Aphids
Aphids, also known as greenfly or plant lice, are minute plant-feeding insects.
About 4,000 species of aphids are known, classified in 10 families; of these, around 250 species are serious pests for agriculture and forestry as well as an annoyance for gardeners. They vary in size from 1-10 mm long.
Important natural enemies include the predatory ladybeetles (Coleoptera: Coccinellidae), hoverfly larvae (Diptera: Syrphidae), and lacewings (Neuroptera: Chrysopidae), and entomopathogenic fungi like Lecanicillium lecanii and the Entomophthorales.
Aphids are distributed world-wide, but they are most common in temperate zones. It is possible for aphids to migrate great distances (mainly through passive dispersal riding on winds) depending on the weather patterns; for example, the lettuce aphid spreading from New Zealand to Tasmania. They have also been spread by human transportation of infested plant materials.
Taxonomy
Aphids, are in the superfamily Aphidoidea in the homopterous division of the order Hemiptera. Recent classification within the Hemiptera has changed the old term ‘Homoptera’ to two suborders: Sternorrhyncha (aphids, whiteflies, scales, psyllids…) and Auchenorrhyncha (cicadas, leafhoppers, treehoppers, planthoppers…) with the suborder Heteroptera containing a large group of insects known as the ‘true bugs’; gnat bugs, pond skaters, shore bugs, toad bugs, water boatmen, backswimmers, etc. More recent reclassifications have resulted in a substantial rearrangement of the constituent families with the Aphidoidea, with some old families reduced to subfamily rank (e.g., Eriosomatidae), and numerous old subfamilies elevated to family rank.
Read more
Ladybugs
Coccinellidae is a family of beetles, known variously as ladybirds (British English, Australian English, South African English), ladybugs (North American English) or lady beetles (preferred by some scientists). The family name comes from its type genus, Coccinella. Coccinellids are found worldwide, with over 5,000 species described, more than 450 native to North America alone. Coccinellids are small insects, ranging from 1 mm to 10 mm (0.04 to 0.4 inches), and are commonly yellow, orange, or scarlet with small black spots on their wing covers, with black legs, head and antennae. A very large number of species are mostly or entirely black, gray, or brown, however, and may be difficult for non-entomologists to recognize as coccinellids (and, conversely, there are many small beetles that are easily mistaken as such, like tortoise beetles).
They are generally considered useful insects as many species feed on aphids or scale insects, which are pests in gardens, agricultural fields, orchards, and similar places. Some people consider seeing them or having them land on one’s body to be a sign of good luck to come, and that killing them presages bad luck. A few species are pests in North America and Europe.
Read more
Biological pest control
Biological control of pests in agriculture is a method of controlling pests (including insects, mites, weeds and plant diseases) that relies on predation, parasitism, herbivory, or other natural mechanisms. It can be an important component of integrated pest management (IPM) programs.
Overview
Diagram illustrating the natural enemies of cabbage pests
Biological Control is defined as the reduction of pest populations by natural enemies and typically involves an active human role. Natural enemies of insect pests, also known as biological control agents, include predators, parasitoids, and pathogens. Biological control agents of plant diseases are most often referred to as antagonists. Biological control agents of weeds include herbivores and plant pathogens. Predators, such as lady beetles and lacewings, are mainly free-living species that consume a large number of prey during their lifetime. Parasitoids are species whose immature stage develops on or within a single insect host, ultimately killing the host. Most have a very narrow host range. Many species of wasps and some flies are parasitoids. Pathogens are disease-causing organisms including bacteria, fungi, and viruses. They kill or debilitate their host and are relatively specific to certain insect groups. There are three basic types of biological control strategies; conservation, classical biological control, and augmentation. These are discussed in more detail below.
