Adaptations of pyrophilous insects to burnt habitats: Odor signals, infrared receptors and behavior
von Thi Phuong Hoang
Datum der mündl. Prüfung:2019-10-22
Erschienen:2020-06-12
Betreuer:Prof. Dr. Carsten Mai
Gutachter:Prof. Dr. Carsten Mai
Gutachter:PD Dr. Helmut Schmitz
Gutachter:Dr. Gerrit Holighaus
Dateien
Name:Doctoral thesis_09.06.2020- FINAL_Corr- Thi ...pdf
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Zusammenfassung
Englisch
Pyrophilous insects are known to invade recently burnt habitats for food, mating and oviposition. They can approach fires due to their ability to recognize fire-specific volatile organic compounds (VOCs). Moreover, some of these insects also possess infrared (IR) receptors to detect fires and hot surfaces. The aim of this thesis is to examine recently burnt habitats for the presence of pyrophilous insects and identify cues suitable for them to find burnt habitats. This includes morphological and chemo-ecological studies unravelling the significance of IR receptors, IR radiation, volatile signals and behavior. Three major questions were selected to investigate how pyrophilous insects approach fires: 1) identify fire-specific VOCs that are released by different Vietnamese plant species and are suitable cues for pyrophilous insects, 2) testing the behavioral responses of pyrophilous insects to volatile and heat (IR radiation) stimuli, and 3) identifying the sensory adaptation of the pyrophilous flat bug Aradus candidatus found to be active in recently burnt habitats. Volatile analysis (gas chromatography – mass spectrometry) was used to identify fire-specific VOCs to be subsequently tested in the field for their ability to influence insect behavior. Electroantennography (EAG) was used to examine the perception of pyrophilous insects to these VOCs. With a scanning electron microscope (SEM), pyrophilous insects were examined for presence of IR receptors. The results were used to conclude how pyrophilous insects are adapted to recently burnt habitats. The trace analysis presented in chapter 3 of this thesis resulted in the detection of 55 VOCs that were released by four different Vietnamese plant species. Four of these VOCs identified as fire-specific were further tested in a behavioral field study. They derive from cellulose (hydroxyacetone, 5-methylfurfural) and lignin (guaiacol and 4-ethylguaiacol) degradation. Traps in a freshly burnt habitat baited with a mixture of these VOCs attracted 13 insect species belonging to the order Coleoptera that were not found in control traps positioned on adjacent unburnt land. Three of these were additionally found by hand collections, where another eight species of insects were found. The biodiversity of plant species seems to be associated with the chemo-diversity of fire-induced VOCs. This might play an important role for pyrophilous insects, thus linking plant diversity to the biodiversity of pyrophilous insects. The attraction of pyrophilous insects to IR and volatile stimuli is investigated in chapter 4. A total of 26 insect species were recorded. The attraction of pyrophilous insects towards fire-specific VOCs, IR and combined stimuli was significantly higher when compared to the controls. One species (Litochrus sp. 1, Phalacridae, Coleoptera) was found in traps of all combinations. Fungivorous insects were caught significantly more often in the IR traps, whereas VOC traps attracted carnivorous insects significantly more often. All traps attracted herbivorous insects. Eight insect species were caught in more than one trap. Among them, only one species was caught in all traps. Two species belonging to the family Cleridae (Coleoptera) were caught in different traps: while Anthicoclerus sp. 1 was recorded exclusively in the IR trap also containing the VOCs mixture, Anthicoclerus sp. 2 was trapped only in the IR trap without VOCs. These results hint at a complex evaluation of IR and olfactory stimuli for resource location by different members of the pyrophilous insect community. The study on adaptation and behavior of A. candidatus in chapter 5 showed that A. candidatus elicits olfactory responses in electroantennograms (EAG) to hydroxyacetone, 5-methylfurfural, guaiacol, 4-methylguaiacol and 4-ethylguaiacol. Additionally, A. candidatus shows attraction to the traps baited with a mixture of fire-specific VOCs. Aradus candidatus also elicits a dose response to three other VOCs: Nonanal, 3-octanone and 2(5H)-furanone. In morphological studies, IR receptors were found in the propleural region of A. candidatus. These IR receptors have an outer shape similar to other species of the genus Aradus, including A. albicornis, A. lugubris and A. fuscicornis. The results of this chapter illustrate that pyrophilous insect species equipped with IR receptors show a highly pyrophilous behavior. The results from these three studies show that pyrophilous insects can detect fire-specific VOCs, which helps them to approach fires. However, not all insects that are able to perceive a single fire-specific VOC are necessarily pyrophilous. A mixture of different fire-specific VOCs is recommended for testing the attraction of pyrophilous insects to fires. By attraction to both fire-specific VOCs and IR, some insect species revealed their distinct pyrophilous behavior. This was confirmed by demonstrating VOC and IR detection in A. candidatus on a morphological and physiological level.
Keywords: Pyrophilous Insects; Chemical ecology; Infrared receptors; Burnt habitats; forest fires; burnt wood volatiles