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

Abstract

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.

Pathogenicity and host specificity of Brazilian and African isolates of the acaropathogenic fungus Neozygites tanajoae to mite species associated with cassava

“…This is in accordance with previous reports, where the Brazilian isolates in general caused the highest levels of mortality in CGM populations (Delalibera and Hajek 2004; Hountondji et al. 2007; Delalibera 2008; Hountondji 2008; V. B. Agboton, R. Hanna and A. von Tiedemann). Interestingly, the Brazilian isolate (Adjohoun1, Brazil–Benin isolate) collected from a post‐release field in Benin (WestAfrica) induced a lower level of mortality similar to the African isolates in the laboratory bioassay.…”

“…Although, the Brazilian isolate collected from post‐release field in Benin showed a difference compared to Brazil–Brazil isolate, it was not different from the African isolates, which confirm the complexity of entomopathogenic fungus N. tanajoae to be separated by bioassays evaluation. Previous virulence studies in the laboratory also failed to reveal significant differences between Brazilian isolates and the African isolates (Hountondji 2008). This finding was corroborated by our results on whole cassava plants that were not able to show significant differences between African and Brazilian isolates although the highest level of fungal infection was observed with the Brazilian isolate.…”

“…Host range is an important characteristic in the selection of biocontrol candidates (Hountondji 2008). The present results showed that Brazilian and African isolates of N. tanajoae were similar in their host range as all failed to infect any of the non‐target mite species tested.…”

“…1992, 2000; Delalibera 2002). It infects the mite through body contact and emission of a germ tube that penetrates the cuticle of the mite and develops into hyphal bodies, which multiply through binary division and progressively fill the haemocoel of mites (Hountondji 2008). Infected mites can still move the first and the second day, and may thus help in the dissemination of the pathogen.…”

“…1996; Dara et al. 2001; Hountondji 2008). The epizootic potential of Brazilian isolates of N. tanajoae has led to experimental introduction of these isolates to Benin, (West Africa) in 1998 and 1999 for the control of cassava green mites (CGM) (Hountondji et al.…”