Magnetic orientation in the mealworm beetle Tenebrio and the effect of light

There is evidence for both light-dependent and light-independent mechanisms of magnetoreception of terrestrial animals. One example of a light-independent mechanism frequently cited is the magnetic compass of the mealworm beetle (Tenebrio molitor). We found that magnetoreception of the mealworm beetle per se is a replicable phenomenon but that, in contrast to earlier findings, Tenebrio only exhibited consistent magnetic compass orientation when light was present. The problem of whether the loss of orientation is due to a light-dependent magnetoreception mechanism or is instead an effect of motivation change is discussed.

Infection increases the value of nuptial gifts, and hence male reproductive success, in the Hymenolepis diminuta-Tenebrio molitor association

During copulation, male insects pass accessory gland components to the female with the spermatophore. These gifts can affect female reproductive behaviour, ovulation and oviposition. Here, we show that female mealworm beetles, Tenebrio molitor, mated with males infected with metacestodes of the rat tapeworm, Hymenolepis diminuta, produced significantly more offspring than those mated with uninfected males. There is a significant positive relationship between parasite intensity in the male and reproductive output in the female. Infection results in a significant increase in bean-shaped accessory gland (BAG) size. We suggest that infected males pass superior nuptial gifts to females and discuss the confounding effects of infection in male and female beetles upon overall fitness costs of infection for the host and the likelihood that the parasite is manipulating host investment in reproduction.

Metabolic activity and water vapour absorption in the mealwormTenebrio molitorL. (Coleoptera, Tenebrionidae): real-time measurements by two-channel microcalorimetry

This work describes a new calorimetric method in which the metabolic heat production and water exchange rates of an insect larva are measured simultaneously and in real time. The experimental set-up is based on two independent calorimetric cells, which are perfused by a stream of air at controlled relative humidity (RH). The resolution for metabolic heat flow and water flux is 1 μW and 5 μg h-1, respectively. The method was used to investigate water vapour absorption (WVA) in drought-stressed larvae of the common mealworm Tenebrio molitor. It was found that during exposure to a linear increment in RH of 3% per hour, the larvae initiated WVA upon passing a threshold value of 92.7±0.6%RH. The rate of water absorption subsequently increased to reach a maximal level of 86±6μg h-1, 10-15 h after passing the threshold value. Concomitantly, the RH in the calorimetric cell was reduced to 88.6±0.5%.

The metabolic heat production of the larvae was 5-6 J h-1g-1 wet mass in the initial part of the experiment. However, this value doubled 2-3 h prior to the onset of WVA, when the RH had reached 88%. This increase in metabolic heat production gradually tapered off over the following 24 h of WVA, during which time WVA remained high. Animals exposed to RH protocols that did not induce WVA showed no such anomalies in metabolic heat flow. This may suggest that the increased metabolism reflects the preparation of the WVA apparatus. Finally, the method was used to quantify water losses in the microgram range associated with wriggling and tracheal ventilation.

Effects of flucycloxuron, a chitin synthesis inhibitor, on reproductive events and thickness of chorion in mealworms

Flucycloxuron (FCX), a benzoylphenylurea derivative, was evaluated on Tenebrio molitor. The compound was incorporated into the diet and administrated to newly emerged females at various doses (2, 5 and 10 mg/kg). FCX was found to affect several reproductive events such as the duration of preovipostion and oviposition period, the fecundity, the viability of eggs and the duration of embryonic development, respectively. Morphological study of ovaries showed that FCX reduced both oocytes number, the ovaries weight and the size and the volume of the basal oocyte during the sexual maturation. In addition, it reduced the thickness of chorion from freshly laid eggs. However, electron microscopic study revealed that this compound had no significant effect on the fine structure of chorion. Finally, measurements of ovarian ecdysteroids production by an enzyme immunoassay indicated a reduction in the hormonal amounts recorded.

Biological evaluation of analogues of an insect neuropeptide proctolin

Continuing our studies on proctolin (Arg-Tyr-Leu-Pro-Thr) we performed the synthesis and biological evaluation of 52 analogues substituted in position 2, 3, 4, and 5 of the peptide chain. The peptides were bioassayed for cardiotropic activity in vitro on Tenebrio molitor and myotropic activity on foregut of Schistocerca gregaria. Twenty analogues retained 20-80% of proctolin activity.

