The Web of Life: 2014

Sunday, November 23, 2014

Food Chain in the Milkweed Patch

Common milkweed. © Beatriz Moisset

The common milkweed teems with life. Numerous insects feed on leaves, stems, and roots or sip nectar from their flowers. It is ironic that a plant so well protected by powerful toxins and sticky sap behaves like a magnet for a large assortment of creatures. The best known dependent of the common milkweed is the monarch butterfly, but there are many others that deserve our interest. Many species have found ways to overcome the defenses of this plant. They have developed resistance against the toxic cardenolides and methods to avoid the milky sap.

The herbivores are in turn eaten by other insects or spiders, which may fall prey to still other carnivores. It is worthwhile to examine one of these so called food chains or food webs.

Oleander aphids on common milkweed. © Beatriz Moisset

One milkweed feeder, the oleander aphid, has become incredibly common in recent years. This bright yellow-orange aphid was accidentally introduced in this country with oleander plants, widely used in ornamental gardening. It established itself successfully and became adapted to milkweeds. It multiplies in huge numbers near the end of the season. It can do so because females reproduce parthenogenetically, that is without help from males.

Parasitized or mummified aphids. One wasp left the corpse through a round hole. © Beatriz Moisset

This aphid has few enemies. One of them is a tiny parasitic wasp. The mother wasp lays one egg inside a growing aphid and the larva completes its entire life cycle inside the unfortunate host. By the end of the aphid's life, it becomes dark, rounded and dried up. We call that a mummy. The fully grown wasp cuts out a round hole and emerges ready to start parasitizing other members of the aphid colony. It isn't easy to see the wasps, but almost every aphid colony has some of these mummified bodies. So you know that the parasitic wasps have been around.

Parasitic wasp. © Beatriz Moisset

Lacewings, lady beetles and syrphid flies also feed on aphids. Their stories are worth telling but we'll let them be for now.

The food web does not end there. Not surprisingly, many predators visit the milkweed patch in search of animal food. Parasitic wasps seem to be a delicacy among some flies. I have found members of two different families of predatory flies dining on the wasps.

Robber fly (Taracticus octopunctatus) feeding on a parasitic wasp. © Beatriz Moisset

One is a member of the family of robber flies, Asilidae. The name describes the members of this family well. They are seen pouncing mercilessly on their prey. One of them is Taracticus octopunctatus (no common name), a slender, hunchbacked fly with large eyes.

Long-legged fly feeding on a parasitic wasp. © Beatriz Moisset

Another one is a longlegged fly, Condylostylus, a shiny metallic green fellow, with long skinny legs. Parasitic wasps are part of its menu.

I marvel about this food preference. Evidently, these flies look down on the most abundant food nearby, the aphids, and go for the far less common parasites. Perhaps, the latter have less cardenolides than the aphids and this is why the predatory flies prefer them as food.

Longlegged fly caught by a spider. © Beatriz Moisset

A second layer of predation is added to the one just described. A spider feeds on a longlegged fly. We can summarize this food chain this way:

Milkweedaphidparasitic wasppredatory flyspider

Will a bird sweep by and eat the spider? Will it in turn fall prey to a hawk or a snake? How many steps can be added to this food chain? Common milkweed feeds many members of the wild life directly and indirectly. The links of this food chain are numerous.

More on milkweed dependents and visitors

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Beginners Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2014

Monday, November 03, 2014

Wasps, Motherhood and Ultrasound

A slender wasp lands on a plant stem and starts gently tapping it with the tips of her thread-like long antennae. Tap-tap-tap, she goes up and down the stem. She may abandon her search and repeat the same process on another plant, and another. When she finally finds what she is looking for, the tapping becomes more pronounced and remains concentrated in a single spot. A Pimpla wasp is delicately built, glossy black with bright orange legs. Its body ends in a sword-like projection used for egg laying and called ovipositor. This is how we know she is a female. Her methodical activity is a preparation for motherhood.

At a hospital an expectant mother is having a sonogram of her fetus. The technician gets the equipment ready, applies gel to the mother's belly and runs a wand over it. The image of the baby inside the womb emerges in the monitor. The invisible becomes visible through the magic of ultrasound technology.

Ultrasound of a fetus. By Pacres. Flickr

These two unrelated events have something in common. The expectant wasp mother is also using ultrasound for the benefit of her progeny. The amazing thing is that she and her ancestors have been using this technology for millions of years. Even more amazing is that she carries all the needed equipment in her tiny body. One big difference is that she is not observing her unborn baby but locating the food her baby will need. Other wasps have an easier time. They hunt for caterpillars, which are relatively easy to find because they make noises when munching away. But a pupa remains perfectly still and requires special equipment to be detected.

The ultrasound equipment used to see a fetus inside the mother's womb consists of a machine that produces high-pitch vibrations, beyond human hearing, and a sensor, called a transducer, that collects and interprets the sounds bounced back from the mother's body, her placenta, and the little body curled up inside.

