The influence of the development rates of immature stages of Eristalis arbustorum (Diptera; Syrphidae) on adult abdominal colour pattern

Abstract. The abdominal colour pattern of Eristalis arbustorum (L.) shows seasonal variation, with animals emerging in spring being darker than those emerging during summer. One of the most important environmental cues influencing the abdominal colour pattern is developmental temperature. An experiment was carried out to establish which period during the immature stages was important in determining final adult colour pattern. The results indicate a good relationship between the length of the pupal period and both the extent of the paler markings on the abdomen and the grey score of these markings. The length of the larval period did not have any effect on adult colour pattern.     

Geographic variation in plasticity in Eristalis arbustorum

To study the evolution of phenotypic plasticity in the field, six populations of the hoverfly Eristalis arbustorum were sampled along two parallel North-South transects over a maximum daily temperature gradient. Three populations were sampled per transect. Egg batches were collected and the offspring were reared in a split family set up over three different pupal temperature regimes in the laboratory to produce population reaction norms of colour pattern, pupal development time, wing length and thorax length. Wing length and colour pattern were corrected for body size. All four characters showed plasticity in response to rearing temperature and significant differences in height, slope and shape of the reaction norms were found. Only male colour pattern showed variation in reaction norms along the North-South gradient. Most other characters showed variation in reaction norms from West to East. The two populations lying in the middle of the transects were frequendy different from the others. Within the populations, significant genotype-environment interactions were frequently found for wing length and colour pattern, indicating that genetic variation for plasticity was present. The results suggest that the populations may have evolved plastic responses to suit local environmental conditions.     

Colour Pattern Plasticity in the Hoverfly,Episyrphus balteatus: The Critical Immature Stage and Reaction Norm on Developmental Temperature

Episyrphus balteatus is phenotypically plastic with respect to abdominal colour pattern. It was hypothesized that developmental temperature was the environmental cue governing this plasticity. The length of different immature stages was manipulated by altering the rearing temperatures. It was shown that all stages of the pupal developmental period were equally important in influencing adult phenotype. Lengthened pupal period, achieved by reducing rearing temperature, resulted in darker individuals. Adjusting the length of the larval period had no affect on adult colour pattern. Colour pattern was quantified using image analysis. Reaction norms of black pigment on each tergite against pupal developmental temperature were constructed. All reaction norms were approximately linear. Females were darker than males at comparable temperatures. In both sexes tergite 2 was the most plastic, whereas tergite 3 was the least plastic. The results are discussed in connection with the colour plasticity having a possible thermoregulatory function.     

Colour patterns of Syrphidae. III. Sexual dimorphism in Eristalis arbustorum

Abstract. 1. The hoverfly Eristalis arbustorum L. (Diptera, Syrphidae) is a sexually dimorphic Batesian mimic of bees and wasps.
2. This dual mimicry entails good mimicry of several small, dark bees (mainly mining bees) by female E.arbustorum , and less specific mimicry of wasps and other yellow and black Hymenoptera by males.
3. There is also variability of colour pattern within both sexes of E.arbustorum .
4. Seasonal fluctuations in the pattern frequencies of males occur because the temperature during pupal development influences the coloration of the adult.
5. Temporal changes in the pattern frequencies of females are attributable to developmental darkening of the abdomen.
6. These effects can be explained by the fact that the phenotypic requirements for thermoregulation and protection against predation will be different for males and females, and will also vary with time.
7. Behavioural differences between males and females are a component of the sexual dimorphism in this species.     

长尾管蚜蝇Eristalis tenax体色变异的研究

通过对长尾管蚜蝇体色变异的研究,发现该种蚜蝇在体色变异方面有如下特点：（1）腹部色斑的变异形式多样,种群中以浅色者为主,深色的个体比例较少;腹部色斑变异表现出明显的性别差异,雄性变异形式比雌性丰富;（2）后足腿节颜色变异呈现出一定的连续性,从主要呈黑色（肉眼观察）到黄褐色;且这种变化与性别无关;（3）翅上暗色云斑的变化仅有2种形式,种群中具暗色云斑者占大多数;云斑的有无与性别无关;（4）体色变异与发生季节、海拔无关.     