The role of juvenile hormone in immune function and pheromone production trade-offs: a test of the immunocompetence handicap principle

The immunocompetence handicap hypothesis postulates that secondary sexual traits are honest signals of mate quality because the hormones (e.g. testosterone) needed to develop secondary sexual traits have immunosuppressive effects. The best support for predictions arising from the immunocompetence handicap hypothesis so far comes from studies of insects, although they lack male-specific hormones such as testosterone. In our previous studies, we found that female mealworm beetles prefer pheromones of immunocompetent males. Here, we tested how juvenile hormone (JH) affects male investment in secondary sexual characteristics and immune functions in the mealworm beetle, Tenebrio molitor. We injected male mealworm beetles with JH (type III) and found that injection increased the attractiveness of male pheromones but simultaneously suppressed immune functions (phenoloxidase activity and encapsulation). Our results suggest that JH, which is involved in the control of reproduction and morphogenesis, also plays a central role in the regulation of a trade-off between the immune system and sexual advertisement in insects. Thus, the results reflect a general mechanism by which the immunocompetence handicap hypothesis may work in insects.

The effects of endogenous diuretic and antidiuretic peptides and their second messengers in the Malpighian tubules of Tenebrio molitor: an electrophysiological study

The Malpighian tubules of Tenebrio molitor provide a model system for interpreting the actions of endogenous diuretic and antidiuretic peptides. The effects of diuretic (Tenmo-DH(37)) and antidiuretic (Tenmo-ADFa) peptides and their respective second messengers (cyclic AMP and cyclic GMP) on basolateral (V(bl)) and transepithelial (V(te)) potentials of Tenebrio Malpighian tubules were determined using conventional microelectrodes. In the presence of 6 mmol l(-1) Ba(2+), Tenmo-DH(37) (100 nmol l(-1)) reversibly hyperpolarized V(bl) and depolarized V(te). A similar response was seen with the addition of 1 mmol l(-1) cyclic AMP; however, the apical membrane potential (V(ap)) then showed a hyperpolarization, whereas a depolarization of V(ap) was observed with Tenmo-DH(37). Bafilomycin A(1) (5 micromol l(-1)) inhibited fluid secretion of stimulated tubules and reversed the hyperpolarization of V(bl) in response to Tenmo-DH(37). In response to 100 nmol l(-1) Tenmo-ADFa or 1 mmol l(-1) cyclic GMP, V(bl) and V(te) depolarized, although cyclic GMP affected membrane potentials somewhat differently by causing an initial hyperpolarization of V(bl) and V(te). In high [K(+)]-low [Na(+)] Ringer, 1 mmol l(-1) amiloride decreased fluid secretion rates, and depolarized both V(bl) and V(te). Amiloride significantly decreased luminal pH in paired experiments, indicating the presence of a K(+)/nH(+) exchanger in tubule cells of Tenebrio. The results suggest that the endogenous factors and their second messengers stimulate/inhibit fluid secretion by acting on the apical V-ATPase, basolateral K(+) transport, and possibly Cl(-) transport.

Effect of ecdysone agonist RH-0345 on reproduction of mealworm, Tenebrio molitor

RH-0345 belongs to a new group of insect growth regulators (IGRs) with a benzoylhydrazine structure that mimic the action of the natural insect molting hormone 20-hydroxyecdysone. After topical application on female adult beetles of mealworm, Tenebrio molitor L. (Coleoptera: Tenebrionidae), first oviposition was delayed, the number of eggs per female was reduced by 32%, the follicular epithelium was thinner (-33%) during sexual maturation, the size of deposited eggs was reduced, and egg viability was lost by 68%. Treatment with RH-0345 had also reduced the ovarian protein content and two protein bands were missing in the ovaries. Ultrastructural observations of the ovaries at the end of vitellogenesis in treated females, however, showed no evident differences with the fine structure of both follicular cells and oocytes in controls. In addition, we measured the amount of ecdysteroids in the medium of treated ovary cultures in vitro and in the eggs deposited by treated females. Possible action sites with the reproductive system at different levels in T. molitor are discussed for this novel group of IGRs.

