Lie to me to lay with me: Females deceive males via terminal investment

Historically, males have frequently been portrayed as the manipulative and deceptive gender, while females are often seen as adopting a coy and passive role. In this context, it is proposed that males use a terminal investment strategy, misleading females about their true poor condition, while females passively opt to mate with these deceptive males. However, we hypothesize that females in suboptimal condition may also engage in a terminal investment strategy by mimicking or enhancing their attractiveness to match that of females in better conditions. We studied this hypothesis in Tenebrio molitor, by subjecting females to three varying doses of lipopolysaccharides of Escherichia coli (LPS; 0.25, 0.5, or 1 mg ml-1), or three doses of the pro-oxidant Paraquat (PQ; 20, 40 or 80 mM), and subsequently assessing their survival and attractiveness to males. The LPS treatments and 20 mM of PQ had no significant effect on the survival or attractiveness of the females. However, females treated with 40 or 80 mM PQ survived fewer days compared to the control group. Those injected with 40 mM were more attractive than their control counterparts, while those treated with 80 mM were less attractive. Since the identical doses of LPS, which induce terminal investment in males, had no effect on females, we suggest sexual dimorphism in terminal investment. Furthermore, similar to males, if the stressor reaches a sufficiently high level, the signal becomes honest. These findings highlight how the quantity of stressors influences support for the terminal investment strategy in both males and females. Notably, this study challenges prevailing notions regarding gender roles in sexual selection, indicating that females, not just males, conceal their poor condition to attract mating partners.

Mapping the nutritional landscape in the yellow mealworm: testing the nutrient-mediated life-history trade-offs

Animals must acquire an ideal amount and balance of macronutrients to optimize their performance, health and fitness. The nutritional landscape provides an integrative framework for analysing how animal phenotypes are associated with multiple nutritional components. Here, we applied this powerful approach to examine how the intake of protein and carbohydrate affects nutrient acquisition and performance in the yellow mealworm (Tenebrio molitor) reared on one of 42 synthetic foods varying in protein and carbohydrate content. Tenebrio molitor larvae increased their food consumption rate in response to nutrient dilution, but this increase was not sufficient to fully compensate for the dilution. Diluting the food nutrient content with cellulose reduced the efficiency of post-ingestive nutrient utilization, further restricting macronutrient acquisition. Tenebrio molitor larvae utilized macronutrients most efficiently at a protein to carbohydrate (P:C) ratio of 1.77:1, but became less efficient at imbalanced P:C ratios. Survivorship was high at high protein intake and fell with decreasing protein intake. Pupal mass and growth rate exhibited a bell-shaped landscape, with the nutritional optima being located around protein-biased P:C ratios of 1.99:1 to 2.03:1 and 1.66:1 to 2.86:1, respectively. The nutritional optimum for development time was also identified at high P:C ratios (1.66:1  to 5.86:1). Unlike these performance traits, lipid content was maximized at carbohydrate-biased P:C ratios of 1:3.88 to 1:3.06. When given a food choice, T. molitor larvae self-composed a slightly carbohydrate-biased P:C ratio of 1:1.24, which lies between the P:C ratios that maximize performance and lipid content. Our findings indicate the occurrence of a nutrient-mediated trade-off between performance and energy storage in this insect.

Nutritional, Physiochemical, and Antioxidative Characteristics of Shortcake Biscuits Enriched with Tenebrio molitor Flour

Edible insects, due to their high nutritional value, are a good choice for traditional food supplementation. The effects of partial replacement of wheat flour and butter with mealworm flour (Tenebrio molitor) on the quality attributes of shortcake biscuits were studied. The approximate composition was analyzed, along with the physical properties and color. Moreover, the antioxidant properties, starch digestibility, and glycemic index were determined in vitro. The protein and ash contents in biscuits supplemented with mealworm flour increased, while the carbohydrates content decreased. The increasing insect flour substitution decreased the lightness (L*) and yellowness (b*) but increased the redness (a*), total color difference (ΔE), and browning index (BI). The spread factor for the sample with the highest proportion of mealworm flour was significantly higher than the other biscuits. Furthermore, higher additions of mealworm flour increased the antioxidant activity of the biscuits and contributed to an increase in the content of slowly digested starch, with a decrease in the content of rapidly digested starch. Therefore, the results of the research are promising and indicate the possibility of using edible insects to enrich food by increasing the nutritional and health-promoting values.

