Observations on the colours of lumpsuckers, Cyclopterus lumpus L.

Ripe unfertilized eggs derived from fish landed at two Icelandic ports were predominantly red and yellow-red, but a small proportion were red-purple. There was a significant difference between the frequencies of hues of eggs from the two landing places. During the phase of blastula formation, fertilized red-purple eggs showed no discernible change in either hue or chroma. However, as the gastrula formed and covered the yolk, the chroma declined dramatically, although the hue remained unaltered. When the embryo formed, the chroma continued to decrease and the hue also began to change as the red-purple pigment disappeared from the yolk and the orange-yellow oil of the yolk became more visible.
The most common plasma colouration in male fish collected at Hafnarfjordur and Husavik was red, but the observed hues covered 60% of the visible spectrum, ranging from green to purple. No significant differences between Hafnarfjordur and Husavik males in terms of hue or value were discerned, but there was a significant difference in chroma score. Female plasma hues were almost as variable as the males (spanning 45% of the visible spectrum) but centred in the green-yellow zone. Plasma, subcutaneous jelly and skin colours were closely linked.
Fish from the oceanic feeding grounds were all green in skin colour, whatever their age or sex; it is suggested that this colouration has a cryptic function in the near surface waters inhabited by lumpsuckers.     

Carotenoid plumage hue and chroma signal different aspects of individual and habitat quality in tits

We hypothesized that Blue Tits Cyanistes caeruleus and Great Tits Parus major from low quality habitat (small woods) would have less yellow ventral plumage than those from high quality habitat (large woods) because they moult faster and/or their diet contains fewer carotenoids. They moult faster because they moult later in the season and are subject to more rapidly shortening daylengths. We tested this using a database of the plumage coloration (chroma, hue and lightness) of birds breeding in woods of different sizes, by manipulating the speed of moult in captive Blue Tits, and by counting the abundance and size of caterpillars (the major source of dietary carotenoids) in the diet of nestlings. In accordance with our hypothesis, juveniles of both species (which moult about three weeks later than adults) were about 8% less saturated in colour (lower chroma) than adults, but there was no significant difference in chroma between habitats. However, both species did differ significantly in hue between large and small woods. Blue Tits forced to moult faster in captivity, at a rate similar to that caused by a month's delay in the start of moult, had yellow flank feathers that were 32% less saturated in colour than those allowed to moult more slowly. Blue Tit nestlings in large woods consumed 47% more caterpillar flesh (per gram of faecal material voided) than those in small woods, and Great Tit pulli 81% more. When habitat effects were controlled for in ANOVAs, Blue Tits mated assortatively on the basis of flank hue and Great Tits on the basis of flank lightness. Flank colour therefore has the capacity to provide information about the potential quality of both habitats, and individual birds, to potential colonists and sexual partners.     

Dietary carotenoids change the colour of Southern corroboree frogs

Animal coloration can be the result of many interconnected elements, including the production of colour‐producing molecules de novo, as well as the acquisition of pigments from the diet. When acquired through the diet, carotenoids (a common class of pigments) can influence yellow, orange, and red coloration and enhanced levels of carotenoids can result in brighter coloration and/or changes in hue or saturation. We tested the hypothesis that dietary carotenoid supplementation changes the striking black and yellow coloration of the southern corroboree frog (Pseudophryne corroboree, Amphibia: Anura). Our dietary treatment showed no measurable difference in colour or brightness for black patches in frogs. However, the reflectance of yellow patches of frogs raised on a diet rich in carotenoids was more saturated (higher chroma) and long‐wave shifted in hue (more orange) compared to that of frogs raised without carotenoids. Interestingly, frogs with carotenoid‐poor diets still developed their characteristic yellow and black coloration, suggesting that their yellow colour patches are a product of pteridines manufactured de novo.     