Juvenile hormone titre and egg production in Tenebrio molitor infected by Hymenolepis diminuta: effect of male and/or female infection, male age and mating

Infection of Tenebrio molitor with Hymenolepis diminuta induces curtailment of female fertility. We examined ovulation and oviposition, and associated titres of juvenile hormone (JH), in relation to parasitism and mating. Oviposition was significantly increased in infected mated and virgin beetles by days 6 and 9 post-emergence. Ovulation was not changed by infection; by the end of the 18-day experiment, the total number of laid eggs was not significantly altered. On day 6, JH levels were significantly higher in virgin infected insects, compared to non-infected controls (236+/-37.7 and 107+/-9.62 pg/g wet weight). Oviposition increased after mating, but total eggs ovulated remained the same. JH levels were higher in mated females on days 12 and 18 post-emergence, for infected and control insects. Previous studies suggested that male reproductive potential might rise following infection, because uninfected females lay more eggs when mated to infected males. We tested whether this caused an increase in female JH. Males were mated on days 5 or 12, when significant changes in their reproductive physiology begin to be observed, and are maximal, respectively. However, male age was of greater significance in promoting JH levels in females (p=0.001), than infection status of either partner (p=0.33).

Comparative action of RH-0345 and pyriproxyfen on molting hormone production and protein analysis in mealworm pupae

RH-0345 (halofenozide) was found to mimic the action of 20-hydroxyecdysone while pyriproxyfen was presented as a juvenile hormone analogue. In this study, RH-0345 (5, 10 micrograms/pupa) and pyriproxyfen (0.10 and 0.20 microgram/pupa), applied topically on newly ecdysed pupae of Tenebrio molitor, were investigated on ecdysteroid titers and hemolymph protein concentrations. During normal pupal development, the ecdysteroid titer measured using an enzyme immunoassay showed a single peak at day 3. The two compounds did not shifted the moment of the pupal ecdysteroid peak. However, RH-0345 at the highest dose (10 micrograms/pupa) increased the ecdysteroid titres recorded from the second day after topical application while pyriproxyfen decreased this hormonal production. In a second series of experiments, the compounds were evaluated on the protein concentrations in the hemolymph. In control pupae, change in protein concentrations showed two peaks. At a 5 micrograms dose, RH-0345 was found to reduce significantly the value of the first peak and at the highest dose, the first peak was not observed and the values recorded following treatment were significantly lower than in controls. Changes in protein concentrations showed that pyriproxyfen suppressed the second peak and the values recorded were either significantly increased at day 2 and 3, either reduced from day 4.

RH-0345 restored partly the effects induced by KK-42 on reproductive events in mealworms

In the mealworm, Tenebrio molitor L., KK-42, an imidazole derivative, was found to reduce ovarian ecdysteroid production, while RH-0345, a benzoylhydrazine analogue, has been reported to affect growth and development of mealworm ovaries in a manner similar to 20-hydroxyecdysone. In order to determine whether the reduction of reproduction events is dependent on inhibition of ecdysteroid production by ovaries, RH-0345 (10 micrograms/insect) was applied before or after topical application of KK-42 (10 micrograms/insect) on newly emerged adult females. KK-42 applied alone increased significantly the pre-oviposition period compared to controls. It also significantly delayed egg-laying compared to combined treatments using KK-42 before or after RH-0345. KK-42 applied alone or with and before RH-0345, was found to reduce significantly the duration of oviposition period. Moreover, there was a significant difference in the duration of oviposition period between the two combined treatments. The fecundity was significantly reduced in all treated series compared to controls. In addition, the fecundity recorded in treated series by RH-0345 alone or before KK-42 was significantly higher than in KK-42 treated series. Lastly, the viability of eggs laid was significantly reduced in all treated series compared to controls. Moreover, the combined treatment pronounced the reduction in egg viability. Free ecdysteroids (ecdysone and 20-hydroxyecdysone) in eggs of control and RH-0345 treated females were analyzed by an enzymo-immunoassay using two specific antibodies.

K(+) transport in Malpighian tubules of Tenebrio molitor L: a study of electrochemical gradients and basal K(+) uptake mechanisms

