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What is this strange bug?
It swarms only on one certain plant with trumpet-shaped red flowers (in the picture the flowers are all shriveled and the leaves are in the foreground) and totally coats it until the bush dries up. It spreads very rapidly but only to this particular plant - will not touch any other. The bugs don't noticeably move, giving the impression that the whole bush has developed white fur.
Picture taken in Israel:
Here's a closeup of a single specimen (taken from one of the leaves in the foreground):
And it seems the plant is a hibiscus: http://homeguides.sfgate.com/hibiscus-leaf-87355.html
As indicated in @KarlKjer 's comment, this insect is a Pseudococcidae, or commonly known as Mealybugs. The exact species is difficult to find due to picture quality.
Mealybugs are insects in the family Pseudococcidae, unarmored scale insects found in moist, warm climates. Many species are considered pests as they feed on plant juices of greenhouse plants, house plants and subtropical trees and also act as a vector for several plant diseases.
Mealybugs occur in all parts of the world. Most occur naturally only in warmer parts, and get introduced into greenhouses and other buildings in cooler countries. It is unlikely that any live in the Arctic or Antarctic, except perhaps in buildings.
Considering that Mealybugs are found basically anywhere on Earth, it's not a surprise to have found them in Israel.
Mealybugs: A common pest of indoor plants
Plants moved indoors for the winter can be a source of insect pests such as mealybugs, so make sure to carefully inspect them.
Multiple life stages of mealybugs. Photo by John A. Weidhass, Virginia Polytechnic Institute and State University, Bugwood.org.
Prized orchids, citrus trees, jade plants and many other house plants are moved outside each summer where they benefit from better light conditions and decorate outdoor spaces. Once moved back indoors, plants can fall victim to outdoor pests that were brought into the house with them. Some pests become a challenge to manage indoors and often spread to other indoor plants. One of the hardest to control is the mealybug. It appears as a white, fuzzy substance found on leaves, tender shoots and in the crevices of branches. Like other house plant pests, many find their way indoors on plants they fed on during summer.
You may say, &ldquoWhat is the big deal? If this insect is such a problem, why did it not harm my plant outdoors?&rdquo Mealybugs may have not yet built up their numbers to where damage would be noticeable. Outdoors predators and parasites may help keep mealybug populations low. Indoors, without predators and parasites, pest populations can quickly develop and damage plants that we have grown for years.
I was given a jade plant that had been grown outdoors during the summer months. The plant looked great. After a few weeks indoors, I noticed small, whitish creatures moving on the branches. Mealybugs! The adult mealybug is about 0.1875 inch long and covered with a white waxy covering.
This insect damages plants by inserting a feeding tube into plant tissue to feed on the sugary sap. Large numbers of mealybugs weaken the plant and may even kill it. A shiny, sticky sap called honeydew is commonly found on branches and leaves where the insect feeds. This shiny, sugary waste from the insect is also a clue that there are sucking insects on the plant.
Ridding your plants of mealybugs is not an easy task. They thrive in crevices between branches in the interior of the plant where it is hard to spray them. Another issue is that one female can lay up to 600 eggs, quickly expanding their population. Once mealybugs are found on a plant, it needs to be isolated from other plants to prevent the infestation from spreading.
The amount of insects on the plant determines your next step. In some cases, the population may be too high and the better choice may be to discard the plant. With smaller infestations, Michigan State University Extension advises using a cotton swab dipped in alcohol on individual insects, but care must be taken to dab it on the insect and not the plant to prevent damage to plant tissue.
If you choose to spray with an insecticide, make sure it is labeled for indoor use. There are a number of pesticides that can be used to treat for mealybugs. Read labels carefully to see if there are lists of plants that can be harmed by specific products. A good article from the University of Minnesota Extension on pesticides for indoor plants can be found at &ldquoHouseplant insect control.&rdquo
The jade plant I treated for mealybugs survived for years, but was never totally free of the pest. It is likely I was not controlling the egg stage. I would not see any insects for long periods, but I&rsquod find them back a few months later. I decided to take a number of cuttings from the new growth and start the plant over. The new growth was free of the insect and from it I was able to grow new plants that were free of the mealybug.
The take-home message is to inspect plants carefully when bringing them back indoors. Continue to monitor them through winter to prevent spread of unwanted pests in your indoor garden. If you do find a pest like a mealybug, isolate the plant right away and determine treatment options, potential for taking clean cuttings to propagate the plant, or whether to replace the plant. This will insure a healthy indoor garden and plants that last generations.
Katja Schulz / Wikimedia Commons / CC by 2.0
Borers are an insidious pest, destroying your flowering plants from the inside out.
The worst borer in the flower garden is the iris borer, which will tunnel through an entire iris rhizome, leaving bacterial rot in its wake. You should be suspicious if you notice sawdust material around the base of your irises or ragged leaf margins. Pinprick holes in the leaves of iris are the signs of tiny caterpillars that have infiltrated the leaves and are making their way down into the rhizomes.
- Discourage borers by removing iris leaves in the fall, which provide a host for borer moth eggs.
