Butterfly Pupae in Living Color

by jjneal

Butterfly collectors have known for over a century that the background color of the environment can affect the color of the chrysalis (pupa) of some species of butterfly. The Black Swallowtail butterfly, Papilo polyxenes, has a range of color morphs from light green to dark brown. On green foliage, the pupa is a light green color. On dark stems (often in the fall) the pupae are brown. The color variation helps the pupa better blend into the environment and provides some measure of protection from predators.

How does the Black Swallowtail know how to match the color of its pupa to the environment? Caterpillars have photo receptors (stemmata) with pigments that presumably can detect the surrounding color when it starts to pupate. The color triggers or inhibits the release of a hormone that controls pupal coloration. High levels of hormone will produce a brown pupa, low levels produce a green pupa. Injection of caterpillars on a green background with a nerve extract from caterpillars that are on a brown background will produce brown pupae.

Adjusting their color so they are harder to detect helps Black Swallowtail pupae avoid predation.

Green Form of the Black Swallowtail Chrysalis

Living With Passion

by jjneal

The Gulf Fritillary, Agraulis vanillae, feeds on vines in the Passion Fruit family, including Passion Fruit vines. Several species of Passiflora vines are cultivated as garden ornamentals in many parts of the Unites States. The Gulf Fritillary has expanded its range to include those areas where gardeners plant vines that can serve as food for larvae.

In the early 1970s, the Gulf Fritillary range was expanded to the Hawaiian Islands. The Gulf Fritillary was intentionally introduced as a possible biological control agent for the banana poka, Passiflora mollissima, an invasive weed from Central America that is one of the worst forest pests in Hawaii.

The Gulf Fritillary, failed to provide adequate control of banana poka but does feed on other species of Passiflora. The Gulf Fritillary is now established in Hawaii where it feeds on species of Passiflora, other than P. mollissima. In some parts of its range, the Gulf Fritillary is considered a pest because it destroys the Passion Fruit vines.

On a trip to the island of Hawaii in 2006, I photographed this Gulf Fritillary resting on the ground.

Gulf Fritillary

Living With Butterfly Colors

by jjneal

Morpho butterflies are a brilliant blue color because they reflect only the blue wavelength light. Longer light wavelengths are scattered. How does this work? The scales on the wings of Morphos have micro ridges that are spaced close together. The distance is shorter than the longer light wavelengths. When red or green light hits the scale, much of the light that is reflected at the surface collides with a nearby micro ridge. Most of the blue and UV light, which is shorter wavelength light, is reflected by the wing scale without hitting the ridges. The shorter light wavelengths “fit” between the ridges and are reflected. The longer light wavelengths do not fit and are absorbed or scattered rather than reflected.

New technology and improvements in fabrication methods are leading to a new wave of nano scale products. Two-Photon Polymerization is a technique for creating nano scale structures using femtosecond lasers. A brief, focused pulse of light applied to a photosensitive material can create structures in the 100 nm range. Using Two-Photon Polymerization it is now possible (still very expensive and time consuming) to produce synthetic materials that have some of the structural color properties of butter fly wings.

Place your advance order for butterfly wall paper today. Delivery will be at least a decade off.

Structural Blue Color on Morpho Butterfly Wings

Living With Lepidoptera Pollinators

Flowers can increase their pollination efficiency by attracting insects that carry their pollen to a nearby flower of the same species. Most flowers act in “good faith”. They reward the insect pollinators with nutrient-containing nectar. One South African orchid, Disa ferruginea, has a single butterfly pollinator, Meneris tulbaghia, but does not reward it for its effort. Instead it mimics another flower, Tritoniopsis triticea, which rewards its pollinators with nectar. Observations by S.D. Johnson in The Biological Journal of the Linnean Society ( DOI: 10.1111/j.1095-8312.1994.tb01003 ) noted that Disa ferruginea, has high levels of pollination and fruit production in locations where Tritoniopsis triticea, grows nearby. In locations where Tritoniopsis triticea, is not present, the orchid bears much less fruit. Disa ferruginea can get by “on the cheap by mimicry. Butterflies used to getting rewards from flowers will inadvertently visit these mimics. However, that strategy also limits the range of the orchid mimic to that of its flower model. In areas where Disa ferruginea, grows without its model flower present, butterflies rarely visit to pollinate them because the butterflies are not rewarded for their effort. Incentives matter.