Malpighian tubules of the mealworm Tenebrio molitor were isolated for intracellular measurement of basolateral (V(bl)) and, indirectly, apical (V(ap)) membrane potentials. In control Ringer (50 mmol l(-1) K(+), 140 mmol l(-1) Na(+)), V(bl) was 24 mV, cell negative, and V(ap) was 48 mV, cell negative with reference to the lumen. Ion substitution experiments involving K(+) and Na(+) indicated that both V(bl) and V(ap) were sensitive to the bathing K(+) concentration, with the change in V(ap) being 60-77% that of V(bl). A 10-fold drop in bath [K(+)] irreversibly decreased fluid secretion rates from 6.38+/-0.95 nl x min(-1) (mean +/- S.E.M.) to 1.48+/-0.52 nl x min(-1) (N=8). In the presence of 6 mmol l(-1) Ba(2+), a blocker of basal K(+) channels, fluid secretion rates reversibly decreased and the hyperpolarization of both V(bl) and V(ap) seen in 50 mmol l(-1) and 140 mmol l(-1) K(+) indicated a favourable electrochemical gradient for basal K(+) entry. In 5 mmol l(-1) K(+), Ba(2+) induced two different responses: V(bl) either hyperpolarized by approximately 10 mV or depolarised by approximately 14 mV, according to the electrochemical gradient for K(+), which was either inward or outward in low bath [K(+)]. Rubidium, a 'permeant' potassium substitute, caused a hyperpolarization of V(bl), indicating the specificity of K(+) channels found in Tenebrio tubule cells. Other possible K(+) uptake mechanisms located in the basolateral membrane were investigated. Blocking of the putative electroneutral Na(+)/K(+)/2Cl(-) cotransporter by 10 micromol l(-1) bumetanide reversibly decreased fluid secretion rates, with no detectable change in membrane potentials. Ouabain (1 mmol l(-1)), an Na(+)/K(+)-ATPase inhibitor, irreversibly decreased fluid secretion rates but had no effect on electrical potential differences either in the absence or presence of Ba(2+). The results implicate K(+) channels, the Na(+)/K(+)/2Cl(-) contransporter and the Na(+)/K(+)-ATPase in basal K(+) and fluid transport of Tenebrio tubule cells.

Cold resistance in the lesser mealworm Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae)

We have investigated cold resistance, measured by the supercooling point (SCP) temperature, in life stages of the lesser mealworm, Alphitobius diaperinus (Coleoptera: Tenebrionidae), collected in Brittany poultry houses. Mean SCP values drastically increased during the insect ontogeny: egg (-26.1 C), first instar larvae (-21.6 C), last instar larvae (-15.5 C), pupae (-11.6 C), teneral adults (-12.0 C) and mature adults (-13.1 C). Nymphal metamorphosis and adult maturation did not promote substantial decrease of freezing resistance. The SCP values reflect the physiological states of the developmental stages especially the absence of ice nucleating agents: (i) lower SCP values in egg and unfed newly-emerged larvae I (i.e. -25.1 C), (ii) higher SCP values in fed larvae (i.e. -14.7 C), pupae and adults most likely due to the presence of ice nucleation sites in the gut. A tropical species, A. diaperinus, seems not to use its potential cold hardiness even in winter to remain in this warm habitat in temperate regions.

Metal uptake from soils and soil-sediment mixtures by larvae of Tenebrio molitor (L.) (Coleoptera)

Bioassays were performed to evaluate the impact of soil characteristics on Cd, Cu, Pb, and Zn uptake by larvae of Tenebrio molitor. Metal accumulation was determined in 13 natural field soils, one metal-spiked field soil, four soil-sediment mixtures, and Cd- or Zn-spiked OECD artificial soil. Statistical analyses were used to investigate covariation of accumulation patterns with various soil metal pools and soil properties. Body concentrations of Cu and Zn in Zn-spiked OECD soils, field soils, and soil-sediment mixtures mostly remained constant. Considerable variation was noted for all Cd and Pb steady-state body concentrations among field soils and soil-sediment mixtures. For the spiked field soil and in the Cd-spiked OECD soil, body concentrations increased almost linearly with time. For the nonessential metals Cd and Pb, larval body concentrations correlated mainly to the total metal pool of the soil. Cd uptake at similar total Cd concentrations was within the same range among spiked OECD soils, field soils, and mixtures. A comparison of the findings with studies on other soil-inhabiting species shows that metal uptake patterns depend on metal type, soil type, and exposed species. It is suggested that soil organisms can be categorized according to gross divergence in ecophysiological characteristics, determined by, for instance, (non)permeability of the outer integument. These characteristics appear as similarities among multivariate functions as derived for the beetle.

K(+) transport in Malpighian tubules of Tenebrio molitor L: is a K(ATP) channel involved?

