MICROBIOLOGICAL CHANGES IN THE NESTS OF LEAF-CUTTING ANTS FED ON SESAME LEAVES

The number of bacteria and yeasts occurring in the organic matter insi de the nests were determined both in colonies of leaf-cutting ants rea red on Eucaliptus alba (control) or Sesamum indicum (experimental). Se same leaves induce imbalance and nests usually die. Ln control nests t he number of bacteria in newer sponge and in older sponge were similar (3.6 x 10(5) and 1.4 x 10(5) CFU/g, respectively) whereas in waste de posit the mean reached 7.3 x 10(7) CFU/g. The Most Probable Number (MP N/g) of yeasts were 2.7 x 10(4), 1.3 x 10(5)/g and 2.2 x 10(4) for new er sponge, older sponge and waste deposit, respectively. Using materia l from older sponge for comparison, the number of bacteria and yeasts reared on sesame leaves showed significant differences. The number of bacteria was 3.3 x 10(7) CFU/g, a value close to that found in waste d eposit of normal (control) nests, whereas the number of yeasts was 6.7 x 10(5)/g. These changes in microbial populations due to the effect o f sesame leaf uptake could be a significant factor in nest imbalance a nd mortality when leaf-cutting ants are consuming toxic plants.