Head movements of the mealworm beetle Tenebrio molitor

Tethered walking imagines of the mealworm beetle Tenebrio molitor wave their heads in random fashion. If a periodic pattern of vertical black and white stripes is rotated around the animal a regular nystagmic head movement is superimposed upon the random waving, the frequency of the latter equals the contrast frequency within large ranges of the angular velocity of the pattern. The nystagmus is inverted: After a short period of tracking, during which the angular velocity of the head is the same as that of the panorama, the head returns slowly toward its normal position according to an exponential-like function. Resting animals do not wave their heads. However, if the above panorama is rotated, the beetle turns its head in the direction of the movement of the panorama and holds it in a side-way position, as long as the rotation is maintained. The angular position reached depends in the same manner on the angular velocity of the panorama as the turning tendency of walking animals established in open loop experiments using the spherical Y-maze method.     

An immunoelectron study of karyosphere and nuclear bodies in oocytes of mealworm beetle, Tenebrio molitor (Coleoptera: Polyphaga)

The karyosphere and nuclear bodies (NBs) were studied in Tenebrio molitor oocytes using immunoelectron cytochemistry. During early diplotene (previtellogenic stage), oocyte chromosomes begin to unite in a small nuclear volume forming the karyosphere. In vitellogenic oocyte nuclei, the chromatin undergoes condensation, and the karyosphere acquires a ring-shaped structure. The karyosphere is the only structure containing DNA in the oocyte nucleus. Pre-mRNA splicing factors [small nuclear ribonucleoproteins (snRNPs) and SC35] are not found in the karyosphere itself. In previtellogenic oocyte nuclei, these factors are present in NBs and in a fibrogranular substance surrounding the chromosomes in the early stages of karyosphere formation. At this stage, larger fibrillar NBs contain the non-snRNP splicing factor SC35. Smaller roundish NBs were shown to contain snRNPs. Some NBs with the same morphology contain neither snRNPs nor SC35. In the vitellogenic oocyte, there are fibrogranular NBs containing both snRNPs and SC35 splicing factors, fibrillar NBs containing snRNPs only, and complex NBs containing both. Complex NBs are often connected with the ring-shaped karyosphere. Based on the obtained immunoelectron data, we suggest that T. molitor oocyte NBs containing both snRNPs and the non-snRNP splicing factor SC35 are homologs of the well-characterized B-snurposomes in amphibian germinal vesicles and clusters of interchromatin granules in mammalian oocyte nuclei. Other NBs containing only snRNPs are suggested to represent a special class of insect oocyte snurposomes. The nuclear organelles mentioned seem to play a role as storage domains for pre-mRNA splicing factors during T. molitor oogenesis.     

Visual edge fixation and negative phototaxis in the mealworm beetle Tenebrio molitor

The visual fixation response of the mealworm beetle Tenebrio molitor, elicited by black stripes upon a bright background is studied in an arena and by means of the Y-maze technique. In the arena the distribution n() of the beetle's angular position is measured at different distances from the centre, which is also the starting point. If the black stripe is narrow, the maximum of n() coincides with the centre of the stripe (centre-fixation Figure 1a). If one half of the panorama is black, the distribution n() has two maxima, which are near the borders between the black and white regions (edge-fixation Figure 1b). In the Y-maze experiments the beetle is tethered, but its head is free to move. The black stripes elicit turning tendencies F(), the strength of which depends upon the angular distance between the centre of the stripe and the animal's body axis. If the black stripe is narrow, the stable zero crossing of F() lies at =0, in agreement with the centre fixation in the arena (Fig. 3). If the stripe is 180° wide, two stable zero crossings are obtained near the border lines between the black and white regions, provided that the panorama is rotated around the animal with an angular velocity w larger than about 0.08°/s (Fig. 4). Below this value of w only one stable zero crossing at =0 exists (Fig. 6). Thus the tethered beetle's response underlies a transition between centre resp. edge fixation at a critical angular velocity of the drum. Some implications of this surprising phenomenon with respect to the mechanism of fixation and negative phototaxis are discussed but at present it is considered primarily a challenge for further investigation.Supported in part by Deutsche Forschungsgemeinschaft     

Influence of canola hulls on gain in weight of larvae of the yellow mealworm, Tenebrio molitor L

