Tuesday, February 21, 2017

Unexpected Liaisons, Mites and Bees

Mason bee with phoretic mites
Wikicommons © Orangeaurochs
We think of mites as annoying tiny parasites that cling to us and make us itch. If we see an insect covered with mites we feel sorry for it, assuming that the poor thing must be itching terribly and being weakened by the blood sucking pest. This is true in most cases, but curiously there are some exceptions. Believe it or not, some bees, wasps and beetles are perfectly happy with such companions. They bus around the little fellows from plants to nests. This earn the passengers the name of phoretic mites.

Carpenter bee (Xylocopa) with phoretic mites
Wikicommons © Gideon Pisanty
Mites and ticks are not insects. They are related to spiders, and most of them have eight legs, just like spiders. Mites are tiny; most of them are smaller than the tip of your ball point pen, so it is not surprising that we know very little about them. We would be quite surprised at the immense variety of mites and the large number of species. Many feed at the expense of animals, like the ones mentioned at the start of this piece, but many more feed on plants, fungi or bacteria.

Acarinarium of carpenter bee (Xylocopa)
Wikicommons © T. B. Fletcher (1914)

Getting back to the mites covering a bee. Little do you know that these particular kind of mites are the bee's friends to the point that the bee provides transport for them. Some bees have a small compartment or pouch on their bodies where mites can ride comfortably to the bee's nest. This organ is called an acarinarium, from the Greek word acarus (plural acari), which means mite.

It turns out that the mites feed on parasites that are prone to invade the bee's nest where she is raising a family. Thus the mite provides a valuable service to the bee which is greatly appreciated and compensated.

Some wasps have a similar mutualistic arrangement with mites and carry them to their nests. Carrion beetles transport mites to fresh carcasses. The mites feed on fly maggots, the beetle's competitors.

Potter wasp with acarinarium

Carrion beetle with phoretic mites
Flickr, Wikimedia. © Bohne, G

Monday, February 20, 2017

Spurs: Hard to Get Nectar

© Beatriz Moisset
 Many flowers are very particular about their clientele. They have developed ways to make themselves attractive to certain flower visitors while discouraging others. They do so by adopting a certain shape. The spurs of many flowers serve this purpose. A petal or a sepal develops an elongated hollow spike. This is what botanists call a spur.

Violet (Viola mirabilis). Note the spur
Wikicommons. © Antti Bilund

Violets have a spur. Nectar is collected at its bottom. A pollinator needs a tongue long enough to reach the hidden nectar waiting in this special vessel. The rest of the flower is so designed that the insect gets covered with pollen while performing this task. If it is carrying pollen from a previous flower visit, it is likely to deposit it on the stigma. Only long tongued insects can take advantage of this flower and they need to develop an efficient way to approach this specially shaped blossom. After a few times they get better and better and proceed faster. The most common pollinators of violets are small, solitary bees.

Bumble bee visiting a jewelweed blossom
© Beatriz Moisset
Jewelweed (Impatiens) also possess a spur. The flower itself is a small chamber just a little larger than a bumble bee. The petals form a curtain that slightly blocks the entrance to this chamber. Bumble bees are pros at collecting nectar from these flowers. Their plump bodies fit inside the chamber like a finger in a glove and their long and flexible tongues are suited to the curved spur.

© Beatriz Moisset

Columbines have not one but five spurs. Each petal is shaped like a long hollow horn ending on a knob. This is where the nectar gathers. Long tongued insects and hummingbirds pollinate these flowers. In most species, the flower nods or points downward, and the spurs point to the sky. This arrangement seems to be agreeable to their most common pollinators, hummingbirds.

© Beatriz Moisset
By contrast, the flowers of the alpine columbine remain erect, don't nod. They are also creamy white, a color favored by moths. And thus, they are preferably pollinated by large moths, the so called hawkmoths. A few other species of columbines, including the Colorado blue columbine, also face upwards and are also pollinated by moths.