Mutual mate choice and its benefits for both sexes

In mating interactions, it is common in nature for both sexes to choose simultaneously. However, this mutual mate choice and its consequences for progeny has received relatively little study; an approach where both male and female condition is manipulated is thus desirable. We compared both sexes' preferences in Tenebrio molitor beetles when individual condition varied (healthy vs infected with a fungus), and observed the direct benefits of those preferences. We predicted that: (a) females and males in good condition would prefer high quality mates; (b) preferences would be weaker when the choosing individual is in poor condition (and thus less selective given, for example, time and energetic constrains); and, (c) high quality mates would lay a larger number of total eggs and/or viable eggs than low quality mates. We found that both males and females in good condition were not more likely to choose mates that were also in good condition. However, poor-condition animals were more likely to prefer similar quality animals, while high-condition animals did not necessarily prefer mates of similar condition. Choosing sick males or females had a negative impact on egg number and viability. Our results suggest a non-adaptive mate choice in this species. Possibly, a deteriorated condition may drive individuals to invest more in attracting mates, because their chances of surviving the infection are very low. However, we do not discount the possibility that the fungus is manipulating individuals to increase its transmission during mating.

Recycling of spent mushroom substrate: Utilization as feed material for the larvae of the yellow mealworm Tenebrio molitor (Coleoptera: Tenebrionidae)

Spent mushroom substrate is made from the waste remaining after the harvest of mushrooms. Here, we evaluated the potential of five spent edible fungi (Auricularia cornea, Lentinus edodes, Pleurotus eryngii, P. citrinopileatus and P. ostreatus) substrates as feed sources for Tenebrio molitor larvae. Young larvae did not survive on any substrate except the spent L. edodes substrate (36.7%). The survival rates in young larvae were similar among the different diets in which wheat bran or rice bran was replaced with 0, 20, 30, 40, 50, or 60% spent L. edodes substrate. The weights of the surviving larvae were decreased only when 70% of wheat bran and > 40% of rice bran was replaced with spent L. edodes substrate. In addition, the middle-aged larvae fed wheat bran only were significantly larger than those fed diets with 30~60% spent L. edodes substrate in dry feed, but the larvae of all treatments failed to pupate. Whereas the green feed was added in dry feed, there were no significant differences in pupal weight, pupation rate, pupal duration, adult emergence, or deformed adults among the three treatments in middle-aged larvae that were fed on diets containing 0, 30, or 40% spent L. edodes substrate. Collectively, these results suggest that spent L. edodes substrate has considerable potential to be used as a partial replacement (< 40%) of conventional feed for T. molitor, and spent mushroom substrate waste may be recycled as feed material for resource insects.

Development and Biomass Composition of Ephestia kuehniella (Lepidoptera: Pyralidae), Tenebrio molitor (Coleoptera: Tenebrionidae), and Hermetia illucens (Diptera: Stratiomyidae) Reared on Different Byproducts of the Agri-Food Industry

The aim of this study was to evaluate five agro-industrial byproducts (apricots, brewer's spent grains, brewer's spent yeast, feed mill byproducts including broken cereal grains, and hatchery waste including eggshell debris, fluff, infertile eggs, dead embryos, and egg fluids) or mixtures thereof as food diets of Ephestia kuehniella (Zeller), Tenebrio molitor (L.), and Hermetia illucens (L.). Eleven out of 26 tested combinations allowed the first instar larvae to reach the adult stage. Results showed that bioconversion parameters and biomass composition can vary depending on the diet composition, especially in the case of E. kuehniella and H. illucens, whose nutritional requirements seem more complex than those of T. molitor. Tenebrio molitor was able to develop in almost all byproducts. However, only when T. molitor was fed with suitable mixtures of byproducts the development parameters were similar to those obtained with the standard diet. The best results in terms of bioconversion parameters were obtained by feeding H. illucens with a diet including dried brewer's spent grain, feed mill byproducts and brewer's spent yeast. The larvae of these three species can be considered interesting from a nutritional point of view, because of their high protein and fat content. However, the fatty acids profile of H. illucens larvae, with high proportions of saturated fatty acids, seems less healthy for human consumption compared with those of E. kuehniella and T. molitor.

Gene functions in adult cuticle pigmentation of the yellow mealworm, Tenebrio molitor

