Rostislav Zemek

A new member of the AKH/RPCH family that stimulates locomotory activity in the firebug, Pyrrhocoris apterus (Heteroptera).

A new member of the AKH/RPCH family was isolated and identified from the corpora cardiaca of the firebug Pyrrhocoris apterus. The peptide was isolated in a single step by reversed phase HPLC and the structure deduced from the multiple MS (MS(N)) electrospray mass spectra and amino acid analysis as that of an octapeptide with the sequence pGlu-Leu-Asn-Phe-Thr-Pro-Asn-Trp-NH(2): this sequence was confirmed by synthesis. The synthetic peptide induced lipid mobilisation and stimulated locomotory activity in macropterous females. This peptide, designated as Pyrrhocoris apterus adipokinetic hormone (Pya-AKH), is the first identified adipokinetic hormone described in a representative species of the suborder Heteroptera.

Adipokinetic Hormone Stimulates Insect Locomotor Activity

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Feeding, drinking and digestive enzyme activities in long- and short-day females of Pyrrhocoris apterus (Heteroptera)

Abstract. .Reproducing females of the firebug, Pyrrhocoris apterus (Linnaeus) (Heteroptera: Pyrrhocoridae), reared under long‐day (LD 18:6h) photocycle (long‐day females), and diapausing females reared under short‐day (LD 12:12h) conditions (short‐day females) were analysed for temporal patterns of feeding, drinking and gut digestive enzyme activities. In long‐day females the highest activities of feeding and drinking were found at the beginning of each reproductive cycle. Significant correlation between feeding and drinking activities in both reproducing long‐day females and short‐day females during pre‐diapause state was found. In pre‐diapausing short‐day females the cyclical pattern of feeding and drinking was maintained despite the inhibition of reproduction. After entering the diapause their feeding activity became very low. Analysis of five gut enzymes revealed that short‐day females differ significantly from long‐day females in higher protease, amylase and esterase activities, in case of lipase only at certain times of their adult life; no significant difference was found in the aminopeptidase activity. Positive correlations between intensity of feeding and gut enzyme activities were observed in short‐day females. Using several protease inhibitors most protease activity in the gut of P.apterus was identified as cysteine and aspartyl proteases, and only a small part of the activity could be caused by some serine proteases.

Topical application of Pya‐AKH stimulates lipid mobilization and locomotion in the flightless bug, Pyrrhocoris apterus (L.) (Heteroptera)

Abstract Two different methods of applying Pya‐AKH to long‐winged (macropterous) females of the firebug, Pyrrhocoris apterus (Linnaeus) (Heteroptera) were compared: both injection and topical application increased the levels of lipids in the haemolymph and stimulated locomotor activity. Lipid mobilization was maximal when 10 pmol was applied by injection or 40–100 pmol by topical application, with the first significant responses occurring 1.5 h after injection and 2 h after topical application. The highest elevations of lipid concentration in the haemolymph were comparable between the treatments, i.e. 14.36 ± 3.59 mg/mL for injection and 14.43 ± 4.07 mg/mL for topical application. However, these maximal elevations were achieved at different times: 3 h after the injection and 7 h after the topical application.

Lipid mobilization and locomotor stimulation in Gryllus bimaculatus by topically applied adipokinetic hormone

Abstract.  Walking activity of 3‐day‐old adult female Gryllus bimaculatus (de Geer) (Ensifera, Gryllidae) was measured over 24 h. A high level of locomotor activity during the scotophase was found, which was two‐ to three‐fold higher than that during the photophase. The titre of lipid in the haemolymph was relatively low 2 h after lights on, increased significantly 2 h after lights off, although, 2 h after lights on in the next photophase, the lipid titre had decreased to the basal level. Topical application of homologous Grybi‐adipokinetic hormone (AKH) (100 pmol in 20% 2‐propanol) led to a significant increase in haemolymph lipids, comparable with the maximal increase caused by injection of AKH (3 pmol in water). Topical application of AKH also stimulated locomotor activity in crickets (maximal stimulation 1.8‐fold with 100 pmol Grybi‐AKH). The results suggest that AKH penetrates the cuticle quickly. It is assumed that AKH stimulates locomotory activity at least in part via the increase of haemolymph lipid titres; however, the stimulation of locomotor activity via a direct neuromodulatory effect of AKH cannot be excluded.

The effect of predation risk on an acarine system

Current theory on trait-mediated interactions in tri-trophic food chains shows that antipredator behaviour of the middle species can cause similar indirect effects giving rise to trophic cascades as mediated by density changes. In this article, the effect of predation risk in a tri-trophic food chain (bean plantetwo-spotted spider mite preyepredatory mite, Phytoseiulus persimilis) is measured, both on plants (changes in leaf damage) and spider mites (changes in egg numbers, mortality rate and dispersal behaviour), under two risk scenarios. In the predator risk treatment a predatory mite was caged in an experimental cell that was placed above a leaf disc with spider mites. This prevented the predator from subduing prey while the predator was perceived by spider mites as a potential threat. In the predator cues treatment a predatory mite was introduced to the leaf disc for 24 h before placing the spider mites on the disc. Compared to control without predators, after four days we observed in both risk treatments a nonsignificant increase in plant damage per spider mite and a significant decline in spider mite fecundity. No significant effect of predation risk on spider mite mortality was observed. We also showed that the above effects are not uniformly distributed in time. For example, the spider mite fecundity and dispersal rate in the predator cues treatment were significantly different from the control only the first day. We also found that under predator cues treatment, walking activity of the spider mites increased significantly.