The Pimpla wasp vibrates her body in a special way, producing ultrasound waves which she transmits to the plant surface through her antennae. She absorbs the bounced back ultrasound through her legs where some tiny organs, called subgenual (below the knee) organs , collect information on the shape, size and location of its quarry. An image develops in her minuscule brain, an image similar to the ones we have all seen of unborn babies inside the womb. Now she knows exactly where to lay her egg.

She bends her abdomen and points the sharp ovipositor toward the hiding moth pupa. She inserts an egg on it and leaves. Her mission accomplished, she starts looking for other occult cocoons to lay more eggs on them.

We marvel about bats and dolphins using a similar process, echolocation. It is remarkable that a tiny insect can also use a version of this complicated technology.

AGRIS. Vibrational sounding by the pupal parasitoid Pimpla turionellae

REDIA. The Subgenual Organ in Pimpla turionellae

List of articles
Beginners Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2014

Sunday, August 17, 2014

Ladybugs, Praying Mantis, and other So-called Beneficials. Are They?

The native polished lady beetle, a good one

I recently published an article on ladybugs, better called lady beetles, in Native Plants and Wildlife Gardens. My purpose was to explain that not all lady beetles are beneficial. Unfortunately some are introduced species which disrupt the ecosystems, competing with and even killing some of the native ones.

Polished lady beetle larva (Cycloneda munda)

In writing the article and later reading people's responses, a more serious problem caught my attention. Companies that sell lady beetles are causing more damage than good. Well-intentioned gardeners buy them without realizing the consequences of introducing non-native lady beetles or the pests that they carry.

An invasion of Asian lady beetles. More trouble than they are worth

This led me to want to learn more about other bio-controls or biological pests controls being sold to unwary gardeners. I will be writing in the future about praying mantis and their commercialization. This seems to be a bigger problem than that of lady beetles. For now, just look at these pictures. More coming up later on.

Tenodera sinensis sinensis (Chinese Mantid)

Praying Mantises
Beginners Guide to Pollinators and Other Flower Visitors

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© Beatriz Moisset. 2013

Hidden Life on a Pear Tree

Bradford pear in bloom, attracting numerous pollinators

Spring finally arrived, although a little later than usual. At the end of April, the Bradford pear trees in front of the Abington Library were in full bloom, white clouds against a sapphire sky. Hordes of little bees eagerly visited the sweet flowers.

Pollinators were not the only visitors to the trees. Surprisingly, life was also present in places you wouldn't think to look at. A cluster of bright yellow dots in a bark's crevice caught my eye just by chance. Afterwards, I began to see many similar clusters, partially hidden by the bark's irregularities. I knew them as lady beetle eggs, so I wasn't surprised to see some adult lady beetles engaged in romance or in search of potential nurseries for their babies.

Lady beetle eggs

A solitary green aphid painstakingly climbed the tree trunk, probably in search of tender shoots to feed on its juices. What was it doing so far from its traditional food? Perhaps, it had fallen to the ground and, obstinately, was engaged in the arduous voyage back to distant branch tips.

I puzzled at the lady beetles' choice of egg-laying sites. The tree trunk may offer refuge for the eggs, but not food for the newborns. The tiny larvae would have a long way to go to find nutritious aphids. Perhaps, just like the lost aphid, they could manage the perilous trek successfully.

I visited the trees a week later. They were still blooming, although slightly past their peak. I looked for the lady beetle eggs and found many of the clusters still in place. Some had darkened, a sure sign that the larvae inside would soon emerge, hungry for aphids. Others had become food for unknown predators and were gone.

An incipient aphid colony

Once again, I wondered where they would find food and looked at the new growth, the clusters of flowers which were already beginning to leaf out. Aha! Just as I suspected, the green aphids were there, small colonies of young and adults, wingless and even some winged ones. I would have never noticed them if I hadn't suspected their presence because of the lady beetles.

Aphids have a way of multiplying at great speed. One female can produce many babies in a mere week and the babies start reproducing in an equally short time. The small colonies I observed would become huge by the time the new leaves reached full size. They would be numerous enough to damage the new growth.

Aphid in search of food

Would something keep the aphids in check? The mentioned lady beetles had their job cut out for them. But they would need lots of help and I was pleased to see other aphid enemies. I caught a glimpse of a parasitic wasp. These tiny wasps lay their eggs inside aphids and their larvae feed and kill their hosts in the process. Another great helper became apparent later on, on further observation. Some minute greenish grubs were thrashing about in the midst of the aphid colony. A syrphid fly had chosen this place to lay her eggs. The recently emerged blind and apparently helpless larvae were busy devouring their favorite food, juicy aphids. They grow fast on this nutritious diet and soon metamorphose into small flies, ready to lay more eggs.

