Butterflies and Skippers

Skipper

Silver Spotted Skipper

Taxonomists have traditionally placed species in groups based on visible characters. The Skippers (Family Hesperiidae) share many visible characters with the butterflies and moths and are considered more “moth-like” than other families of butterflies. Taxonomists in the Pre-Molecular age hypothesized that the skippers were a stepping stone in the evolution of butterflies from moths.

The Molecular Age has given taxonomists many new characters for the reconstruction of phylogenies (evolutionary history). The changes to DNA (through descent with modification) leave patterns such that those groups most recently separated have a greater proportion of DNA in common. DNA from mitochondria has characteristics that are very useful for constructing phylogenies. Complete mitochondria DNA sequences are a published for over 100 species of butterflies and more are expected.

The molecular data from the DNA sequences clearly indicates that the Swallowtails (Papilionidae) not the Skippers (Hesperiidae) are the group most closely related to the moths. The Skippers are descended from the Swallowtails in their own branch of the phylogenetic tree. The other branch leads to all the other butterfly families. This analysis firmly embeds the Skippers within the butterflies. The biology of the Skippers is best understood as one of several families of butterflies.

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Living With Butterfly Hosts

Red Admiral Butterfly

Red Admiral Butterfly

Butterflies can live in urban areas, if the area is suitably planted. Gardeners will plant both hosts of the caterpillar and nectar producing flowers to encourage butterflies. However, some caterpillar hosts may not be desirable in small butterfly gardens. This includes Urtica dioica aka “stinging nettles” a plant that originated in Europe and has become widespread in North America. Urtica dioica is the preferred host of the Red Admiral and several other butterfly species. The stinging nettles can produce a rash and an allergic reaction in sensitive people. They are not recommended for this reason. Nettles are common in open fields and can do well in disturbed abandoned areas. Nettles growing in these “out-of-the-way” urban sites can serve as sites for caterpillars and enhance the urban butterfly population.

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The Diana Fritillary

Speyeria diana

Speyeria diana
Photo: Dr. Thomas G. Barnes,

The range of the Diana Fritillary, Speyeria diana has undergone what Wells and Tonkyn* describe as a collapse. Today its range consists primarily of two upland populations: one in the southern Appalachians and one in the Arkansas-Oklahoma ‘highlands’. The lowland populations have disappeared including sites in lowland Virginia where it was first collected and the Ohio River Valley including Indiana. The last report of the Diana Fritillary in Indiana was from Perry County, Indiana in 1962.

This large butterfly has dimorphic males and females. Females mimic the toxic Pipevine Swallowtail. The Males are orange and white. The retreat to higher elevations may be a response to the warmer climate, the higher elevations generally experiencing lower temperatures.

*CARRIE N. WELLS and DAVID W. TONKYN. 2014. Range collapse in the Diana fritillary, Speyeria diana. Insect Conservation and Diversity. 7: 365–380.
doi: 10.1111/icad.12059

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Living With White Wings

Butterfly

White Monarch Butterfly Photo: Lisa, Flickr;

The color patterns of wings of butterflies are created by a mosaic of scales, each with its own color. A scale is a modified hair, a secretion of the underlying cell. Some scales have structural colors that are produced by the arrangement of molecules that constitute the scales. Other scales contain pigment which gives them their color. The underlying cell that produces the scale also produces the pigment and transports it into the scale. Monarch mutants with wings that are white instead of orange have a mutant protein, thought to be a component of the cytoskeleton of insect cells. The cytoskeleton would be responsible for moving pigment out of the cell and into the growing scale. In mutant white Monarchs, the cytoskeleton transport process is defective, the pigment is not transported into the scale and unpigmented scales are white.

*Kronforst, Marcus R. 2015. Exploring the molecular basis of monarch butterfly color pattern variation. Pigment Cell & Melanoma Research. 28: 127–130.
http://dx.doi.org/10.1111/pcmr.12353

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Living With Bed Bug Attractants

Bed Bug

Underside of Immature Bed Bug

A group of scientists* have reported the discovery of a mix of chemicals that lure bed bugs into a trap. This discovery opens the possibility of detecting bed bug populations in the early stages of an infestation by strategic trap placement.

