76-465: Pests and diseases of cereals : Crop pest A pest is any organism harmful to humans or human concerns. The term is particularly used for creatures that damage crops, livestock, and forestry or cause a nuisance to people, especially in their homes. Humans have modified the environment for their own purposes and are intolerant of other creatures occupying the same space when their activities impact adversely on human objectives. Thus, an elephant
152-493: A " nerve net " is located in the epidermis . Although traditionally thought not to have a central nervous system , nerve net concentration and ganglion -like structures could be considered to constitute one in most species. A jellyfish detects stimuli, and transmits impulses both throughout the nerve net and around a circular nerve ring, to other nerve cells. The rhopalial ganglia contain pacemaker neurones which control swimming rate and direction. In many species of jellyfish,
228-508: A backbone, though shellfish , cuttlefish and starfish are not vertebrates either. In scientific literature, "jelly" and "jellyfish" have been used interchangeably. Many sources refer to only scyphozoans as "true jellyfish". A group of jellyfish is called a "smack" or a "smuck". The term jellyfish broadly corresponds to medusae, that is, a life-cycle stage in the Medusozoa . The American evolutionary biologist Paulyn Cartwright gives
304-577: A bad weed when it out-competes cultivated plants. A different group of weeds consists of those that are invasive, introduced, often unintentionally, to habitats to which they are not native but in which they thrive. Without their original competitors, herbivores, and diseases, they may increase and become a serious nuisance. One such plant is purple loosestrife , a native of Europe and Asia where it occurs in ditches, wet meadows and marshes; introduced into North America, it has no natural enemies to keep it in check and has taken over vast tracts of wetlands to
380-436: A charm to be sung, accompanied by covering the wound with spittle, pounded green centaury, and hot cow's urine. The 20th century "prayer against pests" including the words "By Your power may these injurious animals be driven off so that they will do no harm to any one and will leave our fields and meadows unharmed" was printed in the 1956 Rural Life Prayerbook . Jellyfish Jellyfish , also known as sea jellies , are
456-517: A free-swimming medusa is Burgessomedusa from the mid-Cambrian Burgess Shale of Canada, which is likely either a stem group of box jellyfish (Cubozoa) or Acraspeda (the clade including Staurozoa, Cubozoa, and Scyphozoa). Other claimed records from the Cambrian of China and Utah in the United States are uncertain, and possibly represent ctenophores instead. The main feature of a true jellyfish
532-419: A means to disperse. The nematodes (eelworms) that attack plants are minute, often too small to be seen with the naked eye, but their presence is often apparent in the galls or "knots" they form in plant tissues. Vast numbers of nematodes are found in soil and attack roots, but others affect stems, buds, leaves, flowers and fruits. High infestations cause stunting, deformation and retardation of plant growth, and
608-408: A medusa stage in their life cycle. The basic cycle is egg, planula larva, polyp, medusa, with the medusa being the sexual stage. The polyp stage is sometimes secondarily lost. The subphylum include the major taxa, Scyphozoa (large jellyfish), Cubozoa (box jellyfish) and Hydrozoa (small jellyfish), and excludes Anthozoa (corals and sea anemones). This suggests that the medusa form evolved after
684-532: A nuisance around buildings, roadsides and recreation areas because of its uncomfortably sharp spiny burrs . Disease-causing pathogens such as fungi , oomycetes , bacteria , and viruses can cause damage to crops and garden plants. The term "plant pest", mainly applied to insect micropredators of plants, has a specific definition in terms of the International Plant Protection Convention and phytosanitary measures worldwide. A pest
760-430: A pest is a competitor to humanity. Pests include plants, pathogens, invertebrates, vertebrates, or any organism that harms an ecosystem. Animals are considered pests or vermin when they injure people or damage crops, forestry, or buildings. Elephants are regarded as pests by the farmers whose crops they raid and trample. Mosquitoes and ticks are vectors that can transmit ailments but are also pests because of
