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

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Mother Nature Provides Environmentally Friendly Method For Reducing Mosquitoes

There should be an image here!A scientific breakthrough might assist in the fight against mosquitoes. New research carried out at the University of Haifa in collaboration with researchers from other universities has chemically identified, for the first time, compounds released by mosquitoes’ natural aquatic predators that function as warning signals for egg laying mosquitoes. Introducing these natural chemicals into mosquito breeding sites will cause the mosquitoes to sense risk of predation to their progeny and avoid laying their eggs there. These findings will soon be published in the prestigious journal Ecology Letters.

Ecologists and evolutionary biologists have known for a long time that many prey species can detect predators chemically and, upon detection, take various actions to avoid being eaten or avoid having their progeny eaten. Yet, the chemical identity of the predator-released chemicals has remained elusive. Knowing the chemical identity of these compounds would greatly facilitate scientists’ understanding of predator-prey relationships and the importance of these compounds in affecting ecological communities. They may also provide an eco-friendly alternative for mosquito control.

The new breakthrough research, funded by the Israel Science Foundation, was developed in Prof. Leon Blaustein’s laboratory at the University of Haifa. Prof. Blaustein’s research partners comprised a multi-disciplinary group: Alon Silberbush, a doctoral student, Dr. Shai Markman, a chemical ecologist from University of Haifa-Oranim, Dr. Efraim Lewinsohn and Einat Bar, chemists at the Newe Yaar Research Center, and Prof. Joel E. Cohen, a mathematical and population biologist at Rockefeller and Columbia Universities.

Previous research from Blaustein’s lab demonstrated that the mosquito, Culiseta longiareolata, chemically detects a voracious predator of its progeny in the water, the backswimmer, Notonecta maculata, and avoids laying eggs where the predator is detected. However, until recently, the chemical identity of these predator-released compounds was not known. By screening and comparing the chemicals released by N. maculata with those released by Anax imperator, another aquatic predator that does not elicit a chemical response by the mosquito, they were able to narrow down the potential chemicals that elicited the mosquito’s behavioral response. Blaustein’s group then conducted outdoor experiments on potential chemicals and determined that two of these N. maculata-released chemicals, n-tricosane and n-heneicosane, repelled these mosquitoes from laying eggs. The two compounds together had an additive effect.

Applying such synthetic compounds to mosquito breeding sites would not only result in much fewer mosquitoes in the immediate area but probably reduce mosquito populations overall. Increased searching by pregnant mosquitoes for a breeding site that is perceived as predator-free increases greatly the probability of dying before egg laying; mosquitoes, on average, incur a 20 percent probability of mortality per day. Moreover, mosquitoes, by concentrating their eggs in considerably fewer breeding sites perceived as predation-risk free, would increase competition among the mosquito larvae resulting in fewer and weaker emerging adults.

Prof. Blaustein explains that in the fight against mosquitoes, there are essentially three lines of defense. The first and preferred line of defense is to prevent emergence of adult mosquitoes from aquatic breeding sites. When this has not been done effectively, mosquito control workers resort to trying to kill the adults that have spread to residential areas. This is much more difficult, more expensive, and usually involves chemical pesticides of environmental and health concerns. When these two lines of defense fail, the burden falls on the public to prevent mosquitoes in search of a blood meal from biting them, such as staying indoors and using mosquito repellents applied to the human skin. Prof. Blaustein points out that options for all three lines of defense are often chemicals that negatively affect the environment and are of health concerns to humans. Moreover, mosquitoes often develop resistance to chemical pesticides so there is always a need to find new weapons against mosquitoes. A bacterial pesticide, Bacillus thuringiensis israeIensis, can be very effective in killing mosquito larvae in breeding habitats while having relatively minor non-target effects, but it is rather expensive and is not effective in highly organic-polluted water.

This research group’s new findings of chemical identification of predator-released egg-laying repellants can be a breakthrough in providing a natural, environmentally friendly and inexpensive option to the arsenal in the first line of defense.

Blaustein adds, “While we see this as a potentially large breakthrough in developing another weapon against mosquitoes, the work, is not over. We hope this breakthrough will spur further research to chemically determine other effective predator-released chemicals, particularly ones that are long lasting and then tested for their efficacy.”

