Comparison of volatile blends and gene sequences of two isolates of Metarhizium anisopliae of different virulence and repellency toward the termite Macrotermes michaelseni

Abstract

Previously, we reported an interesting relationship between virulence and repellency of different isolates of the fungus Metarhizium anisopliae towards the termite Macrotermes michaelseni: the higher the virulence of a given isolate, the greater its repellency. In the present study, we compared the volatile profiles of two isolates, one that was more virulent (and repellent) and one that was less virulent (and repellent) to the termite. The prominent components of the two blends were characterized by gas chromatography-mass spectrometry and authenticated by gas chromatography coinjections with synthentic standards. There were both qualitative and quantitative differences between the two blends. The repellencies of synthetic blends of 10 prominent constituents of the volatiles of the two isolates were compared and that of the more virulent isolate was found to be significantly more repellent. Subtractive bioassays were carried out with one of the constituents of each of the two 10-component blends missing at a time to determine its relative contribution to the overall repellency. The results indicated that the repellency of the volatiles of each isolate was primarily due to synergistic effects of a smaller number of constituents. Intraspecific differences between the two isolates were also reflected in their nucleotide sequences.

Comparison of Volatile Blends and Nucleotide Sequences of Two Beauveria Bassiana Isolates of Different Virulence and Repellency Towards the Termite Macrotermes Michealseni

“…Moreover, that study showed a strong correlation between virulence and repellency for different isolates of these fungi. In a subsequent study, we found clear qualitative and quantitative differences in the volatile blends emitted by two selected isolates of M. anisopliae that had different levels of virulence and repellency towards the termite (Mburu et al, 2011). Intra-specific differences between the two isolates of the fungus also were reflected in their nucleotide sequences (Mburu et al, 2011).…”

“…Termite Trapping and Maintenance Worker castes of the termite, Macrotermes michaelseni, trapped in the field (Tamashiro et al, 1973) were transported to the laboratory and maintained as previously described (Mburu et al, 2009(Mburu et al, , 2011. Before repellency bioassays, termites were transferred into an incubator (26±2°C and 90±5 % relative humidity in the dark) where they were kept for 20 min for acclimatization (Mburu et al, 2009(Mburu et al, , 2011.…”

“…Before repellency bioassays, termites were transferred into an incubator (26±2°C and 90±5 % relative humidity in the dark) where they were kept for 20 min for acclimatization (Mburu et al, 2009(Mburu et al, , 2011.…”

“…Scaled-up Production of Dry Conidia for Volatile Collection Conidia for collection of volatiles were grown on long white rice substrates following the technique described previously (Mburu et al, 2011). Conidia were harvested and stored in a refrigerator (4°C) for 1 month before use.…”

“…Volatile blends from dry conidia (40 g) of each isolate were trapped separately using Super-Q polymer (80-100 mesh size; ARS) as previously described (Mburu et al, 2011). Volatiles were eluted with dichloromethane (100 μl) into 2 ml vials on ice and concentrated by flushing with purified nitrogen (3 mlmin -1 ).…”