836-404: A pest plant "any plant that, in the local government authority's opinion, is likely to adversely affect the environment of the district, the value of property in the district, or the health, comfort or convenience of the district's inhabitants." An example of such a plant prescribed under this regulation is caltrop, Tribulus terrestris , which can cause poisoning in sheep and goats, but is mainly
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#1732883841473912-450: A solid surface by a basal disk, and resemble a polyp, the oral end of which has partially developed into a medusa with tentacle-bearing lobes and a central manubrium with four-sided mouth. Most jellyfish do not have specialized systems for osmoregulation , respiration and circulation , and do not have a central nervous system . Nematocysts, which deliver the sting, are located mostly on the tentacles; true jellyfish also have them around
988-399: A suitable stocking density, and minimizing injury and stress to trees. Pest control in buildings can be approached in several ways, depending on the type of pest and the area affected. Methods include improving sanitation and garbage control, modifying the habitat, and using repellents, growth regulators, traps, baits and pesticides. For example, the pesticide Boron can be impregnated into
1064-518: A thick cuticle or waxy deposits, with the second line of defence being toxic or distasteful secondary metabolites . Mechanical injury to the plant tissues allows the entry of pathogens and stimulates the plant to mobilise its chemical defences. The plant soon seals off the wound to reduce further damage. Plants sometimes take active steps to reduce herbivory. Macaranga triloba for example has adapted its thin-walled stems to create ideal housing for an ant Crematogaster spp., which, in turn, protects
1140-405: A wide variety of pests, the most important being rodents , insects , mites , nematodes and gastropod molluscs . The damage they do results both from the direct injury they cause to the plants and from the indirect consequences of the fungal, bacterial or viral infections they transmit. Plants have their own defences against these attacks but these may be overwhelmed, especially in habitats where
1216-463: Is a common name, its mapping to biological groups is inexact. Some authorities have called the comb jellies and certain salps jellyfish, though other authorities state that neither of these are jellyfish, which they consider should be limited to certain groups within the medusozoa. The non-medusozoan clades called jellyfish by some but not all authorities (both agreeing and disagreeing citations are given in each case) are indicated with " ??? " on
1292-423: Is a plant considered undesirable in a particular situation; the term has no botanical significance. Often, weeds are simply those native plants that are adapted to grow in disturbed ground, the disturbance caused by ploughing and cultivation favouring them over other species. Any plant is a weed if it appears in a location where it is unwanted; Bermuda grass makes a good lawn plant under hot dry conditions but become
1368-439: Is an intermediary to a better understanding of how visual systems evolved on Earth. Jellyfish exhibit immense variation in visual systems ranging from photoreceptive cell patches seen in simple photoreceptive systems to more derived complex eyes seen in box jellyfish. Major topics of jellyfish visual system research (with an emphasis on box jellyfish) include: the evolution of jellyfish vision from simple to complex visual systems),
1444-492: Is any species, strain or biotype of plant, animal, or pathogenic agent injurious to plants or plant products. Worldwide, agricultural pest impacts are increased by higher degrees of interconnectedness. This is due to the increased risk that any particular pest problem anywhere in the world (as a system ) will propagate across the entire system. Plants have developed strategies that they use in their own defence, be they thorns (modified stems) or spines (modified leaves), stings,
1520-822: Is capable of multiple task-guided behaviors. Although they lack a true brain, cnidarian jellyfish have a "ring" nervous system that plays a significant role in motor and sensory activity. This net of nerves is responsible for muscle contraction and movement and culminates the emergence of photosensitive structures. Across Cnidaria , there is large variation in the systems that underlie photosensitivity. Photosensitive structures range from non-specialized groups of cells, to more "conventional" eyes similar to those of vertebrates . The general evolutionary steps to develop complex vision include (from more ancestral to more derived states): non-directional photoreception, directional photoreception, low-resolution vision, and high-resolution vision. Increased habitat and task complexity has favored