Nice Flowers Give Butterflies Nectar Rewards

Living With Loopers

by jjneal

Caterpillars, the immature larval forms of butterflies and moths have several styles of movement. Caterpillars of the family Geometridae are called loopers or inchworms. Loopers move by grasping the surface (usually a branch or stem) with their three pairs of tiny thoracic legs. The caterpillar then makes a loop with its abdomen, bringing the end of its abdomen next to the thoracic legs. The end of the looper abdomen has “prolegs”, extensions of the abdominal wall that can grasp a stem or limb. The end of the proleg has hooks called crochets that can hook into the surface of the plants. The looper can grasp the stem with only its abdominal prolegs. This allows the caterpillar to swing its head and thorax away from the end of the abdomen and move forward.

Loopers typically have a relatively thin abdomen that can form loops. Caterpillars with a thick abdomen can not easily form a loop. These caterpillars will move in a forward wave-like motion. The prolegs on the end of the abdomen move first. successive prolegs release, then move forward. When the wave reaches the thorax, the legs will release and move forward form back to front to continue the wave.

Loopers Move By Arching Their Abdomen

Butterflies and Invasive Species

by jjneal

Some species of plants brought to North America from other locations become invasive. Invasive species not only establish, but displace many of the native species of plants. Invasive plants can create shade and prevent native plants from getting the sunlight they need to grow. One example is Chinese privet, Ligustrum sinense. In parts of Northern Georgia, Chinese privet is the dominant shrub that excludes many species of flowering plants.

Butterflies use flowering plants as sources of nectar as adults. Butterfly larvae (caterpillars) often depend on one or only a few species of plants for food. How much do invasive plant species such as Chinese privet affect butterflies?

In a recent paper, James Hanula and Scott Horn describe several methods of Chinese privet removal and the affects in following years on butterfly numbers and species composition. They found that privet removal by all means enhanced butterfly abundance, diversity and evenness. The greatest affect was achieved when the privet was mulched after it was cut. Privet removal had noticeable affects on plant species composition.

Pearl Crescent Butterflies Are Affected By Invasive Plant Species

Invasive species that cause large economic harm attract much attention and effort to either eradicate the species or at least slow their spread. Invasive species that do not have clear economic effects may have ecological effects on other species that are not apparent without detailed investigation. The large increase in global trade over the past several decades has increased the numbers and rates of invasive species introductions. These invasive species are changing our ecosystems in many ways. Efforts to stop or at least slow the rate of exotic species importation are necessary to prevent rapid and undesirable environmental changes.

Friday Caterpillar Blogging: Pathogen Defense

by jjneal

Cut open a potato and leave it exposed to the air. The potato will turn from white to brown. This is due to an enzyme, polyphenol oxidase that leads to production of a dark pigment, melanin. Wound a caterpillar and the hemolymph cells (insect blood) will plug the hole and produce melanin. The caterpillar will have a black spot at the site of the wound. Phenol oxidase reactions are found in most plants and animals. Although the name may be unfamiliar, we are familiar with the phenomena. Phenol oxidase reactions produce the brown color of tea and coffee. Phenol oxidase reactions produce the defensive “ink” of an octopus.

Phenol oxidase has an important role in insect defense against pathogens. At the site of a wound, phenol oxidase will generate reactive chemicals. These chemicals react with the cells of bacteria and other pathogens present at the wound site. Some of the insect cells at the wound site are affected as well. Once released, the reactive chemicals that do not react with cell components, will polymerize to form melanin. Melanin at the site of an insect wound is evidence of the pathogen fighting process.

Circle: Melanin at the site of a Hornworm Caterpillar Wound