Hormonal control of pupal coloration in the painted lady butterfly Vanessa cardui

Pupae of the painted lady butterfly Vanessa cardui exhibit pupal color polyphenism consisting of white, dark and intermediate types. We investigated environmental factors affecting pupal coloration and the physiological mechanisms underlying the control of pupal color polyphenism in this species. Over 80% of larvae reared at 16 °C developed into pupae of dark types, whereas over 82% of larvae at 32 °C developed into pupae of white types irrespective of long/short-day photoperiod conditions. When mature larvae reared at 32 °C were ligatured between thoracic and abdominal parts at three different pharate pupal stages, all of the head-thoracic parts developed into white pupae regardless of pupal stage, but all abdominal parts ligatured at the early pharate pupal stage only developed into dark pupae. These results indicate that temperature during larval stages is an important element affecting pupal coloration as an environmental cue in V. cardui, and that a factor(s) inducing white pupae is released from head-thoracic parts under conditions of high temperature. Additionally, when ligatured abdomens destined to develop into dark pupae were treated with crude extracts prepared from the central nervous system, all of the ligatured abdomens developed into white pupae at a level dependent on dose and pupal stage. These results suggest that the factor inducing white pupae is a key molecule controlling pupal color polyphenism in V. cardui.     

Fluctuations of Vanessa cardui butterfly abundance with El Niño and Pacific Decadal Oscillation climatic variables

Annual 4th of July Butterfly Count data spanning more than 20 years are examined to explore Vanessa cardui (Painted Lady) population fluctuations with ENSO (El Niño) and Pacific Decadal Oscillation (PDO) indices. California, Colorado and Nebraska censuses exhibit a strong positive correlation with the strong El Niño events of 1982–1983 and 1997–1998 and the weaker event of 1991–1992. Regression analysis shows the population fluctuations are strongly coupled to climate variations on both short (El Niño) and longer (Pacific Decadal Oscillation) time scales. Recognizing the sensitivity to these time scales is important for predicting longer‐term global climate change effects.     

Leaf trenching by Indian red admiral caterpillars for feeding and shelter construction

Many folivorous insects sever leaf veins, trench across leaf blades, or girdle petioles prior to feeding on leaves. The purpose of these behaviours is generally thought to be sabotage of the anti-herbivore chemical defences of host plants. For insects that construct leaf shelters, these behaviours may make leaves easier to roll or fold. Larvae of the Indian red admiral butterfly, Vanessa indica (Herbst), cut trenches at the base of host plant leaves and construct leaf-fold shelters. I attempted to determine which of the above functions the trenching behaviour of V. indica larvae serves. If the function of trenching is to facilitate leaf-folding, then larvae should cut trenches before folding leaves. When the larvae used larger leaves, they tended to trench them prior to folding them. This suggests that the function of trenching behaviour is to make leaves easier to fold. However, larvae sometimes cut trenches after folding the leaves, suggesting that this behaviour has additional functions. When the larvae were about to moult or pupate, they did not cut trenches, suggesting that trenching behaviour may also be involved in feeding.     

Long‐range seasonal migration in insects: mechanisms,evolutionary drivers and ecological consequences

Myriad tiny insect species take to the air to engage in windborne migration, but entomology also has its ‘charismatic megafauna’ of butterflies, large moths, dragonflies and locusts. The spectacular migrations of large day‐flying insects have long fascinated humankind, and since the advent of radar entomology much has been revealed about high‐altitude night‐time insect migrations. Over the last decade, there have been significant advances in insect migration research, which we review here. In particular, we highlight: (1) notable improvements in our understanding of lepidopteran navigation strategies, including the hitherto unsuspected capabilities of high‐altitude migrants to select favourable winds and orientate adaptively, (2) progress in unravelling the neuronal mechanisms underlying sun compass orientation and in identifying the genetic complex underpinning key traits associated with migration behaviour and performance in the monarch butterfly, and (3) improvements in our knowledge of the multifaceted interactions between disease agents and insect migrants, in terms of direct effects on migration success and pathogen spread, and indirect effects on the evolution of migratory systems. We conclude by highlighting the progress that can be made through inter‐phyla comparisons, and identify future research areas that will enhance our understanding of insect migration strategies within an eco‐evolutionary perspective.     

Pollen metabarcoding as a tool for tracking long‐distance insect migrations

Insects account for a large portion of Earth's biodiversity and are key players for ecosystems, notably as pollinators. While insect migration is suspected to represent a natural phenomenon of major importance, remarkably little is known about it, except for a few flagship species. The reason for this situation is mainly due to technical limitations in the study of insect movement. Here, we propose using metabarcoding of pollen carried by insects as a method for tracking their migrations. We developed a flexible and simple protocol allowing efficient multiplexing and not requiring DNA extraction, one of the most time‐consuming part of metabarcoding protocols, and apply this method to the study of the long‐distance migration of the butterfly Vanessa cardui, an emerging model for insect migration. We collected 47 butterfly samples along the Mediterranean coast of Spain in spring and performed metabarcoding of pollen collected from their bodies to test for potential arrivals from the African continent. In total, we detected 157 plant species from 23 orders, most of which (82.8%) were insect‐pollinated. Taxa present in Africa–Arabia represented 73.2% of our data set, and 19.1% were endemic to this region, strongly supporting the hypothesis that migratory butterflies colonize southern Europe from Africa in spring. Moreover, our data suggest that a northwards trans‐Saharan migration in spring is plausible for early arrivals (February) into Europe, as shown by the presence of Saharan floristic elements. Our results demonstrate the possibility of regular insect‐mediated transcontinental pollination, with potential implications for ecosystem functioning, agriculture and plant phylogeography.     