1596-691: Is the case with the emerald ash borer , an insect native to north-eastern Asia, which, since its arrival in North America, has killed millions of ash trees. Another example of a beetle species that exhibits pest behavior are Melolontha Hippocastrani , that cause severe, long-term damage on young trees by feeding on roots. Animals able to live in the dry conditions found in buildings include many arthropods such as beetles, cockroaches, moths, and mites. Another group, including termites , woodworm , longhorn beetles , and wood ants cause structural damage to buildings and furniture. The natural habitat of these
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#17328838414731672-424: Is the decaying parts of trees. The deathwatch beetle infests the structural timbers of old buildings, mostly attacking hardwood , especially oak . The initial attack usually follows the entry of water into a building and the subsequent decay of damp timber. Furniture beetles mainly attack the sapwood of both hard and soft wood , only attacking the heartwood when it is modified by fungal decay. The presence of
1748-409: Is the umbrella-shaped bell. This is a hollow structure consisting of a mass of transparent jelly-like matter known as mesoglea , which forms the hydrostatic skeleton of the animal. The mesoglea is 95% or more composed of water, and also contains collagen and other fibrous proteins, as well as wandering amebocytes that can engulf debris and bacteria. The mesogloea is bordered by the epidermis on
1824-553: Is unobjectionable in its natural habitat but a pest when it tramples crops. Some animals are disliked because they bite or sting; wolves , snakes , wasps , ants , bed bugs , fleas and ticks belong in this category. Others enter the home; these include houseflies, which land on and contaminate food; beetles, which tunnel into the woodwork; and other animals that scuttle about on the floor at night, like rats and cockroaches , which are often associated with unsanitary conditions. Agricultural and horticultural crops are attacked by
1900-635: The drugstore beetle , the sawtoothed grain beetle and the Indianmeal moth being found worldwide. The insects may be present in the warehouse or maybe introduced during shipping, in retail outlets, or in the home; they may enter packets through tiny cracks or may chew holes in the packaging. The longer a product is stored, the more likely it is to become contaminated, with the insects often originating from dry pet foods. Some mites, too, infest foodstuffs and other stored products. Each substance has its own specific mite, and they multiply with great rapidity. One of
1976-558: The green fluorescent protein used by some species for bioluminescence . This protein has been adapted as a fluorescent reporter for inserted genes and has had a large impact on fluorescence microscopy . The stinging cells used by jellyfish to subdue their prey can injure humans. Thousands of swimmers worldwide are stung every year, with effects ranging from mild discomfort to serious injury or even death. When conditions are favourable, jellyfish can form vast swarms, which may damage fishing gear by filling fishing nets, and sometimes clog
2052-438: The medusa -phase of certain gelatinous members of the subphylum Medusozoa , which is a major part of the phylum Cnidaria . Jellyfish are mainly free-swimming marine animals , although a few are anchored to the seabed by stalks rather than being motile. They are made of an umbrella-shaped main body made of mesoglea , known as the bell , and a collection of trailing tentacles on the underside. Via pulsating contractions,
2128-429: The 10th century Greek monk Tryphon of Constantinople is said to have prayed "Snails, earwigs and all other creatures, hurt not the vines, nor the land nor the fruit of the trees, nor the vegetables ... but depart into the wild mountains." The 11th-century Old English medical text Lacnunga contained charms and spells to ward off or treat pests such as wid smeogan wyrme , " penetrating worms ", in this case requiring
2204-609: The ants. Pest ranges are heavily determined by climate . The most common example for the longest time has been rainfall : Although drought stress weakens crop disease resistance , drought also retards contagion and infection; and some variability in precipitation is universal. More recently climate change has been rapidly altering ranges, mostly by pushing them towards the poles (both North and South ). From 1960-2013 ranges have shifted poleward by 2.7 ± 0.8 km (1.68 ± 0.50 mi) per year - albeit with significant differences between taxa . (Especially in
