The correct option is E Insulin
Growth hormone (GH), luteinizing hormone (LH), follicle stimulating hormone (FSH) and adrenocorticotrophic hormone (ACTH) all are produced by the anterior pituitary gland, whereas insulin is produced by beta cells of islets of Langerhans situated on the pancreas. Therefore, it will be least affected by the removal of the anterior pituitary gland. Hence the correct answer is 'Insulin'.