In many arthropod species including insects, the cuticle tanning pathway for both pigmentation and sclerotization begins with tyrosine and is responsible for production of both melanin- and quinoid-type pigments, some of which are major pigments for body coloration. In this study we identified and cloned cDNAs of the yellow mealworm, Tenebrio molitor, encoding seven key enzymes involved in this pathway including tyrosine hydroxylase (TmTH), DOPA decarboxylase (TmDDC), laccase 2 (TmLac2), Yellow-y (TmY-y), arylalkylamine N-acetyltransferase (TmAANAT1), aspartate 1-decarboxylase (TmADC) and N-β-alanyldopamine synthase (Tmebony). Expression profiles of these genes during development were analyzed by real-time PCR, revealing development-specific patterns of expression. Loss of function mediated by RNAi of either 1) TmTH or TmLac2, 2) TmDDC or TmY-y, and 3) TmAANAT1, TmADC or Tmebony resulted in pale/white, light yellow/brown and dark/black adult body coloration, respectively. In addition, there are three distinct layer/regional pigmentation differences in rigid types of adult cuticle, a brownish outer exocuticle (EX), a dark pigmented middle mesocuticle (ME) and a transparent inner endocuticle (EN). Decreases in pigmentation of the EX and/or ME layers were observed after RNAi of TmDDC or TmY-y. In TmADC- or Tmebony-deficient adults, a darker pigmented EX layer was observed. In TmAANAT1-deficient adults, trabeculae formed between the dorsal and ventral elytral cuticles as well as the transparent EN layer became highly pigmented. These results demonstrate that knocking down the level of gene expression of specific enzymes of this tyrosine metabolic pathway leads to abnormal pigmentation in individual layers and substructure of the rigid adult exoskeleton of T. molitor.

A novel clean production approach to utilize crop waste residues as co-diet for mealworm (Tenebrio molitor) biomass production with biochar as byproduct for heavy metal removal

Proper management of waste crop residues has been an environmental concern for years. Yellow mealworms (larvae of Tenebrio molitor Linnaeus, 1758) are major insect protein source. In comparison with normal feed wheat bran (WB), we tested five common lignocellulose-rich crop residues as feedstock to rear mealworms, including wheat straw (WS), rice straw (RS), rice bran (RB), rice husk (RH), and corn straw (CS). We then used egested frass for the production of biochar in order to achieve clean production. Except for WS and RH, the crop residues supported mealworms' life activity and growth with consumption of the residues by 90% or higher and degraded lignin, hemicellulose and cellulose over 32 day period. The sequence of degradability of the feedstocks is RS > RB > CS > WS > RH. Egested frass was converted to biochar which was tested for metal removal including Pb(II), Cd(II), Cu(II), Zn(II), and Cr(VI). Biochar via pyrolysis at 600 °C from RS fed frass (FRSBC) showed the best adsorption performance. The adsorption isotherm fits the Langmuir model, and kinetic analysis fits the Pseudo-Second Order Reaction. The heavy metal adsorption process was well-described using the Intra-Particle Diffusion model. Complexation, cation exchange, precipitation, reduction, deposition, and chelation dominated the adsorption of the metals onto FRSBC. The results indicated that crop residues (WS, RS, RB, and CS) can be utilized as supplementary feedstock along with biochar generated from egested frass to rear mealworms and achieve clean production while generating high-quality bioadsorbent for environment remediation and soil conditioning.

Differentiated Effects of Secondary Metabolites from Solanaceae and Brassicaceae Plant Families on the Heartbeat of Tenebrio molitor Pupae

The usage of insects as model organisms is becoming more and more common in toxicological, pharmacological, genetic and biomedical research. Insects, such as fruit flies (Drosophila melanogaster), locusts (Locusta migratoria), stick insects (Baculum extradentatum) or beetles (Tenebrio molitor) are used to assess the effect of different active compounds, as well as to analyse the background and course of certain diseases, including heart disorders. The goal of this study was to assess the influence of secondary metabolites extracted from Solanaceae and Brassicaceae plants: Potato (Solanum tuberosum), tomato (Solanum lycopersicum), black nightshade (Solanum nigrum) and horseradish (Armoracia rusticana), on T. molitor beetle heart contractility in comparison with pure alkaloids. During the in vivo bioassays, the plants glycoalkaloid extracts and pure substances were injected at the concentration 10-5 M into T. molitor pupa and evoked changes in heart activity. Pure glycoalkaloids caused mainly positive chronotropic effects, dependant on heart activity phase during a 24-h period of recording. Moreover, the substances affected the duration of the heart activity phases. Similarly, to the pure glycoalkaloids, the tested extracts also mainly accelerated the heart rhythm, however S. tuberosum and S. lycopersicum extracts slightly decreased the heart contractions frequency in the last 6 h of the recording. Cardioacceleratory activity of only S. lycopersicum extract was higher than single alkaloids whereas S. tubersoum and S. nigrum extracts were less active when compared to pure alkaloids. The most cardioactive substance was chaconine which strongly stimulated heart action during the whole recording after injection. A. rusticana extract which is composed mainly of glucosinolates did not significantly affect the heart contractions. Obtained results showed that glycoalkaloids were much more active than glucosinolates. However, the extracts depending on the plant species might be more or less active than pure substances.

