Archive for February, 2013

…  that’s the remark in the bugguide.net species account about this fellow:

Toxorhynchites rutilus Elephant mosquito nectaring on Solidago Goldenrod

The elegant Elephant Mosquito

This elegant mosquito is actually an Elephant Mosquito (Toxorhynchites rutilus), a species of mosquito native to the eastern US. If the word mosquito conjures up images of swatting at nasty, disease-carrying blood suckers on warm summer evenings, read on, for this is a mosquito of a different ilk.

Gentle giants of the mosquito world

Members of the mosquito genus Toxorhynchites are the largest of the world’s mosquitoes (family Culicidae), with wingspans that can exceed 0.4 inches (12 mm). Unlike most mosquitoes, adult Toxorhynchites don’t take blood meals. Instead, they fill up on protein while they are aquatic larvae—and, lucky for us, they prey upon the larvae of their blood-sucking mosquito relatives. A single Elephant Mosquito larva can down 400 pest mosquito larvae. Elephant Mosquito larvae and their prey are found in water-filled tree holes (they’re also called Treehole Mosquitoes) or human artifacts like tires. Check out this YouTube video by EntoGeek that shows the larvae feeding.

Once they reach adulthood, Elephant Mosquitoes, both males and females, feed only on flower nectar. The male in the above photo was feeding on some goldenrod (Solidago spp) nectar during an afternoon in late summer 2012. You can tell it’s a male from the very feathery antennae that he uses to detect the pheromones of females. The curved appendages on his head are the mouthparts that he uses to feed. Not readily apparent in the photo is the brilliant metallic coloring that Elephant Mosquitoes have.

Effective biocontrol agents

Elephant Mosquitoes have successfully been reared and released to control populations of pest mosquitoes. Although they don’t provide total control, they’re valuable in targeting pest mosquito larvae in tree holes or man-made containers that are difficult to treat with insecticides.

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Lobelia siphilitica Great Blue Lobelia inflorescence raceme

Great Blue Lobelia

My January 12 and 13 posts featured Cardinal Flower (Lobelia cardinalis), a plant with bright red flowers that are pollinated by hummingbirds. Another species of Lobelia native to eastern and central North America is Great Blue Lobelia (Lobelia siphilitica—the species name derives from use of the plant roots by Native Americans in a concoction to cure syphilis).

Great Blue Lobelia is similar in outline to Cardinal Flower, but it grows a foot or two shorter and it has blue flowers. Its flowers are similar in shape to those of Cardinal Flower—they’re tubular shaped with two upper and three lower petals—but the flower parts of Great Blue Lobelia are more compact. Both species of Lobelia share the same bloom time and habitat. But they don’t share pollinators, a fact that I observed last summer.

Lobelia siphilitica Great Blue Lobelia flower close

Great Blue Lobelia with two upper and three lower petals

Lobelia cardinalis Cardinal Flower close

Cardinal Flower

Welcome, Great Blue Lobelia

In summer 2012, I was surprised to discover two plants of Great Blue Lobelia in bloom near the patch of Cardinal Flowers in my backyard. I was surprised because I didn’t plant them. There were some Great Blue Lobelias in the yard until about ten years ago, but they died out, probably due to insufficient moisture. I suspect these new plants may have sprouted from seeds that had laid dormant in the soil. In any case, having these two closely related Lobelia species growing near each other offered a great opportunity to observe the fauna that visited their flowers.

The flower visitors

As described in my earlier posts, the Cardinal Flowers were magnets for Ruby-throated Hummingbirds and Spicebush Swallowtail butterflies. But both of these flower visitors totally ignored the nearby Great Blue Lobelia flowers.

Lobelia siphilitica Great Blue Lobelia w Bombus pollinator

Bumblebees were frequent visitors to Great Blue Lobelia

On the other hand, the Great Blue Lobelias were abuzz with busy pollination by bumblebees that totally ignored the nearby Cardinal Flowers. Bumblebees were the only insects that I saw visiting the Great Blue Lobelia flowers, although I’ve read that other species of bees and wasps also visit the flowers.

But why this segregation of flower visitors? Flower color is key. Hummingbirds have a strong preference for red flowers. Butterflies have more eclectic color preferences that include red. But bees cannot see red. Bees rarely visit red flowers unless the flowers also reflect ultraviolet light that humans can’t see. Bees prefer blue over other colors, and that’s why they’re attracted to Great Blue Lobelias.

Still, it seemed odd that neither hummingbirds nor butterflies even approached the Great Blue Lobelias and that the bumblebees never stumbled upon the Cardinal Flowers. I wasn’t the first person to make this observation though. Thomas Meehan, a naturalist, made similar observations 112 years earlier:

In my garden during the past year, 1900, I had some fifty plants each of Lobelia syphilitica and Lobelia cardinalis in rows side by side. They were so near each other that some of the flower stems of the latter fell over and seemed to be blooming among the plants of the former. It surprised me one day to note that while numerous winged insects visited the blue-flowered species, none cared for the scarlet ones. This excited an interest that led to a continuous observation through the whole flowering period. At no time did I see an insect visitor on the cardinal flower, while every day the blue-flowered species had abundant attention. On one occasion I found a humming-bird, Trochilus colubris, at work on the cardinal flower, and the zest with which numerous flowers were examined by the bird attested to the presence of nectar, a fact which my own test subsequently verified. The bird is not numerous on my ground, and with an abundance of flowers of various kinds over many acres of ground, it may be inferred that it was not a frequent visitor to the cardinal flower. I observed it only on this occasion. It wholly neglected the blue-flowered species, that seemed so attractive to the insects.

Result—few Lobelia hybrids

Plants of related species that bloom at the same time and attract the same pollinators often hybridize, or interbreed and produce intermediate species. The goldenrods (Solidago spp.) that bloom in late summer and autumn are well-known hybridizers. But Cardinal Flowers and Great Blue Lobelias, with their unique pollinators, rarely hybridize in nature. Of course, that doesn’t stop a meddling human from transferring pollen between the species to see what, if any, hybrids result … something I might try next summer.

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