Syrphid fly maggot feeding on aphids

The accidental sight of the lady beetle eggs led me to the related findings, aphids and their predators—an entire mini-ecosystem well hidden in bark cracks and flower clusters of a pear tree. A month later, I visited the trees again and found no traces of this entire food chain. The stems appeared too tough for the aphids; the winged ones had moved elsewhere. The lady beetles and other predators also took their leave in their perennial search for nourishment.

Aphids in the web of life

List of articles

Beginners Guide to Pollinators and Other Flower Visitors

Tuesday, March 18, 2014

You can help pollinators in your own garden

Plant a pollinator garden. Turn some of your lawn into a wildflower meadow. One major objection of gardeners, the fear of stings, doesn’t need to be a serious concern. Most native bees are quite different in this respect from honeybees and hornets; they hardly ever sting and if they do, it is very mild. In fact there are some, such as the Andrenids, that are incapable of doing so. Their stingers are too small to penetrate human skin.

Avoid pesticides or if you absolutely need to use them, inform yourself carefully about the specific pesticides that kill only the target species, rather than decimating many others unintentionally. Furthermore, avoiding pesticides may not be as bad as it sounds since nature has its own checks and balances and manages to keep most pests under control without resorting to pesticides. There are some cases in which use of pesticides backfires by destroying these checks and balances. Avoid herbicides also; they can be bad for pollinators. They either deprive them of food or poison them.

Plant native flowers, that is flowers that grow locally, not just native to the United States; these are best for pollinators. Some bees may be able to adapt to non-native plants, such as many fruit trees or some of the less fancy cultivars. But native pollinators and native plants have become mutually adapted through millions of years, so they make the perfect match in most cases.

Grow a variety of flowers that bloom through the seasons. This is good for native bees; fortunately this is also what most gardeners aspire to have in their gardens. However highly selected cultivars or those with doubled-flowers don’t take care of the needs of pollinators. In general they have lost all the cues that pollinators need, such as scent. In some cases, they have also lost the pollen or nectar and so they don’t provide any food to bees.

Plant the kind of lawn that provides habitat beneficial to bees. A perfectly manicured, pesticide saturated lawn is a desert to wildlife, including pollinators. Reducing the size of the lawn would benefit native pollinators. But it is also possible to have a lawn that is good for bees while being esthetically pleasing. As mentioned before, stay away from pesticides and herbicides as much as possible. Second, allow some small wildflowers; the look of your lawn may change as a result but it will continue to serve its purpose. Clover is great food for native bees; it also fixes nitrogen cutting down the need for fertilizers. Other small plants that benefit bees are ground speedwells (Veronica), wood sorrel (Oxalis acetosella), smartweeds or knotweeds (Polygonum), wild strawberries (Fragaria, several species), etc. Rather than calling them weeds we should call them grass companions or pollinator food.

Provide housing for bees. A simple bare spot here and there (no mulch or grass, just bare soil) may be enough for a few hard-working soil nesters. A sand pile may be even better. It bears repeating: There is no real need to worry about stings from solitary bees.

Dead logs or snags can supply housing for bees. You probably can’t have a dead tree on your property, but it is possible to keep a stump or a standing log and use it as an attractive planter; perhaps it will in turn provide housing for some little bees. Drilling holes on an old post or even a tree trunk would also make good nesting sites. They should be 3/32” to 3/8” in diameter and at least 4” deep.

Or you can make your own bee houses. It is possible and relatively easy to build one by following instructions posted in several websites. Or you can buy one; some resources listed below. I have discovered that watching the comings and goings of those busy mother bees can be as much fun as observing a bird house. Once again, stings don’t seem to be a real problem; I have had my face right in front of their houses and have even let them climb on my finger without any consequences.

Hollow tubes, just about the size of drinking straws, can also be used as bee nests. Some of the suppliers listed sell them. You can also tie up a bunch of hollow twigs, such as elderberry, or paper drinking straws (plastic ones are no good) together or pack them into a container such as a small milk or cream carton and place them horizontally. They should be closed at one end with the open end facing south or southeast. If you have trouble figuring out where the south is, step outside sometime between 10 AM and 1 PM and face the sun. That is how you want to place the nests. (See links below for instructions).

You can let some of your ornamental grasses stay all winter; they can be quite handsome and add variety to your winter landscape while providing nesting to your friendly native bees.

Helping the native bees would benefit us because of their invaluable services to the environment and to our gardens.

Resources
Ross, Edward S. (2003) Pollinator Conservation Handbook. The Xerces Society and The Bee Works. Portland, Oregon ISBN 0-9744475-0-1. (Bee gardens, bee houses, etc.)
The Xerces Society Guide (2011). Attracting Native Pollinators. Storey Publishing. ISBN 978-1-60342-695-4 (Everything you want to know about pollinators and their conservation)
Urban Bee Gardens. Berkeley University
Nests for Native Bees. The Xerces Society
Bee houses. National Wildlife Federation. (How to build a bee house)

Sellers of bee houses
Knox Cellars.
Mason bee homes.

List of articles
Beginners Guide to Pollinators and Other Flower Visitors

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