- In the spring, you can apply the systemic pesticide Merit or the nontoxic spray Garden Shield.
- The best non-toxic control is to dig up affected plants after flowering is done, trim out the rotten rhizomes, and replant the good portions.
Distribution and Biology
Both types are found throughout the continental US, and the large yellow ant is exceptionally abundant on the East Coast.
Citronellas live underground and act like little farmers. They tend aphids and mealybugs that live on plant roots.
What do they get out of this? These insects secrete sugar, which is called honeydew, and the ants feed on this.
Fortunately, citronellas have no interest in human food.
Types of houseplant bugs
The warm, consistent temperature of most homes is ideal for rapid pest breeding. Plus, without ladybugs, parasitic wasps, and other beneficial insects in your home to keep pests in check, houseplant insect pests can go from numbering just a few to an all-out infestation in no time flat. Here are five of the most common types of houseplant bugs and what to do about them.
Adult fungus gnats are super annoying. These minuscule black flies are the classic example of a nuisance pest. When an infested plant is disturbed, a cloud of tiny flies lifts off the soil. Mature gnats life for about a week, and although they’re a pain, they don’t damage your plants. Neither do the larvae, who largely feed on the fungi that naturally grows in potting soil. Because the eggs and larvae need water to survive, fungus gnat infestations are frequently the result of overwatering. A simple reduction in watering is often all that’s needed to control this common houseplant pest. But, if that doesn’t do the trick, a product like Gnatnix will definitely take care of the problem.
Another of the more common types of houseplant bugs, scale is sometimes difficult to spot. There are many different species, each with a unique appearance, but the most common houseplant pest scales look like little bumps and are found along the stems and on leaf undersides. Scale insects often have a hard, shell-like covering that makes them difficult to spot and control. They can be gray, black, brown, or even fuzzy. Most scales leave behind the honeydew I mentioned above, so if you see a shiny glaze on the plant, check it for scale. When it comes to houseplant bug problems, scale is probably the most difficult to control. I like to wipe them off my plants with a special cotton pad (like these) soaked in isopropyl rubbing alcohol. Physically wiping the pest off the plant multiple times over the course of a few weeks offers the best control. But, another option is to use an organic, neem-based pesticide. Take the plant into a garage or outdoors to apply it, and be sure to follow label instructions.
This common houseplant pest does not survive freezing winter temperatures, so it’s typically troublesome outdoors only in southern regions. But, whiteflies are one of the most problematic types of houseplant bugs because when they’re indoors, the insects are protected from freezing temperatures and their populations can grow quite rapidly. Whitefly issues frequently originate via a plant purchased at an infested greenhouse, which makes a careful inspection of any new plants extra important. These tiny, white, moth-like flies are found on leaf undersides and will quickly fly off the plant when it’s disturbed. Since whitefly reproduce so rapidly, their sap-sucking behavior can leave plants wilted, and with stunted growth and yellow foliage. Whiteflies are readily trapped by placing yellow sticky cards just above plant tops. Applications of insecticidal soap and horticultural oil are also effective. Since all three of these products work best when they contact the insect pest directly, try not to disturb the plant when applying, and be sure to cover both upper and lower leaf surfaces.
Though they’re small in size, aphids can cause big problems. Of all the types of houseplant bugs discussed here, aphids are the ones I encounter the most frequently on my own houseplants. Tiny and teardrop-shaped, aphids can be black, green, red, yellow, or brown. Sometimes they have wings and sometimes they don’t, but they’re most often found grouped together on new growth or on the undersides of leaves. As they suck plant sap through their needle-like mouthparts, aphids cause deformed and stunted plant growth. Small infestations are easily wiped off of plants with a soft, plant-friendly cloth soaked in water, but as with all types of houseplant bugs, when there’s a big infestation, other measures may be warranted. Aphids can also be controlled organically with hot pepper wax, horticultural oil, or insecticidal soap. Be sure to apply these products so they come in direct contact with the aphids themselves for the best results.
There are many types of houseplant bugs, but spider mites may just be the ones with the biggest “heebie jeebie” factor. Actually, these guys aren’t bugs at all. Instead, they’re close relatives of spiders. These teeny-tiny houseplant pests cause major issues, not just for plants but also for the homeowner facing the infestation. Though you can barely see them without the help of a magnifying glass, once you know they’re in your house, it’s hard to get them off your mind. Spider mites spin a fine, silky webbing, and collectively, they can cover the entire plant with it. If you look carefully, you’ll see tiny specks crawling around on the webbing those are the mites themselves. But, before you toss your spider mite-infested ivy or palm plant into the garbage, there are a few steps you can take to get this common houseplant pest in check. First, take the plant outdoors or into the shower and “wash” it off with a spray of water. Spider mites are tiny and are easily washed off the plant. Be sure to rinse both upper and lower leaf surfaces. Then, after the plant has fully dried, use a light-weight horticultural oil to smother them. Reapply the horticultural oil every 10-14 days for two more applications for the best control.
