Control of extracardiac haemolymph pressure pulses in Tenebrio molitor

The pupae of Tenebrio exhibit periodic pulsations in the haemolymph pressure which are independent of the heartbeat. Tensometric records of the extracardiac pulses show certain specific modifications caused by changes in either the internal or external environment. Chronological changes in the pulse pattern were associated with adult morphogenesis and ecdysis. The abdominal pump controlling extracardiac pressure pulsations is independent of the brain or of any other cephalic part of the nervous system. The nerve impulses controlling the pump arise only in the mesothoracic ganglion. They are carried by the connectives to certain abdominal ganglia from which they are further transmitted to the contracting intersegmental abdominal muscles. The extracardiac pulses in haemolymph pressure aid in the maintenance of water balance and respiration and assist with the circulation of haemolymph through the appendages.     

Chemosensory cues allow male Tenebrio molitor beetles to assess the reproductive status of potential mates

Males of many insect species, including beetles, choose their mates according to their reproductive status. However, the ways in which male beetles evaluate female reproductive status have received little attention. We tested the existence of male mate choice in the mealworm beetle, Tenebrio molitor, by observing mating and courtship behaviour of males given simultaneous access to pairs of females differing in their reproductive status: (1) mature versus immature; (2) virgin versus previously mated; (3) familiar (mated with the experimental male) versus unfamiliar (mated with a different male). Males courted and mated preferentially with mature and virgin females. To determine whether chemical cues played a role in these discriminations, we exposed males to filter paper squares bearing chemical cues from different types of females: (1) virgin versus mated; (2) mature versus immature. Males were significantly more attracted to those squares bearing chemical cues from virgin and mature females, suggesting that males can assess female reproductive status on the basis of chemical cues alone.     

Cuticular sclerotization in the beetles Pachynoda epphipiata and Tenebrio molitor

The sclerotization of cuticle in two species of beetles, Pachynoda epphipiata and Tenebrio molitor, has been investigated and compared with the sclerotization in the locust, Schistocerca gregaria. Two types of sclerotization, β-sclerotization and quinone tanning, occur in all three species. The main type is β-sclerotization, i.e. cross-linking of proteins by means of N-acetyldopamine which is connected to the proteins through the β-position of its side chain. β-Sclerotization is completed in P. epphipiata when it leaves its cocoon, whereas in adult locusts and in adult Tenebrio β-sclerotization continues for several weeks. The cuticle of all three species contains an insoluble enzyme which activates the β-position of N-acetyldopamine and is presumably responsible for the formation of the cross-links. Locust cuticle contains also small amounts of another enzyme which activates the aromatic ring of N-acetyldopamine, resulting in the formation of an o-quinone, which may be involved in quinone tanning of the cuticle. At emergence adult Tenebrio cuticle is rich in both enzymes, but the quinone-forming enzyme is inactivated after a few days, whereas the β-enzyme first decreases and later increases in activity, so that the β-enzyme is the dominating activity in the cuticle of mature adult Tenebrio. The quinone-forming enzyme is presumably responsible for the formation of the brown colour of Tenebrio exocuticle.The exocuticle of adult beetles contains 3,4-dihydroxyphenylacetic acid, which, although it is not easily extracted from the cuticle, is not covalently bound to cuticular components. In Tenebrio it appears in the cuticle a few days after the final ecdysis.The amino acid compositions of both larval, pupal, and adult cuticle from P. epphipiata have been determined, and they are compared with the composition of the cuticle of the corresponding stages of Tenebrio.     

The effects of 20-hydroxyecdysone on haemolymph pressure pulsations in Tenebrio molitor

Changes in haemocoelic pressure have been studied after the injection of exogenous 20-hydroxyecdysone, using a special tensometric method. Application of the hormone before the endogenous peak of ecdysteroid causes an acceleration of the progressive changes in the pulsation pattern. When given during the endogenous ecdysteroid peak, 20-hydroxyecdysone produces a retention of the existing type of pulsation. Also, administration of the hormone after the endogenous peak induces a retardation in the developmental programme of the pulsations. Shortly before ecdysis, the exogenous hormone does not affect the pulsation programme or the ecdysis. These changes may represent an elegant example of a homeostatic function of ecdysteroids in insect development. Involvement of 20-hydroxyecdysone in regulation of the basic haemolymph pressure is discussed.     

