A tale of three acaropathogenic fungi in Israel: Hirsutella, Meira and Acaromyces

We review published and unpublished studies conducted in Israel with six acaropathogenic fungi, assayed in order to control the citrus rust mite, Phyllocoptruta oleivora (Ashmead) (CRM). Hirsutella thompsonii Fisher was introduced twice, killed 80-90% of the exposed mites, but due to its requirements for near-saturation humidities was deemed unsuitable for local outdoors conditions. Hirsutella kirchneri (Rostrup) Minter et al. and Hirsutella necatrix Minter et al. were also introduced and assayed against CRM and spider mites, but their efficacy was unsatisfactory. Three indigenous fungi found to be associated with mites, Meira geulakonigii, Meira argovae and Acaromyces ingoldii--all three recently described by Boekhout, Gerson, Scorzetti & Sztejnberg--were assayed against several mites. Meira geulakonigii killed 80-90% of several spider mites and of the CRM, and caused some mortality of Iphiseius degenerans (Berlese), one out of three phytoseiid predators assayed. Mortality was not due to parasitization; extracts from the media in which the fungi had developed caused considerable mite death, suggesting that it was a result of fungal toxins. Data from a field study indicated that spraying blastoconidia of M. geulakonigii on grapefruits infested by CRM significantly reduced pest-incurred damage from 23 to 13%. Applying qRT-PCR methodology indicated that M. geulakonigii was endophytic within sealed grapefruit flowers and in the flavedo of the fruits' peel. Neither in the laboratory nor in the field was any evidence ever obtained that this fungus damaged the plants, leading us to hypothesize that M. geulakonigii serves as a “body guard” of grapefruits (and perhaps other plants as well). All three fungi suffered very little mortality after being exposed to various insecticides and acaricides that are in current local use (with the exception of sulfur). The ability of M. geulakonigii to reduce mite numbers without affecting the host plant, the minimal fungal effect on some predatory mites, its endophytic nature along with the apparent tolerance of M. geulakonigii to many insecticides and acaricides, suggest that this fungus could be suitable for integrated pest management (IPM) program.