Chemical and behavioral aspects of insect-microbe interactions

Abstract

Insect microbe interactions were studied with leaf-cutting ants (Atta and Acromyrmex) and Drosophila fruit flies.Not only chemical, but also behavioral parameters were investigated to assist in describing relationships and dependencies of interactions. Rearrangement inside waste chambers and antimicrobial composition of waste particles from leaf-cutting ants and bramble plants as leaf source were studied.All waste heaps had a certain slope, no matter if there was an U-shaped, a donut-like or a nugget-like heap. Fresh waste particles were observed to be released onto the heap, thereafter a passive rolling-down of particles was observed and particles from the lower part of the waste heaps were transported into holes/tunnels by ants. In areas containing fresh waste particles, temporary turnover activities with moving tunnels or surface recirculation were observed. First experiments indicated, that there might be non-mutualistic fungi, whose growth was at least tolerated by leaf-cutting ants. Waste particles and bodies of dead ants showed microbial growth, especially greenish and whitish fungal hyphae. To compare the antimicrobial composition of leaf-cutting ants’ waste from different origins, bioassay-guided fractionation was used. Several differences and similarities were spotted for tested species.To the best of our knowledge, for the first time, bramble leaves and stems were described to contain both, antifungal and antibacterial compounds. The bioactive compounds were extracted using acidified methanol (only antibacterial) or diethyl ether-acetone mixtures (antibacterial and antifungal).Besides investigations in leaf-cutting ants’ waste, also R- and S-γ-octalactone from metapleural glands of Acromyrmex and Atta leaf-cutting ants were analyzed. They were shown to differ in dominance, enantiomer ratio and overall amount. Further experiments are necessary to prove possible influencing parameters, like communication or disinfection issues.For flightless Drosophila hydei, a novel behavioral assay was developed. Bacterial cells of Pseudomonas sp. D2p, isolated from Drosophila fruit flies, were shown to attract them. Cultivation conditions for D2p were studied, to enhance production of attractive volatile compounds. Several compounds like methylated pyrazines were present in GC-MS spectra and therefore tested for their attractiveness. Real-time tracking of fruit fly distribution was achieved by analyzing recorded movies with Matlab scripts.Further projects with different topics, like method development for chemical analysis of secondary metabolites or structure elucidation of degradation products after anaerobic desulfonation of 3-C4-SPC, were followed as well.