Aims
To formulate the entomopathogenic fungus Beauveria
bassiana in invert emulsion, then apply it against adults of almond bark beetle
(Scolytus amygdali) under laboratory and field conditions.
Methods and Results
The effect of formulated B. bassiana in invert
emulsion against S. amygdali adults was shown by comparing the mortality
percentage of adults exposed to the formulated fungus using a Petri dish
treatment method and by field applications to infested peach trees with
mortality of adults exposed to the unformulated fungus or the untreated
control. Results obtained from both exposure methods have indicated that
treatment of S. amygdali adults with the formulated fungus resulted in a
significantly higher mean mortality percentage (P < 0.05) when compared with
the treatment with the unformulated fungus or the untreated control. This
mortality ranged from 81.2 to 100%, 10 days after treatment with the formulated
fungus when compared with 6.7 to 49.6% mortality, 10 days after treatment with
the control or the unformulated fungus, respectively. Viability of the fungus
conidia in invert emulsion was assessed by calculating the germination
percentage of the conidia over time. Results indicated a high storage stability
shown by a small loss of germination percentage for the formulated conidia of
both strains (5.8 to 8.4% over a 12-week period) vs a low storage stability
shown by a high loss of germination percentage for the unformulated conidia of
the same strains (58.9 to 61.0% over the same period). The presence of B.
bassiana in the galleries of beetles following the treatment of infested trees
was shown in the present research.
Conclusions
The results obtained have demonstrated a
significantly higher level of efficacy of formulated B. bassiana in invert
emulsion against S. amygdali adults under laboratory and field conditions. The
ingredients of invert emulsion used in the formulation of the fungus had a
negligible effect on the viability of formulated conidia when compared with the
unformulated.
Significance And Impact Of The Study
Results obtained in the present research are
promising and may be exploited commercially to control S. amygdali adults on
various species of stone fruit trees, especially peach trees. This type of
biocontrol of this insect may be used as an alternative means to chemical
control for management of the insect. No adverse environmental impacts of the
fungus or its formulation have been observed during application.
The occurrence of entomopathogenic fungi was investigated in irrigated vegetable fields and citrus orchards soils, over a nine-month period (April-December 1999), using the Galleria bait method (GBM). Entomopathogenic fungi were found to occur in 33.6% of the soil samples studied, with positive samples yielding 70 fungal isolates, belonging to 20 species from 13 genera. Conidiobolus coronatus was the most frequent and abundant entomopathogenic species recovered, comprising 31.4% of the total number of isolates. Soil pH, soil moisture content and the geographical location had minor or no effect on the isolation of entomopathogenic fungi in the fields studied. On the other hand, organic matter content of soil, and vegetation type were found to significantly affect the occurrence of entomopathogenic fungi in soil habitats, with orchard fields yielding larger numbers of isolates than vegetable fields. Using Koch’s postulates the pathogenicity of fungal isolates to Galleria larvae was found to range from 16–100% (mortality rate). Isolates of C. coronatus proved to be the most virulent isolates recovered. The effect of media and temperature on mycelial growth rate, conidial production and conidial germination of six entomopathogenic fungal species (C. coronatus, Entomophaga grylli, Erynia castrans, Hirsutella jonesii, Paecilomyces farinosus and Sporodiniella umbellata) was also studied.Mycelial growth rate, spore production and spore germination were significantly affected by media, temperature and isolates. In view of the present results, C. coronatus appears to be a good candidate for pest control in agricultural soils, as it has a wide tolerance to agricultural practices, has frequently been isolated from both vegetable and orchard fields, and is characterized by high mycelial growth rate, conidial production and conidial germination.