Conservation
The conservation of natural enemies is probably the most important and readily available biological control practice available to homeowners and gardeners. Natural enemies occur in all areas, from the backyard garden to the commercial field. They are adapted to the local environment and to the target pest, and their conservation is generally simple and cost-effective. Lacewings, lady beetles, hover fly larvae, and parasitized aphid mummies are almost always present in aphid colonies. Fungus-infected adult flies are often common following periods of high humidity. These naturally occurring biological controls are often susceptible to the same pesticides used to target their hosts. Preventing the accidental eradication of natural enemies is termed simple conservation.
Effects of Biological Control on Biodiversity
Effects on Native Biodiversity
Biological control can potentially have positive and negative effects on biodiversity. Most of the time a biological control is introduced to an area to protect a native species from an invasive or exotic species that has moved into its area. The control is introduced to lessen the competition among native and invasive species. However, the introduced control does not always only target the intended species. It can also target native species. When introducing a biological control to a new area, the amount of testing and research that has been preformed does not matter. It could still potentially harm an unwanted native species. If a species is introduced and attacks a native species, the biodiversity in that area can decrease dramatically. When one native species is removed from an area, it may have filled an essential niche, When this niche is absent it will directly affect the entire ecosystem. The cane toad (Bufo marinus) was introduced as a biological control and had significant negative impact on biodiversity. The cane toad was intentionally introduced to Australia to control the cane beetle. When introduced, the cane toad thrived very well and did not only feed on cane beetles but other insects as well. The cane toad soon spread very rapidly, thus taking over native habitat. The introduction of the cane toad also brought foreign disease to native reptiles. This drastically reduced the population of native toads and frogs. “The cane toad also exudes and can squirt poison from the parotoid glands on their shoulders when threatened or handled. This toxin contains a cocktail of chemicals that can kill animals that eat it. Freshwater crocodiles, goannas, tiger snakes, dingos and northern quolls have all died after eating cane toads, as have pet dogs (Cane toad,2003)”. This goes to show a small but deadly organism can alter the native biodiversity in an ecosystem in a very expedient manner. A pyramid effect can take place if native species are reduced or eradicated. The domino effect keeps on going and can potentially exude on other bordering ecosystems. A second example of a biological control that consequently took over native species was the Rhinocyllus concius. The seed feeding weevil was introduced to North America to control exotic thistles (Musk and Canadian). However, the weevil did not only target the exotic thistles, it also targeted native thistles that are essential to various native insects. The native insects solely rely on native thistles and do not adapt to other plant species. Therefore, they cannot survive. Biological controls do not always have negative impacts on biodiversity (Corry 2000). Successful biological control reduces the density of the target species over several years, thus providing the potential for native species to re-establish. In addition, regeneration and reestablishment programs can aid to the recovery of native species. Native species can be affected in a positive way as well. To develop or find a biological control that exerts control only on the targeted species is a very lengthy process of research and experiments. In the late 1800’s, the citrus industry was in great fear when the cottony cushion scale was discovered. This organism could cause a great deal of economic loss to the industry. However, a biological control was introduced. The vedalia beetle and a parasitoid fly were introduced to control the pest. Within a few years time, the cottony cushion scale was controlled by the natural enemies and the citrus industry suffered little financial loss. Many exotic or invasive species can suppress the development of native species, therefore the introduction of an effective biological control that targets the invasive species will be reduced, thus allowing the rejuvenation of the native species. Biological controls can reduce competition for biotic and abiotic factors which can result in the re-establishment of the once over ran native species.
Pesticide
A pesticide is a substance or mixture of substances used for preventing, controlling, or lessening the damage caused by a pest. A pesticide may be a chemical substance, biological agent (such as a virus or bacteria), antimicrobial, disinfectant or device used against any pest. Pests include insects, plant pathogens, weeds, mollusks, birds, mammals, fish, nematodes (roundworms) and microbes that compete with humans for food, destroy property, spread or are a vector for disease or cause a nuisance. Many pesticides are poisonous to humans.
Read more
Spider Mites (Tetranychus urticae)
Spider mites are members of the Acari (mite) family Tetranychidae, which includes about 1600 species. They generally live on the under sides of leaves of plants, where they may spin protective silk webs, and they can cause damage by puncturing the plant cells to feed.