Do museum specimens accurately represent wild birds? A case study of carotenoid,melanin, and structural colours in long‐tailed manakins Chiroxiphia linearis

Museum specimens continue to be an invaluable resource for taxonomic, systematic, and comparative studies, and are increasingly relied upon for novel research purposes. Evaluating variation in the colour of avian study skins forms the basis for a broad range of research questions, yet few studies have investigated whether the plumage colouration of museum specimens accurately reflects colouration in wild birds. In this study, we use reflectance spectrometry to compare the plumage reflectance of avian museum skins and wild birds. We use long-tailed manakins Chiroxiphia linearis , to investigate these potential differences in colour. Long-tailed manakins are ideal for this type of study as their colourful plumage patches result from three primary plumage colouration mechanisms found in birds: melanin pigmentation, carotenoid pigmentation, and structural colouration. These features of their plumage allowed us to independently assess variation in each plumage colouration mechanism. Reflectance spectra obtained from museum specimens were very similar to those obtained from wild birds, and the colouration of specimens was usually well within the range of variation observed in wild birds. As such, museum specimens can accurately represent the colouration of wild birds. Nevertheless, we found significant differences in colouration between museum skins and wild birds. We documented differences in brightness, hue, saturation, and chroma, although the direction and magnitude of these differences varied by mechanism of colouration. Multivariate analyses revealed that the age of museum specimens and the time of year at which they were collected contributed to some of these differences. We discuss potential proximate causes of these changes in colour, many of which apply to both museum specimens and wild birds, and identify the types of studies that are likely to be most sensitive to these changes.     

The anatomical basis of sexual dichromatism in non-iridescent ultraviolet-blue structural coloration of feathers

Despite extensive research on the evolution of avian dichromatism, the anatomical bases for differences between the sexes in species with structurally coloured plumage remain largely unknown. Using full‐spectrum spectrometry and transmission electron microscopy, we compared the colour and morphology of rump feathers of male and female eastern bluebirds (Sialia sialis). The ultraviolet (UV)‐blue feather colour in this species is caused by coherent scattering of light within the medullary ‘spongy layer’ of feather barbs. This spongy layer lies beneath a keratin cortex and on top of a layer of melanin granules that surround a hollow central vacuole. Irregularly shaped electron‐dense regions are present within the cortex. Male and female S. sialis differed substantially in their plumage colour and feather structure. A backwards logistic regression predicted sex with 100% accuracy using the colour variables brightness, UV‐violet (UV‐V) chroma and spectral saturation. A second backwards logistical regression predicted sex with 100% accuracy using relative cortex area and size of air spaces. Thus, S. sialis are dimorphic both in colour and in the structures causing this colour. Multiple regression analyses using data pooled from both sexes indicated that multiple features of feather barb structure contributed to colour variation in complex ways. Brightness was negatively related to the relative surface area of cortex in barb cross‐sections. Hue was positively related and UV‐V chroma was negatively related to the distance between scattering elements (i.e. keratin rods and air spaces) in the spongy layer. In contrast, hue was negatively related and UV‐V chroma was positively related to the thickness of the spongy layer. UV‐V chroma was also negatively related to the relative area of electron‐dense regions in the cortex. Spectral saturation was negatively related to the distance between scatterers and the standard error of the size of air spaces. These results suggest that the dimensions of spongy‐layer elements are critical to colour production, but that UV‐blue coloration can also be modified by the cortex and the thickness of the spongy layer. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 84 , 259–271.     

Is the signal from the mesophyll to the guard cells a vapour‐phase ion?

Previous studies have suggested that the red light and CO₂ responses of stomata are caused by a signal from the mesophyll to the guard cells. Experiments were conducted to test the idea that this signal is a vapour‐phase ion. Stomata in isolated epidermes of Tradescantia pallida were found to respond to air ions created by an electrode that was positioned under the epidermes. Anthocyanins in the epidermes of this species were observed to change colour in response to these air ions, and this change in colour was attributed to changes in pH. A similar change in lower epidermal colour was observed in intact leaves upon illumination and with changes in CO₂ concentration. Based on the change in epidermal colour, the pH of the epidermis was estimated to be approximately 7.0 in darkness and 6.5 in the light. Stomata in isolated epidermes responded to pH when suspended over (but not in contact with) solutions of different pH. We speculate that stomatal responses to CO₂ and light are caused by vapour‐phase ions, possibly hydronium ions that change the pH of the epidermis.     