Though there are a handful of other indoor plant pests that may occasionally prove problematic, these five types of houseplant bugs are by far the most common. But, by following the five preventative steps featured at the beginning of this article and using the suggested mechanical and organic product controls, you’ll be able to keep most of these little buggers from causing any real issues.
Remember, arming yourself with a little information goes a long way toward growing healthy, pest-free houseplants. Be smart about your choice of plants. For apartment dwellers, our list of the best houseplants for small spaces offers plenty of great plant choices. Healthy houseplants are better able to fend off pests, too. We’re sure you’ll find our guide to houseplant fertilizer basics very useful, too.
Furry Bug that swarms only certain plant - Biology
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CCSS: Reading Informational Text: 2
TEKS: 6.2E, 6.12D, 7.13A, 8.11B, B.12E, E.4D
Billions of flying bugs have swarmed parts of Africa and Asia, destroying any crops in their path. Can they be stopped?
AS YOU READ, THINK ABOUT how the rapid growth of an organism’s population can affect an ecosystem.
In 2018, a population of winged insects called desert locusts suddenly exploded in an isolated region of the vast Arabian Desert in western Asia. Storms had soaked the normally dry area with rain, causing plants to grow. With plentiful food available, the locusts began to breed. It was a disaster in the making for the people living in the region.
Monstrous swarms of locusts can contain billions of the insects and stretch over hundreds of miles. When these huge groups take flight, they sweep across an area and devour any vegetation in sight. A relatively small swarm of 40 million desert locusts can eat the same amount of food in a day that 35,000 people consume. These ravenous insects can destroy a whole season’s crop in a single morning—spelling serious trouble for farmers.
In 2018, a population of flying insects called desert locusts suddenly exploded. The bugs were living in part of the vast Arabian Desert in western Asia. Heavy rains had soaked the normally dry area. That caused plants to grow. With plenty of food to eat, the locusts began to breed. It was a disaster in the making for the region’s people.
Giant swarms of locusts can contain billions of insects. The swarms can stretch over hundreds of miles. When these huge groups take flight, they eat any plants in their path. A relatively small swarm might contain 40 million locusts. They can eat the same amount of food in a day as 35,000 people. These hungry bugs can destroy a whole season’s crop in one morning. That spells big trouble for farmers.
ISAK AMIN/ARETE/FAO SOMALIA
CREEPY CRAWLY: Locusts can grow up to four inches long and normally live for three to five months.
Keith Cressman is a locust forecasting expert at the United Nations’ Food and Agriculture Organization, based in Rome, Italy. He had been monitoring the unusual rain in the Arabian Desert and had a hunch a massive locust invasion was on the horizon. “We started to see waves and waves of locust swarms fly out of that remote area into the neighboring countries of Yemen and Saudi Arabia,” says Cressman. “That’s when I knew something really bad had happened.”
Throughout 2019 and 2020, swarms erupted from the Arabian Desert and descended upon the Middle East, spreading southwest into Africa and as far east as India and Pakistan (see Spreading Swarms). Back-to-back seasons of heavy rain have fueled these continuous swarms, leading to the largest locust invasion in decades. If the swarms continue, they stand to threaten the food supply of millions of people and the livelihoods of 10 percent of the world’s population.
Keith Cressman is a locust forecasting expert. He works at the United Nations Food and Agriculture Organization, based in Rome, Italy. He had been monitoring the unusual rain in the Arabian Desert. And he had a hunch a big locust invasion was coming. “We started to see waves and waves of locust swarms fly out of that remote area into the neighboring countries of Yemen and Saudi Arabia,” says Cressman. “That’s when I knew something really bad had happened.”
Throughout 2019 and 2020, swarms erupted from the Arabian Desert. They descended on the Middle East, spreading southwest into Africa. They went as far east as India and Pakistan (see Spreading Swarms). Back-to-back seasons of heavy rain have kept these swarms going nonstop. They’ve led to the largest locust invasion in decades. If the swarms continue, they could threaten the food supply of millions of people. And they could affect the income of 10 percent of the world’s people.
Locust swarms don’t happen often. In fact, they occur only when the insects undergo a remarkable transformation. In small numbers, locusts are harmless, says Hojun Song, an entomologist, or insect scientist, at Texas A&M University. The bugs don’t move around much and mostly avoid one another. Scientists call this the locusts’ solitary phase (see Locust Life Cycle).
But when locust populations start to grow in response to changing conditions in their environment, like they did in the Arabian Desert in 2018, the insects go through a dramatic change. Their colors shift from dark green to bright yellow and black. The insects also group together and become more active. When a locust transforms, “It’s like the Hulk,” says Song. The insects enter a gregarious, or social, phase. They form swarms with a single purpose: finding food.
Locust swarms don’t happen often. They occur only when the insects go through a big change. In small numbers, locusts are harmless, says Hojun Song. He’s an entomologist, or insect scientist, at Texas A&M University. The bugs don’t move around much. They mostly avoid one another. Scientists call this the locusts’ solitary phase (see Locust Life Cycle).