The effect of constant darkness on the content of adipokinetic hormone, adipokinetic response and walking activity in macropterous females of Pyrrhocoris apterus (L.)

Abstract.  Changes in the content of adipokinetic hormone (AKH), the adipokinetic response and the walking activity of 10‐day‐old adult macropterous females of the firebug, Pyrrhocoris apterus (L.), reared under long‐day (LD) photoperiod (LD 18 : 6 h) are compared with those exposed for 3 days to constant darkness (DD). Diel changes of all the parameters studied in LD females persist in females kept in constant dark. A positive correlation exists between diel changes of AKH content in the central nervous system (CNS) in the LD and DD females, and a negative correlation in the AKH level in haemolymph and walking activity. In addition, there is a positive correlation between diel changes of AKH level in haemolymph and walking activity in macropterous females reared under LD conditions, as well as in those transferred to constant darkness. The data suggest that there is some feedback between the release of AKH from CNS into the haemolymph and walking activity in macropterous females. Preliminary studies on the simultaneous expression of mRNA for the period gene and a positive reaction to an antibody against AKH in the same corpus cardiacum cells suggest that the period gene may be involved in regulating the AKH content in this gland.

Wing morph-related physiological differences in adults of temperate population of Pyrrhocoris apterus (L.) (Heteroptera: Pyrrhocoridae).

The reproductive and diapausing adult females of brachypterous morph and macropterous females with reproductive arrest of non-diapause type, originating from the laboratory cultures of Pyrrhocoris apterus, were studied for their feeding and drinking behaviour, digestive enzyme activities, and carbohydrate and lipid contents. The highest feeding and drinking activities were observed in reproductive brachypters, the lowest in macropters. Macropters also differed from brachypters by lower activities of gut lipase, peptidase and protease, lower concentration of haemolymph sugars, and lower weight of fat body, which probably reflects their low feeding activity. The total content of fat body lipids was also lower in macropters (0.6 mg) than in reproductive and diapausing brachypters (4.6 and 7.5 mg, respectively) on day 14. A very high amount of glycogen was found in the fat body of diapausing brachypters, 363 micrograms on day 14, as opposed to 15 and 80 micrograms in macropterous and reproductive brachypterous females, respectively. The obtained data indicate that the most important difference between macropterous and brachypterous females with different types of reproductive arrest consists of an enhanced mobilization of lipids for dispersal in macropters and accumulation of energetic reserves for hibernation in brachypters.

Host plant preference of aphids, thrips and spider mites on GNA-expressing and control potatoes

The effect of snowdrop lectin (Galanthus nivalis agglutinin: GNA) expression on host-plant preference was examined with a two-choice disc test. Discrimination between a transgenic potato [Solanum tuberosum (Solanaceae)] capable of synthesizing GNA, and an isogenic cultivar, was studied under laboratory conditions using the glasshouse potato aphidAulacorthum solani (Hemiptera: Aphididae), the onion thripThrips tabaci (Thysanoptera: Thripidae), and the two-spotted spider miteTetranychus urticae (Acari: Tetranychidae). Adults of these species were placed individually on leaf discs (one half transgenic and one half control) and observed 1, 24, 48, 72 and 96 h after release, at which times also the distributions ofA. solani nymphs andT. urticae eggs on the discs were recorded. Aphids were found more frequently on control leaves at all observation periods, with the highest bias observed at 72 h (only 35.9% of all aphids were found on the GNA halves). Similarly, more aphid nymphs (57.6% of the total) were found on isogenic half-discs. The percentage of thrips found on GNA halves ranged from 36.8% to 48.4%, with significant control-potato bias at the first three observations. Contrary to this, the proportion ofT. urticae females found on GNA halves was significantly lower than the expected proportion (0.5) at 72 and 96 h, with a minimum of 34.0% on GNA. The distribution of spider mite eggs reflected the observed biased distribution of females (only 34.1% of all eggs were laid on GNA half-discs). These results indicate that potatoes expressing GNA for resistance against aphids are less preferred than an isogenic cultivar by all three tested species under a choice test condition using excised leaves.

A novel function of red pigment-concentrating hormone in crustaceans: Porcellio scaber (Isopoda) as a model species.

The RP HPLC and LC/MS QTOF analyses of the methanolic CNS extract from isopod crustacean the woodlouse, Porcellio scaber revealed a presence of the red pigment-concentrating hormone (Panbo-RPCH) in this species. It has been shown that this neuropeptide plays a role in mobilization of energy stores: topical treatments of P. scaber individuals by Panbo-RPCH in a concentration 20 pmol/microl increased the level of glucose in haemolymph about 4 times, while the level of trehalose was only doubled. The results demonstrated that glucose was the main carbohydrate mobilized by the Panbo-RPCH treatment: glucose was responsible for about 97% of total carbohydrate increasing. Despite the demonstration of hyperglycaemic activity of Panbo-RPCH, no stimulatory effect of this hormone on the locomotory activity of P. scaber was observed. The present study is the first discovery of an occurrence of Panbo-RPCH and its hyperglycaemic activity in the representative of the isopod crustaceans. The relationship of the function of Panbo-RPCH in P. scaber to the role of this neuropeptide and adipokinetic hormones in insects is discussed.