Body Mass Increase Induced by Eight Years of Artificial Selection in the Yellow Mealworm (Coleoptera: Tenebrionidae) and Life History Trade-offs

Efforts to improve rearing conditions of Tenebrio molitor L. (Coleoptera: Tenebrionidae) for insect biomass production included selecting for larger size pupae. The effects of an 8-yr continuous selection of T. molitor pupae for larger size were studied. Data consisting of daily counts and weights of pupae were analyzed using regression to determine the effects of selection over time. A preliminary evaluation of food conversion, growth, fecundity, and larval survival was done to compare ancestral versus selected strains. A significant positive correlation was identified between pupal size and time indicating a significant increase in pupal size over time in the selected T. molitor strain. A preliminary comparison of ancestral and selected strains showed significantly larger pupal size, growth rate, fecundity, and efficiency of conversion of ingested food in the selected strain. However, the selected strain also showed significantly lower larval survival than the ancestral strain. The low larval survival impacted the overall productivity of the selected strain resulting in no significant differences in biomass production when compared with the ancestral strain. The potential of using selection to improve biomass productivity in T. molitor is discussed.

Sublethal Effects of Solanum nigrum Fruit Extract and Its Pure Glycoalkaloids on the Physiology of Tenebrio molitor (Mealworm)

BACKGROUND

Solanaceae plants produce glycoalkaloids (GAs) that affect various physiological processes of herbivorous insects and they are being tested as potential alternatives for synthetic pesticides. They cause lethal and sublethal effects. Nevertheless, their mode of action remains unclear. Therefore, we examined the effects of Solanum nigrum fruit extracts and pure glycoalkaloids on a model beetle, Tenebrio molitor.

METHODS

Plant extracts or pure alkaloids were added to the food of the larvae for three days. The lipid, glycogen, and protein content in the fat body and the midgut were determined, and the contractility of the heart, hindgut, and oviduct muscles was tested using the video-microscopy technique. Finally, the ultrastructure of the fat body and the midgut was observed using electron microscopy.

RESULTS

No lethal effects were noted. Sublethal changes were observed in the content of biomolecules, malformations of organelles, chromatin condensation, and heart and oviduct contractility. The observed effects differed between the tested glycoalkaloids and the extract.

CONCLUSIONS

Both the extract and pure GAs have a wide range of effects that may result in impaired development, food intake, and reproduction. Some early effects may be used as bioindicators of stress. The effects of the extract and pure alkaloids suggest that the substances produced by the plant may act additively or synergistically.

Dissemination of Fusarium proliferatum by mealworm beetle Tenebrio molitor

BACKGROUND

Plant pathogenic fungi of the genus Fusarium infect a wide array of crops and produce numerous health-threatening mycotoxins. Recently, we found that larvae of the common pest of stored products Tenebrio molitor preferably fed on grains colonized with Fusarium proliferatum. We draw the hypothesis that the increased attractiveness of infected grains for mealworms facilitates dispersal of the fungus. In this work we examined the dissemination of F. proliferatum and further Fusarium spp. by adults of T. molitor.

RESULTS

Mealworm beetle Tenebrio molitor transmitted Fusarium species F. avenaceum, F. culmorum, F. poae, and F. proliferatum to wheat grains with varying efficiency. F. proliferatum was disseminated most efficiently: 20 days after feeding on Fusarium cultures, the beetles still transmitted F. proliferatum to most grains exposed to feeding. The transmission of F. culmorum gradually declined over time and the transmission of the other Fusarium spp. ceased completely 20 d after beetles feeding of fungal cultures. Propagules of F. proliferatum and F. culmorum were traceable in beetles' feces for 20 days while no colonies of F. poae and F. avenaceum were detectable after 5 days. Because F. proliferatum was transmitted by mealworms most efficiently, this species was further investigated. Mealworm beetles T. molitor preferred feeding on grains colonized with F. proliferatum as compared to uninfected grains. Male beetles infected with F. proliferatum transmitted the fungus by copulation.

CONCLUSIONS

Efficient dissemination of F. proliferatum by mealworm beetle together with the feeding preference of the beetle for grains colonized with F. proliferatum show that the chemical phenotype of the fungus responsible for the enhanced attractiveness of infected grains is subjected to positive selection. This indicates that adaptation of F. proliferatum to transmission by insects involved an alteration of insects' feeding preferences.

Heart mechanical and hemodynamic parameters of a beetle, Tenebrio molitor, at selected ages

The physiological processes that occur during the aging of insects are poorly understood. The aim of this study was to describe the changes in contractile activity and hemodynamic parameters of the heart that take place as the coleopteran beetle, Tenebrio molitor, ages. The frequency of heart contractions in beetles that had just undergone metamorphosis (median 24.7 beats/min) was significantly lower than the frequency of heart contractions in older beetles. In 56% of beetles that were < 1 week of age, a pattern of contractile activity with alternating periods of higher and lower contraction frequency was detected, suggesting that some posteclosion developmental processes occur during the first week of adulthood. All beetles that were 1 week of age showed a regular rhythm of heart contractions (median 72 beats/min). In older beetles, abnormalities such as heart arrhythmias or heart arrest were observed. The incidence of arrhythmia as well as the arrhythmicity index was highest in beetles that were 8-18 weeks old. The calculated stroke volume (SV) was also found to increase from eclosion to 12 weeks of age, and then decreased as adults aged further. Interestingly, cardiac output increased gradually, but the ejection fraction did not change significantly with age.

