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

Abstract

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.

Interactions between the predatory mite Typhlodromalus aripo and the entomopathogenic fungus Neozygites tanajoae and consequences for the suppression of their shared prey/host Mononychellus tanajoa

“…Nevertheless, the interactions reported by Ariori and Dara (2007) is consistent with our results in that high T. aripo densities in the combined treatments were associated with decreased N. tanajoae infections. This mechanism may explain also the failure of N. tanajoae and the predatory mite Neoseiulus idaeus to control a population of CGM in central Bahia, Brazil (Elliot et al 2008). While predation of T. aripo on infected CGM may reduce the level of fungus inoculum, the predator could also indirectly increase fungus inoculum by spreading fungus propagules as it foraged on cassava plants.…”

IPM Potentials of Microbial Pathogens and Diseases of Mites

“…Elliot (1998) considered perennial survival in the field of the fungus in mummies highly improbable as experiments had demonstrated that no viable fungus could be detected in dead mites after 2 month of hot and dry storage, both in the field and in the laboratory. In a later report, Elliot, De Moraes and Mumford (2008) discussed results of an experiment in which they monitored a population of the CGM and its natural enemies in central Bahia. Despite the presence of very high levels of the predatory mite Neoseiulus idaeus, there was an overexploitation of the cassava plants by the cassava green mite, which led to a total leaf loss.…”

“…We know too little how the fungus overcomes unfavorable periods, about the role of resting spores and under which conditions may resting spores sporulates. Interesting observations were made by Elliot et al (2008) in a cassava field in the state on Bahia, Brazil. Epidemics of the fungus were virtually absent when cassava green mite populations reached high densities, as not sufficient fungus inoculum was present.…”