Importance of Insect in Agriculture
Because they dominate all terrestrial environments that support human life, insects are usually our most important competitors for food, fiber, and other natural resources. They have a direct impact on agricultural food production by chewing the leaves of crop plants, sucking out plant juices, boring within the roots, stems or leaves, and spreading plant pathogens. They feed on natural fibers, destroy wooden building materials, ruin stored grain, and accelerate the process of decay. They also have a profound impact on the health of humans and domestic animals by causing annoyance, inflicting bites and stings, and transmitting disease.
The economic impact of insects is measured not only by the market value of products they destroy and the cost of damage they inflict but also by the money and resources expended on prevention and control of pest outbreaks. Although monetary values for these losses are nearly impossible to calculate, especially when they affect human health and welfare, economists generally agree that insects consume or destroy around 10% of gross national product in large, industrialized nations and up to 25% of gross national product in some developing countries.
These and other aspects of economic entomology will be our main emphasis in agriculture; when we focus entirely on insect pests and the tactics used to control them. But despite the tremendous economic losses they may cause, it is not entirely fair to cast the members of Class Insecta as villains who rob us of our food and livelihoods.
They are also cherished allies on whom we depend to keep the natural environment clean and productive. They have shaped human cultures and civilizations in countless ways, they supply unique natural products, they regulate the population densities of many potential pest species, they dispose of our wastes, bury the dead, and recycle organic nutrients.
Indeed, we seldom stop to consider what life would be like without insects and how much we depend on them for our very survival. To paraphrase William Shakespeare, "The evil that insects do lives after them, the good is oft interred with their exoskeletons."
Importance of Spiders in Agriculture
Spiders are practically everywhere. They live on nearly every continent and are part of every common ecosystem imaginable. Spiders are important predators and prey for a multitude of other animals. As any horticulturalist can tell you, they're great garden allies, too.
Here, There, Everywhere
Spiders are endemic to every continent except Antarctica. Some species are terrestrial, that is they live on the ground, while others are arboreal, meaning they live in trees. Beyond this distinction, they've also displayed a penchant for living in far-flung climates and habitats, from tropical forests to ice-cold caves. Some specialist species live in a combination of extreme conditions. Case in point, the Kauai cave spider, who lives in lava-tube habitats in Hawaii. While some spiders are social, most are solitary and interact with each other only to fight or mate.
Spiders eat lots of insects, mostly those smaller than themselves. Taken as a whole and given the diversity of species assemblages in most ecosystems, spiders' primary niche in nearly every ecosystem is controlling insect populations. Because many species overwinter, they can help reduce prey numbers early in the agricultural season, giving farmers, horticulturalists and gardeners a leg up on the season. Spiders also kill other arachnids and spiders -- even those of the same species -- which helps keep their own numbers in check. Furthermore, spiders are an important food source for a variety of birds, lizards, wasps, and, especially in deserts, mammals.
Indeed, studies synthesized and summarized in 2003 show multiple spider species are more effective at reducing insect populations than single species. As such, it's hard to pinpoint a precise niche for a precise spider. They're no go, for instance, in stopping the singular, explosive outbreak of a single pest species. If anything, new, different spider species are important for the simple fact that they're different from those already there.
Chemicals harvested from spider venom help control and treat several diseases. Likewise, spider silk, which has proved to be the strongest natural material, has inspired mechanical engineering to new heights. On the negative side, spider are blamed for numerous bites . All spiders have venom, but, in fact, most of the dangerous ones shy away from people. Moreover, their bites aren't deadly to healthy adults; they're just painful and really uncomfortable.
Importance of Mites in Agriculture:
More than 6000 species of plant feeding (phytophagous) mites are known worldwide. The majority of plant feeding species belong to the obligate plant parasitic Eriophyoidea (e.g. gall mites, erinose mites, bud mites, rust mites) and Tetranychoidea (e.g. spider mites, false spider mites), while a number of species belong to other lineages (e.g. Eupodoidea, Tarsonemidae, and single oribatid mites).
Plant feeding mites form an integral and important part of the natural ecosystem. Some species, especially eriophyoid mites, can be utilized for the biological control of weeds. Many plant feeding mites are of economic importance as pests of crop plants.
All eriophyoid mites are plant feeding. They are extremely tiny, the majority are less than 300 micron long, and essentially invisible to the unaided eye. They have elongated, worm-like bodies, with only two pairs of legs.
Eriophyoid mites are commonly known as gall mites, bud mites, rust mites, erineum mites, witches' broom mites, blister mites and so on.The feeding of almost half of eriophyoid species known, though, does not cause visible damage to their plant hosts.
The eriophyoid mites belong to three families: Phytoptidae, Eriophyidae and Diptilomiopidae. About 3400 species are known, but these probably represent only as little as 5% or less of extant eriophyoid species. Most woody and many herbaceous flowering plants, and gymnosperms and ferns most likely host these minute mites. Most eriophyoid species are highly host specific, restricted to one or single closely related plant species.
External Insect morphology
Insect morphology is the study and description of the physical form of insects. The terminology used to describe insects is similar to that used for other arthropods due to their shared evolutionary history. Three physical features separate insects from other arthropods: they have a body divided into three regions (head, thorax, and abdomen), have three pairs of legs, and mouthparts located outside of the head capsule. It is this position of the mouthparts which divides them from their closest relatives, the non-insect hexapods, which includes Protura, Diplura, and Collembola.
There is enormous variation in body structure amongst insect species. Individuals can range from 0.3 mm (fairy flies) to 30 cm across (great owlet moth); have no eyes or many; well-developed wings or none; and legs modified for running, jumping, swimming, or even digging. These modifications allow insects to occupy almost every ecological niche on the planet, except the deep ocean and the Antarctic. This article describes the basic insect body and some of the major variations of the different body parts; in the process it defines many of the technical terms used to describe insect bodies.