Toxicity of synthetic piperonyl compounds to leaf-cutting ants and their symbiotic fungus

The development of Leucoagaricus gongylophorus, the fungus cultured by the leaf-cutting ant Atta sexdens was inhibited in vitro by synthetic compounds containing the piperonyl group. In addition, worker ants that were fed dai ly on an artificial diet to which these compounds were added had a higher m ortality rate than the controls.:The inhibition of the fungal growth increa sed with the size of the carbon side chain ranging from C-1 through C-8 and decreasing thereafter. 1-(3,4-Methylenedioxybenzyloxy)octane (compound 5) was the most active compound and inhibited the fungal development by 80% at a concentration of 15 mug ml(-1). With worker ants the toxic effects start ed with compound 5 and increased with the number of carbons in the side cha in. Thus, for the same concentration (100 mug ml(-1)) the mortality rates o bserved after 8 days of diet ingestion were 82%, 66% and 42%, for 1-(3,4-me thylenedioxybenzyloxy) decane, 1-(3,4-methylenedioxybenzyloxy) dodecane and compound 5, respectively, whereas with commercial piperonyl butoxide the m ortality was 68%. The latter compound, which is known as a synergist insect icide, was as inhibitory to the symbiotic fungus as the synthetic compound 5. The possibility of controlling these insects in the future using compoun ds that can target simultaneously both organisms is discussed. (C) 2001 Society of Chemical Industry.