小苎麻赤蛱蝶复眼的紫外光敏感性

用电生理方法细胞外记录并测定完整的小苎麻赤蛱蝶(Vanessa cardui)成虫复眼的光谱敏感特性.暗适应下,所测光谱在波长约530毫微米处有最大敏感峰.近紫外光波长355—360毫微米处也呈现较高的敏感次峰,它可被长波段适应光选择性地增高和分离.当复眼为短波段适应光作用时,355—360毫微米峰基本上被抑制,并导致530毫微米处敏感性的增加和分离.小苎麻赤蛱蝶复眼可能分别含有吸收峰在530和355—360毫微米的两类视色素.     

Identification of feeding attractants in oak sap for adults of two nymphalid butterflies, Kaniska canace and Vanessa indica

The active compounds of oak‐sap odour in attracting adults of two butterflies, Kaniska canace (L.) and Vanessa indica (Herbst) (Lepidoptera: Nymphalidae), were identified by chemical analyses, electroantennogram (EAG) and two behavioural assays: proboscis extension reflex (PER) and attraction to artificial tree models. Fourteen compounds were identified from two sap samples collected in 1997 and 1998, of which the major volatiles were ethanol and acetic acid (≈ 900 p.p.m. and 500 p.p.m. in sap, respectively). However, the chemical composition of the minor volatiles varied considerably between the two samples. Among 13 chemicals tested, V. indica showed strong PER to five aliphatic acids (acetic, propionic, butyric, isobutyric and isovaleric), 2‐methylpropan‐1‐ol and 3‐hydroxybutan‐2‐one, whereas the PER‐active compounds for K. canace were these seven compounds and also ethanol, 3‐methylbutan‐1‐ol and 1‐hydroxypropan‐2‐one. In two‐choice behavioural bioassays, the model scented with a sap‐odour mimic, which was an aqueous mixture of the PER‐active compounds, was more attractive to the two butterflies than an unscented control. These results demonstrated that the sap odour stimulates foraging behaviour of the butterfly. Although EAG responses of both butterflies to 3‐methylbutan‐1‐ol and that of V. indica to 2‐methylpropan‐1‐ol were positively dose‐dependent, responses to other compounds were not strong and not dose‐dependent at 1–100 μg doses. These EAG responsiveness suggests that the olfactory receptors for these compounds might be few in the antenna and that the butterflies have enough olfactory sensitivity to the dose of 1 μg.     

Presence of a cerebral factor showing summer-morph-producing hormone activity in the brain of the seasonal non-polyphenic butterflies Vanessa cardui, V. indica and Nymphalis xanthomelas japonica (Lepidoptera: Nymphalidae)

Three species of nymphalid butterflies, Vanessa cardui, V. indica and Nymphalis xanthomelas japonica , do not exhibit seasonal polyphenism in wing coloration. To determine whether seasonal non-polyphenic butterflies possess a cerebral factor affecting wing coloration, we used a Polygonia c-aureum female short-day pupal assay for detection of summer-morph-producing hormone (SMPH) activity in P. c-aureum. When 2% NaCl extracts of 25 brain-equivalents prepared from the pupal brains of V. cardui, V. indica or N. xanthomelas japonica were injected into Polygonia female short-day pupae, all recipients developed into summer-morph adults with dark-yellow wings, and the average grade score (AGS) of summer morphs showing SMPH activity was 3.8, 3.7 and 4.0, respectively. In contrast, when acetone or 80% ethanol extracts prepared from pupal brains were injected into Polygonia pupae, all recipients developed into autumn-morph adults with a dark-brown coloration and each exhibited an AGS of less than 0.5. Our results indicate that a cerebral factor showing SMPH activity is present in the pupal brain of seasonal non-polyphenic nymphalid butterflies, suggesting that a SMPH and cerebral factor showing SMPH activity occur widely among butterfly species. This finding will improve our understanding of the presence of cerebral factors showing interspecific actions of SHPH.     

The nature of migration in the red admiral butterfly Vanessa atalanta: evidence from the population ecology in its southern range

1. The migrant Vanessa atalanta (L.) occurs throughout Europe and North Africa. In autumn, populations emigrate from northern and central Europe to the Mediterranean region to overwinter. In the spring, the northern range is recolonised by migrants from the south. The dynamics of the species in the winter range is poorly known. 2. From 1994 to 1999, adults and immatures of V. atalanta were monitored all year round in Mediterranean habitats in north‐east Spain. 3. Data showed that the Catalonia lowlands is an area to which V. atalanta migrates to breed during the winter. Migrants arrive in October and early November and initiate a period of intensive breeding. Larval development occurs throughout the winter until a first annual generation of adults appears in early spring. 4. Most of the butterflies emerging in the spring emigrate and leave the area without breeding. The data suggest strongly that recolonisation of the northern range is by these butterflies not by wintering adults. Altitudinal migration also seems to be a common phenomenon, allowing a further summer generation of adults to occur at high elevations within the Mediterranean region. 5. The complex phenology of V. atalanta in its southern range has evolved as a strategy to track larval resources through space and time. Autumn migration coincides with the greatest availability of the main food plant, Urtica dioica L. Late spring migration occurs by the time food quality is decreasing.