Saturday, March 31, 2012

The Yucca Moth and the Yucca

Yucca (Yucca glauca), the state flower of New Mexico, illustrates an intimate relationship between a specialized pollinator and its equally specialized flower. The plant and the insect co-evolved; that is, they developed in intimate connection with each other. This is called an obligate mutualism in which if one were to disappear, the other would follow the same path. Originally it was a relationship of exploitation, with the moth larvae feeding on the seeds of the yucca. But, eventually the plant devised methods to take advantage of the situation and as a consequence, the moth also evolved to ensure food for its babies and preservation of its food plant.

Yucca flowers open for a few days, attracting a variety of insects during day hours; but they produce more nectar and send their strong and sweet aroma at night. Flowers with these characteristics are usually pollinated by moths or other nocturnal pollinators.

The yucca adds a special embellishment to this arrangement; of all the insects that visit its flowers, the only ones that can accomplish pollination are the yucca moths (Tegeticula yuccasella and Parategeticula depending on the species of plant).

Yucca moths are small, white, not very noticeable. They spend a good part of their adult life inside the flowers of the yucca, meeting members of the opposite sex and mating. Once mating has taken place, the female, very purposely visits the male parts of the flowers (anthers) to collect pollen which she stores under her chin.

Later, she flies to another flower, inspects it carefully, and if no other female has deposited her eggs, she proceeds to do just that. She refrains from laying more than a small number of eggs. The larvae will feed on the seeds of the plant. She seems to know that if she gets carried away and lays too many eggs, the flower will abort rather than produce a seedless fruit. It would be a no win situation, both for the plant and the moth.

Then, just as purposely as before, she goes to the right place, at the top of the ovary (called stigma), and deposits some of her precious cargo of pollen from under her chin, ensuring, this way, that the seeds will grow and feed her babies. She repeats this operation in other flowers.

The larvae feed on some of the seeds and there are enough left for the plant to reproduce. When fully grown, the larvae drop to the ground, where it goes through the transformation called pupation and finally it emerges as an adult several months later to repeat the cycle.

Without this insignificant little moth, the landscapes of the west would look dramatically different in the absence of yucca.

© Cillas. Wikicommons
Read more:

Moths as Pollinators
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Beginners Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2012

Sunday, March 25, 2012

Plume Moths: More Little Known Pollinators

Himmelman's Plume Moth

The plume moths or Pterophoridae get their name because of their feathery wings. Their aspect is quite unusual for a moth. The wings are narrow and fringed by bristles. When resting they spread their wings looking like the letter T. Their wing span ranges from ½ to 2 ½ inches. Most have a pattern of broken colors, tan and white or brown and white. The legs also present bristles. The combination of these colors and their shape makes them look like a piece of dry grass. Probably this helps them to escape predators' notice. They are easily missed by this photographer although in plain view. You may have seen one resting on your window screen where they are easier to notice

There are about 150 species in North America; most are hard to tell apart. A very common one is the Himmelman's Plume Moth or Geina tenuidactylus.

They are seen at flowers frequently, so they may be pollinators; although I don't know of any studies about it. More is known of their role as pests of some ornamentals and as biological control to keep in check some introduced invasive plants

Himmelman's Plume Moth

Moths as Pollinators
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Beginners Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2012

Wednesday, March 21, 2012

Of Spring Beauties and Lesser Celandines

A few spring beauties surrounded by the invasive lesser celandine

Lesser celandine along the trail where native flowers used to be
Last year I was disheartened to find that the lesser celandine, that attractive but aggressive invader, had spread over the land that once belonged to spring beauties and trout lilies. I am sorry to say that it looks like the non-native continues to make inroads.

Pachysandra, upper right corner; snow drops, bottom; spring beauties, center; lesser celandine. There are also stems of another alien, multiflora rose

Lesser celandines, with the help of snow drops and pachysandra, all of them garden escapees, have taken over the forest floor along my favorite nature trail. Later on, garlic mustard will show up in all the same places, but now it is not in sight. Snow drops were in bloom the last couple of weeks and now they are past their prime. This is another delightful but aggressive invader which brings joy to the hearts of many with its early blooms. Spring beauties struggle to survive hemmed in by all these newcomers to the land. Trout lilies face the same predicament in these areas.