When changes in the environment cause locust populations to grow, the insects change. Their colors shift from dark green to bright yellow and black. The bugs also group together. And they become more active. When a locust transforms, “It’s like the Hulk,” says Song. Scientists call this the gregarious, or social, phase. Locusts form swarms with one goal: finding food. That’s what happened in the Arabian Desert in 2018.
This map shows the location of locust swarms—each containing billions of insects—across Africa and Asia as of September 2020.
This map shows the location of locust swarms—each containing billions of insects—across Africa and Asia as of September 2020.
This map shows the location of locust swarms—each containing billions of insects—across Africa and Asia as of September 2020.
For thousands of years, no one realized that green solitary locusts and yellow gregarious locusts were the same species. A Russian scientist named Boris Uvarov made the discovery in 1920, when he raised locusts in two different environments: alone or crowded in cages. When by themselves, the locusts stayed calm and docile. But when packed together, they switched to their destructive black-and-yellow form.
This ability to transform is an adaptation that helps locusts survive in a harsh desert environment where food is often scarce. Grouping into a fast-moving and determined swarm gives them a better chance of locating something to eat. This adaptation is good for the insects but bad for people.
For thousands of years, no one realized that green locusts and yellow locusts were the same species. A Russian scientist named Boris Uvarov made the discovery in 1920. He raised locusts in two different environments. Some lived alone. Others were crowded in cages. When they were by themselves, the locusts stayed calm and green. But when packed together, they switched to their destructive black-and-yellow form.
This ability to transform is an adaptation. It helps locusts survive in a harsh desert environment where food is scarce. Grouping into a fast-moving swarm gives them a better chance of finding something to eat. This adaptation is good for the insects. But it’s bad for people.
VISHAL BHATNAGAR/NURPHOTO VIA GETTY IMAGES
INSECT INVASION: Swarms of locusts descend on the city of Jaipur, in India.
The best way to stop swarms is to detect locust-breeding hot spots early. Then measures can be taken to reduce the number of insects before their population grows out of control. That’s why locust forecasters like Cressman work to predict where outbreaks will occur. He gathers information about Earth’s surface using satellite images—a technique called remote sensing. In particular, he looks at images taken with cameras that detect green wavelengths of light. These colors indicate the presence of plants. Patches of green in the desert, for example, are warning signs of impending locust booms.
That’s what Cressman saw in the Arabian Desert in 2018. But because the region was so hard to reach, it was difficult for locust survey teams to respond quickly. When a team arrived to assess the situation almost nine months later, it was too late—the swarms were already on the move. Now, says Cressman, the goal is to minimize the destruction caused by the locusts until drier weather returns. Then the insect numbers will die down naturally.
The best way to stop swarms is to find places where the locust population is growing. Then people can try to reduce the bugs’ numbers before they grow out of control. That’s why locust forecasters like Cressman work to predict where outbreaks will happen. He gathers information about Earth’s surface using satellite images. It’s a method called remote sensing. He looks at images taken with cameras that detect green light. These colors show where plants are growing. Patches of green in the desert are warning signs of locust booms coming soon.
That’s what Cressman saw in the Arabian Desert in 2018. But the region is hard to reach. So it was difficult for survey teams to respond quickly. When people arrived to check on the situation almost nine months later, it was too late. The swarms were already on the move. Now, says Cressman, the goal is to minimize the destruction the locusts can cause. When the weather gets drier, the insect numbers will drop again.
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Why Locusts Abandon A Solitary Life For The Swarm
By applying an old theory that has been used to explain water flow through soil and the spread of forest fires, researchers may have an answer to a perplexing ecological and evolutionary problem: why locusts switch from an innocuous, solitary lifestyle to form massive swarms that can devastate crops and strip fields bare.
Their report, published online on December 18th in Current Biology, a Cell Press publication, concludes that once the insects' ranks grow to a certain threshold size, banding together prevents predators from moving from one patch of insects to the next and easily picking the bugs off one by one.
"A predator can only move continually across a landscape, consuming locusts as it goes, if there is a landscape-spanning pathway of connected, high-yielding patches containing locusts in abundance," said Andy Reynolds of Rothamsted Research. "If the locusts were to remain dispersed when their numbers become sufficiently high, then such predator-sustaining pathways would always exist. By grouping together, locusts can reduce the number of connections between patches, and there is a significant probability that the predator will locate too few locusts to sustain itself."
Locusts are a notorious outbreak pest, with the ability to increase sharply in abundance when conditions are right. They've also been of interest because of their remarkable ability to shift from a cryptic, solitary state to form migratory bands when their numbers grow. At such times, the insects not only behave differently, but the two "phases" also differ from each other in their physiology, color, shape, and many other traits&mdashso much so that the phases were sometimes thought to be completely different species.
Despite the interest, scientists had no satisfactory explanation for the evolution of this behavior. Until now, that is.