Intraspecific variation in wing and pupal melanization in copper butterflies (Lepidoptera: Lycaenidae)

Melanin is a widespread pigment causing variation in skin darkness, with darker phenotypes typically reaching higher equilibrium temperatures than lighter ones. Therefore, selection is expected to favour darker phenotypes in colder environments. In the present study, we show intraspecific variation in pupal (and wing) melanization along an altitudinal gradient in two species of copper butterflies. Both, pupal and wing melanization increased with increasing altitude. Consistent with the thermal melanism hypothesis, darker (high-altitude) pupae reached higher equilibrium temperatures than paler (low-altitude) ones. However, as temperature differences were rather small despite pronounced differences in melanization, we cannot rule out that factors (e.g. ultraviolet protection, disease resistance) other than temperature comprise the principal selective agents. Mechanistically, variation in melanization might be related to variation in hormone titres, as demonstrated by low-altitude pupae showing higher ecdysteroid and juvenile hormone titres compared to high-altitude ones. Furthermore, we report sex differences in wing melanization, with males being darker than females, which is potentially related to a higher flight activity of males.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 301–312.     

芍药的访花昆虫和传粉昆虫

20 0 0～ 2 0 0 2年对内蒙古赤峰市高格斯台罕乌拉自然保护区内野生芍药 (PaeonialactifloraPall.)和内蒙古农校芍药园内栽培品种芍药的访花昆虫进行调查 ,经整理鉴定有 2 9种 ,自然保护区内芍药的访花昆虫种类有 1 7种 ,芍药园内的访花昆虫有 1 7种。根据传粉行为和数量的比较确定了自然保护区内主要传粉昆虫为丽斑芫菁、黄胫宽花天牛、黑胫宽花天牛、短毛斑金龟、饥星花金龟、白星花金龟和大淡脉隧蜂 ;芍药园内的主要传粉昆虫为意大利蜜蜂、棕边管食蚜蝇、长尾管食蚜蝇、大淡脉隧蜂、灰带管食蚜蝇和小淡脉隧蜂。     

Nymphal colour/pattern polymorphism in the leafhoppers Eupteryx urticae (F.) and E. cyclops Matsumura (Hemiptera: Auchenorrhyncha): spatial and temporal variation in morph frequencies

Variation in colour/pattern morph frequencies in Eupteryx urticae and E. cyclops is described for various field populations. Eupteryx urticae populations in S Wales exhibit a steep morph-ratio cline, such that black morph frequencies are positively correlated with altitude. High melanic frequencies at high-altitude sites, and the absence of the two darker morphs in lowland populations, suggest a similar trend in E. cyclops , but the data are insufficient to confirm this statistically. No differences in morph frequencies were detected on different parts of the primary host plant or on alternative host species. Similarly, there were no consistent trends within or between the two annual generations of either species, although melanic morph frequencies in one E. urticae population were heterogeneous over 10 generations. It is suggested that the polymorphism in E. urticae is strongly influenced by climate selection, darker morphs being at an advantage in cooler environments where their coloration enhances absorption of solar radiation. The advantage gained through thermal melanism is probably balanced by visual selection against black morphs by entomophagous parasitoids.     

Pupal colour dimorphism in swallowtail butterflies: timing of the sensitive period and environmental control

ABSTRACT. Two North American swallowtail butterflies with pupal colour dimorphism, Eurytides marcellus (Cramer) and Papilio troilus L., use chiefly the colour of the pupation substrate to determine pupal colour, and are affected hardly ( P.troilus ) or not at all ( E.marcellus ) by substrate texture. The use of colour cues in these species is in contrast to the greater importance of texture in two other sympatric swallowtails (Hazel & West, 1979). E.marcellus larvae evacuate the gut and start prepupal wandering around mid-day. If they have not reached the sensitive period for pupal colour determination by nightfall they will delay the sensitive period until the next day. Among other North American swallowtails with pupal colour dimorphism there is no tendency for those species that use textural cues for pupal colour determination to evacuate the gut later in the day than those using pupation site colour.     

Behavioural mimicry of honeybees (Apis mellifera) by droneflies (Diptera: Syrphidae: Eristalis spp.)