Columbine and carpenter bee
stealing nectar
© Beatriz Moisset
Jewelweed and ants
stealing nectar
© Beatriz Moisset
This specialization has advantages but it also has some disadvantages. Not all flower visitors behave like honest pollinators. These difficult flowers are an invitation to cheating. Some visitors learn to take a shortcut, especially if their tongues aren't long enough to reach the bottom of the spur. They approach the flower from the side. Perhaps, they can smell the sweets through the walls of the spur. A quick bite or a stab through the delicate petal may be all it takes to reach the hidden food. Carpenter bees, bumble bees and even ants have been seen performing this robbery.

Sunday, February 12, 2017

Butterfly Pollination

Fritillary butterfly on butterfly weed
© Beatriz Moisset
When you mention pollinators to people, the immediate answer is: bees and butterflies. Bees, yes, the 20,000 species or so do a huge percentage of pollination. Some plants depend entirely on bees for this function. However, when it comes to butterflies, a different story emerges. Other insects, such as flies, wasps and moths are known to do a respectable amount of pollination, probably far more than butterflies do. Some of the mentioned insects are indispensable to certain plants, such as figs, cacao and yucca. Some flies are used in farming.

A great variety of pollinators and flower visitors
© Beatriz Moisset
Butterflies visit flowers but that alone doesn't make them good pollinators. They are easily noticed because of their large size and color. That is why the general public takes notice, but biologists have not paid a lot of attention to the role of butterflies as pollinators. So it would be nice to know a little more about them and how much credit they deserve.

Bumble bee on Helenium
© Beatriz Moisset

Let us compare a bumble bee with a butterfly in a field full of ragworts, for instance. Ragworts are pretty, daisy-like, rather weedy yellow flowers. A bumble bee hastily gathers pollen and nectar and moves on quickly from blossom to blossom in one plant, next it moves on to the next plant and the next, without wasting any time. It finally rushes home to feed a hungry brood with the gathered supplies. A butterfly, on the other hand, is free from family obligations. It only needs some nectar to quench its thirst so it lazily sits on a flower, unfolds its long tongue and drinks at leisure. It takes off and wanders away apparently aimlessly. Farther down it may finally land on another flower and drink some more nectar. Later on it may visit another plant a good distance from the previous ones and so on.

It is obvious that the bumble bee performs more pollination because of its diligent behavior. However, the butterfly is doing something important by transporting pollen to plants that are a good distance from each other. It is performing cross pollination and ensuring a good mixing of genes. Plants benefit from this increase in genetic diversity. Furthermore, recently researchers have learned that the pollen, stuck to a butterfly's long tongue stays fresh for a good time and ensures this valuable pollination at a distance.

Red banded hair streak butterfly on Helenium
© Beatriz Moisset
Butterflies seem to do more pollination in tropical regions than in temperate ones. Butterflies and hummingbirds are good at finding nectar inside long-necked or trumpet shaped flowers. They are attracted by red flowers, which are rather common in the tropics. Bees are color blind to the red color and prefer yellow and blue or purple ones. Butterflies, like hummingbirds, have a good vision for the red color.

A number of flowers are completely dependent on butterflies for pollination. Some South African orchids fall in this category. Another flower dependent on a butterfly for pollination is a member of the pea family, the Peacock Flower that grows in the Caribbean.

Orange sulphur butterfly on asters
Notice the long tongue
© Beatriz Moisset

In summary, butterflies, while not the most efficient pollinators, are important, even essential, in some instances.

Also see:
Pollinator Foraging Behavior and Gene Dispersal in Senecio (Compositae) (contribute to cross pollination, farther distances than bumble bees)

Monday, November 14, 2016

It is Cold Outside. Where did all the Butterflies Go?

