The nocturnal leopard gecko (Eublepharis macularius) uses UVb radiation for vitamin D3 synthesis.

Vitamin D is an important regulator of calcium and phosphorus homeostasis in animals. It can be acquired from the diet or synthesised de novo when skin is exposed to UVb. Vitamin D deficiency can lead to a complex of diseases collectively called metabolic bone disease (MBD). Diurnal lizards without access to UVb are prone to develop vitamin D deficiency, even when dietary vitamin D3 is provided. A trial was conducted to determine whether juvenile nocturnal lizards require access to UVb to prevent vitamin D deficiency. All leopard geckos (Eublepharis macularius) were supplemented with dietary vitamin D3. One group was exposed to low level UVb radiation (33-51 µW/cm2) from hatching until 6 months of age and a second group remained unexposed. Animals were fed ad libitum and their growth and weight gain compared with non-exposed controls. At the end of the trial, blood samples were analysed for vitamin D3 metabolites. The concentration of the vitamin D3 metabolite, 25(OH)D3, was higher in UVb exposed animals (61 ± 20 vs. 38 ± 8 nmol/L), confirming cutaneous synthesis with UVb exposure. Growth and weight gain were similar in both groups, and this, together with the absence of clinical symptoms, suggests that dietary vitamin D3 alone can meet the vitamin D requirements for growth of this nocturnal gecko, during the first six months of life. It remains to be investigated whether the higher vitamin D metabolite levels holds other health benefits for this species, such as improved bone density or immune response.

Evidence of vitamin D synthesis in insects exposed to UVb light.

Vertebrates obtain the prohormone vitamin D primarily by endogenous cutaneous synthesis under ultraviolet b (UVb) exposure. To date, endogenous synthesis of vitamin D in insects has never been investigated. In an initial experiment, we exposed four insect species which differ in ecology and morphology (migratory locusts, house crickets, yellow mealworms and black soldier fly larvae (BSFL)) to a low irradiance UVb source. In a second experiment we exposed these species to a higher UV irradiance, and in a third we tested the effect of exposure duration on vitamin D concentrations in yellow mealworms. Low irradiance UVb tended to increase vitamin D3 levels in house crickets, vitamin D2 levels in BSFL and vitamin D2 and D3 in yellow mealworms. Higher UVb irradiance increased vitamin D3 levels in all species but BSFL. Both BSFL and migratory locusts had increased vitamin D2 levels. Longer UVb exposure of yellow mealworms increased vitamin D2 and increased vitamin D3 until a plateau was reached at 6400 IU/kg. This study shows that insects can synthesize vitamin D de novo and that the amounts depend on UVb irradiance and exposure duration.

A comparison of UVb compact lamps in enabling cutaneous vitamin D synthesis in growing bearded dragons.

The effect of exposure to different UVb compact lamps on the vitamin D status of growing bearded dragons (Pogona vitticeps) was studied. Forty-two newly hatched bearded dragons (<24 h old) were allocated to six treatment groups (n = 7 per group). Five groups were exposed to different UVb compact lamps for two hours per day, with a control group not exposed to UVb radiation. At 120 days of age, blood samples were obtained and concentrations of 25(OH)D3 , Ca, P and uric acid were determined. In addition, plasma 25(OH)D3 concentration was determined in free-living adult bearded dragons to provide a reference level. Only one treatment resulted in elevated levels of 25(OH)D3 compared to the control group (41.0 ± 12.85 vs. 2.0 ± 0.0 nmol/L). All UVb-exposed groups had low 25(OH)D3 plasma levels compared to earlier studies on captive bearded dragons as well as in comparison with the free-living adult bearded dragons (409 ± 56 nmol/L). Spectral analysis indicated that all treatment lamps emitted UVb wavelengths effective for some cutaneous vitamin D synthesis. None of these lamps, under this regime, appeared to have provided a sufficient UVb dose to enable synthesis of plasma 25(OH)D3 levels similar to those of free-living bearded dragons in their native habitat.

Uptake of Cadmium, Lead and Arsenic by Tenebrio molitor and Hermetia illucens from Contaminated Substrates.