2280-474: The beetles only becomes apparent when the larvae gnaw their way out, leaving small circular holes in the timber. Carpet beetles and clothes moths cause non-structural damage to property such as clothing and carpets. It is the larvae that are destructive, feeding on wool, hair, fur, feathers and down. The moth larvae live where they feed, but the beetle larvae may hide behind skirting boards or in other similar locations between meals. They may be introduced to
2356-456: The bell can provide propulsion for locomotion through open water. The tentacles are armed with stinging cells and may be used to capture prey or to defend against predators. Jellyfish have a complex life cycle , and the medusa is normally the sexual phase, which produces planula larvae. These then disperse widely and enter a sedentary polyp phase which may include asexual budding before reaching sexual maturity. Jellyfish are found all over
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2432-452: The bell pulsates, allowing box jellyfish to swim faster than true jellyfish. Hydrozoans are also similar, usually with just four tentacles at the edge of the bell, although many hydrozoans are colonial and may not have a free-living medusal stage. In some species, a non-detachable bud known as a gonophore is formed that contains a gonad but is missing many other medusal features such as tentacles and rhopalia. Stalked jellyfish are attached to
2508-622: The birth of civilisation. Plagues of locusts caused devastation in the ancient Middle East, and were recorded in tombs in Ancient Egypt from as early as 2470 BC, and in the Book of Exodus in the Bible, as taking place in Egypt around 1446 BC. Homer 's Iliad mentions locusts taking to the wing to escape fire. Given the impact of agricultural pests on human lives, people have prayed for deliverance. For example,
2584-510: The case of viruses and nematodes which show the opposite trend, toward the equator . This may be due to their lack of airborne dispersal , so their trend conforms with the trend of human-aided dispersal ; or identification difficulties in the field.) In Europe, crop pests are expected to burgeon as the vertebrate predators which control them are expected to be suppressed by future climatic conditions. Together pests and diseases cause up to 40% yield losses every year. The animal groups of
2660-448: The cooling systems of power and desalination plants which draw their water from the sea. The name jellyfish, in use since 1796, has traditionally been applied to medusae and all similar animals including the comb jellies ( ctenophores , another phylum). The term jellies or sea jellies is more recent, having been introduced by public aquaria in an effort to avoid use of the word "fish" with its modern connotation of an animal with
2736-455: The cooling systems of power and desalination plants which draw their water from the sea. Many of the animals that we regard as pests live in our homes. Before humans built dwellings, these creatures lived in the wider environment, but co-evolved with humans, adapting to the warm, sheltered conditions that a house provides, the wooden timbers, the furnishings, the food supplies and the rubbish dumps. Many no longer exist as free-living organisms in
2812-416: The damage done by molluscs becomes of greater significance. Terrestrial molluscs need moist environments; snails may be more noticeable because their shells provide protection from desiccation, while most slugs live in soil and only come out to feed at night. They devour seedlings, damage developing shoots and feed on salad crops and cabbages, and some species tunnel into potatoes and other tubers. A weed
2888-408: The difficulty of examining entire trees, and the certainty that pesticides would damage many forest organisms other than the intended pests. Forest integrated pest management therefore aims to use a combination of prevention, cultural control measures, and direct control (such as pesticide use). Cultural measures include choosing appropriate species, keeping competing vegetation under control, ensuring
2964-494: The distress caused by their bites. Grasshoppers are usually solitary herbivores of little economic importance until the conditions are met for them to enter a swarming phase , become locusts and cause enormous damage. Many people appreciate birds in the countryside and their gardens, but when these accumulate in large masses, they can be a nuisance. Flocks of starlings can consist of hundreds of thousands of individual birds, their roosts can be noisy and their droppings voluminous;
