Laboratory evaluation of temperature effects on the germination and growth of entomopathogenic fungi and on their pathogenicity to two aphid species

Abstract

As part of an approach to select potential mycoinsecticides for aphid biocontrol, we investigated the effects of temperature on the growth, germination and pathogenicity of some hyphomycete fungi. Commercially available mycoinsecticides (based on Beauveria bassiana (Balsamo) Vuillemin and Verticillium lecanii (Zimmermann) Viegas) and other isolates of B bassiana, V lecanii, Metarhizium anisopliae (Metschnikoff) Sorokin and Paecilomyces fumosoroseus (Wize) Brown & Smith were evaluated. The rate of in vitro conidial germination of all isolates was slower at 10 and 15 degrees C than at 20 and 25 degrees C. Similarly, in vitro growth of most isolates was adversely affected at 10 and 15 degrees C. The greatest reduction at 10 degrees C in rates of conidial germination and colony growth, compared with other temperatures, was for M anisopliae isolates. Germination of V lecanii (isolate HRI 1.72) was fastest at 10 degrees C compared with the other fungi. It was also the most pathogenic of three isolates tested against Aphis fabae Scopoli and Myzus persicae Sulzer at 10, 18 and 23 degrees C. Generally, A fabae was more susceptible than M persicae to infection by the fungal isolates tested. A significant interaction between aphid species and temperature indicated that the pathogenic nature of an isolate was dependent not only on the target aphid species but also the temperature conditions of the bioassay. The series of studies, detailed above, allowed a temperature profile to be formed for the different isolates. Verticillium lecanii isolate HRI 1.72 (commercialised as Vertalec) was the most promising isolate selected from results of the series of experiments. Temperature profiles in conjunction with infectivity assays can be useful in selecting appropriate isolates for a particular thermal environment.

Selection of fungal isolates for virulence against three aphid pest species of crucifers and okra

“…Radial growth data were fitted by regression analysis (y = vt ? b), and then the linear regression slope (v), which indicated the growth rates (velocity in mm d -1 ), used as the main parameter to evaluate the influence of temperature on fungal growth Ouedraogo et al 1997;Yeo et al 2003;Davidson et al 2003). Means were separated using Tukey HSD test.…”

“…This study has identified M. anisopliae isolate ICIPE 62 as potential candidate for further development as biopesticide for the control of the three aphid species based on the following desirable traits: virulence against the three target aphid pests, high conidial production, speed of kill (LT 50 ), lower LC 50 values, and efficacy across a broad range of temperatures (Yeo et al 2003). In addition, since aphids usually form large colonies on plant surfaces, the isolate of M. anisopliae ICIPE 62 profusely sporulated on dead aphids and could serve as source of inoculum for infection of healthy aphids which may lead to acute mortality.…”

Variation in growth at different temperatures and production and size of conidia in hybrid strains of Verticillium lecanii (Lecanicillium spp.) (Deuteromycotina: Hyphomycetes)

“…A further study of conidial traits of hybrid strains, including the study of the germination rate, conidia productivity on insect cadavers, and mode of conidiation, should be conducted. Yeo et al (2003) suggested that the screening procedure should follow a "biorational approach" based on the selection of isolates on many traits, including the ability to grow and germinate quickly at temperature and humidity conditions under which the mycoinsecticide would be used, virulence to the target pest, production potential, and compatibility with chemical pesticides and other natural enemies. This method enables the selection of more appropriate isolates that possess the ability to operate over a range of abiotic conditions under which they will be used, with little impact on nontarget natural enemies.…”

Effect of temperature on the in vitro radial growth of Zoophthora radicans and Pandora blunckii, two co-occurring fungal pathogens of the diamondback moth Plutella xylostella

“…Although, there are some reports that show some correlation between thermal preferences of entomopathogenic fungi (Ascomycetes: Hypocreales) and geographical origin (Fargues et al 1992;Vidal et al 1997;Thomas and Jenkins 1997;Dimbi et al 2004), there are also reports where no correlation between origin and thermal preferences is indicated (e.g. Moorhouse et al 1994;Yeo et al 2003).…”