Effects of two adipokinetic hormones (Pyrap-AKH and Peram-CAH-II) on the presence of diacylglycerol (DG) molecular species and their fatty acid (FA) constituents in the haemolymph of the firebug Pyrrhocoris apterus were investigated using liquid chromatography (HPLC) and electrospray ionization mass spectrometry (ESI-MS). The results show that DGs with characteristic FAs are preferentially mobilized from the fat body (FB) by the action of both the AKHs produced by P. apterus. Both the macropterous and brachypterous morphs have similar DG and FA profiles. A difference in the action of the Pyrap-AKH and the Peram-CAH-II, however, results in distinct differences in the distribution of FAs in the macropterous morph. It seems that C16 to a slight extent and unsaturated C18 FAs mainly play a dominant role in the AKH based action, in particular linoleic acid (18:2), which represents 50-60% of the total DG mobilized. The metabolically active C16 and C18 FAs are preferentially absorbed from the linden seeds and accumulated in the FB. The relationships between AKH action and FA distribution in DGs in P. apterus, compared to other insect species are summarized and discussed in detail.
In the present study the hypothesis that there is a feedback between juvenile hormone and adipokinetic hormones (AKHs) was investigated by topical application of the juvenoid methoprene on 9-day-old adult males of the firebug Pyrrhocoris apterus. This juvenoid (2 µg) induced a significant reduction of haemolymph lipids 24 h after treatment; however, it did not significantly reduce the ability of Pyrap-AKH (10 pmol/bug) to mobilize fat body lipids 6-72 h after the methoprene application. The same methoprene treatment elicited a significant increase of AKH content in the CNS (central nervous system: brain + corpora cardiaca + corpora allata) of experimental males 24 and 48 h after the juvenoid application. A significant decrease in the AKH level in the haemolymph was recorded at the same times and under the same experimental conditions. Similar results were observed when production of the AKHs from the CNS of topically treated males was measured under in vitro conditions. It is suggested that methoprene may reduce AKH release from the CNS resulting in an increase in the AKH content of the CNS due to accumulation rather than stimulation of AKH synthesis. Possible consequences of this phenomenon on the physiology of P. apterus are discussed.