Droneflies (Syrphidae: Eristalis spp. resemble honeybees (Apis mellifera) in appearance and have often been considered to be Batesian mimics. This study used a focal watch technique in order to compare the foraging behaviour of droneflies Eristalis tenax, Eristalis pertinax, Eristalis arbustorum and Eristalis nemorum) whilst they were feeding on patches of flowers with the behaviour of honeybees and other hymenopterans and dipterans. It was found that, on a range of plant species, the time droneflies spent on individual flowers and the time spent flying between them was more similar to that of honeybees than to the times of other hymenopterans and dipterans. These results suggest that dronefly behaviour has evolved to become more similar to that of honeybees and they support the hypothesis that droneflies are Batesian mimics.     

Thermoregulatory differences between phenotypes in the speckled wood butterfly: hot perchers and cold patrollers?

Males of the speckled wood butterfly Pararge aegeria L. (Satyrinae), actively search for females (“patrolling”) or wait for them at particular places (“perching”). Darker males are more likely to patrol than pale ones, which are mainly territorial perchers. We studied whether this morphological variation relates to thermoregulatory differences. The relationship between thoracic temperature and ambient temperature differed between the colour types under natural conditions: darker males had on average lower body temperatures than paler males. Different activities (e.g. resting, flying) and behavioural strategies (perching or patrolling) were associated with differences in thoracic temperature: patrolling males which mainly engaged in long flights and periods of basking afterwards, had lower thoracic temperatures than perching males which engaged in very short flights, fights and basking. When resting for a while thoracic temperatures did not differ between males practising different strategies. Under laboratory conditions, darker males heated up faster than pale males but there was no difference in the thoracic temperature at which they started to fly. These results indicate that thermal requirements (or general conditions) differ between the behavioural strategies, and that behavioural differences between phenotypes (colour types) relate to differences in thermal ecology. This supports the idea that darker males are better adapted to patrolling. There is no evidence that one mate-locating strategy is always superior to the other, which coincides with the observation that both strategies co-exist. More generally, this study shows that relatively small differences in colour can have a considerable effect on thermoregulation and hence on the behavioural strategies a heliothermic insect will adopt. Received: 15 August 1997 / Accepted: 15 December 1997     

Landscape genetics and spatial pattern of phenotypic variation of Eristalis tenax across Europe

A study of population connectivity of the migratory insect species, such as dronefly Eristalis tenax (Diptera, Syrphidae), has an essential importance in understanding the relative influence of the evolutionary forces and environmental features that interact in the spatial distribution of molecular and morphological diversity. However, specific study aiming to understand spatial genetic structure of dronefly populations and its migratory potential is lacking. Hence, we studied a spatial pattern of genetic and phenotypic variation of seven European populations of E. tenax incorporating landscape genetic methods using allozyme data, wing size and shape and abdominal colour pattern. Based on the observed lack of genotypic structuring, we suggested that there has been sufficient long‐distance gene flow to effectively homogenize population structuring at a broader geographical scale. Wing shape similarity among populations and an overlap of abdominal colour variation showed no clear clustering related to geography, which is in congruence with genetic data. However, genetic (F_ST values) and phenotypic (wing size) data and landscape genetics indicated subdivision between the Balkan populations (four Serbian samples) and populations from Central (Germany and Switzerland) and Northern (Finland) Europe. These findings indicated a potential connection between the Central and Northern Europe supporting the Central European origin of the flies caught in Finland. Thus, by performing spatial analysis and combining genetic–morphological approach, we shed light on the movement pattern in complex landscapes and thus provided the necessary guidelines to a broad‐scale analysis of this widespread generalist pollinator.     