Peptide hormones regulate the physiological functions of reproductive organs in Tenebrio molitor males

In insects, the majority of studies have been conducted on the hormonal regulation of female reproduction. Thus far, little is known about the regulation of male reproductive physiology, especially by peptide hormones. We report here, for the first time in insects, the effects of three peptides, Neb-colloostatin (SIVPLGLPVPIGPIVVGPR), Neb-TMOF (NPTNLH) and Lepde-NPF-I (ARGPQLRLRFa), on various aspects of reproduction in male Tenebrio molitor beetles. All three tested peptides increased the soluble protein concentration in the testes and the dry mass of the beetle's testes. They also significantly changed the protein profiles of the testes. Injection of these peptides also significantly changed the number of sperm cells in the testes. However, the observed effects were age specific. The most prominent changes were observed in 4-day-old males. Neb-colloostatin and Neb-TMOF decreased the number of sperm cells, whereas Lepde-NPF-I increased the number of spermatocytes. Moreover, in vitro experiments revealed that Neb-TMOF and Lepde-NPF-I increased the contractility of the ejaculatory duct of T. molitor males. The results obtained suggest that different reproductive processes in males might be regulated by complex mechanisms.

Cuticular colour reflects underlying architecture and is affected by a limiting resource

Central to the basis of ecological immunology are the ideas of costs and trade-offs between immunity and life history traits. As a physical barrier, the insect cuticle provides a key resistance trait, and Tenebrio molitor shows phenotypic variation in cuticular colour that correlates with resistance to the entomopathogenic fungus Metarhizium anisopliae. Here we first examined whether there is a relationship between cuticular colour variation and two aspects of cuticular architecture that we hypothesised may influence resistance to fungal invasion through the cuticle: its thickness and its porosity. Second, we tested the hypothesis that tyrosine, a semi-essential amino acid required for immune defence and cuticular melanisation and sclerotisation, can act as a limiting resource by supplementing the larval diet and subsequently examining adult cuticular colouration and thickness. We found that stock beetles and beetles artificially selected for extremes of cuticular colour had thicker less porous cuticles when they were darker, and thinner more porous cuticles when they were lighter, showing that colour co-varies with two architectural cuticular features. Experimental supplementation of the larval diet with tyrosine led to the development of darker adult cuticle and affected thickness in a sex-specific manner. However, it did not affect two immune traits. The results of this study provide a mechanism for maintenance of cuticular colour variation in this species of beetle; darker cuticles are thicker, but their production is potentially limited by resource constraints and differential investments in resistance mechanisms between the sexes.

Effects of various diets on the calcium and phosphorus composition of mealworms (Tenebrio molitor larvae) and superworms (Zophobas morio larvae)

OBJECTIVE To evaluate whether the nutritive quality of Tenebrio molitor larvae and Zophobas morio larvae, which are commonly cultured as live food sources, is influenced by 4 commercially available diets used as nutritional substrates; identify which diet best improved calcium content of larvae; and identify the feeding time interval that assured the highest calcium intake by larvae. ANIMALS 2,000 Zophobas morio larvae (ie, superworms) and 7,500 Tenebrio molitor larvae (ie, mealworms). PROCEDURES Larvae were placed in control and diet treatment groups for 2-, 7-, and 10-day intervals. Treatment diets were as follows: wheat millings, avian hand feeding formula, organic avian mash diet, and a high-calcium cricket feed. Control groups received water only. After treatment, larvae were flash-frozen live with liquid nitrogen in preparation for complete proximate and mineral analyses. Analyses for the 2-day treatment group were performed in triplicate. RESULTS The nutrient composition of the high-calcium cricket feed groups had significant changes in calcium content, phosphorus content, and metabolizable energy at the 2-day interval, compared with other treatment groups, for both mealworms and superworms. Calcium content and calcium-to-phosphorus ratios for larvae in the high-calcium cricket feed group were the highest among the diet treatments for all treatment intervals and for both larval species. CONCLUSIONS AND CLINICAL RELEVANCE A 2-day interval with the high-calcium cricket feed achieved a larval nutrient composition sufficient to meet National Research Council dietary calcium recommendations for nonlactating rats. Mealworm calcium composition reached 2,420 g/1,000 kcal at 48 hours, and superworm calcium composition reached 2,070g/1,000 kcal at 48 hours. These findings may enable pet owners, veterinarians, insect breeders, and zoo curators to optimize nutritive content of larvae fed to insectivorous animals.