In the new study, the researchers applied percolation theory&mdashthe study of how randomly generated clusters connect and behave&mdashto the problem. The theory, so named from the way in which coffee flows through a percolator, is known to play a fundamental role in a diverse range of disorderly physical phenomena, but it had received rather little attention in ecological quarters, Reynolds said. Using the theory, they now show that it would be highly disadvantageous for individual locusts to continue indefinitely in a dispersed distribution as their population explodes. That's because the switch to a swarm disrupts the connections in the predators' network of tempting food patches.
The finding suggests that selection pressure from predators has been a key factor in driving the evolution of the insects' gregarious tendencies. And, they said, the theory will no doubt apply to other species and circumstances as well.
"We suspect that for any natural enemy that exploits patches of hosts, percolation theory warrants consideration as a generally applicable model underlying the ecology and evolution of aggregative behavior," Reynolds said. "For example, aggregation behaviors may have evolved in insects as an anti-parasite defense mechanism because by aggregating in groups, there is a greater probability that a parasite or pathogen will fail to breach the gap between infectious hosts."
The researchers include Andy M. Reynolds, Rothamsted Research, Harpenden, Hertfordshire, UK Gregory A. Sword, The University of Sydney, Sydney, Australia Stephen J. Simpson, The University of Sydney, Sydney, Australia and Don R. Reynolds, University of Greenwich, Kent, UK Rothamsted Research, Harpenden, Hertfordshire, UK.
Materials provided by Cell Press. Note: Content may be edited for style and length.
Furry Bug that swarms only certain plant - Biology
'Hairy' Insects and Spiders
Spurs, Spines, Setae, and Sensilla.
by Ray Dessy, Blacksburg, VA USA
ABSTRACT: As mammals with mammalian friends, we are familiar with hair, fur, eye-lashes, beards, coats, manes and tails. We seldom recognize the similar projections that some arthropods possess, unless we look carefully. This article illustrates some of these analogs, and discusses their functions. It was prompted by noticing the many “hairs” on specimens that I had previously just ignored.
US AND THEM : Like many parts of our anatomy, we mentally dump those small diameter strands of protein that occur all over our body into a basket called “hair”. We know that some keep on growing longer, some stop at a certain length, patches may fall out and cease to exist entirely, or we remove them by shaving or chemical means. Our pets, farm animals, and wilder neighbors possess these valuable small protein rods or tubes and use them for coats in winter, shedding them in summer have several different types and colors in their seasonal clothes create manes and tails which often continue to grow form whiskers that are used to detect objects and employ the ensemble for protection against abrasive skin damage and insect attacks. But insects! They are different, they are not like us! Well, maybe. Let us inquire. Arthropods have hair-like structures call setae. Photos 1-21 illustrate the points made in the following paragraphs. (In what immediately follows an older, simpler entomology anatomy is used. Where possible, terms that are not used subsequently appear as [ italics ] items.)
Cuticula and Chitin : One can detect, more or less, three distinct layers in the insect body wall. There is an outer protecting layer, the cuticula an intermediate cellular layer, the hypodermis and an inner delicate membranous layer called the basement membrane. The hypodermis is a living part of the body-wall. Certain of these cells become specialized and produce hollow hair-like organs which remain connected through pores in the cuticula. These specialized cells are called trichogen. 1 Outside of the hypodermis is a firm layer that serves as a support for the internal organs, and protects the body. (Fig. A) The larger portion of this cuticula is formed from chitin, a horn like substance. Chitin is a polymer of 2-acetylaminoglucose a glucose molecule where the hydroxyl (HO-) group on carbon #2 is replaced by an acetylamino [CH 3 CONH-] group. (Fig. B) Chitin was used by trilobites as a refracting interface to correct for the spherical aberration of the calcite-like dome lenses in its compound eyes. Chitin is often cited as the lenses of the compound eyes of Dipteran insects like the house-fly. And aminoglycan polymers occur in mammalian eyes, and are used for ophthalmologic purposes. Chitin forms the protective sheath in beetles, and the cuticula of other arthropods. Chitin even is used in the development of powerful teeth in some arthropods. The mandibles of a few beetles have a Mohs scale hardness of
3, like calcite crystals, and they can chew on soft metals like lead, tin or copper. Chitin occurs in both flexible transparent or translucent forms, and a hard, dark rigid form. Protein components are often linked together by quininone copolymer linkages, resulting in a “tanned” brown material. Chitin is oriented in such a way that insect exoskeleton fragments show little birefringence. The chitin is laid down in parallel microfibers forming a sheet, and each successive sheet has its fibers on a bias with the previous layer. The muscles in your abdomen are similarly biased, since it gives added strength, just like biased layering in rubber tires. When flexibility is required, as in wing hinges or leg joints, an elastic rubber-like material involving coiled protein chains is present. The epidermis is the location of cuticular pigments. (Photo 1)
Figure A Body wall, diagrammatic cross sectional structures
Figures adapted from Introduction to Entomology, J. Comstock, 9 th Ed., 1940
Figure B 2-acetylaminoglucose, building block of chitin
light blue=carbon, dark blue=nitrogen, red=oxygen, white=hydrogen
Photo #1 beetle- chitin tanned sheath
PROTUBERANCES : The outer surface of the cuticle presents a magnificent variety of projections. Some are connected to the cuticula by a joint. Others form an integral part of the cuticula. Large projections are termed spines. These are of multicellular origin. Appendages on the legs of insects, but joint connected, are called spurs. The wings of some insects, like the Lepidoptra, also present large numbers of structures, in addition to normal setae, which are spatulate, or scale-like in shape, and are often highly colored.