Various stages in the life cycle of syrphid flies (Eristalis tenax; diptera: Syrphidae) as potential mechanical vectors of pathogens causing mycobacterial infections in pig herds

We defined the role of the syrphid fly Eristalis tenax in the survival and transmission of mycobacteria in pigs. The conditionally pathogenic mycobacterial (CPM) species Mycobacterium chelonae was isolated from 10 % of liquid dung samples, and both M. chelonae and another CPM species M. fortuitum were isolated from 7 (78 %) of the examined E. tenax larvae collected from the same location. Mycobacteriosis of the lymph nodes of pigs from 3 infected farms was caused by M. avium subsp. avium, M. avium subsp. hominissuis, and M. fortuitum. M. avium subsp. avium and M. avium subsp. hominissuis of identical genotype and serotypes and M. fortuitum were isolated from 7 (1.9 %) larvae, 2 (7.4 %) puparia, and one (1.6 %) imago. The count of colony forming units isolated from larval skin covering (pouch) was higher (p < or = 0.01) than that isolated from the internal organs of larvae. These results showed the potential for E. tenax larvae to spread mycobacteria throughout pig herds and the surrounding environment.     

Phenotypic plasticity in hoverflies: the relationship between colour pattern and season in Episyrphus balteatus and other Syrphidae

1. The abdominal colour patterns of some multivoltine species of hoverfly are phenotypically plastic and change through the flying season.
2. It was predicted how the abdominal colour pattern of one species, Episyrphus balteatus , should change in the field with season based on a hypothesis that the pattern influences the thermoregulatory capabilities of the animal. The colour patterns were quantified using image analysis. The observed changes in the colour pattern through the year supported the thermoregulation hypothesis.
3. A further three Metasyrphus species were analysed similarly to allow a comparative study of the forms of the plasticities of the above four species and four Eristalis species from a previous study.
4. Whilst it was clear that the abdominal colour patterns of many of the species were plastic, it was also apparent that not all species used the same developmental pathway to control the seasonal colour pattern changes. This suggests convergent evolution towards a general type of plasticity and that abdominal colour pattern plasticity in hoverflies is functional.     

Latitudinal variation in thermal reaction norms of post‐winter pupal development in two butterflies differing in phenological specialization

Latitudinal clines in thermal reaction norms of development are a common phenomenon in temperate insects. Populations from higher latitudes often develop faster throughout the range of relevant temperatures (i.e countergradient variation) because they must be able to complete their life cycle within a shorter seasonal time window compared to populations at lower latitudes. In the present study, we experimentally demonstrate that two species of butterflies Anthocharis cardamines (L.) and Pieris napi (L.) instead show a cogradient variation in thermal reaction norms of post‐winter pupal development so that lower latitude populations develop faster than higher latitude populations. The two species share host plants but differ in the degree of phenological specialization, as well as in the patterns of voltinism. We suggest that the pattern in A. cardamines, a univoltine phenological specialist feeding exclusively on flowers and seedpods, is the result of selection for matching to the phenological pattern of its local host plants. The other species, P. napi, is a phenological generalist feeding on the leaves of the hosts and it shows a latitudinal cline in voltinism. Because the latitudinal pattern in P. napi was an effect of slow development in a fraction of the pupae from the most northern population, we hypothesize that this population may include both bivoltine and univoltine genotypes. Consequently, although the two species both showed cogradient patterns in thermal reaction norms, it appears likely that this was for different reasons. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 981–991.     

Homosexual behaviour and its longevity cost in females and males of the seed beetle Acanthoscelides obtectus

The level of homosexual behaviour is evaluated in one laboratory population of seed beetle and derived lines selected to reproduce early (E) or late in life (L), where inadvertent selection for either low or high heterosexual activity has been detected. The magnitudes of homosexual interaction, measured as chasing and mounting individuals of the same sex, are estimated over different age classes. These magnitudes are correlated with previously observed levels and patterns of age‐specific variation of heterosexual activity of both sexes in the E and L experimental lines. The results obtained support the perception error hypothesis proposing that a low degree of sexual discrimination is genetically correlated with high sexual activity. The fitness costs of the same‐sex interactions are tested by assessing their effects on longevity. In both sexes, the longevities of homosexual pairs are reduced relative to individually‐housed virgin beetles in both the E and L lines, although homosexual interactions have a more pronounced effect on male survival than on female survival. Although the results obtained suggest that the longevity cost of homosexual interactions can be substantial, this cost is much smaller than the cost of heterosexual interactions.     

The effect of larval photoperiod on pupal colour and diapause in swallowtail butterflies

ABSTRACT.