Balanced intake of protein and carbohydrate maximizes lifetime reproductive success in the mealworm beetle, Tenebrio molitor (Coleoptera: Tenebrionidae)

Recent developments in insect gerontological and nutritional research have suggested that the dietary protein:carbohydrate (P:C) balance is a critical determinant of lifespan and reproduction in many insects. However, most studies investigating this important role of dietary P:C balance have been conducted using dipteran and orthopteran species. In this study, we used the mealworm beetles, Tenebrio molitor L. (Coleoptera: Tenebrionidae), to test the effects of dietary P:C balance on lifespan and reproduction. Regardless of their reproductive status, both male and female beetles had the shortest lifespan at the protein-biased ratio of P:C 5:1. Mean lifespan was the longest at P:C 1:1 for males and at both P:C 1:1 and 1:5 for females. Mating significantly curtailed the lifespan of both males and females, indicating the survival cost of mating. Age-specific egg laying was significantly higher at P:C 1:1 than at the two imbalanced P:C ratios (1:5 or 5:1) at any given age throughout their lives, resulting in the highest lifetime reproductive success at P:C 1:1. When given a choice, beetles actively regulated their intake of protein and carbohydrate to a slightly carbohydrate-biased ratio (P:C 1:1.54-1:1.64 for males and P:C 1:1.3-1:1.36 for females). The self-selected P:C ratio was significantly higher for females than males, reflecting a higher protein requirement for egg production. Collectively, our results add to a growing body of evidence suggesting the key role played by dietary macronutrient balance in shaping lifespan and reproduction in insects.

Biodegradation and Mineralization of Polystyrene by Plastic-Eating Mealworms: Part 2. Role of Gut Microorganisms

The role of gut bacteria of mealworms (the larvae of Tenebrio molitor Linnaeus) in polystyrene (PS) degradation was investigated. Gentamicin was the most effective inhibitor of gut bacteria among six antibiotics tested. Gut bacterial activities were essentially suppressed by feeding gentamicin food (30 mg/g) for 10 days. Gentamicin-feeding mealworms lost the ability to depolymerize PS and mineralize PS into CO2, as determined by characterizing worm fecula and feeding with (13)C-labeled PS. A PS-degrading bacterial strain was isolated from the guts of the mealworms, Exiguobacterium sp. strain YT2, which could form biofilm on PS film over a 28 day incubation period and made obvious pits and cavities (0.2-0.3 mm in width) on PS film surfaces associated with decreases in hydrophobicity and the formation of C-O polar groups. A suspension culture of strain YT2 (10(8) cells/mL) was able to degrade 7.4 ± 0.4% of the PS pieces (2500 mg/L) over a 60 day incubation period. The molecular weight of the residual PS pieces was lower, and the release of water-soluble daughter products was detected. The results indicated the essential role of gut bacteria in PS biodegradation and mineralization, confirmed the presence of PS-degrading gut bacteria, and demonstrated the biodegradation of PS by mealworms.

Biodegradation and Mineralization of Polystyrene by Plastic-Eating Mealworms: Part 1. Chemical and Physical Characterization and Isotopic Tests

Polystyrene (PS) is generally considered to be durable and resistant to biodegradation. Mealworms (the larvae of Tenebrio molitor Linnaeus) from different sources chew and eat Styrofoam, a common PS product. The Styrofoam was efficiently degraded in the larval gut within a retention time of less than 24 h. Fed with Styrofoam as the sole diet, the larvae lived as well as those fed with a normal diet (bran) over a period of 1 month. The analysis of fecula egested from Styrofoam-feeding larvae, using gel permeation chromatography (GPC), solid-state (13)C cross-polarization/magic angle spinning nuclear magnetic resonance (CP/MAS NMR) spectroscopy, and thermogravimetric Fourier transform infrared (TG-FTIR) spectroscopy, substantiated that cleavage/depolymerization of long-chain PS molecules and the formation of depolymerized metabolites occurred in the larval gut. Within a 16 day test period, 47.7% of the ingested Styrofoam carbon was converted into CO2 and the residue (ca. 49.2%) was egested as fecula with a limited fraction incorporated into biomass (ca. 0.5%). Tests with α (13)C- or β (13)C-labeled PS confirmed that the (13)C-labeled PS was mineralized to (13)CO2 and incorporated into lipids. The discovery of the rapid biodegradation of PS in the larval gut reveals a new fate for plastic waste in the environment.