The most effective attractant has six chemical components. Five are volatile and effective at a distance. The sixth, histadine, has low volatility and does not attract bed bugs from a significant distance. Histamine functions as arrestant that encourages bed bugs to remain in a shelter once it is entered.

The five volatile chemicals that attract bed bugs from a distance are: dimethyl disulfide, dimethyl trisulfide, (E)-2-hexenal, (E)-2-octenal, 2-hexanone. The five component blend is more attractive to bed bugs than any of the chemicals singly or in other combinations. The volatile components could attract bed bugs from longer distance, but the histamine was essential to getting the bed bugs to stay in the trap. The scientists found all immature stages and both male and female bed bugs in their traps. The traps with attractants caught more bed bugs than commonly used sticky traps. A sticky coating on the trap may deter bed bugs from entering and contacting the histamine arrestant.

Solving our problems with bed bugs will not be easy, however, we are making progress.

*Regine Gries, Prof. Robert Britton, Michael Holmes, Huimin Zhai, Jason Draper & Prof. Gerhard Gries. 2015. Bed Bug Aggregation Pheromone Finally Identified. Angewandte Chemie. Volume 127: 1151–1154.
DOI: 10.1002/ange.201409890

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Free To Travel

painting

Departure of the Winged Ship
Artist: Vladimir Kush

Butterflies are admired for their free and seemingly effortless flight. They are an inspiration to those who long to travel or embark on a life’s journey. Russian-born artist, Vladimir Kush captures the beauty, emotions and hope for the journey in his 2000 painting, Departure of the Winged Ship. Prints of this painting have been popular.

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Choosing a Host Plant

Comma butterflies.  Note the white "comma" on the underside of the wing (left).

Comma butterflies. Note the white “comma” on the underside of the wing (left).

The Comma Butterfly, Polygonia c-album, is one of the most polyphagous butterfly species. Butterflies frequently lay eggs, grow and develop on only a small number of plant species. Butterflies typically find host plants through visual or olfactory cues. For a species like the Comma that can survive on a multitude of plant with widely disparate odors and visual images, how does the female choose? One idea promoted by A.D. Hopkins was that the adult females might remember their larval host plant or have a chemical imprint that would lead them to oviposit on the same plant species of their larval development. This idea has several permutations, but all attempts to demonstrate a link have proved fruitless.

In one of the recent tests, a group of scientists* reared larvae on 3 host plant species, then measured the oviposition preference of the female. In two species choice tests, the females laid more eggs on Urtica dioica that the other host plants regardless of the plant the female consumed as a larva. Larvae do grow the fastest on Urtica dioica so the females lay more eggs on the better host plant and fewer on the less good host. Memory of the larval host did not occur in this test.

This result is conistent with host plant choice theory. The simplest model is that an insect makes a series of yes and no decision based on the information available and the “internal state” of the insect. In this model, the Comma Butterfly visits a plant and decides at that time whether or not to deposit an egg. If the perceived plant quality is too low or the oviposition cues too weak, the insect will leave and eventually visit another plant where the process is repeated. However, as time passes without finding a suitable plant, the insect becomes less choosy and will accept lower quality plants or plants with weaker oviposition cues. Humans have similar experience. If we have recently eaten and are satisfied, only a tempting delicacy can induce us to eat. If we are starving, many more foods are appealing. As an optimal strategy, a comma butterfly would lay eggs on Urtica dioica as best for the offspring. However, if the butterfly has not found Urtica dioica recently, that may mean it is not available. Thus, the best strategy involves laying eggs on lesser plants as they are found but continuing to search for the most desirable plants.

Alternative models to the series of yes or no decisions requires that the insect have a memory of the previous plant it visited, a means of comparing the quality of the two and the ability to locate the plants it remembers. This is a far more complicated mechanism and there is little evidence that insects use this method.

*NIKLAS JANZ, LINA SÖDERLIND and SÖREN NYLIN. 2009. No effect of larval experience on adult host preferences in Polygonia c-album: on the persistence of Hopkins’ host selection principle. Ecological Entomology. 34:50–57
DOI: 10.1111/j.1365-2311.2008.01041.x

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