Conidiobolus lunulus, a new entomophthoralean species isolated from leafcutter ants.

Entomophthoralean fungi with pathogenic abilities to infect social insects are rare. Here, we describe a fungus isolated from leafcutter ants. Morphologically, the fungus has spherical primary conidia and two types of microconidia: one with the same shape as the primary conidia and another with an elliptical to half-moon shape. The fungus also produces villose conidia known previously only from Conidiobolus coronatus. A multilocus phylogenetic analysis was performed with nuc rDNA sequences from three regions (28S, 18S, and internal transcribed spacer [ITS]). Our isolates are distinguished as a new species, described here as Conidiobolus lunulus, and is more closely related to C. brefeldianus than to C. coronatus, despite the greater morphological resemblance to the latter. Morphological differences, unique phylogenetic placement, and isolation from an altogether new host support this finding. This is the first record of an entomophthoralean species isolated from leafcutter ants.

Purpureocillium lilacinum, potential agent for biological control of the leaf-cutting ant Acromyrmex lundii.

Many leaf-cutter ant species are well known pests in Latin America, including species of the genera Acromyrmex and Atta. An environmentally friendly strategy to reduce the number of leafcutter ants and avoid indiscriminate use of chemical pesticides is biological control. In this work we evaluated the effectiveness of a strain of the entomopathogen Purpureocillium lilacinum, against worker ants from six Acromyrmex lundii field colonies, after immersions in pure suspensions at a concentration of 1×10(6)conidiaml(-1). Survival of ants treated with P. lilacinum was significantly lower than that recorded in controls, and median lethal time (LT50) was 6-7days. P. lilacinum was responsible for 85.6% (80.6-89.7) of the mortality in inoculated ants, in which we found that the percentage of other entomopathogens that naturally infected ants decreased also, suggesting a good competitive capability of the fungus. Horizontal transmission to non-inoculated ants was also evidenced, given that 58.5% (41.9-64.2) of them died because of P. lilacinum. Moreover, we tested pathogenicity for three concentrations of this strain (1.0×10(4), 10(6) and 10(8)conidiaml(-1)) and found a significantly faster mortality of ants and greater median percentage of infection at 10(8)conidiaml(-1) of P. lilacinum. CL50 value was 2.8×10(5)conidiaml(-1). We thus propose the use of P. lilacinum as a biological control agent of leafcutter ants in crops and plantations.