Rachel Feldman @ University of Haifa

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

[awsbullet:mosquito repellent]

Underwater Sponges And Worms May Hold Key To Cure For Malaria

There should be an image here!Healing powers for one of the world’s deadliest diseases may lie within sponges, sea worms and other underwater creatures.

University of Central Florida scientist Debopam Chakrabarti is analyzing more than 2,500 samples from marine organisms collected off deep sea near Florida’s coast. Some of them could hold the key to developing drugs to fight malaria, a mosquito-borne illness that kills more than 1 million people worldwide annually. Chakrabarti is pursuing this study with Amy Wright of Harbor Branch Oceanographic Institute, Fort Pierce, whose team has collected these samples from a depth up to 3000 feet.

Chakrabarti is excited about the early promising results — preliminary tests identified about 300 samples that can kill malaria parasites. He’s also concerned, however, that the Gulf of Mexico oil spill may wipe out species that could hold healing properties for many deadly diseases.

“There is a very good possibility that the answers to cancers, malaria and other diseases may be found in the ocean,” he said. “Why am I so optimistic? Just consider that the oceans cover 70 percent of the planet. Among 36 of the phyla of life, 34 are found in marine environment whereas the land represents only 17 phyla, and we haven’t even begun to explore the oceans’ depths.

“But I’m worried. Who knows what we may be losing.”

He watches the news while continuing his research in hopes of finding answers to malaria, a disease he’s dedicated his life to combating. There is no FDA-approved vaccine for malaria, and people are becoming more resistant to the drugs available to treat it.

Chakrabarti and Wright landed a $500,000 grant from the National Institutes of Health and National Institute of Allergy and Infectious Diseases for their study.

So far, Chakrabarti and his two graduate students have conducted preliminary testing of more than 2,500 samples from the Harbor Branch collection. They conducted tests to evaluate growth inhibitory properties of these samples for malaria parasite growing inside human red blood cells in culture.

One active sample derived from a marine sponge contained the compound Nortopsentin. Because of this compound’s initial promise, Chakrabarti said, he’s already filed an application for patent protection.

Harbor Branch is one of only three organizations in the country that has the capability to collect deep-sea samples. It has submersible vehicles that dive 3,000 feet underwater to collect samples off Florida’s coast. Wright directs the biomedical-marine research program at Harbor Branch.

Chakrabarti’s approach of identifying new drugs from marine sources builds on prior research around the globe.

In May, the American Society of Clinical Oncology announced results from a Japanese study concluding that the drug eribulin, derived from sea sponges, was effective in helping patients fight breast, colon and urinary cancer. Scientists in Australia are diving into the Great Barrier Reef to explore the potential healing powers of marine creatures living there.

Locally, Gregory Roth, director of medical chemistry and exploratory pharmacology at the Sanford-Burnham Medical Research Institute is working with Harbor Branch on similar research. Sanford-Burnham is one of the UCF College of Medicine’s partners at its new health sciences campus in Lake Nona.

Chakrabarti will continue analyzing samples, particularly the 300 already identified as promising, during the next year.

“If we can find two or three good molecules that can be easily synthesized in a lab and that can prevent malaria, I’d be very happy,” he said.

Zenaida Gonzalez Kotala @ University of Central Florida

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Poor Data On Key Mosquito Control Tool A Threat To Effective Malaria Prevention

There should be an image here!Despite wide acclaim as a successful policy there is currently almost no quantitative evidence showing how well spraying the walls of people’s homes with mosquito-killing insecticide really works against malaria. This is the key finding of a new Cochrane Systematic Review.

The method, known as “Indoor Residual Spraying” (or IRS), has been widely used in the world since 1950. While it clearly works, it is impossible at present to quantify its protective effect. As a result, international agencies, donors and national programmes working on malaria control are not able to compare the benefits of IRS with any other approach.

“At a time of major investments into malaria prevention (over 500 million dollars in 2009) this is of great concern,” says Prof. Christian Lengeler who works as an epidemiologist at the Swiss Tropical and Public Health Institute, in Basel, Switzerland.

In this regard, IRS has been a victim of its own success. Almost as soon as people started spraying the walls of their homes in the 1950s, they saw a marked drop in the level of malaria. Outstanding successes were recorded in Europe, Asia and the Americas. The benefit was clear, but no one stopped to quantify the impact.

