Question

what does DDT cause

Answer 1

"In insects it opens sodium ion channels in neurons, causing them to fire spontaneously, which leads to spasms and eventual death. Insects with certain mutations in their sodium channel gene are resistant to DDT and other similar insecticides. DDT resistance is also conferred by up-regulation of genes expressing cytochrome P450 in some insect species,[18] as greater quantities of some enzymes of this group accelerate metabolism of the toxin into inactive metabolites—in essence, these enzymes are natural antidotes to the poison.

In humans, however, it may affect health through genotoxicity or endocrine disruption (see Effects on human health below)."

http://en.wikipedia.org/wiki/DDT