3040-715: The droppings are acidic and can cause corrosion of metals, stonework, and brickwork as well as being unsightly. Pigeons in urban settings may be a health hazard, and gulls near the coast can become a nuisance, especially if they become bold enough to snatch food from passers-by. All birds are a risk at airfields where they can be sucked into aircraft engines. Woodpeckers sometimes excavate holes in buildings, fencing and utility poles, causing structural damage; they also drum on various reverberatory structures on buildings such as gutters, down-spouts, chimneys, vents and aluminium sheeting. Jellyfish can form vast swarms which may be responsible for damage to fishing gear, and sometimes clog
3116-630: The exclusion of native species. In forestry, pests may affect various parts of the tree, from its roots and trunk to the canopy far overhead. The accessibility of the part of the tree affected may make detection difficult, so that a pest problem may already be far advanced before it is first observed from the ground. The larch sawfly and spruce budworm are two insect pests prevalent in Alaska and aerial surveys can show which sections of forest are being defoliated in any given year so that appropriate remedial action can be taken. Some pests may not be present on
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3192-421: The exterior, perhaps supplying good oxygenation to the gonads. Near the free edges of the septa, gastric filaments extend into the gastric cavity; these are armed with nematocysts and enzyme-producing cells and play a role in subduing and digesting the prey. In some scyphozoans, the gastric cavity is joined to radial canals which branch extensively and may join a marginal ring canal. Cilia in these canals circulate
3268-694: The eye morphology and molecular structures of box jellyfish (including comparisons to vertebrate eyes), and various uses of vision including task-guided behaviors and niche specialization. Experimental evidence for photosensitivity and photoreception in cnidarians antecedes the mid 1900s, and a rich body of research has since covered evolution of visual systems in jellyfish. Jellyfish visual systems range from simple photoreceptive cells to complex image-forming eyes. More ancestral visual systems incorporate extraocular vision (vision without eyes) that encompass numerous receptors dedicated to single-function behaviors. More derived visual systems comprise perception that
3344-764: The fibres of cellulose insulation to kill self-grooming insects such as ants and cockroaches. Clothes moths can be controlled with airtight containers for storage, periodic laundering of garments, trapping, freezing, heating and the use of chemicals. Traditional mothballs deter adult moths with strong-smelling naphthalene ; modern ones use volatile repellents such as 1,4-Dichlorobenzene . Moth larvae can be killed with insecticides such as permethrin or pyrethroids . However, insecticides cannot safely be used in food storage areas; alternative treatments include freezing foods for four days at 0 °F (−18 °C) or baking for half an hour at 130 °F (54 °C) to kill any insects present. Pests have attracted human attention from
3420-400: The fluid in a regular direction. The box jellyfish is largely similar in structure. It has a squarish, box-like bell. A short pedalium or stalk hangs from each of the four lower corners. One or more long, slender tentacles are attached to each pedalium. The rim of the bell is folded inwards to form a shelf known as a velarium which restricts the bell's aperture and creates a powerful jet when
3496-960: The following phylogenetic tree by the presence of citations. Names of included jellyfish, in English where possible, are shown in boldface; the presence of a named and cited example indicates that at least that species within its group has been called a jellyfish. Anthozoa (corals) Polypodiozoa and Myxozoa (parasitic cnidarians) Staurozoa ( stalked jellyfish ) [REDACTED] Cubozoa ( box jellyfish ) [REDACTED] Discomedusae [REDACTED] Coronatae ( crown jellyfish ) [REDACTED] Aplanulata [REDACTED] Siphonophorae [REDACTED] Some Leptothecata e.g. crystal jelly [REDACTED] Filifera e.g. red paper lantern jellyfish [REDACTED] Limnomedusae , e.g. flower hat jelly [REDACTED] Narcomedusae , e.g. cosmic jellyfish [REDACTED] The subphylum Medusozoa includes all cnidarians with
3572-562: The following cladogram of the animal kingdom: Porifera Ctenophora (comb jellies) ??? [REDACTED] Cnidaria [REDACTED] (includes jellyfish and other jellies) Protostomia Ambulacraria Tunicata (includes salps ) ??? [REDACTED] Vertebrata Jellyfish are not a clade , as they include most of the Medusozoa, barring some of the Hydrozoa. The medusozoan groups included by authorities are indicated on
