Hymenoptera (e.g., the wheat stem sawfly, Cephus cinctus) are occasionally important The most significant deleterious role played by Hymenoptera is derived from reaction that humans have to being stung Although a few species of parasitic Hymenoptera are capable of jabbing their ovipositor through the skin of a person, this usually requires that the person actually hold the wasp in his or her hand This is not a health concern Aculeate Hymenoptera, however, inject venom through the sting apparatus into the subject of their attention In some cases, the venom can cause severe pain by virtue of the properties of the chemicals The most significant hazard, though, lies with the reaction of the human immune system to the components of the injected venom The typical response of swelling, pain, and itching may become life threatening for individuals that become hypersensitive to the components of the venom In extreme cases, the resulting loss in blood pressure and shock can cause death, even from the sting of a single bee The so-called killer bees or Africanized honeybees are perceived as a serious health risk in the New World These bees are not an aggressive exotic species that has invaded the Western Hemisphere, but rather are the same species as the honeybee that is used in apiculture throughout the world (A mellifera) Colonies of the honeybee from Africa were brought to Brazil in order to try to breed some of their useful traits into the colonies of European honeybees being maintained in the tropics Unfortunately, African bees escaped from confinement and became established as feral colonies This strain of bees has spread and interbred with both feral and domesticated colonies of honeybees throughout South and Central America and into the southern US The African subspecies of the honeybee is notorious because the colony more vigorously defends its nest against marauders than the European bees and is generally more sensitive to disturbance In defense, the bees attack the animal or person disturbing the colony by stinging, just as European bees The difference between the two types of bees lies not in a more toxic venom but in the fact that the African forms are quicker to attack and are more persistent in pursuit and stinging Numerous deaths of humans and livestock have been recorded that result from the high number of stings inflicted and not from hypersensitivity of the person or animal being attacked In areas in which the honeybees have become more aggressive, greater care is needed by persons approaching the hives 183 locating their hosts in a complexly structured environment; and parasitoid populations respond to those of their hosts, increasing when host populations increase and decreasing when the availability decreases The importance of parasitoids as regulators of the populations of their hosts is most clearly seen when, for example, a phytophagous species is accidentally introduced into a new region without its normal complement of natural enemies Populations of such species are capable of explosive growth in the new environment, rapidly becoming important pests, for example, gypsy moths (Lymantria dispar) in North America and the cassava mealybug (Phenacoccus manihoti) in tropical America Biological control programs involve the discovery of the natural environment and enemies of such pests and the importation of these natural enemies for control Some examples of biological control have been spectacularly successful, with effective long-term control of pests The parasitoid families Encyrtidae and Aphelinidae have been particularly effective in biological control programs of many species of sternorrhynchous Hemiptera Pollination The successful development of seeds and fruit of many species of flowering plants depends on pollination – the movement of pollen from one flower to another Although some species of commercially important plants, particulary grasses, are wind pollinated, a great many others rely on animal agents for the transfer of pollen Under natural conditions pollinators can include vertebrates, such as bats and hummingbirds, and a wide variety of insects, including flies and beetles Hymenoptera, however, and in particular the bees, are extremely important as pollinators Recall that bees provision their nests with plant pollen on which their developing larvae feed In the process of collecting pollen for their nests and also in collecting nectar from within the flowers, pollen grains that adhere to the hairy body of a bee can be transferred to the style of the flower Natural pollinators include a vast array of native bees, but for many commercial crops colonies of honeybees are used to effect pollination The honeybee is a polylectic species, that is, it gathers and its larvae feed on pollen from a wide variety of plant species Colonies are regularly transported to fields in order to temporarily increase population levels to maximize fruit and seed production Biological Control Agents Honey and Other Bee Products Although some species of Hymenoptera have negative impacts on humans and their commerce, by and large the order is considered to be very beneficial One of the most important categories of such beneficial species consists of those that either parasitize or prey on pest arthropods These species, by eventually killing the other insects, act as biological control agents that reduce the population levels of their hosts Such control agents have many advantages: Parasitoids are often fairly host specific, and thus their effects are focused on the pest problem; a population of biological control agents is capable of maintaining itself through time, thus providing continuous control; parasitoids are often extremely effective at The large colonies of social bees also store honey within the nests that they construct Honey is the modified and concentrated product of the nectar gathered principally at flowers and is used as an energy source for the adult bees The most familiar species that serve as sources of honey for human consumption belong to the genus Apis, including the domesticated honeybee, but both bumblebees and stingless bees also produce and store honey Honey production and the sale of it often provide a significant income supplement for small farmers Another product from honeybee colonies that is of some value is beeswax, used variously in cosmetics, pharmaceuticals, and candles