Insects have potential as a novel source of protein in feed and food production in Europe, provided they can be used safely. To date, limited information is available on the safety of insects, and toxic elements are one of the potential hazards of concern. Therefore, we aimed to investigate the potential accumulation of cadmium, lead and arsenic in larvae of two insect species, Tenebrio molitor (yellow mealworm) and Hermetia illucens (black soldier fly), which seem to hold potential as a source of food or feed. An experiment was designed with 14 treatments, each in triplicate, per insect species. Twelve treatments used feed that was spiked with cadmium, lead or arsenic at 0.5, 1 and 2 times the respective maximum allowable levels (ML) in complete feed, as established by the European Commission (EC). Two of the 14 treatments consisted of controls, using non-spiked feed. All insects per container (replicate) were harvested when the first larva in that container had completed its larval stage. Development time, survival rates and fresh weights were similar over all treatments, except for development time and total live weight of the half of the maximum limit treatment for cadmium of the black soldier fly. Bioaccumulation (bioaccumulation factor > 1) was seen in all treatments (including two controls) for lead and cadmium in black soldier fly larvae, and for the three arsenic treatments in the yellow mealworm larvae. In the three cadmium treatments, concentrations of cadmium in black soldier fly larvae are higher than the current EC maximum limit for feed materials. The same was seen for the 1.0 and 2.0 ML treatments of arsenic in the yellow mealworm larvae. From this study, it can be concluded that if insects are used as feed materials, the maximum limits of these elements in complete feed should be revised per insect species.

Photoreceptor spectral sensitivity of the compound eyes of black soldier fly (Hermetia illucens) informing the design of LED-based illumination to enhance indoor reproduction.

Mating in the black soldier fly (BSF) is a visually mediated behaviour that under natural conditions occurs in full sunlight. Artificial light conditions promoting mating by BSF were designed based on the spectral characteristics of the compound eye retina. Electrophysiological measurements revealed that BSF ommatidia contained UV-, blue- and green-sensitive photoreceptor cells, allowing trichromatic vision. An illumination system for indoor breeding based on UV, blue and green LEDs was designed and its efficiency was compared with illumination by fluorescent tubes which have been successfully used to sustain a BSF colony for five years. Illumination by LEDs and the fluorescent tubes yielded equal numbers of egg clutches, however, the LED illumination resulted in significantly more larvae. The possibilities to optimize the current LED illumination system to better approximate the skylight illuminant and potentially optimize the larval yield are discussed.

The diet of free-roaming Australian Central Bearded Dragons (Pogona vitticeps).

The central bearded dragon (Pogona vitticeps) is one of the most popular pet lizards. However, little is known regarding their nutrient requirement, or their natural diet. Therefore, the stomach contents of 14 free-roaming P. vitticeps were determined by flushing. These stomach contents were described taxonomically, and analyzed for crude protein content as well as fatty acid content and composition. Most of the dry matter intake was in the form of animal material (61%) stemming from nine arthropod orders. The most abundant were alates of the termite Drepanotermes sp., accounting for 95% of the total number of prey items and more than half of the total dry matter (DM) intake. Plant material contributed 16% of the total DM intake. The diets were high in crude protein (41-50% DM) and the total fatty acid content was 14-27% of the DM intake. The main fatty acid was C18:1n9c (51-56% of total fatty acids), and polyunsaturated fatty acids (n3 and n6) comprised 6-8% of the total fat intake. Our data suggest that P. vitticeps is an opportunistic predator, which exploits the seasonal availability of prey. Based on our data and other studies, a diet consisting of several insect species, supplemented with leafy vegetables, rich in n3 FA's, would best resemble the expected natural diet of P. vitticeps.

Blood vitamin D(3) metabolite concentrations of adult female bearded dragons (Pogona vitticeps) remain stable after ceasing UVb exposure.

Vitamin D deficiency can lead to several health problems collectively called metabolic bone disease (MBD). One commonly kept reptile species prone to develop MBD if managed incorrectly is the bearded dragon (Pogona vitticeps). This study aimed to determine the extent to which adult female bearded dragons fed a diet low in vitamin D can use stored vitamin D and its metabolites to maintain plasma 25(OH)D(3) and 1,25(OH)(2)D(3) concentrations after discontinuing UVb exposure. Blood samples of healthy adult female bearded dragons, exposed to UVb radiation for over 6 months were collected (day 0) after which UVb exposure was discontinued for 83 days and blood was collected. Blood plasma was analysed for concentrations of total Ca, total P, ionized Ca, uric acid, 25(OH)D(3) and 1,25(OH)(2)D(3). There was no significant change in plasma 25(OH)D(3) and 1,25(OH)(2)D(3) concentrations during the study. While total Ca and P in whole blood was found to significantly decrease over time (P < 0.0088 and 0.0016, respectively), values were within the reference range. Plasma ionized Ca tended (P = 0.0525) to decrease during the study. Adult female bearded dragons, previously exposed to UVb, are able to maintain blood vitamin D metabolite concentrations when UVb exposure is discontinued for a period of up to 83 days.