3648-497: The following general definition: Typically, medusozoan cnidarians have a pelagic , predatory jellyfish stage in their life cycle; staurozoans are the exceptions [as they are stalked]. The Merriam-Webster dictionary defines jellyfish as follows: A free-swimming marine coelenterate that is the sexually reproducing form of a hydrozoan or scyphozoan and has a nearly transparent saucer-shaped body and extensible marginal tentacles studded with stinging cells. Given that jellyfish
3724-560: The general collection. There are over four thousand species of cockroach worldwide, but only four species are commonly regarded as pests, having adapted to live permanently in buildings. Considered to be a sign of unsanitary conditions, they feed on almost anything, reproduce rapidly and are difficult to eradicate. They can passively transport pathogenic microbes on their body surfaces, particularly in environments such as hospitals, and are linked with allergic reactions in humans. Various insects attack dry food products, with flour beetles ,
3800-401: The greatest importance as agricultural pests are (in order of economic importance) insects , mites , nematodes and gastropod molluscs . Insects are responsible for two major forms of damage to crops. First, there is the direct injury they cause to the plants as they feed on the tissues; a reduction in leaf surface available for photosynthesis, distortion of growing shoots, a diminution of
3876-510: The high-resolution visual systems common in derived cnidarians such as box jellyfish . Basal visual systems observed in various cnidarians exhibit photosensitivity representative of a single task or behavior. Extraocular photoreception (a form of non-directional photoreception), is the most basic form of light sensitivity and guides a variety of behaviors among cnidarians. It can function to regulate circadian rhythm (as seen in eyeless hydrozoans ) and other light-guided behaviors responsive to
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#17328838414733952-527: The home in any product containing animal fibres including upholstered furniture; the moths are feeble fliers but the carpet beetles may also enter houses through open windows. Furniture beetles, carpet beetles and clothes moths are also capable of creating great damage to museum exhibits, zoological and botanical collections, and other cultural heritage items. Constant vigilance is required to prevent an attack, and newly acquired items, and those that have been out on loan, may need quarantining before being added to
4028-646: The intensity and spectrum of light. Extraocular photoreception can function additionally in positive phototaxis (in planula larvae of hydrozoans), as well as in avoiding harmful amounts of UV radiation via negative phototaxis . Directional photoreception (the ability to perceive direction of incoming light) allows for more complex phototactic responses to light, and likely evolved by means of membrane stacking. The resulting behavioral responses can range from guided spawning events timed by moonlight to shadow responses for potential predator avoidance. Light-guided behaviors are observed in numerous scyphozoans including
4104-662: The most damaging is the flour mite , which is found in grain and may become exceedingly abundant in poorly stored material. In time, predatory mites usually move in and control the flour mites. The control of pests in crops is as old as civilisation. The earliest approach was mechanical, from ploughing to picking off insects by hand. Early methods included the use of sulphur compounds, before 2500 BC in Sumeria. In ancient China, insecticides derived from plants were in use by 1200 BC to treat seeds and to fumigate plants. Chinese agronomy recognised biological control by natural enemies of pests and
4180-470: The mouth and stomach. Jellyfish do not need a respiratory system because sufficient oxygen diffuses through the epidermis. They have limited control over their movement, but can navigate with the pulsations of the bell-like body; some species are active swimmers most of the time, while others largely drift. The rhopalia contain rudimentary sense organs which are able to detect light, water-borne vibrations, odour and orientation. A loose network of nerves called
4256-447: The mouth, which also functions as the anus, at its tip. There are often four oral arms connected to the manubrium, streaming away into the water below. The mouth opens into the gastrovascular cavity , where digestion takes place and nutrients are absorbed. This is subdivided by four thick septa into a central stomach and four gastric pockets. The four pairs of gonads are attached to the septa, and close to them four septal funnels open to