Larvae of the yellow mealworm, Tenebrio molitor L., Gembloux strain, race F, were reared on diets in which the protein component was supplied by defatted ground seed, defatted ground dehulled fraction, or defatted ground hulls of Brassica napus L. cv. Tower or Brassica campestris L. cv. Candle, obtained from autoclaved seed. They were also fed casein diets to which defatted ground hulls of Tower or Candle seed were added. Gain in weight was equally good for all diets containing Candle seed fractions and for diets containing Tower ground seed. However, it was lower for diets containing the ground dehulled fraction or the ground hulls of Tower. Addition of Candle hulls or of a mixture of equal proportions (w/w) of Candle and Tower hulls to diets containing dehulled Tower did not improve the gain in weight of larvae, compared with that of larvae fed diets containing the dehulled fraction, alone. Similar additions of Tower hulls or of the mixture to diets containing the dehulled fraction of Candle had no adverse effect on larval gain in weight, compared to that registered by larvae fed the dehulled fraction of Candle. Significant improvement in weight gain in comparison with that recorded for larvae fed the unsupplemented casein diet could not be demonstrated when ground hulls of Tower or Candle were added to this diet. Considered collectively, weight gains of larvae of T. molitor were consistently greater when Candle products were fed than when Tower products provided the protein fraction of the diet.     

Cajal bodies in insect oocytes. I. Identification and immunocytochemical characteristics of Cajal bodies in vitellogenic oocytes of the yellow mealworm beetle

In vitellogenic oocytes of Tenebrio molitor (inactive stage), numerous fibrogranular nuclear bodies (NBs) are present. Using immunofluorescent microscopy, these NBs were shown to contain pre-mRNA splicing factors (small nuclear [sn] RNPs and SR-protein, SC35) as well as RNA polymerase II. A limited set of NBs also contained coilin, a marker protein for Cajal bodies (CBs). We suggest that in T. molitor oocytes, coilin-containing NBs, which also contain splicing factors and RNA polymerase II, seem to represent CBs. In the species studied, no morphological features of CBs were established as compared with other NBs, which do not contain coilin. Microinjectons in oocytes of myc-tagged coilin mRNA, followed by revealing newly translated protein with antibody specific for this tag, have shown targeting of myc-coilin with CBs. The own and literary data on the morphology and molecular composition of CBs are discussed in terms of searching for criteria for CB identification in cells of different origin, and at active and inactive stages.     

Effect of commercial processing of canola and rapeseed on growth of larvae of the yellow mealworm, Tenebrio molitor L

Larvae of Tenebrio molitor L., Gembloux strain, race F, were used to determine the nutritional quality of commercial canola and rapeseed products. Application of heat in commercial processing increased considerably the nutritive values of Midas, Tower and Torch cultivars, and to a lesser extent that of Candle. This improvement was most noticeable for thigh-glucosinolate cultivars, presumably through the destruction of a mechanism for production of isothiocyanates that may be phagodeterrent or toxic to the larvae. For low-glucosinolate varieties, the improvement may be related to inhibition of nitrile production in heated material. The processing also reduced the concentration of available lysine in the products of all four cultivars; however, growth was unimpaired by this reduction. The latter results suggest that the feed products resulting from processing may exceed the optimal dietary requirement of lysine by larvae of Tenebrio molitor.     

Effects of fumonisin B1 on growth and metabolism of larvae of the yellow mealworm, Tenebrio molitor

The chronic and acute toxicity of fumonisin B₁ (FB₁), a mycotoxin from Fusarium moniliforme, to the larvae of the yellow mealworm, Tenebrio molitor, was assessed. The toxin was administered via the diet or injected directly into the larvae. Young T. molitor larvae fed on a diet containing 450 µg FB₁ per g diet exhibited reduced growth performance but only after consuming the fumonisin-contaminated diet for several weeks. FB₁-contaminated diet also reduced the rate of carbon dioxide production, food consumption and protein metabolism. The concentrations of FB₁ in the diet did not increase mortality, even when tested at the highest dose of 450 µg FB₁ per g of diet. Injection of 25 ng FB₁ per larva decreased the CO₂ production, but became significant only 11 days after the injection and was reversible with time. A parallel analysis of the retention of FB₁ by the larvae indicated that about 40% of the ingested FB₁ was excreted in the faeces.     

Developmental and environmental regulation of antifreeze proteins in the mealworm beetle Tenebrio molitor.