An investigation into the chemical composition of alternative invertebrate prey.

The aim of this study was to determine the chemical composition of eight invertebrate species and evaluate their suitability as alternative prey. The species selected were rusty red cockroaches (Blatta lateralis), six-spotted cockroaches (Eublaberus distanti), Madagascar hissing cockroaches (Gromphadorhina portentosa), fruit flies (Drosophila melanogaster), false katydids (Microcentrum rhombifolium), beetles of the mealworm (Tenebrio molitor), and superworm beetles (Zophobas morio), as well as woodlice (Porcellio scaber). Dry matter (DM), crude protein, crude fat, neutral detergent fiber, acid detergent fiber, ash, macro and trace minerals, vitamins A and E, and carotenoid concentrations were quantified. Significant differences were found between species. Crude protein content ranged from 38 to 76% DM, fat from14 to 54% DM, and ash from 2 to 8% DM. In most species, calcium:phosphorus was low (0.08-0.30:1); however, P. scaber was an exception (12:1) and might prove useful as a dietary source of calcium for insectivores. Vitamin E content was low for most species (6-16 mg/kg DM), except for D. melanogaster and M. rhombifolium (112 and 110 mg/kg DM). The retinol content, as a measure of vitamin A activity, was low in all specimens, but varied greatly among samples (0.670-886 mg/kg DM). The data presented can be used to alter diets to better suit the estimated requirements of insectivores in captivity. Future research on the topic of composition of invertebrate prey species should focus on determination of nutrient differences owing to species, developmental stage, and diet.

Effects of diet on the chemical composition of migratory locusts (Locusta migratoria).

An experiment was conducted to determine the effects of diet on the chemical composition of migratory locusts (Locusta migratoria L.). Fresh and dry weight and the contents of dry matter, ash, lipid, protein, Ca, K, Mg, Na, P, Cu, Fe, Zn, retinol, lutein, zeaxanthine, cryptoxanthin, carotenes, lycopene and gross energy were determined in penultimate instar and adult locusts, that had been fed three different diets. The locusts received a diet of grass or grass+wheat bran or grass+wheat bran+carrots. Adding wheat bran decreased the protein content and increased fat content (633 vs. 583 and 182 vs. 231 g/kg DM, respectively). Addition of carrots to the diet increased fat content further from 231 to 271 g/kg DM. Mineral concentrations of Ca, K, Mg, and Na, were significantly affected by diet. P, K, Cu, and Fe concentrations were significantly different in penultimate migratory locusts compared with adults. Wheat bran decreased the α-carotene content, which did not change by incorporating carrots in the diet. However, carrots did result in higher ß-carotene concentrations. Retinol concentrations were increased by incorporating both wheat bran and carrots in the diet compared with the diet containing only grass. This study shows that the chemical composition of migratory locusts can be manipulated through the diet. As such, it enables nutritionists to adapt the chemical composition of live feeder insects to better meet the nutritional demands of predators.

Effects of vitamin D3 supplementation and UVb exposure on the growth and plasma concentration of vitamin D3 metabolites in juvenile bearded dragons (Pogona vitticeps).

The effectiveness of dietary vitamin D3 and UVb exposure on plasma vitamin D metabolites in growing bearded dragons (Pogona vitticeps) was studied. A total of 84 (40 males and 44 females) newly hatched bearded dragons were allocated to six levels of oral vitamin D3 supplementation (0 to 400%) or six UVb exposure times (2 to 12 h). At 3 and 6 months of age, blood samples were obtained from each animal and analysed for 25(OH)D3 and 1,25(OH)2D3. At 3 months of age, plasma concentrations of 25(OH)D3 did not increase with increasing vitamin D3 supplementation unlike the 1,25(OH)2D3. At 6 months of age, plasma concentrations of both 25(OH)D(3) and 1,25(OH)2D3 increased with increasing vitamin D(3) supplementation. Plasma concentrations in UVb-exposed animals were 18 times higher for 25(OH)D3 (178.4+/-9.0 vs. 9.9+/-1.3 nmol/L) and 5.3 times higher for 1,25(OH)2D3 (1.205+/-0.100 vs. 0.229+/-0.025 nmol/L) than in vitamin D(3) supplemented animals at 6 months of age. This study shows that 2h of UVb exposure enables adequate physiological concentrations of plasma vitamin D metabolites to be maintained in growing bearded dragons. Oral supplementation of vitamin D(3) is ineffective in raising plasma concentrations of 25(OH)D3 and 1,25(OH)2D3 to concentrations observed in UVb-exposed animals.