Effects of insect cuticular fatty acids on in vitro growth and pathogenicity of the entomopathogenic fungus Conidiobolus coronatus.

Eighteen fatty acids identified in the cuticle of three insect species representing differing susceptibilities to C. coronatus infection, were tested for effects on the in vitro growth and pathogenicity of the parasitic fungus. At all applied concentrations (0.1-0.0001% w/v) growth was inhibited by C(16:0), C(16:1), C(18:0), C(18:1), C(18:2), C(18:3), C(20:0) and C(20:1). At high concentrations spore germination was inhibited by C(7:0), C(8:0), C(9:0), C(10:0), C(12:0), C(18:2) and C(18:3) and hyphal growth was merely retarded by C(5:0), C(6:0), C(6:2), C(14:0), C(16:0), C(16:1), C(18:0,) C(18:1), C(20:0) and C(20:1). The presence of C(15:0) at the 0.1% concentration stimulated growth of C. coronatus. Sporulation was inhibited by all concentrations of C(16:0) and C(18-20) fatty acids. Low concentrations of C(5:0), C(6:0), C(6:2) and C(7:0) enhanced sporulation. Fatty acids C(5-12) as well as C(18:3), C(20:0) and C(20:1) decreased the ability of fungal colonies to infect G. mellonella while C(16:1) elevated it thus suggesting that C(16:1) may stimulate production of enzymes involved in the host invasion. Toxicity of metabolites released into incubation medium decreased with varying degrees in the presence of C(6:0), C(6:2,) C(7:0), C(9:0), C(12:0), C(16:1), C(18:2), C(18:3), C(20:0) and C(20:1); other fatty acids had no effect. Further work is needed to analyse the effects of exogenous fatty acids on the C. coronatus enzymes implicated in fungal pathogenicity as well as on the production of insecticidal metabolites.

In vitro assessment of the influence of nutrition and temperature on growing rates of five Duddingtonia flagrans isolates, their insecticidal properties and ability to impair Heligmosomoides polygyrus motility.

Diverse effects of two temperature regimes (20 and 30 degrees C) on the growing rates of five Duddingtonia flagrans isolates (MUCL 28429, CBS 143.83, CBS 561.92, CBS 565.50, and CBS 583.91) propagated on two liquid (MM, LB) and four solid substrates (CMA, SAB, SAB-GM, and SAB-HP) were observed. All D. flagrans isolates were able to produce chlamydospores but not on all substrates. None of the isolates produced trapping nets and conidia under applied growing conditions. D. flagrans isolates showed moderate insecticidal properties against Galleria mellonella larvae with mortality rates below 20%. Preincubation (18 h) of Heligmosomoides polygyrus infective (L3) larvae in fungal homogenates highly impaired in vitro spontaneous motility of nematodes. This may indicate the potential of D. flagrans bioactive substance(s) for use as biocontrol agents of parasitic nematodes.