Rockpool Gobies Change Colour for Camouflage

Camouflage is found in a wide range of species living in numerous habitat types, offering protection from visually guided predators. This includes many species from the intertidal zone, which must cope with background types diverse in appearance and with multiple predator groups foraging at high and low tide. Many animals are capable of either relatively slow (hours, days, weeks) or rapid (seconds and minutes) colour change in order to better resemble the background against which they are found, but most work has been restricted to a few species or taxa. It is often suggested that many small intertidal fish are capable of colour change for camouflage, yet little experimental work has addressed this. Here, we test rock gobies (Gobius paganellus) for colour change abilities, and whether they can tune their appearance to match the background. In two experiments, we place gobies on backgrounds of different brightness (black or white), and of different colours (red and blue) and use digital image analysis and modelling of predator (avian) vision to quantify colour and luminance (perceived lightness) changes and camouflage. We find that gobies are capable of rapid colour change (occurring within one minute), and that they can change their luminance on lighter or darker backgrounds. When presented on backgrounds of different colours, gobies also change their colour (hue and saturation) while keeping luminance the same. These changes lead to predicted improvements in camouflage match to the background. Our study shows that small rockpool fish are capable of rapid visual change for concealment, and that this may be an important mechanism in many species to avoid predation, especially in complex heterogeneous environments.     

Comparing plumage colour measurements obtained directly from live birds and from collected feathers: the case of the great tit Parus major

Birds frequently display a colourful plumage which is important both in inter and intraespecific communication, and either in sexual and social contexts. In last years some methodologies have been developed to, analyse plumage coloration, but the use of the spectrometers has been particularly important for UV range. Measurement of plumage coloration with the spectrometer may be taken directly on the bird or, alternatively by collecting some feathers and measuring them later in the laboratory. However, few is known about the reliability of measures obtained from feathers and whether these are really representative of plumage coloration. We tested this assumption analysing measurements of carotenoids-based coloration components (lightness, chroma and hue) and lutein peak of the yellow breast of the great tit Parus major. We used two spectrometers (Ocean optics and Minolta) which calculate differently the colour components. Our results showed that direct measurement of bird was highly repeatable to determine lightness, chroma and hue for both spectrometers. Similar results we found for collected feathers procedure for both devices. Collected feathers provided high representative measurements of colour values with Minolta spectrometer. Lightness was highly repeatable when we used Ocean optic spectrometer, but chroma and hue were moderate. Lutein peak was also highly repeatable in all cases. The number of feathers used to measure plumage coloration in collected feathers procedure strongly influenced values of colour plumage variables. In general, values of lightness, chroma and hue stabilised when more than 10–15 feathers were used although we found slight differences between spectrometers. However, only four feathers were needed for lutein peak. Thus, our results stress the need to use a minimum number of feathers in measuring plumage coloration from collected feathers.     

The environmental control of colouration in a bushcricket, Mygalopsis marki Bailey (Orthoptera: Tettigoniidae)

The environmental factors proximately influencing variable colouration in the bushcricket, Mygalopsis marki , were studied in natural populations and under controlled laboratory conditions. Two major components of variable colouration were identified; a green/brown dimorphism in ground colour hue (dominant wave length) and continuous variation in the darkness of brown insects, representing a contrast between ground colour value (brightness) and the intensity of overlying black pattern. Ground colour hue differed between natural populations in different seasons and at different localities. The proportion of brown individuals was greater in populations developing over late summer than over spring at the same locality, and in populations from drier localities, as indicated by vegetation type, in the same season. Experimental studies showed that colour change occurred at moults, with green colouration promoted by increased water intake in developing nymphs. Ground colour value and pattern differed between natural populations at different localities, but not in different seasons. Ground colour value was less, and pattern was greater, in populations from localities with a dense cover of forbs and grasses. Experimental studies showed that ground colour value and pattern were influenced by the intensity of incident radiation received by developing nymphs, with decreased intensity promoting lower value and greater pattern.     

Bill colour and correlates of male quality in blackbirds: an analysis using canonical ordination

Carotenoid-dependent plumage displays are widely assumed to be honest indicators of individual health or quality, which are used as cues during mate choice and/or agonistic signalling. Despite the fact that red, yellow and orange pigmentation of bills is common, and also variable between individuals, comparatively little is known about bill colouration as a condition-dependent trait. Furthermore, many studies of avian colouration are confounded by the lack of objective colour quantification and the use of overly simplistic univariate techniques for analysis of the relationship between the condition-dependent trait and individual quality variables. In this study, we correlated male blackbird bill colour (a likely carotenoid-dependent sexually selected trait) with body/condition variables that reflect male quality. We measured bill colour using photometric techniques, thus ensuring objectivity. The data were analysed using the multivariate statistical techniques of canonical ordination. Analyses based on reflectance spectra of male blackbird bill samples and colour components (i.e. hue, chroma and brightness) derived from the reflectance spectra were very similar. Analysing the entire reflectance spectra of blackbird bill samples with Redundancy Analysis (RDA) allowed examination of individual wavelengths and their specific associations with the body/condition variables. However, hue, chroma and brightness values also provided useful information to explain colour variation, and the two approaches may be complimentary. We did not find any significant associations between male blackbird bill colour and percent incidence of ectoparasites or cloaca size. However, both the colour component and full spectral analyses showed that culmen length explained a significant amount of variation in male blackbird bill colour. Culmen length was positively associated with greater reflectance from the bill samples at longer wavelengths and a higher hue value (i.e. more orange-pigmented bills). Larger males may have larger territories or be better at defending territories during male-male interactions, ensuring access to carotenoid food sources. Future studies should elucidate the relationship between bill colour and behavioural measures such as aggressiveness, territory size, song rate and nest attendance.     

