Scientists Discover How Chemical Repellants Trip Up Insects

There should be an image here!Fire up the citronella-scented tiki torches, and slather on the DEET: Everybody knows these simple precautions repel insects, notably mosquitoes, whose bites not only itch and irritate, but also transmit diseases such as West Nile virus, malaria and dengue.

Now, Johns Hopkins scientists have discovered what it is in the bugs’ molecular makeup that enables citronellal (the aromatic liquid used in lotions, sprays and candles) and DEET, to deter insects from landing and feeding on you. A better understanding of these molecular-behavioral links already is aiding the team’s search for more effective repellants.

In separate studies published Thursday, August 26, in Neuron and Current Biology, the Johns Hopkins researchers reveal how mosquitoes and other insects taste DEET — a man-made compound that’s been the most widely used insect repellent for more than 50 years — and smell citronellal, a commonly used botanical repellant.

Three taste receptors on the insects’ tongue and elsewhere are needed to detect DEET. Citronellal detection is enabled by pore-like proteins known as TRP (pronounced “trip”) channels. When these molecular receptors are activated by exposure to DEET or citronellal, they send chemical messages to the insect brain, resulting in “an aversion response,” the researchers report.

“DEET has low potency and is not as long-lasting as desired, so finding the molecules in insects that detect repellents opens the door to identifying more effective repellents for combating insect-borne disease,” says Craig Montell, Ph.D., a professor of biological chemistry and member of Johns Hopkins’ Center for Sensory Biology.

Scientists have long known that insects could smell DEET, Montell notes, but the new study showing taste molecules also are involved suggests that the repellant deters biting and feeding because it activates taste cells that are present on the insect’s tongue, legs and wing margins.

“When a mosquito lands, it tastes your skin with its gustatory receptors, before it bites,” Montell explains. “We think that one of the reasons DEET is relatively effective is that it causes avoidance responses not only through the sense of smell but also through the sense of taste. That’s pretty important because even if a mosquito lands on you, there’s a chance it won’t bite.”

The Johns Hopkins study of the repellants, conducted on fruit flies because they are genetically easier to manipulate than mosquitoes, began with a “food choice assay.”

The team filled feeding plates with high and low concentrations of color-coded sugar water (red and blue dyes added to the sugar), allowing the flies to feed at will and taking note of what they ate by the color of their stomachs: red, blue or purple (a combination of red and blue). Wild-type (normal) flies preferred the more sugary water to the less sugary water in the absence of DEET. When various concentrations of DEET were mixed in with the more sugary water, the flies preferred the less sugary water, almost always avoiding the DEET-laced sugar water.

Flies that were genetically engineered to have abnormalities in three different taste receptors showed no aversion to the DEET-infused sugar water, indicating the receptors were necessary to detect DEET.

“We found that the insects were exquisitely sensitive to even tiny concentrations of DEET through the sense of taste,” Montell reports. “Levels of DEET as low as five hundredths of a percent reduced feeding behavior.”

To add to the evidence that three taste receptors (Gr66a, Gr33a and Gr32a) are required for DEET detection, the team attached recording electrodes to tiny taste hairs (sensilla) on the fly tongue and measured the taste-induced spikes of electrical activity resulting from nerve cells responding to DEET. Consistent with the feeding studies, DEET-induced activity was profoundly reduced in flies with abnormal or mutated versions of Gr66a, Gr33a, and Gr32a.

In the second study, Montell and colleagues focused on the repellent citronellal. To measure repulsion to the vapors it emits, they applied the botanical compound to the inside bottom of one of the two connected test tubes, and introduced about 100 flies into the tubes. After a while, the team counted the flies in the two tubes. As expected, the flies avoided citronellal.

The researchers identified two distinct types of cell surface channels that are required in olfactory neurons for avoiding citronellal vapor. The channels let calcium and other small, charged molecules into cells in response to citronellal. One type of channel, called Or83b, was known to be required for avoiding DEET. The second type is a TRP channel.

The team tested flies with mutated versions of 11 different insect TRP channels. The responses of 10 were indistinguishable from wild-type flies. However, the repellent reaction to citronellal was reduced greatly in flies lacking TRPA1. Loss of either Or83b or TRPA1 resulted in avoidance of citronellal vapor.

The team then “mosquito-ized” the fruit flies by putting into them the gene that makes the mosquito TRP channel (TRPA1) and found that the mosquito TRPA1 substituted for the fly TRPA1.

