Diehl, Peter-Allan

1992, Lösel, P. M., Guerin, Patrick, Diehl, Peter-Allan

Feeding behaviour of partially engorged Rhipicephalus appendiculatus (Neumann) (Acari: Ixodidae) on rabbit serum held in capillary tubes and placed over the tick mouthparts was studied using the feeding electrogram technique with simultaneous macro video photography. Correlation of electrical events with fluid movement in the vicinity of the tick's mouthparts and the capillary meniscus, permitted the characterization of an orderly sequence of signals, termed the ‘Feeding Complex’, associated with highest weight gains. This complex consisted of a 3–8 Hz fast-sucking waveform typically lasting 4–5 min, a sharp drop in potential at salivation, and rest lasting 1 or 2 min where no waveform or fluid movements occur. Very high impedence recordings from within the tick capitulum indicate that the fast-sucking waveform coincides with bursts of potentials corresponding to contraction of the pharyngeal dilator muscles, whereas during rest a tonic series of spikes signifies that the floor of the salivarium is actively lowered. Feeding electrograms of ticks fed on serum from tick-resistant rabbits showed significantly fewer feeding complexes. The weight gains achieved by these ticks were reduced correspondingly. This suggests that some of the humoral effectors of immunity have an antifeedant effect on this unusual parasite of rabbits.

1986, Connat, Jean-Louis, Diehl, Peter-Allan, Thompson, M. J.

Ornithodoros moubata females proved to be extremely sensitive to ingested 22,25-dideoxyecdysone; 15-20 ng provoked molting in all females and temporarily inhibited vitellogenesis. In contrast, this tick was very resistant to ingested ecdysteroids containing 22-OH groups, such as ecdysone, 20-hydroxyecdysone, ponasterone A, and makisterone A. Dosages about 500 times greater were necessary to produce supermolting and reduce fecundity [Connat et al: Z Ang Ent 96, 520 (1983)]. Ingested tritiated ecdysone, 20-hydroxyecdysone, 2-deoxyecdysone, and ponasterone A were rapidly converted to apolar esterase-labile metabolites having approximately the same retention time as the AP2 identified as esters of ecdysteroids at C-22 with long-chain fatty acids (C16:0, C18:0, C18:1, C18:2) [Diehl et al: Int J Invert Reprod Dev 8, 1 (1985)]. These products were then gradually transformed to the more polar apolar conjugates, AP1. A more detailed study with ingestion of large quantities of 20-hydroxyecdysone (10 μ/ml blood) demonstrated that only small amounts of free hormone were present in the hemolymph during the first day after the blood meal. The hormone was rapidly metabolized to AP2, then to AP1, in the intestinal cells and to a lesser extent in the peripheral tissues. Finally, AP1 accumulated in the intestinal cells and midgut content, probably because excretion outside the animal is impossible in this tick species. In contrast, ingested 22,25-dideoxyecdysone was not metabolized to apolar products. This could account for its high biological activity. This compound was converted to unidentified more polar products. Two of them comigrated with ecdysone and 20-hydroxyecdysone on RP-18 HPLC column, but not on silica column, and therefore cannot correspond to these compounds.
We hypothesize that esterification of ecdysteroids at the C-22 position with fatty acids represents a detoxification mechanism for ingested ecdysteroids that might be present in blood from herbivorous or parasite-infected hosts.

1985, Diehl, Peter-Allan, Connat, Jean-Louis, Girault, Jean P., Lafont, René

Nymphs of the argasid tick Ornithodoros moubata rapidly transform most of the ingested molting hormone 20-hydroxy-ecdysone (20-hydroxy-E) into a family of 4 major apolar conjugates which are hydrolyzable by carboxylic-ester hydrolase. These conjugates - new among zoo- or phytoecdysteroids - are composed of 20-hydroxy-E esterified at C22 with the common long-chain fatty acids C_16:0, C_18:0, Cig_18:1, or C_18:2;. The chemical structure of the purified metabolites was identified by fatty acid analysis, by CI/D mass spectrometry and by comparison with a chemically prepared 20-hydroxy-E-22-palmitate.
The significance of the apolar metabolic pathway is discussed. It may serve to inactivate molting hormones which could be ingested with blood from hosts that feed on plants containing phytoecdysteroids. In addition, the conjugates may act as a storage form of hormones for the developing embryo.