The yellow mealworm beetle, Tenebrio molitor, contains a family of small Cys-rich and Thr-rich thermal hysteresis proteins that depress the hemolymph freezing point below the melting point by as much as 5. 5 degrees C (DeltaT = thermal hysteresis). Thermal hysteresis protein expression was evaluated throughout development and after exposure to altered environmental conditions. Under favorable growth conditions, small larvae (11-13 mg) had only low levels of thermal hysteresis proteins or thermal hysteresis protein message, but these levels increased 10-fold and 18-fold, respectively, by the final larval instar (> 190 mg), resulting in thermal hysteresis > 3 degrees C. Exposure of small larvae (11-13 mg) to 4 weeks of cold (4 degrees C) caused an approximately 20-fold increase in thermal hysteresis protein concentration, well in excess of the less than threefold developmental increase seen after 4 weeks at 22 degrees C. Exposure of large larvae (100-120 mg) to cold caused 12-fold and sixfold increases in thermal hysteresis protein message and protein levels, respectively, approximately double the maximum levels they would have attained in the final larval instar at 22 degrees C. Thus, thermal hysteresis increased to similar levels (> 4 degrees C) in the cold, irrespective of the size of the larvae (the overwintering stage). At pupation, thermal hysteresis protein message levels decreased > 20-fold and remained low thereafter, but thermal hysteresis activity decreased much more slowly. Exposure to cold did not reverse this decline. Desiccation or starvation of larvae had comparable effects to cold exposure, but surprisingly, short daylength photoperiod or total darkness had no effect on either thermal hysteresis or message levels. As all environmental conditions that caused increased thermal hysteresis also inhibited growth, we postulate that developmental arrest is a primary factor in the regulation of T. molitor thermal hysteresis proteins.     

The interaction between visual edge fixation and skototaxis in the mealworm beetle Tenebrio molitor

Summary (1) It has been shown in earlier experiments that during the visually guided orientation response of the mealworm beetle,Tenebrio molitor, edge fixation and skototaxis interact. Under certain stimulus conditions these two effects act against each other and relative movement between the retina and the surroundings shifts the balance in favour of edge fixation. In this paper, three further parameters are described which change the contribution of the two mechanisms to the turning tendency of the animals. (2) When the centre of a broad black stripe lies on one side and one of the edges on the other side of the animal (Fig. 1B, C) then motion of an edge from front to back (progressive movement) more effectively increases the relative weight of edge fixation than do regressive movements (motion of an edge from back to front). (3) In the same situation temporal modulation of the overall illumination weakens skototaxis, dimming more than brightening (Fig. 2 A). From this it was predicted — and confirmed — that the dependence on the direction of motion will be reversed if both the centre and the edge closest to the midline of a broad black stripe lie on the same side of the animal (Fig. 2 B). (4) Animals with one eye blinded can fixate an edge (Fig. 3). Furthermore, edge fixation is mediated mainly by the ventral part of the eyes and skototaxis by the dorsal (Fig. 5). (5) The possible significance of the results for the animal's natural behaviour and for the underlying neural circuitry is discussed.     

Interaction of wheat monomeric and dimeric protein inhibitors with alpha-amylase from yellow mealworm (Tenebrio molitor L. larva).

The highly purified alpha-amylase from Tenebrio molitor L. larva (yellow mealworm) reversibly combines with two closely related homogeneous glycoprotein inhibitors, one dimeric (termed 'inhibitor 0.19') and one monomeric (termed 'inhibitor 0.28'), from wheat flour. As established by means of difference spectroscopy and kinetic studies, molar combining ratios for the amylase--inhibitor-0.19 and amylase-inhibitor-0.28 complexes were 1:1 and 1:2 respectively. Two amylase--inhibitor-0.19 complexes with slightly different retention volumes on Bio-Gel P-300 and only one amylase--inhibitor-0.28 complex were observed. Dissociation constants of the amylase--inhibitor-0.19 and amylase--inhibitor-0.28 complexes were 0.85 nM and 0.13 nM respectively. A strong tendency of both complexes to precipitate under an ultracentrifugal field was observed; the minimum molecular weight calculated for the two complexes under such conditions was approx. 95 000. The two complexes showed difference spectra indicating involvement of structurally related or identical tryptophyl side chains in the binding of inhibitors 0.28 and 0.19 to the amylase. A model summarizing the main features of the inhibition of the insect amylase by the two wheat protein inhibitors is proposed.     

Fine structure of the spermatheca of the mealworm beetle (Tenebrio molitor L.)

The spermatheca of the female mealworm beetle is an inflorescence of branching cuticular ducts which is connected to the bursa copulatrix via a cuticular neck surrounded by a muscular coat. The infolded bursal cuticle consists of a distinct outer epicuticle, inner epicuticle, procuticle, and a subcuticular zone; the latter is rich in mucopolysaccharides. The cuticle of the neck lacks a distinct procuticle. The cuticle of the spermatheca itself is mostly inner epicuticle with two thin underlying lamellae of procuticle. The cells of the bursa are loosely coupled to the procuticle, whereas cuticular projections bind the epithelia of the "neck" and the spermatheca proper to the underlying epithelia. The apical plasma membranes of the spermathecal epithelium are sinuous and much infolded; we believe that this epithelium controls the micro-environment within the cuticular ducts.