood phylogeny based on LSU illustrates the fungal classes occurring in Brazil.

An association between the Antarctic mite Alaskozetes antarcticus and an entomophthoralean fungus of the genus Neozygites

A fungal pathogen provisionally identified as Neozygites cf. acaridis has recently been isolated from the Antarctic oribatid mite Alaskozetes antarcticus. The identification of the fungus is discussed with reference to recent changes in the taxonomy of Neozygites. The potential role of the fungus in the Antarctic mite populations is considered in relation to the known mite life cycles, and the particular environmental conditions in the Antarctic.

Failure of the mite-pathogenic fungus Neozygites tanajoae and the predatory mite Neoseiulus idaeus to control a population of the cassava green mite, Mononychellus tanajoa

Monitoring of a population of the phytophagous cassava green mite, Mononychellus tanajoa (Bondar), and its natural enemies was undertaken in central Bahia, Brazil, in mid-1996. In spite of the presence of extremely high densities of the predatory phytoseiid mite Neoseiulus idaeus Denmark & Muma, the phytophagous mite population reached such high densities itself that there was total overexploitation of the cassava plants, leading to total leaf loss. Meanwhile, the mite-pathogenic fungus Neozygites tanajoae Delalibera, Humber & Hajek did not affect the M. tanajoa population in its growth phase as there was no inoculum present, even though we predict from a simple regression model that there was the potential for epizootics at that time. Soon after the M. tanajoa population crashed due to defoliation, there could have been an epizootic but there were simply no mite hosts to infect. These data demonstrate the ineffectiveness of one natural enemy (the predator) in terms of prey population regulation and demonstrate the importance of timing in the possible effectiveness of the other (the pathogen). For the pathogen, this probably explains its sporadic effect on host populations as previously reported. We conclude that the fungus is likely to be most useful as an adjunct to biological control with predatory mites other than N. idaeus.

Diversity of acaropathogenic fungi in Poland and other European countries

The occurrence, species diversity and some aspects of taxonomical affinity and host selectivity of acaropathogenic fungi associated with phytophagous, saprotrophic and predacious mites in Poland and other European countries were investigated on wild and cultivated plants, in insect feeding sites under the bark and in decayed wood. From among 33 species of fungi affecting mites only five species of Entomophthorales were separated and the most numerous were Neozygites floridana mostly on Tetranychus urticae, N. abacaridis on a few eriophyid species, and Conidiobolus coronatus attacking gamasid mites most frequently of the genus Dendrolaelaps. The most frequent mite pathogens occurring in mite communities on plants and in wood infested by insects were of the genus Hirsutella. Until now 13 of their form-species have been recognized in these habitats, but only H. kirchneri, H. necatrix and H. thompsonii (including its variety synnematosa) can be treated as exclusive oligophagous pathogens of phytophagous mites, though their potential host range seems to embrace only selected eriophyid or tarsonemid mites. Taxonomical differentiation of fungal strains was based on close morphological observations and molecular analysis of ITS region sequences. Two new species of acaropathogenic fungi were described in these studies. Hirsutella danubiensis sp. nov. was found in the tetranychid T. urticae, whereas H. vandergeesti sp. nov. affected phytoseiid mites of the genera Amblyseius, Neoseiulus, Seiulus and Typhlodromus, and the tarsonemid Tarsonemus lacustris.

Lessons from interactions within the cassava green mite fungal pathogen Neozygites tanajoae system and prospects for microbial control using Entomophthorales

Most fungal pathogens lack the capacity to search for their host but rather develop sit-and-wait strategies that favour contact with them. The success of these strategies depends upon the interactions of the pathogen with its host, the host plant and the environmental conditions, which altogether determine its transmissibility. Given the limited success that has characterized application of sustainable microbial control, particularly using Entomophthorales, interaction studies have been conducted with the entomophthoralean fungus Neozygites tanajoae, pathogenic to the cassava green mite (CGM), Mononychellus tanajoa, to help understand differences observed between laboratory and field performances of this pathogen. Reciprocal pathogen-host interactions as well as tritrophic interactions involving the host plant were studied. It was found that herbivory triggers the release of volatiles that promote sporulation of isolates of N. tanajoae, whereas the host mite avoids haloes of spores of this pathogen. However, the host mite does not avoid the pathogen when inside the mummified fungus-killed cadaver. The status of microbial control of CGM in Africa is reviewed and implications of these interactions are discussed for prospective application of microbial control using Entomophthorales.