Effect of Larval Density on Food Utilization Efficiency of Tenebrio molitor (Coleoptera: Tenebrionidae)

Crowding conditions of larvae may have a significant impact on commercial production efficiency of some insects, such as Tenebrio molitor L. (Coleoptera: Tenebrionidae). Although larval densities are known to affect developmental time and growth in T. molitor, no reports were found on the effects of crowding on food utilization. The effect of larval density on food utilization efficiency of T. molitor larvae was studied by measuring efficiency of ingested food conversion (ECI), efficiency of digested food conversion (EDC), and mg of larval weight gain per gram of food consumed (LWGpFC) at increasing larval densities (12, 24, 36, 48, 50, 62, 74, and 96 larvae per dm(2)) over four consecutive 3-wk periods. Individual larval weight gain and food consumption were negatively impacted by larval density. Similarly, ECI, ECD, and LWGpFC were negatively impacted by larval density. Larval ageing, measured as four consecutive 3-wk periods, significantly and independently impacted ECI, ECD, and LWGpFC in a negative way. General linear model analysis showed that age had a higher impact than density on food utilization parameters of T. molitor larvae. Larval growth was determined to be responsible for the age effects, as measurements of larval mass density (in grams of larvae per dm(2)) had a significant impact on food utilization parameters across ages and density treatments (in number of larvae per dm(2)). The importance of mass versus numbers per unit of area as measurements of larval density and the implications of negative effects of density on food utilization for insect biomass production are discussed.

Growth performance and feed conversion efficiency of three edible mealworm species (Coleoptera: Tenebrionidae) on diets composed of organic by-products

Insects receive increasing attention as an alternative protein-rich food source for humans. Producing edible insects on diets composed of organic by-products could increase sustainability. In addition, insect growth rate and body composition, and hence nutritional quality, can be altered by diet. Three edible mealworm species Tenebrio molitor L., Zophobas atratus Fab. and Alphitobius diaperinus Panzer were grown on diets composed of organic by-products originating from beer brewing, bread/cookie baking, potato processing and bioethanol production. Experimental diets differed with respect to protein and starch content. Larval growth and survival was monitored. Moreover, effects of dietary composition on feed conversion efficiency and mealworm crude protein and fatty acid profile were assessed. Diet affected mealworm development and feed conversion efficiency such that diets high in yeast-derived protein appear favourable, compared to diets used by commercial breeders, with respect to shortening larval development time, reducing mortality and increasing weight gain. Diet also affected the chemical composition of mealworms. Larval protein content was stable on diets that differed 2-3-fold in protein content, whereas dietary fat did have an effect on larval fat content and fatty acid profile. However, larval fatty acid profile did not necessarily follow the same trend as dietary fatty acid composition. Diets that allowed for fast larval growth and low mortality in this study led to a comparable or less favourable n6/n3 fatty acid ratio compared to control diets used by commercial breeders. In conclusion, the mealworm species used in this study can be grown successfully on diets composed of organic by-products. Diet composition did not influence larval protein content, but did alter larval fat composition to a certain extent.

Geometric analysis of nutrient balancing in the mealworm beetle, Tenebrio molitor L. (Coleoptera: Tenebrionidae)

Geometric analysis of the nutritional regulatory responses was performed on an omnivorous mealworm beetle, Tenebrio molitor L. (Coleoptera: Tenebrionidae) to test whether this beetle had the capacity to balance the intake of protein and carbohydrate. We also identified the pattern of ingestive trade-off employed when the insect was forced to balance the costs of over- and under-ingesting macronutrients. When allowed to mix their diet from two nutritionally imbalanced but complementary foods (protein-biased food: p35:c7 or p28:c5.6; carbohydrate-biased food: p7:c35 or p5.6:c28), beetles of both sexes actively regulated their intake of protein and carbohydrate to a ratio of 1:1. When confined to one of seven nutritionally imbalanced foods (p0:c42, p7:c35, p14:c28, p21:c21, p28:c14, p35:c7 or p42:c0), beetles over-ingested the excessive nutrient from these foods to such an extent that all the points of protein-carbohydrate intake aligned linearly in the nutrient space, a pattern that is characteristic of generalist feeders and omnivores. Under the restricted feeding conditions, males ate more nutrients but were less efficient at retaining their body lipids than females. Body lipid content was higher on carbohydrate-rich foods and was positively correlated with starvation resistance. Our results are consistent with the prediction based on the nutritional heterogeneity hypothesis, which links the nutritional regulatory responses of insects to their diet breadth and feeding ecology.

Efficacy of Metarhizium anisopliae isolate MAX-2 from Shangri-la, China under desiccation stress

BACKGROUND

Metarhizium anisopliae, a soil-borne entomopathogen found worldwide, is an interesting fungus for biological control. However, its efficacy in the fields is significantly affected by environmental conditions, particularly moisture. To overcome the weakness of Metarhizium and determine its isolates with antistress capacity, the efficacies of four M. anisopliae isolates, which were collected from arid regions of Yunnan Province in China during the dry season, were determined at different moisture levels, and the efficacy of the isolate MAX-2 from Shangri-la under desiccation stress was evaluated at low moisture level.

