Pesticides & Effects
Quantity and variety of pesticides
In 2006 and 2007, the world used approximately 5.2 billion pounds of pesticides, with
- Herbicides constituting the biggest part of the world pesticide use at 40%, followed by
- Insecticides (17%) and
- Fungicides (10%).
For the global market of crop protection products, market analysts forecast revenues of over 52 billion US$ in 2019.
Pesticides may cause acute and delayed health effects in workers who are exposed. Pesticide exposure can cause a variety of adverse health effects, ranging from simple irritation of the skin and eyes to more severe effects such as those affecting the nervous system, mimicking hormones, causing reproductive problems and cancer.
Pesticide-use raises a number of environmental concerns. Over 98% of sprayed insecticides and 95% of herbicides reach a destination other than their target species, including non-target species, air, water and soil. Pesticide drift occurs when pesticides suspended in the air as particles are carried by wind to other areas, potentially contaminating them. Pesticides are one of the causes of water pollution, and some pesticides are persistent organic pollutants, and contribute to soil contamination.
Human health and environmental cost from pesticides in the United States is estimated at $9.6 billion:
|Harm||Annual US Cost|
|Public Health||$1.1 billion|
|Pesticide Resistance in Pest||$1.5 billion|
|Crop Losses Caused by Pesticides||$1.4 billion|
|Bird Losses due to Pesticides||$2.2 billion|
|Groundwater Contamination||$2.0 billion|
|Other Costs||$1.4 billion|
|Total Costs||$9.6 billion|
Nocturnal Insects’ Attraction to Light
Phototaxis is a kind of taxis, or locomotory movement, that occurs when a whole organism moves in response to the stimulus of light. This is advantageous for phototrophic organisms as they can orient themselves most efficiently to receive light for photosynthesis. Phototaxis is called positive if the movement is in the direction of increasing light intensity and negative if the direction is opposite. http://en.wikipedia.org/wiki/Phototaxis
Using Lights to Attract Insects
That light attracts many insects is common knowledge, lights (incandescent, fluorescent, and ultraviolet) that attract insects from dark or dimly lit surroundings, but making use of light and its component colours in visual lures requires considerably more detailed understanding.
A great number of insect species are attracted to light of various wavelength. Although different species respond uniquely to specific portions of the visible and nonvisible spectrum (as perceived by humans), most traps or other devices that rely on light to attract insects use fluorescent bulbs or bulbs that emit ultraviolet wavelengths (black lights). Hundreds of species of moths, beetles, flies, and other insects are attracted to artificial light. They may fly to lights throughout the night or only during certain hours. Key pests that are attracted to light include the European corn borer, codling moth, cabbage looper, many cutworms and armyworms, diamondback moth, sod webworm moths, peach twig borer, several leaf roller moths, potato leafhopper, bark beetles, carpet beetles, adults of annual which grubs (Cyclocephala), house fly, stable fly, and several mosquitos.) The mosquitoes Ochlerotatus (formerly Aedes) triseriatus, Ochlerotatu (also formerly Aedes) hendersoni, and Aedes albopitus are not attracted to light, however.) Lights and light traps are used with varying degrees of success in monitoring populations and in mass trapping. http://edis.ifas.ufl.edu/in080
Why are moths attracted to light?
According to Mike Saunders, the answer is simple: “Moths often use the moon to orient themselves during night flight,” explains Saunders, a professor of entomology at Penn State. In visual terms, the moon appears at “optical infinity,” i.e., far enough away that the rays of light it reflects toward Earth are parallel as they enter a moth’s (or a human’s) eye. This constant makes an excellent navigational tool. “Using the moon as a reference, moths can sustain linear flight in a given direction.”
But technology has been unkind to the moth. “Artificial lights seem brighter than the moon,” Saunders notes, “and moths end up orienting to them even though the artificial light is not at optical infinity.” The moon remains safely out of reach, but a candle or lamp is a different story. As the moths get closer to the light, their ability to triangulate is thrown off.
Says Saunders, “Maintaining a constant frame of reference to the artificial light results in the moth circling the light over and over again.” So the moth winging around your kitchen light is doing so more out of confusion than desire. As to why moths tend to remain close to a light source once they have reached it,
Some researchers have suggested that, having reached a brightly lighted spot, a nocturnal moth is tricked into thinking the sun is out, and settles in to sleep.
Another theory holds that candle flames emit wavelengths similar to those of female moth pheromones, attracting male moths intent on romance.
Yet another attributes the moth’s seeming fondness for light to the search for food. Most moths are nocturnal, and many feed on the nectar of flowers, which often reflect ultraviolet light. They may mistake artificial ultraviolet light for a potential food source. “It is certainly possible that night-blooming flowers are detected by moths as a function of reflected moonlight,” says Saunders. But nocturnal moths have other means of finding their night-time meals, he adds. “Recent research indicates that the moth is capable of detecting high levels of CO2 being emitted by flowers. It is believed that these high CO2 levels signal increased metabolic activity in the flower, which may tip off the moth to the presence of nectar.”
While these explanations may account for some light-seeking moth behaviour, the vast majority are drawn to light due to navigational snafus, says Saunders.http://www.rps.psu.edu/probing/moths.html
Insects’ phototaxis and light wavelength
Light is essentially an electromagnetic wave, which shows different characteristics due to different wavelengths. Human eyes can sense wavelength between 390-750nm, but are incapable to sense short wave called ultraviolet. Short wave between 300-390nm is close-ultraviolet, also called black light. Wavelength above 750nm is infrared. Long wave between 750-1,000nm is distant infrared. Insects’ eyes are different from human’s, the close ultraviolet and distant infrared can all be sensed by insects’ eyes, although the wavelength range are different depending on the type of insects.
Different insects have different biological and ecological characteristics, which are reflected in their phototaxis and selection of wavelength. Duafy (1964) studied 8 types of Noctuidae, individually tested 3-5 wavelength between 365-675nm, to compare the difference of their phototaxis. The result showed that the peak points were 365nm, 450nm, 525nm.
Similar to other biological bodies, insects’ physical structure relates to their behaviour and habits. The major behavioural difference between nocturnal insects and diurnal insects is phototaxis. Insects’ compound eyes have photoreceptor function, which enables their night vision in the presence of weak light in the natural environment. Different compound eyes physical structure serves different functions.
Nocturnal insects are always active at night, their compound eyes are able to adapt different strength of light. The adaptability of brightness and darkness of nocturnal insects’ compound eyes bares close relationship to the insects’ phototactic behaviour and this adaptability affects the compound eye’s functionality.