Great spangled fritillary (Speyeria cybele)
Its tiny caterpillars will survive the winter
© Beatriz Moisset
Winter has arrived. What happened to all the six legged creatures we saw in summer? Where did the crawling, scuttling, flitting, buzzing multitudes go? Those of us who live in temperate and colder climates notice the disappearance of practically all insects when the weather gets cold. We are talking about the ones that live outdoors, not about those aggravating creatures that turn our houses into their homes.

Red admiral (Vanessa atalanta), one of the travelers
© Beatriz Moisset
Some of our favorite butterflies illustrate three different winter strategies.
1. Most adult butterflies die, the next generation lives on
2. A few migrate to warmer climates
3. Even fewer hunker down and wait for spring to come

Read the whole article

Monday, September 26, 2016

Ecosystem Engineers and the Web of Life

Goldenrod in bloom
© Beatriz Moisset

Goldenrod bunch gall
© Beatriz Moisset

This time of the year, fields and meadows are usually covered by a plethora goldenrods particularly the tall variety, known as Solidago altissima. Goldenrods nurture a huge variety of small creatures. Some feast on the rich pollen and nectar of their flowers. Others find ways to feed on the not so nutritious leaves and stems. The plants are so abundant and vigorous that they survive quite well the onslaught of all these feeders.

Rhopalomyia solidaginis
(Goldenrod bunch gall midge)
© Beatriz Moisset

Rhopalomyia solidaginis
Larva inside gall
© Beatriz Moisset

The goldenrod bunch gall midge is one of a number of goldenrod feeders that have developed interesting techniques to feed and stay safe from predators at the same time. The larva of this midge injects special substances into the tips of the goldenrod stems. These substances stimulate an unusual vigorous sprouting of the growing stem and leaves. A tight bunch or cluster of leaves with a nutritious, tender center develops. These clusters can be quite numerous in a field of goldenrods. They are easy to spot and they are known by the name of bunch galls. They provide both nourishment and shelter to the insect.

Parasitic wasps, Platygaster sp
© Beatriz Moisset
This story doesn't end there. The midge creates conditions favorable to other small creatures when it builds the bunch gall. Tiny beetles and wasps find a nice place to hide and even raise their families in the bunches of leaves. Curiously, the galls go beyond that. When dead, they become compost and enrich the soil in a larger scale than goldenrod plants free from galls.
Microrhopala vittata (Goldenrod Leaf Miner)
Inside bunch gall
© Beatriz Moisset
Microrhopala vittata (Goldenrod Leaf Miner)
© Beatriz Moisset
This is reminiscent of what beavers do. These animals build dams which provide habitat for fish and frogs and other animals. This have earned them the name of ecosystem engineers. The goldenrod gall midge is also an ecosystem engineer, although in smaller scale. It is surprising how such an insignificant and easily ignored tiny insect can contribute to the web of life.

Further Readings


Sunday, June 19, 2016

Bees and Biodiversity

Bombus ternarius, Tricolored bumble bee on mountain mint
 Recently I discussed the idea of allowing dandelions on the lawn to benefit pollinators. I pointed out that such practice only benefits a handful of generalist pollinators, but not the specialists. The latter can be more numerous than the former when they are all counted. They also account for the wide diversity of nature.
Bombus impatiens, Common Eastern Bumble Bee on blanket flower

Andrena cornelli, Azalea andrena on azalea
Let me expand on the concept of biological diversity or, as it is often called by ecologists, biodiversity. There are 4,000 species of bees in North America, from the familiar, big and plump bumble bees to tiny bee species that remain unnoticed to all except to those who study bees. Bear in mind that even bumble bees aren't just one single species but about 46 in North America.

Augochlora pura on thistle
Nomada, cuckoo bee on spring beauty
Bee species vary not only in size but in many other ways. Some are active from early spring to the end of fall. Others complete their whole cycle in just a few weeks and remain dormant the rest of the year. Some are adapted to different climates and cover a large area, others are more limited in their geographic distribution.

