A new fungal isolate for the control of Diabrotica speciosa.

CONSOLO, V. F.; CABRERA, G.; SALERNO, G. L.; BERÓN, C.

Foz do Iguassu. Brasil

Congreso; XXI International Congress of Entomology; 2000

Many species of cucumber beetles occur in South America. Particularly, in Argentina the most important coleopteran pest is Diabrotica speciosa as important cucumber pest. Both larvae and adults cause serious damage in all plant organs (flowers, roots and tubers). Entomopathogenic fungi are key regulatory factors in insect populations and also are the pathogens of choice for Coleoptera. Thus the use of biological agents will be alternative in the control of cucumber pest. The goal of this project was the search of new strains with potential toxicity for the control of D. speciosa. Sixteen fungal isolates were obtained from soil samples and dead insects (Maecolaspis bridariolii larvae and D. speciosa adults). In a screening assays the isolate FDH13, identified as Beauveria bassiana, caused 70% of mortality in the third instar of D. speciosa. The CL50 value calculated using six different concentrations was 3.5 x 1010 conidia/ml. Then FHD 13 was selected for preparing biological formulations in different oils. The conidial viability in the formulates was estimated at different temperatures (4, 17and 26°C) and periods of storage. The best formulates conditions (99.5% viability) resulted in the preparation with corn oil stored at 4°C during 28 days. It was evaluated in preliminary assay the pathogenicity of conidial formulation in the third instar of D. speciosa reaching 65% of mortality. In addition protease activities were measured in the culture media of the isolates in the presence and absence of D. sopeciosa cuticles. Enzymes activity was several times higher in the presence than in the absence of cuticles in all cases. However, it could not be established a correlation between proteolitic activity and mortality. The isolate FHD 13 may be a good candidate in the tested as bioinsecticide in large scale.