September | 2016 | Pest Control India

A protein in mosquito spit can keep Dengue virus in check

Working on ways to reduce DENV transmission, Michael Conway, from Central Michigan University College of Medicine in Mt. Pleasant, USA, and colleagues, explore the targeting of mosquito saliva or midgut proteins to block transmission of DENV. This strategy has advantages compared with vaccines based on viral proteins because it does not need to take into account the different circulating DENV strains or adapt to rapidly evolving viruses.

The researchers had previously isolated proteins from the salivary glands of Aedes aegypti, the mosquito that transmits the Dengue, Zika, and Chikungunya viruses, and tested batches of proteins to see if they could either enhance or block DENV transmission to human cells. In this study, they focused on proteins that could inhibit DENV.

Analyzing batches of proteins with inhibitory function, the researchers found high levels of so-called D7 proteins. Members of the D7 family are known to be present in mosquito saliva and thought to assist the blood feeding process. Comparing uninfected Aedes mosquitoes with DENV-infected ones, the researchers found that the latter had increased levels of D7 proteins in the salivary glands compared with uninfected controls.

They then produced one of the D7 proteins in insect cells and used it in further functional analyses. Treating cells that are susceptible to DENV infection with the D7 protein either before or during exposure to the virus significantly reduced DENV RNA levels in the cells, suggesting that D7 might both modulate the host cell as well as possibly act on the virus directly to inhibit infection or multiplication.

To determine whether D7 can inhibit DENV2 infection in vivo, the researchers exposed mice that are susceptible to DENV either to virus alone or to a combination of virus and D7. The presence of D7, they found, significantly reduced the levels of DENV RNA both at the exposure site and in neighboring lymph nodes (from where virus spreads to the rest of the body).

To understand how D7 protein mediates its antiviral effect, the researchers tested whether D7 can interact with DENV directly. They found that D7 can bind the DENV via the virus’s envelope protein (which covers the viral surface). These results, the researchers say, “support that D7 protein mediates its antiviral effect through direct protein-protein interaction […], although it is possible that modulation of the inflammatory response also occurs in vivo.”

D7 proteins can provoke strong immune responses, and individuals exposed to mosquitoes have high levels of anti-D7 antibodies. Because these antibodies likely inhibit D7 protein function, the researchers speculate that “although anti-D7 antibodies may prevent efficient blood feeding by a mosquito, they may also enhance disease transmission and disease severity.” “Characterizing the complex interplay of virus-vector-host interactions,” they conclude, “will lead to the development of better models of pathogenesis, strategies to limit disease transmission, and promote the development of therapeutics and transmission-blocking vaccines.”

Source: PLOS

Picky ants maintain color polymorphism of bugs they work with

Researchers at Hokkaido University in Japan and colleagues investigated whether this symbiotic relationship played a role in the genetic selection of the red and green aphids that feed on the mugwort plant — known as Macrosiphoniella yomgicola. The presence of two or more clearly different forms in a species is known as “polymorphism.” Previous research had shown that aphid colonies that were more polymorphic tended to survive longer. This could be due to the number of ants attending to these colonies.

The team first experimented by removing ants from aphid colonies and found that most colonies whose attending ants were removed did not survive. This demonstrated that ants were necessary for the survival of the mogwort aphids.

They then experimented with colonies that had varying proportions of red and green aphids and found that the number of attending ants was highest when green aphids comprised 65% of the colony.

“This result suggests that these polymorphic colonies are protected more efficiently from predators by the attending ants than less polymorphic colonies,” write the researchers in their study published in the journal Science Advances. “Thus, ant attendance may maintain the observed colour polymorphism in M. yomogicola,” they say.

This result is particularly significant because it does not fall under previously known predatory-dependent methods of genetic selection that result in a balance of polymorphisms.

There is much room for future research on this topic, the researchers say, because many questions remain unanswered. The team is now investigating why the ants prefer an intermediate colour ratio of aphid colonies.

Source : Hokkaido University

It’s a boy: Controlling pest populations with modified males

Withholding tetracycline in the larval diet essentially means “It’s a boy” when the genetically modified male flies successfully mate with females in the field, says Max Scott, an NC State entomologist who is the corresponding author of a paper describing the research.

“Genetic suppression of a pest population is more efficient if only males survive, so we manipulated screwworm genes to promote a female-lethal system that works when a common antibiotic is not provided at larval stages,” Scott said. “If we feed the larvae the antibiotic both male and female survive and are as fit as the wild type strain.”

The study shows that the genetically modified males both compete well for the attention of fertile females and mate successfully with fertile females. The genetically modified flies also do not mate with other very closely related fly species.

New World screwworm flies (Cochliomyia hominivorax) parasitize warm-blooded animals in the Western Hemisphere tropics and sub-tropics, causing massive financial and animal losses. The flies were eradicated from North and Central America years ago using the sterile insect technique, which has resulted in annual savings of more than $1 billion per year. However, the flies continue to wreak havoc across South America and some Caribbean islands.

Scott says that a sterile insect technique has been used to keep the South American flies at bay. This technique involves irradiating both male and female flies to make them sterile and then releasing them — in an area between the Panama Canal and Colombia — to mate with fertile flies in order to prevent screwworm re-introduction to Central and North America.

“This is a bit inefficient, as sterile males will mate with sterile females, which is totally unnecessary,” Scott says. “Releasing only males, would cut down on the costs of rearing sterile female flies and should significantly increase the efficiency of the suppression program. Plus, it would take fewer resources to begin screwworm eradication program in other afflicted areas, like the west coast of South America, for example.” In addition, the technology should be easily transferable to other flies that are pests of livestock such as the Old World screwworm.

Scott added that COPEG will now evaluate one of the genetically modified screwworm fly lines. That commission has worked to prevent the reintroduction of the pest into North and Central America and is responsible for the current sterile insect technique program. All of the genetically modified strains were developed within the COPEG biosecure facility in Panama, which will facilitate incorporation of the strains into the ongoing operational program.

The study was published online in the journal BMC Biology. Funding was provided by USDA’s Agricultural Research Service and its National Institute of Food and Agriculture BRAG program, COPEG and NC State.

Source : North Carolina State University