RESULTS

M. anisopliae isolates MAX-2, MAC-6, MAL-1, and MAQ-28 showed gradient descent efficacies against sterile Tenebrio molitor larvae, and gradient descent capacities against desiccation with the decrease in moisture levels. The efficacy of MAX-2 showed no significant differences at 35% moisture level than those of the other isolates. However, significant differences were found at 8% to 30% moisture levels. The efficacies of all isolates decreased with the decrease in moisture levels. MAX-2 was relatively less affected by desiccation stress. Its efficacy was almost unaffected by the decrease at moisture levels > 25%, but slowly decreased at moisture levels < 25%. By contrast, the efficacies of other isolates rapidly decreased with the decrease in moisture levels. MAX-2 caused different infection characteristics on T. molitor larvae under desiccation stress and in wet microhabitat. Local black patches were found on the cuticles of the insects, and the cadavers dried without fungal growth under desiccation stress. However, dark black internodes and fungal growth were found after death of the insects in the wet microhabitat.

CONCLUSIONS

MAX-2 showed significantly higher efficacy and superior antistress capacity than the other isolates under desiccation stress. The infection of sterile T. molitor larvae at low moisture level constituted a valid laboratory bioassay system in evaluating M. anisopliae efficacy under desiccation stress.

Adaptation of the egg of the desert beetle, Microdera punctipennis (Coleoptera: Tenebrionidae), to arid environment

Microdera punctipennis Kaszab (Coleoptera: Tenebrionidae) is an endemic species in Guerbantonggut desert in China. To explore the ways that M. punctipennis egg adapts to dry desert environment, morphological characteristics of the egg was investigated along with the egg of the nondesert beetle Tenebrio molitor (Coleoptera: Tenebrionidae). Water loss rate and survival rate of these eggs under different dry treatments (relative humidity0, 10, and 20%) were measured to evaluate the desiccation resistance of the eggs at different developmental stages (day 0, 2, and 5 eggs). Our results showed that the 50-egg weight in T. molitor was heavier than M. punctipennis, while the 50-first-instar larva weight in T. molitor was almost the same as in M. punctipennis. The water loss rate of M. punctipennis egg under dry conditions was significantly lower than T. molitor, and the egg survival rate was significantly higher than T. molitor. The estimated developmental threshold temperature of M. punctipennis egg was 18.30°C, and the critical thermal maximum of M. punctipennis egg is above 39°C. These features partly account for the adaptability of M. punctipennis to desert environment in egg stage.

The role of multiple partners in a digestive mutualism with a protocarnivorous plant

BACKGROUND AND AIMS

The protocarnivorous plant Paepalanthus bromelioides (Eriocaulaceae) is similar to bromeliads in that this plant has a rosette-like structure that allows rainwater to accumulate in leaf axils (i.e. phytotelmata). Although the rosettes of P. bromelioides are commonly inhabited by predators (e.g. spiders), their roots are wrapped by a cylindrical termite mound that grows beneath the rosette. In this study it is predicted that these plants can derive nutrients from recycling processes carried out by termites and from predation events that take place inside the rosette. It is also predicted that bacteria living in phytotelmata can accelerate nutrient cycling derived from predators.

METHODS

The predictions were tested by surveying plants and animals, and also by performing field experiments in rocky fields from Serra do Cipó, Brazil, using natural abundance and enriched isotopes of (15)N. Laboratory bioassays were also conducted to test proteolytic activities of bacteria from P. bromelioides rosettes.

KEY RESULTS

Analyses of (15)N in natural nitrogen abundances showed that the isotopic signature of P. bromelioides is similar to that of carnivorous plants and higher than that of non-carnivorous plants in the study area. Linear mixing models showed that predatory activities on the rosettes (i.e. spider faeces and prey carcass) resulted in overall nitrogen contributions of 26·5 % (a top-down flux). Although nitrogen flux was not detected from termites to plants via decomposition of labelled cardboard, the data on (15)N in natural nitrogen abundance indicated that 67 % of nitrogen from P. bromelioides is derived from termites (a bottom-up flux). Bacteria did not affect nutrient cycling or nitrogen uptake from prey carcasses and spider faeces.

CONCLUSIONS

The results suggest that P. bromelioides derive nitrogen from associated predators and termites, despite differences in nitrogen cycling velocities, which seem to have been higher in nitrogen derived from predators (leaves) than from termites (roots). This is the first study that demonstrates partitioning effects from multiple partners in a digestion-based mutualism. Despite most of the nitrogen being absorbed through their roots (via termites), P. bromelioides has all the attributes necessary to be considered as a carnivorous plant in the context of digestive mutualism.