Need help on short answer question quickly-it will probably seem easy to you but it feels like a riddle?

Question

In Taiwan, two mites are found on rice plants. One mite feeds on the rice plant and produces a huge number of young. The second mite is larger and is predatory on the rice mite, but like most predators, produces fewer young. The field is sprayed with a broad spectrum insecticide that kills both mites. However, with no further spraying, the rice is far more seriously infested with mites the next few years than before the spraying. Why?

Answer 1

Well it certainly is all there for you, just takes a little guidance. The key is that the predatory mite produces fewer young. With all else being equal, the larger mite will simply go day to day eating the smaller mite and will reproduce at a slower rate but thats ok since the mite will just eat many more of the plant mites throughout its life. It can likely be expected that each predatory mite will eat several plant mites in its life, but that isn't necessary for this to work. The predatory mite keeps the plant mite population in check allowing the crop to be minimally affected.

Now you spray the field. The problem here is numbers, with a slower reproductive rate the larger predatory mite likely has fewer in number across the field and will be less able to quickly come back to normal after a mass extinction even like the pesticide would be. Lets say for instance that the pesticide kills off 50% of both mites populations, but if the plant mite grows twice as fast then in the year following the spraying you will have many more of the plant mites. Much more then the predatory mite is able to control. No pesiticide ever kills all, its more a percentage thing

Here is what is important to understand and what likely your teacher will like to see, the predatory mite population will eventually return to normal. The boom in plant mite population is beneficial to the predatory mite and the population will be able to come back, but it will do so very slowly and the crop will suffer in the mean time.  

Answer 2

The spraying had a greater effect on the population of predator mites.

The spray kills both mites lets say it reduces it by 90% of 100 of each.  Now 10 mites of each are left.  If the 10 rice mites produce 100 young and the predator mites produce 10, we have a disparity in the numbers that will continue to grow.  The predator mites remaining will have little effect on their total population number.

Check out the website below on predator prey relationships.

http://www.globalchange.umich.edu/global...

Answer 3

predators control the population of the pray.  The insecticide must have killed all of the predators but some of the prey might have been immune so without the predators their population grows unchecked.