The presence of ATP-regulated K(+) (K(ATP)) channels in Tenebrio molitor Malpighian tubules was investigated by examining the effect of glibenclamide on both fluid secretion and basolateral membrane potentials (V(bl)). Glibenclamide, a K(ATP) channel blocker, slowed fluid secretion of Tenebrio tubules. In low bath K(+) concentration (5 mmol l(-1)), glibenclamide either hyperpolarized or depolarized V(bl), resembling the effect seen with Ba(2+). Subsequent addition of 6 mmol l(-1) Ba(2+) caused a further hyper- or depolarization of V(bl). In control Ringer (50 mmol l(-1) KCl, 90 mmol l(-1) NaCl), glibenclamide had no visible effect on V(bl). The effect of ouabain was investigated in low bath [K(+)] in the presence of Ba(2+). V(bl) responded by a small but significant hyperpolarization from -51+/-4 mV to -56+/-4 mV (n=16, P<0.001) in response to 1 mmol l(-1) ouabain. Repeating the experiments in the presence of both glibenclamide and Ba(2+) resulted in a depolarization of V(bl) when ouabain was added. In low bath [K(+)] (high Na(+)), the Na(+)/K(+)-ATPase is expected to function at a high rate. In the presence of Ba(2+), replacing Na(+) by K(+) rapidly depolarized V(bl), but this was followed by a repolarization. Repeating the experiments in the presence of glibenclamide markedly reduced the depolarizing effect and abolished the repolarization, with a gradual decrease in the sensitivity of V(bl) to the surrounding [K(+)]. These results suggest the presence of K(ATP) channels in the basolateral membrane. Glibenclamide had no visible effect on V(bl) in high K(+) or in the absence of Ba(2+), indicating that other highly conductive K(+) channels may mask the effect on K(ATP) channels. This is the first demonstration of the presence of K(ATP) channels in an insect epithelium.

In vitro effects of RH-0345 and KK-42 on ecdysteroid levels and cuticle synthesis by pupal integument of mealworms

In this study, the effects of two insect growth regulators (KK-42 and RH-0345), applied either alone or in combination, were evaluated on the ecdysteroid production in vitro. Integument explants from the abdominal sternites of newly ecdysed pupae of mealworms, Tenebrio molitor, were cultured and the amounts of ecdysteroids, released into the culture medium, were determined by an enzyme immunoassay (EIA) after various intervals of incubation. In combined treatments, explants were cultured for the first two days in a medium added with the first compound and then transferred in new medium containing the second compound. EIA measurements showed that RH-0345, either alone or followed by KK-42, resulted in higher amounts of ecdysteroids as compared to controls. In contrast, KK-42 alone caused a significant reduction. But, when KK-42 was followed by RH-0345, the ecdysteroid amounts were equal to controls. In another series of experiments, the effects on cuticle secretion were examined. Only in the case that explants were treated with RH-0345, either alone or followed by KK-42, new cuticle synthesis was observed.

Comparative effects of some ecdysteroid agonists in mealworms: ecdysteroid amounts and protein analysis in developing ovaries under in vivo conditions

Some ecdysteroid agonists (RH-0345, RH-5849, RH-5992) were tested topically (10 microg/female) on newly emerged adult females of mealworms under in vivo conditions. In a first series of experiments the compounds were assayed on ovarian ecdysteroid production measured at day 2 and 4 following treatment, corresponding to the beginning and the end of vitellogenesis. All tested compounds resulted in a significant increase in ovarian ecdysteroid amounts. RH-5992 and RH-0345 were more active than RH-5849. In a second series of experiments, the activity of the compounds was investigated on ovarian proteins. The ecdysteroid agonists caused a significant reduction of protein amounts in the ovaries, and electrophoretic separation of ovary extracts from treated series showed that one or two bands were missing. These observations may an interference with the vitellogenesis process.

Copulation corrupts immunity: a mechanism for a cost of mating in insects

There are well documented costs of mating in insects but little evidence for underlying mechanisms. Here, we provide experimental evidence for a hormone-based mechanism that reduces immunity as a result of mating. We examined the mealworm beetle Tenebrio molitor and show that (i) mating reduces a major humoral immune effector-system (phenoloxidase) in both sexes, and (ii) that this down-regulation is mediated by juvenile hormone. Because both juvenile hormone and phenoloxidase have highly conserved functions across all insects, the identified mechanism is similarly likely to be highly conserved. The positive physiological function of mating-induced juvenile hormone secretion is gamete and accessory gland production: we propose that its negative effects on immune function are the consequence of physiological antagonism. Therefore, we have identified a physiological tradeoff between mating and immunity. Our results suggest that increasing mating success can result in increasing periods of immune suppression, which in turn implies that reproductively successful individuals may be more vulnerable to infection by, and the negative fitness effects of, pathogens.

