All living beings including humans, animals and plants fall prey to the US politics once the government decides the practice of policies and acts that would affect the environment drastically. The major concern in the present discussions is the increasing CO2 levels in the atmosphere due to human interferences. The major contributor in solving this problem was President George W. Bush who took immediate steps to control the emission of green house gases in to the atmosphere. But what lay controversial is that soon after President Bush campaigned against the release of CO2 from the US power plants, he declined the Kyoto Protocol. This protocol demands every country to limit the release of green house gases and also treat the gases before they are emitted in to the environment. This step put the environment's protection against CO2 in dilemma. For instance, according to M.G. Dyck et al., 2007 the polar bears are worst hit by the green house gases.
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The scientists worldwide and Entomologists in particular grew more concerned for the insects which would be adversely affected by the increasing CO2 levels in the atmosphere. According to the studies conducted by Lincoln et al., 1984, the green house gases would for sure affect the insect populations, feeding habits and distribution throughout the world. When one concentrates more on self to think about the plant crop yield with elevated CO2 levels the pressure increases on the government but the herbivore insect communities did not make a huge impact. Studies based on this issue mainly deal with observing changes in the plant physiology, insect feeding habits, plant - insect interactions etc. The major problem with such studies is when there are many varying factors involved; the cost of study is unpredictable. According to Cannon et al., 1998, the insects may be directly affected by the changes in the temperature caused due to the elevated CO2 levels. Stiling et al., 1999 proposed that the increase in CO2 levels could directly change the behavioural aspects of predators and pathogens which usually check the insect populations from time to time. While Bezemer et al., 1998 suggested that it is the changes in the plants due to elevated CO2 levels that dictate the insect populations as the insects are dependent on various plants for food and shelter. According to Arnone et al., 1995 and Roth et al., 1997 most of the insects use different plants as hosts to reproduce and the elevated CO2 levels could affect the plant physiology causing a negative impact on the insect populations. According to Ball et al., 1997, Jones et al., and Kandeler et al., 1998 the plants depend on several aspects of the ecosystem for their survival and changes in CO2 levels can sabot ash such interactions causing deprived plant populations. The insects which depend on such plants will not be able to utilize the plants causing a decrease in their populations. While a few scientists like Coviella & Trumble, 1999 feel that we are not prepared for an increasing level of green house gases in the atmosphere. According to Hunter, 2001 the atmospheric CO2 has already risen 25% above threshold, a potential danger which has to be take care as soon as possible.
CHANGES IN PLANTS:
It is a known fact that carbon is a primary source for energy assimilations. Studies by Lincoln et al., 1993, Curtis et al., 1998 and Mousseau et al., 1994 revealed that the increased CO2 levels would obviously cause a change in photosynthetic levels causing changes in the plant physiology and phenotypes. Several contributions by various scientists lead to knowledgeable literature. Drake et al., 1997 suggested that an increased level of CO2 lead to an increased rate of photosynthesis. Studies conducted by Saxe et al., 1998 and Leadley et al., 1999 proved that elevated CO2 lead to increased carbon fixation and this in turn lead to potential increase in plant biomass. One could assume that in the scenarios where there is an increased biomass due to high carbon fixation there would be an increase in other elemental content in the plants but according to Lindroth et al., 1995 the nitrogen content in plants decreases by 15- 25% as the biomass increases. Tagged with this study is the appreciable work done by Baxter et al., 1994 and Bunce et al., 1997 which stated that elevated CO2 decreases the water content in the plant tissues and foliage. This brings about the phenomenon called early senescence in plants. The increase in CO2 also showed the development of high concentrations of secondary products like Tannins in plants like aspen and maple by Roth et al., 1998 ad Agrell et al., 2000. A phenomenal study by Coviella et al., 2000 on transgenic plants showed that transgenic cotton grown in conditions where the CO2 levels are high produced lower Bt protein. This affected the cotton industry drastically.
CHANGES IN INSECTS:
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As discussed above the elevate CO2 levels sometimes affects the plants adversely and sometimes has a positive impact on the plants. It is interesting to note the level of change this can bring about in the insects since majority of insects depend on plants for shelter, feeding and reproduction. Any change in the plant physiology can as well affect the insects. The point which is yet to be understood is how an insect maintains its fitness levels in spite of all the adversities. For instance, it is interesting to note the work by William et al., 1994 where it was showed that red headed pine sawfly potentially peaks its nitrogen utilization capacity and metabolism when plants become deficient in nitrogen content due to elevated CO2 levels. Such adaptations help the insects to keep up with the nutritional balances and also maintain their fitness in the populations. Another insect adaptation studied by Lindroth et al., 1993 was the increase in the enzymes related to detoxification with the increase in the metabolite products like tannins in the plants.