“We found that the mosquito-version of TRPA1 was directly activated by citronellal,” says Montell who discovered TRP channels in 1989 in the eyes of fruit flies and later in humans.

Montell’s lab and others have tallied 28 TRP channels in mammals and 13 in flies, broadening understanding about how animals detect a broad range of sensory stimuli, including smells and tastes.

“This discovery now raises the possibility of using TRP channels to find better insect repellants.”

There is a clear need for improved repellants, Montell says. DEET is not very potent or long-lasting except at very high concentrations, and it cannot be used in conjunction with certain types of fabrics. Additionally, some types of mosquitoes that transmit disease are not repelled effectively by DEET. Citronellal, despite being pleasant-smelling (for humans, anyway), causes a rash when it comes into contact with skin.

[Photo above by nick kulas / CC BY-ND 2.0]

Maryalice Yakutchik @ Johns Hopkins Medical Institutions

[awsbullet:mosquito DEET]

Proteins In Unroasted Coffee Beans May Become Next-Generation Insecticides

There should be an image here!Scientists in Brazil are reporting for the first time that coffee beans contain proteins that can kill insects and might be developed into new insecticides for protecting food crops against destructive pests. Their study, which suggests a new use for one of the most important tropical crops in the world, appears in ACS’ Journal of Agricultural and Food Chemistry, a bi-weekly publication.

Peas, beans and some other plant seeds contain proteins, called globulins, which ward off insects. Coffee beans contain large amounts of globulins, and Paulo Mazzafera and colleagues wondered whether those coffee proteins might also have an insecticidal effect. The high heat of roasting destroys globulins, so that they do not appear in brewed coffee.

Their tests against cowpea weevil larva, insects used as models for studying the insecticidal activity of proteins, showed that tiny amounts of the coffee proteins quickly killed up to half of the insects. In the future, scientists could insert genes for these insect-killing proteins into important food crops, such as grains, so that plants produce their own insecticides, the researchers suggest. The proteins appear harmless to people.

Michael Bernstein @ American Chemical Society

[Photo above by GenBug / CC BY-ND 2.0]

[awsbullet:insecticide natural]

Tick Bites – Can Mean Death to Children!

With the onset of symptoms, ranging from 7 to 14 days, it is often hard for victims and/or parents to associate the illness with the tick bite. Two of the major diseases spread by the common tick are Ehrlichiosis and Lyme disease. Both of the diseases produce symptoms that mimic the flu and include fever, headache, rash, nausea, chills, weakness, and/or joint pain. Many times people will wait the normal ten days expecting the symptoms to disappear, and by then it can be too late. Advanced symptoms of Ehrlichiosis can be similar to meningitis and often will result in low white blood cells, platelet and liver enzyme counts.

The warning by the medical community is for anyone who lives in rural-type, tick-infested areas, to seek immediate medical care if they are bitten by a tick and experience any flu-type symptoms.

Advanced symptoms of Lyme disease can include extreme fatigue, arthritic joints with pain, disorientation, memory loss, and in extreme cases even death and sadly if the patient doesn’t mention being bitten by a tick the medical community may be at a loss as to the cause of the illness.

The good news, however, is that once diagnosed the treatment is relatively simply and includes large doses of vitamin C, a strict diet of fresh fruits and vegetables, lots of water, and the right antibiotic. However, if the diagnoses is delayed it can take years for symptoms to be eradicated.

To prevent tick bites doctors suggest using Avon’s Skin-So-Soft on your skin and taking daily supplements of vitamin B1 and garlic tablets. The B1 and the garlic changes the smell of the skin, so ticks don’t like it and while the ticks may crawl on you they won’t find a piece of skin to bite. Skin-So-Soft works because it contains an alternative ingredient to DEET a chemical repellent that guards against tick bites.

To protect your children and yourself it is recommended that exposure to tick-infested areas be minimized but if that is impossible and you are bitten by a tick take extreme caution and watch for any symptoms that could indicate one of the two above mentioned diseases. One quick note is that these are only two of the diseases spread by ticks there are in actuality many more including Rocky Mountain Spotted Fever.

[tags]Ticks, Tick bites, Ehrilichiosis, Lyme Disease, Rocky Mountain Spotted Fever, flu-like symptoms, Skin-So-Soft, DEET, diagnosing Tick related illnesses, medical regimen, vitamin C, death[/tags]