4332-680: The nematodes can transmit viral diseases from one plant to another. When its populations are high, the potato cyst nematode can cause reductions of 80% in yield of susceptible potato varieties. The nematode eggs survive in the soil for many years, being stimulated to hatch by chemical cues produced by roots of susceptible plants. Slugs and snails are terrestrial gastropod molluscs which typically chew leaves, stems, flowers, fruit and vegetable debris. Slugs and snails differ little from each other and both do considerable damage to plants. With novel crops being grown and with insect pests having been brought more under control by biological and other means,
4408-500: The oldest multi-organ animal group. Jellyfish are eaten by humans in certain cultures. They are considered a delicacy in some Asian countries, where species in the Rhizostomeae order are pressed and salted to remove excess water. Australian researchers have described them as a "perfect food": sustainable and protein-rich but relatively low in food energy . They are also used in cell and molecular biology research, especially
4484-441: The open for brief periods as adults, primarily to mate and disperse. The import and export of timber has inadvertently assisted some insect pests to establish themselves far from their country of origin. An insect may be of little importance in its native range, being kept under control by parasitoid wasps, predators, and the natural resistance of the host trees, but be a serious pest in a region into which it has been introduced. This
4560-402: The open lagoon, where they feed, and back again. Box jellyfish have more advanced vision than the other groups. Each individual has 24 eyes, two of which are capable of seeing colour, and four parallel information processing areas that act in competition, supposedly making them one of the few kinds of animal to have a 360-degree view of its environment. The study of jellyfish eye evolution
4636-415: The outside and the gastrodermis on the inside. The edge of the bell is often divided into rounded lobes known as lappets , which allow the bell to flex. In the gaps or niches between the lappets are dangling rudimentary sense organs known as rhopalia , and the margin of the bell often bears tentacles. On the underside of the bell is the manubrium, a stalk-like structure hanging down from the centre, with
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#17328838414734712-532: The outside world, and can therefore be considered to be domesticated. The St Kilda house mouse rapidly became extinct when the last islander left the island of St Kilda, Scotland in 1930, but the St Kilda field mouse survived. Plants may be considered pests, for example, if they are invasive species or weeds . There is no universal definition of what makes a plant a pest. Some governments, such as that of Western Australia, permit their authorities to prescribe as
4788-452: The plant from herbivores. In addition to providing housing, the plant also provides the ant with its exclusive food source in the form of food bodies located on the leaf stipules. Similarly, several Acacia tree species have developed stout spines that are swollen at the base, forming a hollow structure that provides housing for ants which protect the plant. These Acacia trees also produce nectar in nectaries on their leaves as food for
4864-417: The plant's growth and vigour, and the wilting of shoots and branches caused by the insects' tunneling activities. Secondly there is the indirect damage, where the insects do little direct harm, but either transmit or allow entry of fungal, bacterial or viral infections. Although some insects are polyphagous, many are restricted to one specific crop, or group of crops. In many cases it is the larva that feeds on
4940-456: The plant, building up a nutritional store that will be used by the short-lived adult; sawfly and lepidopteran larvae feed mainly on the aerial portions of plants while beetle larvae tend to live underground, feeding on roots, or tunnel into the stem or under the bark. The true bugs, Hemiptera , have piercing and sucking mouthparts and live by sucking sap from plants. These include aphids , whiteflies and scale insects . Apart from weakening
5016-442: The plant, they encourage the growth of sooty mould on the honeydew the insects produce, which cuts out the light and reduces photosynthesis, stunting the plant's growth. They often transmit serious viral diseases between plants. The mites that cause most trouble in the field are the spider mites . These are less than 1 mm (0.04 in) in diameter, can be very numerous, and thrive in hot, dry conditions. They mostly live on