In order to get a proper measure of impact, scientists need to divide an area with malaria into many small units, generally villages, and allocate randomly IRS to half of these areas, while the other areas remain as controls — either without IRS or using another approach such as insecticide-treated mosquito nets (ITN). This systematic approach was only used in four out of the 143 studies ever done on IRS; these four were included in the review, together with two additional studies of different but adequate design. “Clearly, this is disappointing. With such a large body of evidence it is sad that so few of the studies provide high-quality scientific evidence. This represents a great waste of resources and efforts, and we are left with a very poor evidence base” says Prof. Lengeler.

The data from the six trials was consistent with the idea that IRS is successful in malaria-endemic populations, but the number of studies was too low to properly quantify that effect. There was an indication that ITNs, the other commonly applied vector control tool, may have a slightly better protective effect than IRS, but again the evidence was not good enough to be sure.

“Because we know that IRS works, it is no longer ethically possible to carry out studies with control groups that don’t receive anything. Consequently, we urgently need more high-quality studies that compare IRS with the other widely implemented vector control method, ITNs.” says Prof Lengeler.

Given the World Health Organization’s 2007 decision to move towards world-wide malaria eradication, policy makers now also require good evidence on the combination of both IRS and ITNs. “Currently we have no evidence to show whether or not a combination would be justified both from the cost and the impact side and this needs to be urgently generated,” says Lengeler.

Jennifer Beal @ Wiley Blackwell

[Photo above by Sean McCann / CC BY-ND 2.0]

[awsbullet:malaria prevention]

Gorillas Carry Malignant Malaria Parasite, Study Reports

There should be an image here!The parasite that causes malignant malaria in humans has been detected in gorillas, along with two new species of malaria parasites, reports a study co-authored by UC Irvine biologist Francisco Ayala.

The study also confirms a recent discovery by Ayala and colleagues that human malignant malaria, caused by Plasmodium falciparum, originated from a closely related parasite found in chimpanzees in equatorial Africa. P. falciparum is responsible for 85 percent of malignant malaria infections in humans and nearly all deaths from the disease.

The researchers cautioned that increased contact between primates and humans — mostly because of logging and deforestation — creates a greater risk of new parasites being transmitted to humans. It also could further jeopardize endangered ape populations by spreading diseases to them. Finding P. falciparum in gorillas also complicates the challenge of eradicating malaria.

“Hundreds of billions of dollars are spent each year toward ridding humans of malignant malaria. But success may be a pyrrhic victory, because we could be re-infected by gorillas — just as we were originally infected by chimps a few thousand years ago,” said Ayala, corresponding author of the study, published this week in the Proceedings of the National Academy of Sciences.

The researchers analyzed fecal samples from 125 wild chimpanzees and 84 gorillas in Cameroon and tested blood samples from three gorillas in Gabon. They identified two new closely related species of malaria parasites — Plasmodium GorA and Plasmodium GorB — that infect gorillas. The animals also were found to harbor P. falciparum, previously thought to only infect humans.

In August, Ayala and colleagues published a study reporting that P. falciparum had been transmitted to humans from chimpanzees perhaps as recently as 5,000 years ago — and possibly through a single mosquito. Before then, malaria’s origin had been unclear.

Chimpanzees were known to carry the parasite Plasmodium reichenowi, but most scientists assumed the two parasites had existed separately in humans and chimpanzees for the last 5 million years.

The discovery could aid the development of a vaccine for malaria, which each year causes 2 million infant deaths and sickens about 500 million people, mostly in sub-Saharan Africa. It also furthers understanding of how infectious diseases such as HIV, SARS, and avian and swine flu can be transmitted to humans from animals.

In addition to Ayala, French scientists Franck Prugnolle, Patrick Durand, Cecile Neel, Benjamin Ollomo, Celine Arnathau, Lucie Etienne, Eitel Mpoudi-Ngole, Dieudonne Nkoghe, Eric Leroy, Eric Delaporte, Martine Peeters and Francois Renaud worked on the gorilla study.

Funding was provided by France’s Institute of Research for Development, National Center for Scientific Research, Ministry of Foreign Affairs and National Agency for Research on AIDS, as well as Gabon’s International Center for Medical Research in Franceville.

Jennifer Fitzenberger @ Univeristy of California, Irvine

[Photo above by Matthijs Rouw / CC BY-ND 2.0]

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