There are even some species, called cuckoo bees, that don't bother raising a family. Instead, just as cuckoo birds, lay their eggs in the nests of other bees.

Some bees have a long tongue that enables them to reach into fairly deep throated flowers. Others can only visit flowers that are relatively flat and open. Finally, some are very particular about the flowers they visit.They collect pollen from only one species of plants (monolectic) or a few related species (oligolectic). They may visit a wider range of flowers for nectar, but only their choice plants will satisfy their pollen needs.
Agapostemon splendens on seaside goldenrod

Lasioglossum pilosum on coneflower
Losing a few of these specialists may not be catastrophic, but it is preferable to preserve as many of them as possible. A rich variety of species confers resilience to an ecosystem. This is why it is important to have a wide range of specialists along with the handful of generalists. One way to help the specialists is to plant a variety of native plants to ensure that some of them satisfy their needs.
Colletes on Cerceris canadensis
Bombus perplexus, confusing bumble bee on common milkweed
Long horned bee on sunflower

 All images © Beatriz Moisset

Monday, May 16, 2016

Early Spring Pollinators and their Flowers

Dandelion visited by a cuckoo bee
© Beatriz Moisset

Many gardeners are developing a new concern for pollinators. They look for ways to help them. Aware that a perfectly manicured, pesticide-laden lawn is not good for pollinators they enthusiastically adopt a scattering of dandelions in the early spring.

This is certainly beneficial to pollinators. However some of the passionate claims that accompany this activity are somewhat exaggerated. It is not true that pollinators “need” dandelions. They would prefer other flowers if they had a chance.

Spicebush in bloom
© Beatriz Moisset
Spicebush and pollinator
© Beatriz Moisset
Before dandelions were introduced from Europe and before lawns became so rampant in our suburbs, early spring pollinators were faced with a smorgasbord of early spring flowers. Here is an incomplete list of the so-called spring ephemerals prevalent where I live, in the Mid-Atlantic region: spring beauty, trout lily, trillium, columbines, rue anemones, Dutchman's britches, bloodroot and bluebells. These and others can still be found in nature areas, although they have become extremely rare in gardens and parks. Perhaps even more important to early spring pollinators are a number of trees and shrubs, such as willows, maples (some, not all of them), serviceberry, sassafras, spicebush, redbud, and a little later, azaleas and dogwoods, just to name a few.

Spring beauty and spring beauty Andrena
© Beatriz Moisset
This assortment of flowering plants offers a rich and diverse diet to newly awakened queen bumble bees, early Andrena bees, and other bees and flies seeking pollen and nectar. Some pollinators are specialists on just one or a limited variety of flowers. The spring beauty Andrena, trout lily Andrena and several willow blossom devotees would look at dandelions in despair, not being able to make any use of them.

Trout lily, frequently visited
by the trout lily Andrena
© Beatriz Moisset
The biotic community described above not only nourishes early-riser pollinators but also provides food and habitat for local wildlife. For instance, the red maple serves as a host plant for more than 100 moth species, willows provide food for several hundred species of moths. In turn, these caterpillars nourish birds and other wildlife. By contrast a lawn with dandelions is an impoverished ecosystem with very limited ecological value, more similar to a refugee camp than to a healthy, lively community.

Azalea and its specialist
the azalea Andrena
© Beatriz Moisset
If the goal is to help pollinators we would reduce the size of the lawn and grow some of the plants mentioned above rather than simply allowing dandelions among the blades of grass.

Bloodroot and Red-necked False Blister Beetle
© Beatriz Moisset
Such a goal is hard to achieve for most gardeners and probably impossible or nearly impossible for many of them. So, reducing the use of pesticides and allowing dandelions, as well as a few other small lawn “weeds,” is a good decision. But anybody seriously committed to protecting, not just pollinators, but entire ecosystems would do well to take a look at other alternatives.

Bluebells and carpenter bee
© Beatriz Moisset

Dandelion and ants
© Beatriz Moisset