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.
A comparative study of mitotic activities and haemolymph ecdysteroid levels was performed in the phasmid Clitumnus extradentatus. Temporal correlation was found between increases in mitotic frequency in mandibular and general epidermis, and variations of ecdysteroid levels in the haemolymph of the insects. Whereas, mitotic waves occurring in the fat body cells or in the basal cells of the midgut did not appear to be strictly correlated with these hormonal variations. During the fourth larval instar of this phasma; an accurate study of mitotic figures, monitored from histological sections, indicated a time-lag in their stimulation according to the studied area, with a peak on day 2 in the mandible tips, on day 5 in the mandible bases and on day 7 in the head capsule, thorax and abdomen epidermis: namely a five-day delay with respect to the 12 days of the fourth instar. Simultaneously, the evolution of ecdysteroid levels in the haemolymph showed three increases of different importance. Each hormonal increase occurred 24 h before the triggering of each increase in the mitotic activity, whereas a fourth and very high peak, occurring on day 8, corresponded to the sudden fall in the number of epidermal mitoses.