City of Irvine
2020 Local Hazard Mitigation Plan
• Mosquitoes are parasitic insects that feed on the blood of mammals, including humans. They use a needle-like part of their mouth, called the proboscis, to breach the epidermis and reach the blood vessels beneath the skin. As mosquitoes withdraw the blood from their host, they can potentially transfer infectious diseases they are carrying to the host. Only certain diseases may be transmitted by mosquito. The Human
Immunodeficiency Virus (HIV), for example, cannot be transferred from human to human since the HIV virus cannot survive in mosquitoes. The Zika or West Nile viruses, on the other hand, are highly transmissible infections via mosquitoes, and this is the most common form of transmission. 39 • Mice and rats are small rodents that can transmit disease or be a vector for other disease-carrying organisms. The most well-known and historical example of this is the Bubonic Plague. In the 14 th Century, mice and rats infested with fleas traveled to Europe from Asia. The fleas carried the Bubonic Plague in their bodies and transmitted the infection to human populations as the fleas left the rats and mice for new human hosts. 40 Tree Mortality The entirety of a city’s trees is generally referred to as an urban forest. These trees may be publicly owned An Asian Tiger Mosquito, which may attack during the day, bites its host. Image from San Diego County News Center.
or maintained, such as trees in a public park or street median, or privately owned, such as the ornamental trees found in a property owner’s landscaping. Urba n forests represent important assets for a city as they provide shade, which helps keep the community cool. They also provide aesthetic beauty to a community and are known to help humans feel calm and less stressed. Tree mortality refers to the death of numerous tree specimens in a forest, including urban forests. The death of a tree represents a significant loss since trees are expensive and require extensive time and care to be properly raised. Tree mortality may result from numerous causes, including but not limited to extreme heat, uprooting from severe weather, over- or under-irrigation, or chemical
Asian Citrus Psyllids feed on the leaves and stems of citrus trees. Image from California Citrus Threat.
contamination. Like other living beings, trees are also subject to vector-borne diseases spread by pests. These diseases can cause the tree to produce misshapen fruit or discolored leaves. The disease can also kill the tree over an extended period. Pests that cause tree mortality are of concern since they may be difficult to detect and quarantine.
Pests that are currently afflicting trees in Orange County include the following:
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