Antagonistic control of fluid secretion by the Malpighian tubules ofTenebrio molitor: effects of diuretic and antidiuretic peptides and their second messengers

Fluid secretion by insect Malpighian tubules is controlled by haemolymph-borne factors. The mealworm Tenebrio molitor provides the first known example of antagonistic interactions between endogenous neuropeptides acting on Malpighian tubules. The two corticotropin-releasing-factor (CRF)-related diuretic peptides previously isolated from Tenebrio molitor, Tenmo-DH37 and Tenmo-DH47, were found to stimulate Tenebrio molitor tubules in vitro in a dose-dependent manner with EC50 values of 0.12 nmol l–1 and 26 nmol l–1 respectively. However, no synergistic or additive effect was observed when these two peptides were tested simultaneously. We then investigated antagonism between second messengers: dose–response curves were constructed for stimulation of Tenebrio molitor tubules by cyclic AMP and their inhibition by cyclic GMP. When both cyclic nucleotides were included in the bathing Ringer, the stimulatory effect of cyclic AMP was neutralised by cyclic GMP. Similarly, the stimulatory effect of Tenmo-DH37 was reversed on addition of an antidiuretic peptide (Tenmo-ADF), which was recently isolated from Tenebrio molitor and acts via cyclic GMP. The cardioacceleratory peptide CAP2b, originally isolated from Manduca sexta, also increases intracellular cyclic GMP levels and inhibited fluid secretion by Tenebrio molitor tubules, with an EC50 value of 85 nmol l–1. This inhibitory effect was reversed by Tenmo-DH37. Endogenous diuretic and antidiuretic peptides, effective at low concentrations and acting via antagonistic second messengers, have the potential for fine control of secretion rates in the Malpighian tubules of Tenebrio molitor.

A parasite that increases host lifespan

Tenebrio molitor is an intermediate host for the rat tapeworm, Hymenolepis diminuta. Parasite oncospheres hatch in the beetle midgut and burrow through into the haemocoel, where they rapidly grow and mature into metacestodes. Repair of damage incurred during invasion and the nutritional demands of the parasites are likely to impose costs on the host. Despite these costs, there is an overall very highly significant difference in survival time (p < 0.001) between infected and control populations of beetles, with a hazard ratio of 2.35 (control versus infected). Infected females showed a 40% increase in survival time to 50% mortality and males showed a 25% increase in survival time to 50% mortality. This parasite-induced increase in host longevity is discussed in the light of changes in resource allocation that may occur in infected beetles. Previous findings have demonstrated that reproductive success is significantly reduced in infected females. The outcome of changes in the reproductive effort made by male beetles is less clear. We suggest that the optimum trade-off between reproduction and longevity may be altered to favour longer host survivorship, which is likely to enhance parasite transmission.

The response of Gregarina niphandrodes (Apicomplexa: Eugregarinida: Septatina) to host starvation in Tenebrio molitor (Coleoptera: Tenebrionidae) adults

Numerous studies of host starvation have emphasized pathological effects of parasites on their insect host, but little attention has been focused on the effects of host starvation on the parasites. This study addressed the possibility that parasite life-cycle events could be manipulated by withholding food from the host. The system used was Gregarina niphandrodes (Apicomplexa: Eugregarinida) in Tenebrio molitor (Coleoptera: Tenebrionidae) adults. Gregarine gametocyst formation and shedding ceased after 1 day in starved beetles but continued in fed controls. There were no statistically significant differences between total lengths of associated (3 of 5 trials) or unassociated (5 of 5 trials) gregarines found between experimental and control groups, but average numbers of the 2 life cycle events were generally higher in fed hosts than in starved ones. If infected, fed control beetles continued to form gametocysts throughout the 7-day trial periods, and gametocysts could be observed in the gut. Starved experimental beetles had no gametocysts in their guts. Refeeding of starved beetles after 4 days resulted in resumption of gametocyst formation and shedding. The studies demonstrated that the gregarine life cycle could be stopped and then started at the gametocyst formation stage like an off/on switch, simply by withholding food from, then refeeding, the host.

