Selection and yield optimisation of a Beauveria bassiana isolate for the biological control of leaf cutter ants

ABSTRACT

Leaf cutter ants are one of the most important pests to agriculture and forestry in the Neotropics. One environmentally friendly solution to control them is biological control with the use of conidia of some fungi, such as Beauveria bassiana. We tested several isolates of this fungus (obtained from leaf cutter ants) by inoculating ants from seven colonies of Acromyrmex lundii with 5 × 10⁶ conidia ml⁻¹ suspensions. All the isolates proved to be good controllers, but isolate 5 (B5) was found to be the best performing option, because it caused the death of 92.3% of the ants in 4–5 days. Isolate 7 (B7) was the second-best option and used for comparative purposes. Further assays were performed with the isolate B5 to optimise yield production. Three types of rice (brown, parboiled and white rice), soybean hull and yerba mate (Ilex paraguariensis leaves) were tested as substrates, and following that, different conditions of solid-state fermentation (SSF) were changed so as to select the most productive combination. Among treatments, we selected brown rice as substrate and a temperature of 28°C and 75–85% relative humidity in the SSF chamber because this allowed a production of 6.4 × 10⁸ and 1.2 × 10⁹ conidia of B5 and B7 per gram of final substrate with a 98% and 97.5% of germination, in 10 days, respectively. The differences in yield obtained under the same conditions for both isolates show that yield is isolate-dependent. A description of the customised design of the SSF chamber used is included.

KEYWORDS:

• Ant control
• entomopathogens
• conidia production
• solid fermentation

Acknowledgements

The authors thank Dr Migheli and Dr Glare for their comments. The authors also thank Norberto Toth for technical support on the construction of the new device. María Laura Terrone helped with the English version. The authors thank CONICET and ANPCyT.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

D. Goffré http://orcid.org/0000-0002-9706-2974

Additional information

Funding

This work was funded by grants by the National Agency for Science and Technology Promotion (ANPCyT) under Grant PICT START UP 1936 to PJF; Quilmes National University under Grant Research Program in Biological Interactions 1009/11 to PJF; and Quilmes National University under Research Support Grant SAI 2128/2013 to DG.