Bed bugs might sound like an old-fashioned problem, but now they are back with a vengeance. Fifty years ago, the blood-sucking pests were nearly eradicated in the United States thanks in part to the use of pesticides like DDT. Today, they are creeping over sheets and tormenting sleepers across the country. New York was recently declared America's most bed-bug-infested city in America. In the past, we countered the bed bugs by using pesticides called pyrethrins and pyrethroids. These compounds work by attacking the nervous system. Insects have channels in the membranes of their nerve cells that can be opened to allow sodium into the cells, triggering a nerve impulse. Pyrethrins and pyrethroids alter the nervous system by binding to the sodium channels, locking them in the open position. This allows sodium to pour into the cell continuously, causing the nerve to fire repeatedly and eventually leading to paralysis. Todays bed bugs seem to be more resistant to the chemicals that previously killed them. Cases of resistance have been reported in all classes of pests: crop diseases, human diseases, weeds, rodents, and insects, with crises in insect control beginning shortly after the introduction of pesticide use in the 20th century. Why do insect pests become resistant so readily to the pesticides used for control

Environmental science studies the interactions between the physical, chemical, and biological components of the environment, including their effects on all types of organisms. earth science (also known as geoscience), is an inclusive term for all sciences related to earth (geology, meteorology, oceanogr maphy, etc).  although environmental and earth science cover essentially the same material, environmental science places greater emphasis on the biological realm, while earth science places greater emphasis on the physical realm.    environmental and earth science study the interactions of four major systems or “spheres” (figure 8.6).  the  geosphere  consists of the core, mantle and crust of the earth.the  atmosphere  contains all of the earth’s air and is divided into troposphere, stratosphere, mesosphere, thermosphere and ionosphere.the  hydrosphere  contains all of the solid, liquid and gaseous water on earth, extending from the depths of the sea to the upper reaches of the troposphere where water is found.  ninety-seven percent of the hydrosphere is found in salty oceans, and the remainder is found as vapor or droplets in the atmosphere and as liquid in ground water, lakes, rivers, glaciers and snowfields.  the  biosphere  is the collection of all earth’s life forms, distributed in major life zones known as biomes:   tundra, boreal forest, temperate deciduous forest, temperate grassland, desert, savannah, tropical rainforest, chaparral, freshwater, and marine.although the four systems have their unique identities, there is substantial interaction between them.  environmental scientists study the effects of events in one sphere on the other spheres. for example, a volcanic eruption in the geosphere may cause profound direct and indirect effects on the hydrosphere, atmosphere and biosphere as follows: example 1 (volcano)    on may 18, 1980, mount saint helens, in the state of washington, erupted.  this event altered the surrounding environment, and provided scientists with an opportunity to study the effects of volcanic eruptions on the geosphere, hydrosphere, atmosphere and biosphere.  such studies are vital because volcanic eruptions will continue to occur, and will have increasing impact on humans as people continue to settle lands closer to dormant volcanoes. the following are but a few of the myriad of interactions resulting from a volcanic 

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