Myotropic effects of new proctolin analogues modified in the position 5 of peptide chain in insects

To explain the role of the Thr5 residue of proctolin (Arg-Tyr-Leu-Pro-Thr) in the myotropic activity of this insect neuropeptide, we synthesized two groups of its analogues: 1) Arg-Tyr-Leu-Pro-X-OH with X = Val (1), D-Val (2), Ile (3), D-Ile (4), Ala (5), D-Ala (6), Asn (7), Gln (8), Ser (9), Pro (10), Phe (11), Asp (12), Glu (13), Arg (14), D-Arg (15), Lys (16) and Gly (17) and 2) Arg-Tyr-Leu-Pro-R', where R' = isobutylamine (18), S-1-methyl-1-phenylmethylamine (19), R-1-methyl-1-phenylmethylamine (20), R-2-amino-1-propanol (21), S-2-amino-1-propanol (22), R-1-amino-2-propanol (23), S-2-amino-1-propanol (24), 3-amino-1-propanol (25). Decapeptide proctolylproctolin (H-Arg-Tyr-Leu-Pro-Thr-Arg-Tyr-Leu-Pro-Thr-OH) (26) was synthesized. Syntheses of these peptides were carried out by solid-phase method. All peptides were bioassayed in vitro on the semi-isolated hearts of Tenebrio molitor using a cardioexcitatory test and on the foregut of locust (Schistocerca gregaria). Peptides 1, 3, 5, 9, 13, 14, 16, 22, and 23 retained about 30-50% of the cardioexcitatory activity in T. molitor. Analogues 1 and 3 preserved about 50% and analogue 8 about 80% of the myotropic activity, whereas compound 4 and 9 showed a very weak contractile activity in S. gregaria.

The pacemaker activity generating the intrinsic myogenic contraction of the dorsal vessel of Tenebrio molitor (Coleoptera)

Combined intracellular and extracellular recordings from various parts of the isolated dorsal vessel of Tenebrio molitor revealed some of the following electrophysiological properties of the heart and the aorta. (i) The wave of depolarization causing forward pulsation of the dorsal vessel was always transmitted from posterior to anterior, with a conduction velocity of 0.014 m s(−1) in the heart and 0.001 m s(−1) in the aorta when the heart rate was 60 beats min(−1). (ii) There was no pacemaker activity in the aorta. (iii) The duration of the compound action potential in the aortic muscle depended on the duration of the pacemaker action potential generated in the heart. (iv) Isolated parts of the heart continued to contract rhythmically for hours, indicating powerful pacemaker activity in individual cardiac segments. (v) There was a direct relationship between action potential duration and the length of the preceding diastolic interval. (vi) The rhythmic wave of depolarization was dependent on the influx of Ca(2+). (vii) The recovery of the electrical properties of myocardial cells that had been disrupted by sectioning was rapid. (viii) In hearts sectioned into two halves, the rhythmic pacemaker action potentials recorded simultaneously from the two isolated halves eventually drifted out of phase, but they had the same intrinsic frequency. In the light of these data, we discuss two alternative models for the generation of spontaneous rhythmic pumping movements of the heart and aorta.

[Sand-desert tenebrionid beetle Trigonoscelis gigas reitter: a promising biological model for space chronobiology]

The beetle proposed for studying has a unique feature: unusually precise and reliable circadian clock that evolved as an advanced adaptation to extreme arid environment. Consequently this clock became functionally similar to that of vertebrates, i.e. it has a narrow range of entrainment, stable free-running period, strong endogenous component of rhythm. This beetle is also using due to its high viability, good tolerance to housing and handling, small size and safety in use. Space flight experiments with beetles on BION, PHOTON satellites and on MIR orbital station proved that parameters of circadian rhythms are dependent upon gravity. Future studies will focus on electrophysiology and comparative ecology of these beetles. This biological species together with developed methods represent a new promising technology of research in gravitational chronobiology.

Predation of beetles (Tenebrio molitor) infected with tapeworms (Hymenolepis diminuta): a note of caution for the manipulation hypothesis

Previous laboratory studies have indicated that tenebrionid beetles infected with Hymenolepis diminuta display behavioural alterations. These are assumed to increase the likelihood of this intermediate host being predated by the Rattus sp. definitive host, and hence provide support for the Manipulation Hypothesis. We tested this hypothesis by both assessing beetle behaviour and predation rates in semi-naturalistic environments. Behavioural assays showed that infected beetles were more often exposed (not concealed under boxes) than uninfected beetles. However, there were no differences in predation rates between infected and uninfected beetles. We discuss this in terms of the historical and evolutionary contexts under which such altered behaviours could evolve and their implications for the Manipulation Hypothesis.