• 1 There are significant differences in the effects of larval photo-period on diapause and pupal colour among the species Papilio polyxenes Fabr., P.troilus L., Battus philenor (L.) and Eurytides marcellus (Cramer).
• 2 Diapause and pupal colour in P.polyxenes and P.troilus are strongly influenced by larval photoperiod, short photophase eliciting brown diapausing pupae. Photoperiods of 15L:9D permit the expression of the green and brown pupal colour alternatives.
• 3 Pupal colour in B.philenor and E.marcellus is not affected by larval photoperiod, but short photophase induces diapause in these species.
• 4 All species except B.philenor show an association between brown pupal colour and diapause: Emarcellus when reared on long (midsummer) photophase, P.polyxenes and P.troilus when reared on short (autumnal) photophase.
• 5 In P.polyxenes, short photophase can affect pupal colour responses directly, whether the individual enters diapause or not.
• 6 Differences among the species are related to differences in the ecology of their natural pupation sites.

     

Why are there good and poor mimics?

Among the many Batesian mimetic hoverflies (Diptera: Syrphidae) some have a very precise resemblance to the presumed model ('good' or 'specific' mimics) while others have a much less precise resemblance ('poor' or 'general' mimics). Intuitively one might expect that the specific mimics would be commoner and more successful than the general mimics. However, many specific mimics (e.g. Serkomyia silentis, Volucella bombylans) are quite rare, while general mimics are common (e.g. Syrphus ribesii, Episyrphus balteatus and Eristalis intricarius). Similarly, some ant-mimicking spiders from several different families are very good morphological and behavioural mimics of just one species of ant while others have a less detailed resemblance to ants in general. Six hypotheses are presented to explain the occurrence of so many poor mimics, and a theoretical model is outlined (the multi-model hypothesis) which shows how a poor general mimic can have a larger population than a good, specific mimic. This hypothesis may apply to some species of hoverfly and to some ant-mimicking spiders.     

The phenology of Syrphidae (Diptera): are they Batesian mimics of Hymenoptera?

The phenology of aculeate Hymenoptera and of syrphids which are believed to mimic them has been investigated at three semi-natural ancient woodland sites in north-west England. It is concluded that the abundance and phenology of most of the hoverflies is consistent with their being Batesian mimics of particular species of bee or wasp. The main exceptions are Eristalis spp., Helophilus spp., Syrphus spp. and Episyrphus balteatus which are often much more abundant than their supposed models. These four taxa may still benefit from mimicry, but further research is needed to confirm this. With the possible exceptions of Eristalis pertinax and E. tenax , there is no strong evidence from north-west England in support of Waldbauer's hypothesis that mimics are rare when fledgling birds are abundant but may be commoner in autumn and spring. The data also indicate that mimics which closely resemble their models (specific mimics) are usually rarer than their models, whereas mimics with a less precise resemblance (non-specific mimics) are often commoner than models.     

The roles of colour change and behaviour in the hygrothermal balance of a littoral isopod,Ligia oceanica

Summary Ligia oceanica can change its colour using melanophores, the animal's reflectance varying between about 2 and 10%. Darker individuals heat up more quickly, and to higher body temperatures, than do pale ones. Colour change shows an underlying circadian rhythm, though the pattern of this rhythm varies with temperature, humidity, background and time of year. In general the rhythm is such as to ensure maximum camouflage at the critical dusk period, but in some conditions hygrothermal needs are overriding and the animals are paler (to stay cool) or darker (to warm up). In addition, animals show short term colour modification; when transferred to differing backgrounds and temperatures their colours initially reflect background matching, but after 30–45 min are modified into thermally appropriate shades, dark at 5° C and pale at 20° C. Field-caught specimens showed body temperatures that varied with colouration, and modification of colour in relation to thermal needs, particularly by being paler than expected when forced into the open by daytime high tides, and darker than expected when active prior to dusk. Animals invariably selected dark backgrounds in choice chambers. However, choice of humidity depended on previous experience; saturated air was normally preferred, but warm animals chose drier air (to allow evaporative cooling) unless also water-stressed. They also tended to disperse to facilitate cooling, whereas aggregation increased with increasing RH and with decreasing temperature. The interactions of colour changes, behavioural choices, and activity patterns in controlling the hygrothermal belance of Ligia in the intertidal environment are discussed in the light of these results.