Cone contrast computations: physical versus perceived background and colour constancy

The light reflected from an object depends both on the object's surface and on the illuminant. Visual systems attempt to resolve this intrinsic ambiguity by comparing the light reflected from the object with respect to the background by computing the difference between the object-background light sampled by three cones. The cone-contrasts for the sample-background stimulus under the test illumination should correspond to the cone-contrasts for samples matched in appearance under the standard background (C). The validity of this cone-contrast rule (Whittle, 2003) and its possible link with stability of perceived colour was studied here using six test illuminants. A successive asymmetric colour-matching task with 40 simulated Munsell samples (value 7, chroma 4) on a neutral background (N7) was used. The subject adjusted the sample under standard illuminant C to match the colour appearance of the test sample under one of the test illuminants. Brunswik Ratio (BR) was used as an index of stability of colour appearance. When computed with respect to the reference illuminant C, the cone contrast rule was violated (particularly for S-cone-contrast). However, if a new reference point based on the perceived colour of the neutral background under the test illumination was used, the cone contrast rule applied. That is, when cone contrasts of the matching samples are computed with respect to this perceived background, they correspond to cone contrasts of the test stimuli. This represents a form of discounting the illuminant for the purpose of determining an object's cone-contrast against the background, which does not vary with background illumination. These cone contrasts, however, do not provide any information about the colour appearance of objects under particular viewing conditions, unless calibrated against a standard by allowing subjects to learn particular colours.     

Cryptic sexual dichromatism occurs across multiple types of plumage in the Green-backed Tit Parus monticolus

Several recent studies have found instances of cryptic sexual dichromatism within avian taxa. Although this dichromatism has been found in plumage produced through a variety of proximate mechanisms, little is known about how dichromatism varies across these types of plumage within a single species. We used a reflectance spectrometer to measure colour within the Green-backed Tit Parus monticolus , a species which displays multiple types of pigment and structural colours. We found significant differences in spectral measurements corresponding to hue, chroma, and brightness between male and female carotenoid, melanin, structural white, grey and structural blue plumage. The only plumage that did not appear to show sexual dichromatism was the olive plumage of the back. These findings suggest that the mechanism(s) producing cryptic dichromatism in the Green-backed Tit are non-specific and act across multiple types of plumage, rather than within a single type, such as carotenoid-based or structurally produced.     

Condition‐dependence,pleiotropy and the handicap principle of sexual selection in melanin‐based colouration

The signalling function of melanin‐based colouration is debated. Sexual selection theory states that ornaments should be costly to produce, maintain, wear or display to signal quality honestly to potential mates or competitors. An increasing number of studies supports the hypothesis that the degree of melanism covaries with aspects of body condition (e.g. body mass or immunity), which has contributed to change the initial perception that melanin‐based colour ornaments entail no costs. Indeed, the expression of many (but not all) melanin‐based colour traits is weakly sensitive to the environment but strongly heritable suggesting that these colour traits are relatively cheap to produce and maintain, thus raising the question of how such colour traits could signal quality honestly. Here I review the production, maintenance and wearing/displaying costs that can generate a correlation between melanin‐based colouration and body condition, and consider other evolutionary mechanisms that can also lead to covariation between colour and body condition. Because genes controlling melanic traits can affect numerous phenotypic traits, pleiotropy could also explain a linkage between body condition and colouration. Pleiotropy may result in differently coloured individuals signalling different aspects of quality that are maintained by frequency‐dependent selection or local adaptation. Colouration may therefore not signal absolute quality to potential mates or competitors (e.g. dark males may not achieve a higher fitness than pale males); otherwise genetic variation would be rapidly depleted by directional selection. As a consequence, selection on heritable melanin‐based colouration may not always be directional, but mate choice may be conditional to environmental conditions (i.e. context‐dependent sexual selection). Despite the interest of evolutionary biologists in the adaptive value of melanin‐based colouration, its actual role in sexual selection is still poorly understood.     