Setae might be referred to as insect “hair”. Some deer’s hairs are hollow for insulation. Setae are also hollow, and associated with one single cell- the trichogen. Setae serve many purposes. There may be gland cells opening into the setae, or a nerve may extend into the hollow shaft, forming a sensory device—a sensillum (pl. sensilla). (Fig. C) In such cases the trichogen cell grows the conical hair, another cell [ tormogen ] grows the socket. A sensory neuron cell grows a dendrite into the hair and an axon extends inwardly to form a nerve connected to the central nervous system. Imagine a root canal on many of these on your next trip to the endodontist. In tactile structures the setae are relatively long. For taste, smell, temperature or other sensing they may appear as pegs, pits, buttons, or cones and often several neurons and their dendrites/axons are present. The setae can also serve as chemical weapons, and let insects walk on water. Some of the setae serve merely as “clothing hairs”. The setae may be birefringent. The birefringence of insect setae is never as high as in cellulose plants, but it is higher than in the exoskeleton fragments.” 2 (Photos 2-5)
Figure C Basic diagrammatic sensing structure
Photo #2 setae
Photo #3 setae foreleg
Photo #4 setae tibia, tarsus
Photo #5 tibia spines, foot-tarsomeres, setae, claw
Setae nerve polarization and depolarization, works like ours— that is, action potentials are generated in the dendrite (input side of a neuron), depolarization travels along the length of the nerve, and output sent along an axon (output side of a neuron). Depolarization causes neurotransmitters to be released into the connection [ synapse ] between the axon and dendrite. Common insect neurotransmitters include molecules [ acetylcholine and catecholamines, like dopamine ] that are used in human neurotransmision. Many pesticides act by interfering with the functioning of the nervous system neurotransmitters. The fundamental difference between invertebrate and vertebrate nervous systems is the number of cells: insects may have half a million neurons, while vertebrates may have 10 billion or more.
Grasshoppers, LOCUSTS AND CICADAS : The hind femur of the grasshopper is the enlarged jumping spring of the hindlegs. The hind tibia has two rows of spines and as many as six enlarged movable spurs at its apex. Note that a spur is inserted into a socket and is movable while a spine lacks a socket and is fixed. Stimulation of a single prominent sensillum (sensing appendage) on the hind foot [ tarsus ] of different species of locusts can activate the fast extensor tibiae muscle. The grooming reflex of the locust's front leg is mediated by hair sensilla of the sternum region. These hairs are
50-200 um in length. Studies of electrical nerve pulse propagation after manual stimulation of an insect setae by touch of just a single human hair have been made. 3 (Photos 6,7)
Photo #6 grasshopper- spines
Photo #7 cicada- transparent-wing, spines, spurs
Butterflies AND MOTHS : In moths the adult uses its thoracic legs for several types of behavior not displayed by the larva. These include walking with an alternating gait, grooming the antennae and mouthparts, landing on a substrate after flight, perching on a leaf during oviposition, and more subtle behaviors such as "tasting" the leaves of a host-plant. The adult leg has new structures such as tibial spurs on the thoracic legs. The tibial spurs on these legs contain scalelike tactile hairs, and chemosensory sensilla. 4
In butterfly larvae, tactile setae are scattered fairly evenly over the whole body. You can see these setae on Monarch larvae with a simple magnifying lens. Larvae have a variety of responses to touch, like coiling into a tight spiral. Adults have tactile setae on almost all of their body parts. The setae play an important role in helping the butterfly sense the relative position of its many body parts (e.g., where is the second segment of the thorax in relation to the third segment). This is especially important for flight, and there are several collections of specialized setae and nerves that help the adult sense wind, temperature, and the position of head, body, wings, legs, antennae, and other body parts. 5 The fringes or “feathering” on insect wings also help aid flight. (Photos 8-15)
Photo #8 butterflies- wings, veins, scales
Photo #9 moth- wing, scales
Photo #10 transparent-wing, setae, veins
Photo #11 moth- wing, veins, scales
Photo #12 butterfly- wing, scales, color
Photo #13 butterfly- wing spatulate scales
Photo #14 moth-antennae
Photo #15 moth- wing “feathered” edge, antennae
In some cases, like butterflies, setae and vein structures strengthen the wings. Butterfly and moth scales themselves are modified setae, overlapping pieces of chitin. Butterfly wings are made of two chitonous layers (membranes) that are nourished and supported by tubular veins. The veins also function in oxygen exchange ("breathing"). Covering the wings are thousands of the colorful scales, together with many normal hairs (setae). The name Lepidoptera (which includes butterflies and moths) means "scale wing" in Greek. The colour of the Eurema lisa butterfly originates from light diffraction. The bright colour of the Morpho butterfly originates from light interference and diffraction, and the blue colour of the Polyommatus daphnis is caused by photonic crystal effects. A beautiful TEM and SEM study of some butterflies has recently appeared. 6 The scales are usually arranged regularly from the front to the end of the wing just like the tiles on the roof. The scales are all tilted and have the same angle to the wing plane. Each single scale is likes a tiny shield with 50 to 80 um width and 150 to 200 um length. Our optical microscopes can hint at their beauty.
