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Cuticular lipids of the parasitoid Lariophagus distinguendus (Hymenoptera: Pteromalidae): Chemistry and behavioural function
| Content Provider | Semantic Scholar |
|---|---|
| Author | Kühbandner, Stephan |
| Copyright Year | 2015 |
| Abstract | Animals communicate with each other by means of optical, acoustic, tactile, electrical and chemical signals. This doctoral thesis deals with the contact sex pheromone of the parasitic wasp species Lariophagus distinguendus (Hymenoptera: Pteromalidae). Males respond to the cuticular lipids of conspecific females by stereotypic courtship behaviour. Young males and pupae of either sex also produce the cuticular lipids that release courtship behaviour in conspecific males. However, with increasing age, males actively remove 3 MeC27 and some other straight-chain alkanes and methylalkanes from their cuticular lipid profile. The disappearance of these components is accompanied by a loss in their attractiveness towards other males. The capability of the males to actively remove components of their cuticular lipid profile probably rendered a non-communicative barrier against water loss and pathogen attack into a species-specific contact sex pheromone. These findings from previous work led to some questions: is 3-MeC27 actually part of L. distinguendus contact sex pheromone? If this is true, is 3 MeC27 alone bioactive or only in combination with other cuticular lipids? Do L. distinguendus males respond enantioselectively towards 3-MeC27? Can the addition of synthetic 3-MeC27 onto the cuticle of aged males restore their bioactivity? Can 3-MeC27 be replaced by structurally related methylalkanes that differ in their chain length or the position of the methyl-branch? Or does the application of additional n-alkanes and structurally related methylalkanes interfere with the intact cuticular profile? During this doctoral thesis, I have shown that 3-MeC27 is the key component of the female contact sex pheromone of L. distinguendus. However, unlike in other insects studied so far, the key component 3-MeC27 alone is not attractive to L. distinguendus males. For a full behavioural response, 3-MeC27 has to be perceived by the males together with a chemical background consisting of the other cuticular hydrocarbons (CHC) and hitherto widely ignored cuticular triacylglycerides (TAG). The occurrence of cuticular TAGs has probably been underestimated in the past and a behavioural function for TAGs is described here for the first time. Behavioural experiments with fractionated wasp extracts and synthetic 3-MeC27 and other structurally related components revealed that the cuticular lipid profile of aged males can be rendered attractive again by the addition of synthetic 3-MeC27 in physiological amounts. L. distinguendus males responded specifically to even small variations of chain length or methyl-branch position of monomethylalkanes because chemically related components such as 3-MeC29 or 5-MeC27 could not replace 3-MeC27. On the contrary, the addition of such components rendered behaviourally active cuticular lipid profiles of females and young males unattractive. These results demonstrate that the contact sex pheromone in L. distinguendus is perceived as a whole, possibly by means of a specialized sensillum type as used by ants in the context of nestmate recognition. The males of L. distinguendus were able to differentiate between the two enantiomers of 3 MeC27, but this was only behaviourally relevant when fractionated extracts combined with (R) or (S)-3-MeC27 were applied onto filter paper and offered to the responding males. In experiments with three-dimensional wasp dummies, however, L. distinguendus males did not show a preference for one of the enantiomers implying that a visual component of the dummy also plays a role. During the development of parasitoids, the host is typically the only available food source. Hence, host species and quality might affect the CHC profiles of parasitoids and thus also its intraspecific communication. In this doctoral thesis it was shown that the CHC profiles of L. distinguendus wasps are host specific. CHC profiles of wasp strains reared on different host species were distinguishable by a non-metric multidimensional scaling (NMDS) and a non-parametric multivariate analysis of variance (NPMANOVA). In particular, wasps reared on Stegobium paniceum could be significantly distinguished from all wasps reared on other hosts according to their CHC profile. Remarkably, a host shift from Sitophilus granarius to Stegobium paniceum lead to a significant shift of the CHC profiles within one generation. Provided that these differences actually influence the mate recognition behaviour in L. distinguendus, these results suggest that host shifts might result in the reproductive isolation of host races and, in the long-term, end in speciation. As part of this doctoral thesis, SPME-FAME-GC-MS was developed as a new easy-to-use method for the solvent-free analysis of more polar cuticular TAGs. With this method, the TAGs were sampled from the insect cuticle with the solid phase microextraction (SPME) and transesterified in situ with trimethylsulphonium hydroxide into more volatile fatty acid methyl esters (FAME). These can be analysed easily by standard gas chromatography coupled with mass spectrometry (GC-MS) techniques. The occurrence of TAGs on the insect cuticle might have been widely underestimated, because their high melting points make them undetectable with standard GC-MS. Furthermore, the use of solvents for the extraction of cuticular lipids runs the risk of additionally extracting lipids from internal tissues. Six insect species from four different orders were analysed with the new method of SPME-FAME-GC-MS, and TAGs were detected on the cuticle of all examined species. Thus, TAGs might be far more common cuticular components of insects than usually thought. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://epub.uni-regensburg.de/30097/1/Doktorarbeit_Stephan_K%C3%BChbandner.pdf |
| Alternate Webpage(s) | https://epub.uni-regensburg.de/30097/1/Doktorarbeit_Stephan_K%C3%BChbandner.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