5092-413: The plants are already stressed, or where the pests have been accidentally introduced and may have no natural enemies. The pests affecting trees are predominantly insects, and many of these have also been introduced inadvertently and lack natural enemies, and some have transmitted novel fungal diseases with devastating results. Humans have traditionally performed pest control in agriculture and forestry by
5168-448: The polyps. Medusozoans have tetramerous symmetry, with parts in fours or multiples of four. The four major classes of medusozoan Cnidaria are: There are over 200 species of Scyphozoa, about 50 species of Staurozoa, about 50 species of Cubozoa, and the Hydrozoa includes about 1000–1500 species that produce medusae, but many more species that do not. Since jellyfish have no hard parts, fossils are rare. The oldest unambiguous fossil of
5244-404: The rhopalia include ocelli , light-sensitive organs able to tell light from dark. These are generally pigment spot ocelli, which have some of their cells pigmented. The rhopalia are suspended on stalks with heavy crystals at one end, acting like gyroscopes to orient the eyes skyward. Certain jellyfish look upward at the mangrove canopy while making a daily migration from mangrove swamps into
5320-407: The roots or the aerial parts of plants and transmit viruses. Some examples are the big bud mite that transmits the reversion virus of blackcurrants , the coconut mite which can devastate coconut production, and the cereal rust mite which transmits several grass and cereal viruses. Being exceedingly minute, many plant mites are spread by wind, although others use insects or other arthropods as
5396-404: The second half of the 19th century, starting with the vedalia beetle against cottony cushion scale . All these methods have been refined and developed since their discovery. Forest pests inflict costly damage, but treating them is often unaffordable, given the relatively low value of forest products compared to agricultural crops. It is also generally impossible to eradicate forest pests, given
5472-455: The tree all year round, either because of their life cycle or because they rotate between different host species at different times of the year. In forestry, pests may affect various parts of the tree, from its roots and trunk to the canopy far overhead. The larvae of wood-boring beetles , for example, are notorious for spending years excavating tunnels under the bark of trees, leading to significant structural damage. These larvae only emerge into
5548-448: The underside of leaves and puncture the plant cells to feed, with some species forming webbing. They occur on nearly all important food crops and ornamental plants, both outdoors and under glass, and include some of the most economically important pests. Another important group of mites is the gall mites which affect a wide range of plants, several mite species being major pests causing substantial economic damage to crops. They can feed on
5624-470: The use of pesticides ; however, other methods exist such as mechanical control , and recently developed biological controls . A pest is any living thing which humans consider troublesome to themselves, their possessions, or the environment. Pests can cause issues with crops, human or animal health, buildings, and wild areas or larger landscapes. An older usage of the word "pest" is of a deadly epidemic disease, specifically plague . In its broadest sense,
5700-686: The varying of planting time to reduce pests before the first century AD. The agricultural revolution in Europe saw the introduction of effective plant-based insecticides such as pyrethrum , derris , quassia , and tobacco extract. The phylloxera (a powdery mildew ) damage to the wine industry in the 19th century resulted in the development of resistant varieties and grafting , and the accidental discovery of effective chemical pesticides, Bordeaux mixture (lime and copper sulphate ) and Paris Green (an arsenic compound), both very widely used. Biological control also became established as an effective measure in
5776-552: The world, from surface waters to the deep sea. Scyphozoans (the "true jellyfish") are exclusively marine , but some hydrozoans with a similar appearance live in fresh water . Large, often colorful, jellyfish are common in coastal zones worldwide. The medusae of most species are fast-growing, and mature within a few months then die soon after breeding, but the polyp stage, attached to the seabed, may be much more long-lived. Jellyfish have been in existence for at least 500 million years, and possibly 700 million years or more, making them
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