San Mateo County: New Repellent Discovery

Entomology Report February 2009, San Mateo County Mosquito and Vector Control District

Chemist Aijun Zhang, of the USDA, along with collaborators from Nanjing Foresty University in China and the US Army Medical Department Center and School, discovered a compound in the South American Tauroniro tree that is as effective as DEET at repelling mosquitoes and ticks.  Tests were performed on two mosquito species (Aedes aegypti, and Anopheles stephensi), and two ticks, (Ixodes scapularis and Amblyomma americanum). The new compound is more repellant than DEET to mosquitoes.  For ticks, the new compound’s repellency is equal to that of DEET.

The repellent compound, isoflongifolenone, is already a component of several commercial products, including cosmetics, fragrances, deodorants and some paper. Because of its widespread use, it is presumed to be safer than DEET, which is not recommended to be worn under clothes, around broken skin, near eyes or mouth, and should be used in lower concentrations on children. The study authors have devised a way of inexpensively synthesizing the compound from turpentine feed stock. Some previously discovered natural compounds with insect repellent qualities haven’t become widely available because of the high cost of producing them. The study is available in the January 2009 issue of the Journal of Medical Entomology.

Here is the journal article:

Isolongifolenone: A Novel Sesquiterpene Repellent of Ticks and Mosquitoes

Authors: Zhang, Aijun; Klun, Jerome A.; Wang, Shifa; Carroll, John F.; Debboun, Mustapha

Source: Journal of Medical Entomology, Volume 46, Number 1, January 2009 , pp. 100-106(7)

San Mateo County: Ticks and Lyme Disease

Entomology Report November 2008, San Mateo County Mosquito and Vector Control District

In November, district staff began annual surveillance activities for Lyme disease bacteria in ticks. This year, the program will focus on surveying sites of potential risk that have not been thoroughly evaluated in the past. Tick surveys were conducted this month in Portola Valley Ranch and on a previously unsurveyed trail in Laurelwood Park (San Mateo). The western black-legged tick is the primary vector of the Lyme disease spirochete in California. Adults of this tick begin appearing on trails in November, reach peak abundance in January-February and persist into early May. The immature stage (nymph) reaches peak abundance in April-May and is found in dense hardwood forest. Nymphs present a higher risk for transmitting Lyme disease to people because they are harder to see and a high proportion may be infected.

In San Mateo County, Lyme disease spirochetes have been found in 1-3% of both adult and nymphal western black-legged ticks. However, nymphal ticks are more difficult to collect than adult ticks and have only been evaluated from four sites. The lab will be working to expand collection and testing of nymphs this spring in a greater number of locations.

San Mateo County: Tularemia Survey

Entomology Report October 2008, San Mateo County Mosquito and Vector Control District

District laboratory and operational staff trapped ground squirrels at a rural site in Portola Valley this month to survey for tularemia. Tularemia is a disease carried by wild mammals including rabbits, squirrels and mice. It can be transmitted to humans through the bite of ticks, fleas, horse flies and other insects, as well as by direct contact with infected animals. Cases of tularemia have occurred in primates housed at a site north of Alpine Road for the past several years. District staff have been working with staff from Stanford University to identify the source of infection in these monkeys. Past investigations have included trapping for mosquitoes and biting flies, flagging vegetation for ticks, and trapping small mammals. Previous attempts to collect small mammals and arthropods yielded very little. Although numerous ground squirrel burrows were observed at the site, no rodents were present.

This year, ground squirrels have re-colonized the area, prompting renewed trapping efforts. Trapping on October 22 and 23 yielded 8 squirrels. Blood samples and fleas were collected from each animal. Blood samples from the squirrels will be tested by the Centers for Disease Control (CDC). Fleas were “cleared” and identified using a taxonomic key. Clearing is a chemical process that makes the body more transparent, so that internal structures are visible. Some features that are important for determining flea species are the position and presence of hairs on the body surface, the shape of reproductive structures, and the size of body segments. Two species of fleas were found on the squirrels, Hoplopsyllus anomalus and Oropsylla montanus. Both flea species are potential vectors of tularemia and plague.

Aside from spreading disease, fleas are insects worthy of our admiration. Relative to their size, they are spectacular jumpers, second in the animal kingdom only to another insect, the froghopper. Fossils of fleas suggest that fleas have been around
for about 100 million years. It is estimated that around 2,000 different flea species exist today. During the two or three month lifespan of most fleas, a female can lay 2,000 eggs, allowing fleas to persist as a problem for a variety of animal hosts.