An electrophysiological study of the junctional membrane of epidermal cells in Tenebrio molitor

The insect epidermis is normally a coupled network with respect to the movement of inorganic ions through the junctional membranes connecting adjacent cells. The high ionic permeability of the junctional membrane may be reversibly abolished by either the iontophoretic injection of Ca into single cells or by replacing the Na in the external medium with Li. After Ca injection, a concomitant loss in ionic permeability of the junctional membrane and of the membrane potential of the injected cell was recorded within 3 min. Ionic coupling was restored by hyperpolarizing current pulses within a few minutes. Li substitution tripled the resistance of the junctional membrane within 30 min although the membrane potential remained stable during this period. After 60 min exposure to Li the membrane potential had decayed to zero and ionic coupling was unrecordable. Junctional membrane permeability and cell membrane potential were restored within 30 min re-exposure to normal saline. Since Li is thought to act by indirectly raising the free Ca level in the cytoplasm by its interaction with cytoplasmic Na, we suggest that a reduction in junctional permeability is a direct consequence of increased Ca activity in the cytoplasm of the epidermal cells.     

An electrophysiological study of the non-junctional membrane of epidermal cells in Tenebrio molitor

The contribution of K and Cl to the membrane potential of the epidermal cells of the recently-ecdysed larva of the mealworm was examined. The ionic basis for the membrane potential is complex. Although increasing the external K level depolarized the cell membrane, the relationship obtained suggests that ions other than K contribute largely to the recorded membrane potential. In particular, exposing the cells to K concentrations below the normal level of 40 mM has only slight effects on membrane potential, irrespective of whether K is lowered by direct substitution with Na or under conditions in which Na and Cl levels are held constant. Increasing the external Cl levels from 4 mM to 154 mM while holding K and Na levels constant resulted in a 10 mV hyperpolarization. The slight hyperpolarizing effects of high external Cl could be mimicked by citrate, but not by acetate, the latter drastically hyperpolarizing the cell membrane at levels of K that normally maintain a reduced membrane potential. External Na has little effect on the membrane potential at normal physiological levels of K, but may depolarize the cell at low K levels. The results suggest that several inorganic ions, and possibly organic acids, participate in generating the membrane potential of the epidermal cell. The passive ionic properties of non-junctional epidermal membrane and muscle membrane appear to the similar in this insect.The electrical resistance on the non-junctional membrane is highly dependent on the external K level, and can be reduced by three orders of magnitude by increasing external K from 1 mM to 120 mM. The resistance of the junctional membrane remains constant over this range of external K concentrations.     

Humidity behavior and the identification of hygroreceptors in the adult mealworm, Tenebrio molitor

The humidity behavior of undesiccated and desiccated adult Tenebrio molitor was investigated at 72 and 92%r.h. The behavior of the sexes was analyzed separately. The moist responses of desiccated beetles were correlated with the distribution of smooth-surfaced peg organs by removing various antennal segments. The dry responses of undesiccated beetles were associated with grooved and flat-tipped peg organs by removing various types of antennal sensilla with a laser. On the basis of their morphology and the results of the behavioral experiments, it has been concluded that the smooth-surfaced, grooved, and flat-tipped peg organs are likely to function as humidity receptors. A behavioral model has been proposed to explain the humidity responses of the beetle.     

Patterns of leucine incorporation in the spermathecal accessory glands of the post-ecdysial adult female Tenebrio molitor

The spermathecal accessory glands of female mealworm beetles become fully active by six days after pupal-adult ecdysis. Coincident with the morphological maturation, increases occur in protein and RNA content and in total leucine incorporation. Three classes of differentiation-specific proteins are increasingly prominent and show heightened rates of leucine incorporation by the sixth day.     

Predation by bluegill sunfish (Lepomis macrochirus rafinesque) upon mealworm larvae (Tenebrio molitor)

Eleven responses comprise behaviour of bluegill sunfish (Lepomis macrochirus Rafinesque) preying upon mealworm larvae of Tenebrio molitor. Since each response could be repeated during an attack, behaviour can become quite complex in terms of total number of components comprising a predatory chain. When sunfish attacked the first prey of feeding sessions, predatory sequences contained an average of 8·0 components. Sequences dealing with the second and with all subsequent prey averaged 9·5 and 12·4 components respectively. Increased sequence complexity with increasing satiety depended upon increases in the frequencies of orienting and approaching prey as well as stopping and turning away from prey. Accordingly, satiety is hypothesized to produce more selective responsiveness to prey rather than simple diminution of feeding behaviour.     

The frequency distribution of Hymenolepis diminuta cysticercoids in natural,sympatric populations of Tenebrio molitor and T. obscurus

Rau M. E. 1979. The frequency distribution of Hymenolepis diminuta cysticercoids in natural, sympatric populations of Tenebrio molitor and T. obscurus. International Journal for Parasitology9: 85–87. Natural, sympatric populations of Tenebrio molitor and T. obscurus were examined for cysticercoids of Hymemlepis diminuta. The distribution of cysticeroids in both species and both sexes conformed to the negative binomial. Cysticeroids were more prevalent and the mean intensity of infection was higher in T. obscurus than in T. molitor. No differences in the intensity of infection were detected between the sexes. Larvae of both beetle species were always very lightly infected. The significance of these factors in the transmission of the infection to the rat definitive host is discussed.     