Multidendritic sensilla occur in antennae. A male silkworm moth has
17,000 sensilla, each containing up to 3000 pores, 10-15 nanometers in diameter. Less than a hundred sex pheromone molecules could initiate an upwind behavioral response. Human fashion perfumes and noses just cannot compete.
Caterpillars : Caterpillars sense touch through tiny hairs (setae) that are all over the caterpillar's body. These tactile hairs often grow through holes in the dark, flattened plates on a caterpillar's body. These hairs are attached to nerve cells, and relay information about touch to the insect's brain. (Photos 16-18)
Photo #16 larva- setae
Photo #17 caterpillar- setae
Photo #18 caterpillar- setae
But caterpillar setae are also the source of defensive mechanisms. Some involve chemical toxicity, while others are “cloaking” in nature, making it difficult for parasites or predators to deposit, inject or attack. Recently a new effect has been seen in Mare Reproductive Loss Syndrome (MRLS). Having an interest in breeding horses, it is noted that our neighboring state of Kentucky has reported 60% or higher early loss of foals after birth. Losses in the vicinity of $400,000 occurred. Studies showed that the losses resulted from ingestion by the pregnant mares of Eastern Tent Caterpillar bodies. Autoclaved caterpillars did not result in MRLS, but frozen specimens did. The white, dense “tent” material had no effect. The foals died of bacterial infection associated with co-habiting [ commensal ] organisms that occur in the mares mouth and GI tract.
One current explanation is that the hollow setae serve as well-protected hypodermic syringes that penetrate the gums and intestinal wall of the mare, and migrate to receptive sites like the uterus, with the bacteria lodged in the lumen of the setae shielded from normal antibody reactions. Although the “Septic Penetrating Setae” hypothesis has yet to be experimentally confirmed, many people are also affected by irritation and allergic responses due to handling caterpillars indiscriminately. 7 Handling hay on hot summer days is prickly too.
Spiders, Setae, and Prey : Setae in spiders certainly are used to provide a sense of touch, and they are involved in proprioception. The latter allows an animal to determine where its various body parts are deployed during movement. Is this important? Years ago, before a visiting lecture, a colleague asked me to taste a leaf—deliberately neglecting to tell me that it anesthetized the proprioceptors of the tongue. Try talking when you don’t know the shape and position of your tongue. Beautiful arachnid setae SEM photos are available 8 , but optical microscopy can reveal some of their secrets. (Photos 19, 20)
Photo #19 orb-spider- limb setae
Photo #20 spider- body, leg setae
A fascinating WMD (weapons of mass destruction) story surrounds the size, shape and positioning of insect setae, compared to the nature of the web of preying spiders. Some of the latter are “primitive” and consist of fibril populated threads with thousands of fibrils that are
20 nm in diameter. They can entangle setae temporarily, allowing the quick spider to gain its prey. Other webs have viscous sticky droplets periodically arrayed on the thread, with different species having droplet volumes that range from 0.1-10 um 3 , and with 25 to 5 drops/mm. “The volume of viscous material per mm of thread length differed by as much as 22-fold among the four spider species’ threads studied. The length of setae on the four insect surfaces studied differed by as much as 230-fold and their densities by as much as 7170-fold. …
The study showed that the surface features of an insect body determine how much of a capture thread's potential adhesion contributes to insect retention. This operational thread adhesion combines with features of web architecture, such as capture-spiral spacing, and with a spider’s running speed and mode of prey immobilization, to determine how securely insects are held by a web and which are most likely to be captured by a spider.” 9 The positioning angle and shape of its setae can determine the destruction or survival of the insect. Many publications focus on the combination of van der Waals’ forces and capillary attraction forces in any adhesion process. The van der Waals’ forces arise when molecular entities come into close proximity, and the charges of one molecule are attracted by charges in the other. These are weak forces, but if there are large numbers of liaisons and enforced intimacy the result can be significant. Capillary attraction is associated with the surface tension of water and the wet-ability of the surfaces. Cohesion can be formidable. If you have a hot/cold faucet with just one control handle it may involve two finely polished ceramic disks mounted concentrically on a rod with each disk having holes along a radius. A very thin water layer between the disks can create sufficient capillary adhesion to withstand the pressure of the water mains and keep the faucet from dripping. Pulling the disks apart manually requires strong muscles. Viscous threads seem to need a relative humidity of
45% for this effect to be active. The nature of the glycoproteins in the droplet is also important.
