 Hi, welcome back to the class. After actually understanding the insects, their abundance and diversity, in this class let us know about the pest, its different categories and the reasons for their outbreak. So, basically if you know that insects as a group can be related to the human being in two different ways, for example the insects which are economically important and those groups of insects which are not economically important, it is from the human point of view. So, under the insects which are economically important group, we are more interested in and we are ignoring the insects which are not economically important. Under the economically important group, the insects are broadly categorized as the injurious group, the beneficial group and the helpful group. The injurious group mainly includes those groups of insects which cause certain physical and physiological damage to our crop plants or to the human beings and to the animals. Those which cause damage to the agricultural crops are referred under the agricultural entomology and those which are pest to the forest plants are referred as forest entomology and those which cause damage to the storage grains, we refer it as the storage entomology. Similarly, the insects which either directly or indirectly cause damage or annoyance to the human beings are referred under medical entomology and those which cause a similar kind of the damage to the animals are referred under veterinary entomology. Coming to the beneficial group of insects, like we have some insects such as honeybee which are directly giving some kind of a product in the form of honey, wax, etc. and the silkworm which gives the silk. Similarly, the lac insects which gives the lacs are all referred as a productive insects and in many parts of the world including India, we know that insects also serve as food and the insects in a medicinal field also is used. The drosophila melanogaster is a classic example both in case of the scientific research also and we know the beautifullness of the butterflies and the beetles and the insects are also considered as the aesthetic value. Under the helpful group of insects, some of the insects which actually feed on those insects which are pestiferous in nature or those which are injurious, we refer those insects as predators and parasitoids and which are indirectly are going to help in the agricultural ecosystem and majority of the groups of insects like bees and the butterflies which do the pollination service is an helpful the way and some of the insects which feed on the plants which are considered to be the weed, we refer them as a weed killers and of course many insects will help in a many way by decomposing the waste material and they are referred as the scavengers. Now in this course we are mainly concentrating on this agricultural entomology where we are dealing with the pest which causes damage to the agricultural crops and also the predators and the parasitoids which actually feed on these agricultural pest and cause beneficial to the human being. Now we call this group as a pest then what is a pest? So pest can be an any organism whose population is increases to such an extent which causes an economic loss to the crop or causes a nuisance or the health hazards to the human beings and the livestock. The world pest is mainly derived from the French called the pestae and the Latin term called pastis which means the plague or the contagious disease. The pest status of an insect species may be determined in a number of ways such as increase in the number of insects like the insects may suddenly develop and then they multiply and make into a huge population and thus they become the pest or by change in the type of damage inflicted on the crop in the sense like if a pest or an insect which is a defoliator might not be a serious threat but if it shifts it is the feeding size to the fruits then it becomes a serious pest. Then a method of cultivation or harvesting depending upon how the crop has been cultivated or harvested so the pestiferous nature of an insect can be decided. Then based on the market value of the crop like the best example I can quote is like onion and tomato where when there is a huge market demand for these crops then even a smaller damage caused by the insect may be considered as a serious pest and vice versa. Now, the pest can be anything not only the insect it can be a nematode it can be mites snails slugs etcetera and even in the mammals like rats and birds but in this course we are mainly concentrating on the insects as a major pest. Now, what is the extent of the loss that an insect can cause? So, along with the other groups of organisms or the animals the insects are believed to be contributing nearly 26 percent of the loss to the cropping ecosystem. So, of course the weeds will take a major toll but the insects and the diseases are one of the major things. It has been estimated that annually there will be around 60,000 crores of rupees been lost due to a damage by insects on various agriculture crops. And if you look at this table so which actually gives an idea about the extent of loss caused by the insects in various crops. So, quote as some example like in cotton nearly 30 percent of crop loss has been caused by the insects rise around 25 percent and so on and so forth it goes like that. And an average we can say around 18 percent of the economic loss is caused by the insects. Now, why these insects have become pestiferous? It is very important to know the reasons behind this and we can call that the reasons for the outbreaks of these insects as pest. Most of these reasons if you just look into it or we can say it is a man made. So, first and foremost is the destruction of the forest or an deforestation. So, what happened with this? So, when you actually destroy the natural habitat of the insect then those insects will do not have any other way but to actually start feeding on the cultivated crops and thus they become pests. And another important the reason is the destruction of the natural enemies by means of the deforestation or also by means of the indiscriminate use of pesticides we are going to kill the natural enemies of these insects and making them quite convenient to multiply and then become pest. Then another third reason is an extensive and the intensive cultivation of the crop. For example, we see sometimes see the thousands and thousands of area will be covered under a single crop like paddy or sugar cane or cotton something like that. If this happens what happens the insects which are thriving on such crops will get a tremendous opportunity to multiply and thus they becomes quite pestiferous. The next one is introduction of new crops or the improved variations this will also lead to a formation of the pest. For example, any agronomic practices that we are going to introduce so will may quite beneficial to these insects and then leads to a pestiferous nature. And improved agnorm practices such as the fertilizer application we will know that that is a more and more nitrogenous fertilizer if you apply to the crops like paddy then that leads to the development of the newer pests such as the leaf holders, brown plant hoppers etcetera. Introduction of new pest in new areas and the introduction of a foreign pest is a very classic examples that we have so when these insects which are not actually in those areas when they have been accidentally introduced then what happens they get in a good environment and there will not be any natural enemy for them and this gives a boost for their multiplication and they started becoming pest. And resurgence of the pest the resurgence of the second pest is another reason like for example if you look at it here is a schematically it is represented so there is a pest and also there is a natural enemies here and when you go for some kind of a spray which actually kills all these natural enemies and leaves some of these pest what happens because of absence of the natural enemies then the pest will multiply and become quite serious and storage of large quantity of the grains like this will also provide a good opportunity for the insect to become colonized and then multiply and leads to a pestiferous nature. Then in the next class we are going to talk about so how this pest can be actually decided on economic basis and how the categories of the pest can be made. Thank you.