Tenebrio molitor-mediated entomopathogenic fungal library construction for pest management

Entomopathogenic fungi are soil-dwelling microorganisms that infect host insects, and some have been used as biological control agents. Construction of an entomopathogenic fungal library provides a strong platform for the development of highly effective biopesticides, but the traditional method using antibiotic media has low isolation efficiency. Herein, to increase the efficiency of isolation, a Tenebrio molitor pathogenicity-based fungal collection method was used for the construction of a library. The isolation efficiency using the T. molitor larvae-based pathogenicity assay was 55.4%, which was significantly higher than the method of antibiotic medium with dodine (6.0%). We named it the Jeonbuk (Chonbuk) National University Entomopathogenic Fungi (JEF) library. It consisted of 279 isolates belonging to 12 genera and 29 species. Main features of the species-representative 15 isolates were characterized in terms of morphology, virulence, conidiogenesis, thermotolerance and production of biologically active materials such as virulence-related enzymes. Some of the species-representative isolates showed higher virulence against T. molitor, Riptortus pedestris and Plutella xylostella in laboratory conditions. The production of enzymes such as chitinase, Pr1 protease and lipase all related to pathogenesis in LB medium was higher than in the SDB and PDB media. In the thermotolerance assay, a Purpureocillium lilacinum isolate showed higher thermotolerance than other isolates. This work reports an efficient library method using T. molitor for building a library for development of fungal biopesticides for pest management.     

Possible role of hormones in the control of midgut amylolytic activity during adult development of Tenebrio molitor

Midgut amylolytic activity (MAA) increases spontaneously during adult development in isolated, unfed adults. Neck-ligation of adults applied at 0 to 1 hr and 18 to 20 hr after adult emergence exhibits a significant decrease in MAA 72 hr after treatment. MAA decrease was higher when 18 to 20 hr old adults were ligated than those 0 to 1 hr old. Injection of head extracts increases MAA considerably in young adults (0–6 hr) whereas in older ones (18–20 hr) the same dose of the extract does not change the activity of the enzyme examined. It may be supposed that amylase synthesis of the midgut epithelial cells in T. molitor adults is closely related to the cytodifferentiation of the midgut.     

Number of mating males and mating interval affect last-male sperm precedence in Tenebrio molitor L.

Polyandrous females often mate with more than two males, and yet most studies of postcopulatory sexual selection involve only two males. In insects, second-male sperm precedence is usually taken as evidence of overall last-male sperm precedence despite some studies to the contrary. Furthermore, the processes or mechanisms causing the patterns are often unknown and yet are important when estimating how postcopulatory sexual selection might act on males. Whether the patterns and processes change in normal sperm competitive situations and the effects of other factors besides mating order need to be examined to better assess the evolutionary potential of postcopulatory sexual selection. In this study, I assessed the effects of mating interval and number of mating males on sperm precedence patterns and their causal mechanisms in the mealworm beetle, Tenebrio molitor. Last-male sperm precedence was the same when two or three males mated, but also depended on mating intervals and hence mechanisms of paternity bias. However, when females mated with many males, one of the mechanisms no longer created last-male sperm precedence. This example illustrates the importance of knowing both the patterns and mechanisms of paternity bias and whether they change depending on female mating frequency to make reasonable inferences about the potential for postcopulatory sexual selection on males. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.      

The onset of metamorphosis in Tenebrio molitor L.: Effects of a juvenile hormone analogue and of 20-hydroxyecdysone

Sensitivity to juvenile hormone and to 20-hydroxyecdysone has been investigated during the last-larval stages of Tenebrio molitor. Topical applications of a juvenile hormone analogue (K-421d) showed that the sensitive period, occurring before apolysis, is relatively short (less than 4 days in a 3-week instar) and divided into two phases. Treatment during the first and longest phase induced a delay in development and then an increase in larval moult percentage. Treatment during the second phase induced several abnormal moults (prothetelic larvae and larval-pupal intermediates).Injections of massive doses of 20-hydroxyecdysone (10 μg per animal) also evidenced a period of disturbance of the morphogenetic programme, beginning before pupal apolysis but continuing several days after.Comparison of the sensitive periods to both hormones suggests that a very important and rapid step of the larval-pupal programme change is controlled hormonally just before pupal apolysis.