Most of these studies are limited to a short period and are most often carried out with detached leaves. The present paper by Brooks & Whittaker 1999 talks about long term experimentations on plant and insect interactions to measure the effects of such interactions in the presence of elevated CO2 levels. They revealed conclusions like standard changes can be noticed in the plant insect interaction when studied for many generations. The results vary based on conditions prevailing during the plant growth and most importantly due to the insect's interaction with the plant like the freedom of motion, selection of feeding regions on the plants etc. This paper illustrates the scientists attempt to create conditions similar to natural world in order to study the host insect interaction under the varying condition of CO2 . They study the insect (Neophilaenus lineatus L.) and its host and natural food source (Juncus squarrous L.) and compare their interaction in different conditions. The monolith was extracted and grown in a solar dome chamber. This study of host and insect interaction with population dynamics was carried out over a period of 2 years and movement along with fertility of the following generations was studied in the third generation.
The Neophilaenus lineatus L. is probably the first ever reported plant xylem feeder. But according to Raven et al., 1983, insects belonging to Cercopidae are also reported to feed on the xylem saps of the plants. These insects produce relevant amount of excreta called 'cuckoo spit' which serve as a home to the insect nymph. These insects are very favourable to experimental studies as they are sessile and prominently noticeable as they are surrounded by the cuckoo spits according to Tribe et al., 1998. The population dynamic data was used from the previous studies conducted by Whittaker 1965a,b, 1971.
LIFE HISTORY & METHODOLOGY:
The review of the life history of Neophilaenus lineatus reveals that the adult female deposits its eggs on the dead and decomposing plant material in the plant vicinity usually in the months between August and September. The adults have a shot life span. They die after laying eggs on the plant matter. According to Whittaker 1997, the eggs are usually known to hatch during the months of May/ June. The life history of this insect contains fine nymphal instars which are characterized by the presence of the cuckoo spit around them. Amazingly these insects show a phenomenon called host switching. Study by Whittaker 1965a suggested that the larva of the insect actively fed on Festuca ovina L. during its developmental stages but the instars switch to Juncus squarrosus. The stages 4 and 5 of the instars are highly mobile and this explains their aggregation in the cuckoo spits. The solar dome models are explained in the experiments conducted by Wolfenden and Diggle 1995. The whole experiment is conducted in these solar domes which contain the monoliths that were extracted from the fields of Moor House National Nature Reserve. These monoliths were collected only after the eggs had been laid on plants. Every year an examination was conducted on the insects starting from 1993 (year 1) and continued through 1994 (year 2). The data for the index of development was taken from the previous study by Hodkinson et al., 1979 which was based on the measurement of the larval dry weight. Later on the plant samples were collected from Juncus and the carbon: Nitrogen content was determined using a Carbon Erba Elemental Analyser. At the end of every experiment the adults were caged and encouraged to mate to determine the fertility and mortality in these insects. But as they are reared in different conditions then the third generation cannot be compared to the first two generations.
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In order to obtain a good statistical data, the scientists used monolith replicates which were devoid of any drastic changes in the temperature, moisture, feeding conditions and carbon dioxide as they were moved in and between the solar domes. Statistical tools such as analysis of variance were used to determine the weight of Juncus and the insect nymph. The discrete time proportion regression model of Prentice and Gloeckler 1978 was used to calculate the survival and developmental rates of the insects. Most important of all the Chi square test was used to determine the aggregation of the insect in the cuckoo spits.
RESULTS & CONCLUSION:
In this study the insect was affected by the increased levels of carbon dioxide. The study was carried out for three generations and the results showed that the fertility and survival rates of the insect was drastically affected with elevated carbon dioxide levels (600rpm) when compared with ambient levels (350rpm). The survival rate went down by 20% in the first year and by 27% in the second year. When the carbon dioxide was maximized to 600rpm, the nitrogen content in the plant parts and foliage decreased. The deformation and under development of the insect during the instars 5 stage was due to the reduced nitrogen. According to Loretta L et al, seedlings of Triadica grow well in high inorganic N and an invasive species called Morella helps providing it with N. Since it is not possible to measure the xylem content on which the insect has fed, Brodbeck et al., 1993 have conducted experiments to quantify the amino acid content in the insects and in the plant foliage and tried to relate with the consumption rates and the concerned development rates. Overall this paper highlighted the experimentation and the talked about many papers which observed the changes in the fertility, population dynamics and development of the herbivorous feeders in the presence of elevated carbon dioxide.