The impact of epidermal melanin on objective measurements of human skin colour

Objective measurements of human skin colour were made with a tristimulus (L*a*b*) chromameter in a range of different ethnic skin types. These were compared with biochemical measurements of melanin content, melanin composition and melanosome size in skin biopsies obtained from the same sites. L*, a* and b* values were found to vary significantly with ethnicity. In general, constitutively dark skin types have lower L* values, higher a* values and higher b* values than constitutively light skin types. Total epidermal melanin content appears to be the primary determinant of L* values in human skin (r = -0.88; P < 0.00001), whilst melanosome size also has a significant but more subtle influence on L* values (r = -0.73; P < 0.00001). There is also a strong positive contribution to a* values from epidermal melanin (r = 0.66, P < 0.00001), which accounts for the ethnic variation in a* values observed in this study. Melanin is also a major contributor to b* values in lighter skin types (r = 0.71, P < 0.00001). However, this relationship breaks down in darker skin types where b* values actually reach a maximum and then decrease as the concentration of melanin in the skin increases. This appears to be because of optical masking of yellow light by high concentrations of melanin in the epidermis. Analysis of the relationships between L*, a* and b* values in human skin indicate that they are very closely interrelated, and suggest that the optical properties of melanin in the epidermis are very similar to those of a dye on a fabric substrate.     

Interaction and developmental activation of two neuroendocrine systems that regulate light‐mediated skin pigmentation

Lower vertebrates use rapid light‐regulated changes in skin colour for camouflage (background adaptation) or during circadian variation in irradiance levels. Two neuroendocrine systems, the eye/alpha‐melanocyte‐stimulating hormone (α‐MSH) and the pineal complex/melatonin circuits, regulate the process through their respective dispersion and aggregation of pigment granules (melanosomes) in skin melanophores. During development, Xenopus laevis tadpoles raised on a black background or in the dark perceive less light sensed by the eye and darken in response to increased α‐MSH secretion. As embryogenesis proceeds, the pineal complex/melatonin circuit becomes the dominant regulator in the dark and induces lightening of the skin of larvae. The eye/α‐MSH circuit continues to mediate darkening of embryos on a black background, but we propose the circuit is shut down in complete darkness in part by melatonin acting on receptors expressed by pituitary cells to inhibit the expression of pomc, the precursor of α‐MSH.     

Genetic basis and fitness correlates of dynamic carotenoid‐based ornamental coloration in male and female common kestrels Falco tinnunculus

Knowledge of the genetic basis of sexual ornaments is essential to understand their evolution through sexual selection. Although carotenoid‐based ornaments have been instrumental in the study of sexual selection, given the inability of animals to synthesize carotenoids de novo, they are generally assumed to be influenced solely by environmental variation. However, very few studies have directly estimated the role of genes and the environment in shaping variation in carotenoid‐based traits. Using long‐term individual‐based data, we here explore the evolutionary potential of a dynamic, carotenoid‐based ornament (namely skin coloration), in male and female common kestrels. We first estimate the amount of genetic variation underlying variation in hue, chroma and brightness. After correcting for sex differences, the chroma of the orange‐yellow eye ring coloration was significantly heritable (h² ± SE = 0.40 ± 0.17), whereas neither hue (h² = 0) nor brightness (h² = 0.02) was heritable. Second, we estimate the strength and shape of selection acting upon chromatic (hue and chroma) and achromatic (brightness) variation and show positive and negative directional selection on female but not male chroma and hue, respectively, whereas brightness was unrelated to fitness in both sexes. This suggests that different components of carotenoid‐based signals traits may show different evolutionary dynamics. Overall, we show that carotenoid‐based coloration is a complex and multifaceted trait. If we are to gain a better understanding of the processes responsible for the generation and maintenance of variation in carotenoid‐based coloration, these complexities need to be taken into account.     