Walking on the Ceiling, Walking on Water : The feet of some insects, and hunting spiders, are often covered with setae that branch out into smaller fibers [ setules ]. With miniscule van der Waals’ forces acting on large numbers of these small fibers on each furry seta, an arthropod can hang and walk upside down on a leaf or a wall with ease. Capillary adhesion is also usually invoked. The gecko is often mentioned in association with these phenomena. Every square millimeter of a gecko's footpad contains about 14,000 hair-like setae. Each seta has a diameter of 5 microns. Each seta is in turn tipped with between 100 and 1,000 spatular fibers. Each spatula is 0.2 microns long, or near the wavelength of visible light. Recent publications suggest that van der Waals’ forces and capillary adhesion are involved. 10 You decide between the rivalry! Someday you might buy rolls of “Gecko Tape” since engineers would like robots that can climb walls.
Setae also aid some aquatic insects in locomotion and enable them to “walk on water”. Many “brushlegged” caenid larvae have extremely long and profuse hairlike setae present on the legs 11 . Yet the adults swarm in hordes and lie, dead, floating flat in our horse trough. But butterflies somehow avoid sticking of their wings and water striders float and move on a water surface. “The natural super-hydrophobic surfaces generally have three common features: (a) they are coated by wax or a hydrophobic film (b) they are decorated by textures such as bumps, pillars, or grooves at a scale of typically a few micrometers and (c) they have a secondary texture superposed on the first one at the nanometer scale. Besides surface chemistry, the surface roughness and geometry have a crucial role in affecting the super-hydrophobicity. Recent studies suggest that the super-hydrophobic property of the water strider’s legs is due to the long inclining spindly cone-shaped setae at the surface.” 12 First, the air trapped in the cavities and texture features of the super-hydrophobic surfaces can provide extra buoyancy forces, which can reduce the apparent density of a water strider to 0.71 g/cm 3 in water. 13 Second, t he water strider leg owes its hydrophobicity to its complex surface cover of hairs coated with water-repellant cuticle wax and contoured with fine fluted nanogrooves. 14 Water-walking insects [ e.g., Microvelia and Mesovelia ] generally keep three legs on the water surface at all times in order to maintain static stability. The exception is the water strider, which generally keeps its pairs of front and hind leg tips on the water surface while its middle legs row. ( Photo 21) In this photograph the circular dark shadows on the stream bottom are consistent with the divergent lensing effect of the dimples created in the water surface by the insect’s super-hydrophobic feet. 15
Photo #21 water-strider- “feet-shadows” on stream bed
( Consistent with divergent lens images from water-surface dimpling )
And some insects use chemical propulsion. This means of propulsion [ Marangoni Propulsion ] is used as an escape mechanism by a number of water-walking insects, as well as beetles and terrestrial insects that accidentally fall onto the water surface. They release a lipid that reduces the surface tension behind them, propelling themselves forward at peak speeds of the order of 20 cm/sec.. 16 When a pine needle falls into a lake or pond, it is similarly propelled across the surface since the resin at its base decreases the local surface tension. Imagine fabrics that are super-hydrophobic, or something that you could paint on your feet to make swimming easier. Unfortunately, humans are too heavy, and the Olympics’ Committee would forbid it.
Insects created a nano-world first, and imagined a “better living through chemistry” long before we began to imagine our superiority.
Photographs: The macro-photographs were largely taken with live subjects, either in the field or captured and temporarily cooled to 50°F to reduce motion. The camera was a Nikon 5700 with extended zoom [250 mm (35 mm eq.)] and a 4 diopter or 10 diopter close-up lens. Maximum magnification was 1 to 2X. Natural lighting or clip-on reading-flex-lights with high intensity Nichia LEDS were used for front illumination. Backlighting employed a fluorescent “trouble-light” housed in a flat translucent plastic container. Zoom-stereo photos employed the Nikon 5700 with a Martin Microscope relay lens attachment inserted into one of the binocular ports of an American Optical 1-4X objective stereo microscope. Magnification was 12-50X. Lighting was by a 48 LED ring-light with pulse modulated intensity control obtained from Martin Microscope. Microscope photos used a modified BH Olympus Scope with incandescent normal and epi-illumination capability, and the Nikon 5700, with relay lens attachment, inserted in the third camera port. Full extension zoom, infinity focusing lock, and manual infinity adjustment was used. Preset white balance was employed. Magnifications of 60-120X were employed. Focusing was aided by an LCD video display attached to the camera output. All photos are uncropped, and adjusted only for normal LCD monitor gamma requirements.
Comments to the author Ray Dessy are welcomed.
Acknowledgements : Thanks to Eric Day, Entomology Dept., Virginia Tech, for his help in focusing on the subject. Compression, editing, and organizing of the photographs was done with the free downloads of PhotoFiltre, FastStone Image Viewer, and Picasa (Google).
References (Click each ref. number to return to respective article text.)
1 P. Gullan, The Insects An Outline of Entomology, 2005 C. Gillot, Entomology, 2005
The simple cross sections used are from an older text J. Comstock. An Introduction to Entomology .
2 MicrlabNW, Web Site collection of insect photographs Insect%20Hair_MicroLab_files/InsectHair7A58807.jpg