what are the risks/benefits of using pesticides and there any alternatives?

2,000,000 people dead every year. That is the risk of not using pesticides to kill all the mosquitoes that carry malaria.

We still use pesticide to kill many mosquitoes around the world just not enough.

That is one example of a need for pesticides and there are as many as their are parasites that are transmitted by bugs.

During the building of the Aswan damn all work was halted because there was tremendous increase in deaths due to blood worms. This was because backed up water allowed snails numbers to increase radically carrying the worms to human hosts.

Sometimes it is all on the benifit side in lives saved.
 
Sometimes it is all on the loss side with decreased biodiversity and an increase in the bottom line.

But to quote Joni Mitchell
"farmer farmer put away your DDT,
Don't care about spots on my apples
just leave me the birds and the bees."

To use pesticides in areas to just increase crop output where famine is not a problem is just irresponsible.

Pesticides are toxic to humans and animals and some bugs actually develop resistance to them.

Alternatives include genetically modified crops that produce their own defense against insects (such as a protein). Spraying the crops is no longer needed.

There are a lot of risks to using pesticides. Unfortunately in my job, I see the risk, the consequences all the time of using pesticides, the main one being dead waterways, no fish, no bugs, overgrown with algae. I would agree that in a few cases pesticides may be necessary, but generally less toxic pesticides, better managed application of those pesticides, and using those pesticides after monitoring the crop pest load, would solve a lot of our problems.

The thing I see most people assume though and I see it in this question, is that pesticides are only a problem in agriculture. That is NOT in fact the case. As a pesticide regulator, we are seeing at least half the problem of pesticides in urban areas, where people overspray their lawn because they think they have too, people emptying out an entire can of raid on an ant's nest, and then the pesticide either poisons their kids, pets or runs into the waterways.

Back to your question, there are TONS of alternatives, including realizing that a few pests are okay, not overwatering, spacing plants out....

A cool website that I use a lot that has a lot of info (that you can cite if this is homework) is http://ipm.ucdavis.edu . I recommend it because it can give you the easy understanding or more information if you want it. It is peer-reviewed I think, and just a really good reliable source about how to manage pests rather than spray for them.