Effects of Long Term Use of Pesticides In addition to selection for pests with genetic resistance long term use of pesticides causes imbalances in ecosystemS. Beneficial organisms and even natural enemies of the pests may be among the species 1400 1.300 eliminated by pesticides. May lose 1,100 1.000 keystone species. May develop new 800 DDT treated trees dominant pest species Untreated control trees 50 ∠ conomic injury leve 1967Effects of Long Term Use of Pesticides In addition to selection for pests with genetic resistance, long term use of pesticides causes imbalances in ecosystems. Beneficial organisms and even natural enemies of the pests may be among the species eliminated by pesticides. May lose keystone species. May develop new dominant pest species