Spider mites are less than 1 mm in size and vary in color. They lay small, spherical, initially transparent eggs and many species spin silk webbing to help protect the colony from predators; they get the ’spider’ part of their common name from this webbing. Hot, dry conditions are often associated with population build-up of spider mites.
Whitefly
The whiteflies, comprising only the family Aleyrodidae, are small homopterans. More than 1550 species have been described. Whiteflies typically feed on the underside of plant leaves. While feeding damage can cause economic losses, it is the ability of whiteflies to transmit or spread viruses that has had the widest impact on global food production. In the tropics and subtropics, whiteflies (Hemiptera: Aleyrodidae) have become one of the most serious crop protection problems. Economic losses are estimated in the hundreds of millions of dollars. While several species of whitefly cause crop losses through direct feeding, a species complex, or group of whiteflies in the genus Bemisia are important in the transmission of plant diseases. Bemisia tabaci and B. argentifolii, transmit African cassava mosaic, bean golden mosaic, bean dwarf mosaic, bean calico mosaic, tomato yellow leaf-curl, tomato mottle, and other Begomoviruses, in the Family: Geminiviridae. The world-wide spread of emerging biotypes, such as B. tabaci biotype B, also known as, ‘B. argentifolii’, and a new biotype Q, continue to cause severe crop losses which will likely continue to increase, resulting in higher pesticide use on many crops (tomatoes, beans, cassava, cotton, cucurbits, potatoes, sweet potatoes). Efforts to develop integrated pest management, IPM, systems aimed at environmentally friendly strategies to also reduce insecticide use will help re-establish the ecological equilibrium of predators, parasitoids, and microbial controls that were once in place. New crop varieties are also being developed with increased tolerance to the whiteflies, and to the whitefly-transmitted plant diseases. A major problem is the fact that the whiteflies and the viruses they carry can infect many different host plants, including agricultural crops and weeds. This is complicated by the difficulty in classifying and detecting new whitefly biotypes and Begomoviruses. Proper diagnosis of plant diseases depends on using sophisticated molecular techniques to detect and characterize the viruses and whiteflies which are present in a crop. A team of researchers, extension agents and growers working together are needed to follow disease development, using dynamic modeling, to understand the incidence of disease spread.
Hydrogen peroxide
Hydrogen peroxide (H2O2) is a very pale blue liquid which appears colorless in a dilute solution, slightly more viscous than water. It is a weak acid. It has strong oxidizing properties and is therefore a powerful bleaching agent that is mostly used for bleaching paper, but has also found use as a disinfectant, as an oxidizer, and in rocketry (particularly in high concentrations as high-test peroxide (HTP) as a monopropellant, and in bipropellant systems. The oxidizing capacity of hydrogen peroxide is so strong that the chemical is considered a highly reactive reactive oxygen species.
History
Hydrogen peroxide was first isolated in 1818 by Louis Jacques Thénard by reacting barium peroxide with nitric acid. An improved version of this process used hydrochloric acid, followed by sulfuric acid to precipitate the barium sulfate byproduct. Thénard’s process was used from the end of the 19th century until the middle of the 20th century. Modern production methods are discussed below.
Read more
Root rot
Root rot is a condition found in both indoor and outdoor plants, although more common in indoor plants with poor drainage. As the name states, the roots of the plant rot. Usually, this is a result of overwatering. In houseplants, it is a very common problem, and is slightly less common in outdoor plants. In both indoor and outdoor plants, it is usually lethal and there is no treatment.
Pythium
Pythium is a genus of parasitic oomycete. Because this group of organisms were once classified as fungi, they are sometimes still treated as such.
Morphology
- Hyphae
Pythium, like others in the family Pythiaceae, are usually characterized by their production of coenocytic hyphae, hyphae without septations.
- Oogonia
Generally contain a single oospore
- Antheridia
Contain an elongated and club-shaped antheridium.