A patch of lesser celandine
This spring I want to see how our native spring beauties and their pollinators are faring among the many introduced plants. So a few days ago I sat on my little stool on front of a patch of lesser celandine. It was a warm and sunny day and insects were quite active, including some gnats that enjoyed attacking my ears and forehead. During my forty minutes of observation I saw a number of little dark insects approach the patch and inspect the blooms by briskly hovering above them. Only one landed on a flower and stayed long enough for me to recognize it as an Andrena bee, the kind that would be loading her leg baskets with pollen from spring beauties if there were any around. Soon it left without attempting to gather anything from the flower. Perhaps it was just using it as a perch to pause during an exhausting and frustrating search for its favorite food.

Another patch of lesser celandine, near a stream
I continued my observations two days later. For more than an hour I walked along the trail illustrated above. I kept my eyes open for flower visitors and made frequent stops. I found only a handful of spring beauties nearly smothered by the lesser celandines. Even that very low number managed to have a few visiting bees. On the other hand, the bright yellow blossoms of lesser celandine remained neglected by anybody other than a small gnat and a beetle.

Finally, I sat for half an hour on front of another patch of lesser celandine, as on the previous time and intently looked for flower visitors. Finally a honey bee showed up and methodically worked the flowers. Let us remember that both honey bees and lesser celandines are European imports. There were no native pollinators in sight.

I should be glad that the lesser celandines don't get pollinated; but I can't. The variety brought from Europe propagates primarily by small bulbs (bulbils) with no need for pollinators. It reproduces this way only too well. Its abundance and the growing scarcity of spring beauty flowers forces the Andrena bees to travel longer and longer distances to gather pollen for their young. As a result, they can raise fewer and fewer babies each year. Both the flower and its pollinator continue to lose ground to the invaders.
A spring beauty and its pollinator, a rarer sight each year

List of articles
Beginners Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2012

Sunday, March 11, 2012

Zygaenidae, more little known pollinators

Harrisina americana (Grapeleaf Skeletonizer) on common milkweed

Another family of moths with a number of species that visit flowers is Zygaenidae. Many of them are day flying moths and, as usual, they are more colorful than night flying ones. Some are known to pollinate orchids. Their larvae feed on foliage, eating everything but the veins of leaves, so one common name for them is leaf-skeletonizers.
Acoloithus falsarius (Clemens' False Skeletonizer)

Two of them are frequently seen on milkweed flowers, the grapeleaf skeletonizer and Clemen's false skeletonizer. They are both dark blue or blue gray with a bright orange collar. The Clemen's moth is smaller than the grapeleaf skeletonizer. What is interesting about this imitative pattern is that it also mimics that of another common flower visitor, the yellow-collared scape moth. As mentioned before, the latter is toxic to predators and uses its colors to advertise its toxicity. The same thing is true of members of the Zygaenidae family. These, as well as some beetles, form part of a large mimicry complex, a fine example of Mullerian mimicry, in which they all benefit from this use of a similar warning pattern; predators need to learn their lesson only once, so more members of the guild escape attacks.
Cisseps fulvicollis (Yellow-collared Scape Moth). An unrelated moth member of the guild

Asclera ruficollis (Red-necked False Blister Beetle). A bettle member of the same mimicry guild

Another Zygaenidae that frequents flowers is the orange-patched smoky moth. Its wings are dark gray or black near the farther tip; the front half is orange. They too are members of another group of moths and also beetles with a pattern that warns predators. You can see some in a previous post: the black and yellow lichen moth and the end band net-wing lycid beetle.
Pyromorpha dimidiata (Orange-patched Smoky Moth)

Moths as Pollinators
List of articles
Beginners Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2012

Wednesday, March 7, 2012

Noctuids, another family of little known pollinators

Cirrhophanus triangulifer (Goldenrod Stowaway)

The noctuids or owlet moths are part of a very large family, perhaps the largest one of Lepidoptera; although some of the subfamilies deserve to be considered as families in their own right. The taxonomy is still in flux.

The name Noctuidae of this family means night or nocturnal. One would think that these are night moths and many of them, in fact, are. But in such large family there are many representatives that choose to fly during the day. Once again some of these tend to be more colorful than night fliers. And, once again the day fliers are more likely to visit flowers and to be pollinators.

Alypia octomaculata (Eight-spotted Forester), a colorful noctuid moth

A number of them are found on flowers sipping nectar and are probably pollinators; although, once again, very little is known about this activity.

Here are a few of the most common ones:
Xestia c-nigrum/dolosa complex
Nephelodes minians (Bronzed Cutworm)

Lacinipolia renigera (Bristly Cutworm)

Moths as Pollinators
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© Beatriz Moisset. 2012