"Pesticides" are chemicals that are used to kill any life forms that are considered a "pests", but I assume you are referring to insecticides. The problems caused by insecticide use goes beyond the issue of cruelty to insects.
Firstly, the people that apply pesticides are exposed to much higher doses than anyone consuming the food products. It is especially unfortunate when this happens in poor countries because protective gear is not likely to be worn or used properly. The use of pesticides on crops causes unnecessary exposures to many people, several of which are children.
Pesticides also kill a lot of non-target species, many of which are beneficial and act as instrumental parts of ecosystems. With rain and irrigation, pesticides also get washed into the local water bodies causing toxic effects to various aquatic species.
Regarding the effects on the intended species the pesticides are being used for, every vegan will likely have a different answer. However, most would likely agree that it is unfortunate that humans and several other non-target species on land and in water are being exposed.
> What answer might a vegan give to the question: "What about having to
> kill "pests" which endanger our crops?"
> (By: David Taplin)