The ear of sweet corn often is already inhabited by corn earworms. Insects transmit plant diseases. Often, the insect itself causes little damage when it pauses to feed on a plant. However, many insects can pick up viruses, bacteria and other disease organisms as they feed then later transmit them to healthy plants, resulting in severe damage and even death of the plant. For example, aphids transmit viruses that cause disease in wheat and barley, bark beetles move fungi which cause Dutch elm disease that kills American elm, and the aster leafhopper can inject the bacteria causing aster yellows, a common problem for lettuce, carrots and many flowers.
Insects transmit diseases to humans and animals .
Insects and other arthropods also can transmit diseases to animals. Perhaps best known are mosquitoes, which spread malaria, yellow fever, dog heartworm and many other very important diseases. In the Rocky Mountain region the most important diseases that mosquitoes spread are types of equine encephalitis, which can be very serious to horses and occasionally infects humans as well. Insects sting, bite or otherwise create annoyance . Many insects feed on the blood of animals.