The cryptic responses of hatchery-reared sole to a natural sand substratum

In laboratory experiments, both reared and wild sole Solea solea selected a sand substratum in preference to a hard substratum. Reared sole with no previous experience of sand buried quickly when placed on sand. Light motivated burial, and the motivation of reared sole to bury was as strong as that of wild sole. The burial efficiency (the proportion of the ocular side covered by sand after a single burial attempt) of reared sole was lower than that of wild sole, but increased to that of wild sole after a period of 12 days maintenance on sand. Motivation to bury is therefore innate, but efficiency is affected by experience. The reactive distance of reared sole to a standardized predation threat was the same as that of wild sole and was shorter when buried (6 cm) than when not buried (15 cm). Burial therefore affected the response to a predation threat, indicating that burial is a cryptic behaviour. Munsell colour charts were used to determine the time required for reared sole to match the skin colour 'tone' of wild sole after placement on sand. Adaptation of colour value (lightness) took 4–7 days, but adaptation of chroma (intensity of colour) and hue took 33 and 69 days respectively. It is therefore recommended that flatfishes reared for stock enhancement exercises are conditioned to sand prior to release due to the relatively long time required for crypsis to improve through colour adaptation and burying.     

Evidence suggests that modified setae of the crab spiders Stephanopis spp. fasten debris from the background

Crab spiders (Thomisidae) are known by their ability to change their body colouration via change in epithelial pigments. However, the crab spider genus Stephanopis appears to match the colouration of the bark they are sitting on by having debris attached to its dorsal cuticle. The functional morphology, colouration, and evolution of this phenomenon were investigated in Stephanopis cf. scabra and S. cambridgei. Analysis under the microscope revealed that debris originated from the bark they were sitting on. Using scanning electron microscopy, three different types of setae likely related in the retention of debris were found in S. cf. scabra and one in S. cambridgei. These setae are branched and possess barbs, unlike the more filiform setae found in other crab spider species. In addition, the presence of debris improved the brightness background matching of spiders against the bark, but not hue and chroma matching. Ancestral character state reconstruction suggested that presence of debris evolved two to three times within Thomisidae. The evolution of both masking and colour change among crab spiders indicates that they are under a strong selection to avoid detection.     

Generalised Chromaticity Diagrams for Animals with <Emphasis Type="Italic">n</Emphasis>-chromatic Colour Vision

Chromaticity diagrams for tri- and tetrachromatic animals (with three and four cone classes in their retina, respectively, contributing to colour perception) are widely used in studies of animal colour vision. These diagrams not only allow the graphical representation of perceived colours, but the coordinates of colours plotted within these diagrams can be used to extract colour metrics, such as hue and chroma, or can be used directly in statistical analyses, and therefore aid our understanding of vision-mediated behaviour. However, many invertebrate species have more than four cone classes in their retina, and may therefore have pentachromatic or hexachromatic (or greater) vision. This paper describes an extension to the triangular and tetrahedral chromaticity diagrams commonly used for tri- and tetrachromats, respectively, that allows colour coordinates (and hence colour metrics) to be calculated for animals with more than four cone classes. Because the resulting chromaticity diagrams have more than three dimensions, meaningful ways to visualise the spatial position of plotted colours are discussed.     

Light stimulates conidiation of the entomopathogenic fungus Beauveria bassiana

Beauveria bassiana is a commercially important entomopathogenic fungus. Like other insect fungal pathogens, B. bassiana usually produces asexual reproductive bodies, conidia, for dispersal, transmission and infection of insects. Adequate mass-production of high quality conidia is crucial to development of an efficient B. bassiana insecticide. However, little is known about details of conidiation in this fungus in response to environmental signals, which limits understanding of the mechanism of conidiation and improvement in conidia production. Here, morphologenetic changes of B. bassiana under different light conditions are reported. When cultured in total darkness, B. bassiana hyphae can grow continuously with few reproductive structures differentiated, while illumination with white light resulted in prolific formation of conidiophores bearing abundant conidia, indicating that light could stimulate conidiation of B. bassiana. Among the single colour lights tested, blue light was the most effective to stimulating sporulation. Colonies became adapted for blue light stimulus only after hyphae had grown in total darkness for at least 96 h, whereas the photoadaptation obviously declined after 144 h. For the exposure time, 3 min of blue light pulse was enough to stimulate conidiation in the photoadapted mycelia, while prolonged light exposure over 3 min resulted in a decrease in conidia yield. Our results provided useful clues for understanding the mechanism of conidiation mediated by light in B. bassiana.