Natural incidence and environmental profiling of the mite-pathogenic fungus Hirsutella thompsonii Fisher for control of the coconut mite in Sri Lanka.

Biological control using the mite-pathogenic fungus Hirsutella thompsonii is being investigated, targeting the economically important coconut mite (Aceria guerreronis) in Sri Lanka. Local surveys were carried out to assess background levels of H. thompsonii from coconut mite populations. Environmental profiling, based primarily in the laboratory, assessed the suitability of each isolate as a biological control agent. Coconut mites infected with H. thompsonii were found in each district we surveyed. Profiling indicated an optimum temperature for isolate growth of 25–30°C, with growth recorded at 35°C, for all isolates. Six hours of simulated tropical sunlight reduced spore viability, although viability still exceeded 84%. There were more pronounced losses in viability after 2 h of uninterrupted natural sunlight in a coconut plantation. However, there were indications that spore viability was being inhibited by a combined sunlight/temperature effect. There was no lethal effect on one of the coconut mite's p...