pests

Insects resist genetic methods to control disease spread, study finds

The research, reported in the journal Science Advances, combines advanced genetic and statistical analyses to show how certain genetic and behavioral qualities in disease-carrying insects, like mosquitoes, make these species resistant to genetic manipulation.

This resistance could complicate attempts to use CRISPR-Cas9 in the fight against malaria — a deadly mosquito-borne disease that threatens over 3 billion people worldwide — or crop blights such as the western corn rootworm, an invasive species that costs the U.S. about $1 billion in lost crops each year.

The discovery of the CRISPR-Cas9 system — or simply “CRISPR” — in the early 2010s introduced an unprecedented level of accuracy in genetic editing. Scientists can use the method to design highly precise genetic “scissors” that snip out and replace specific parts of the genome with sequences of their choosing. Two English scientists were the first to show the method could spread infertility in disease-carrying mosquitoes in late 2015.

“We found that small genetic variation within species — as well as many insects’ tendency to inbreed — can seriously impact the effectiveness of attempts to reduce their numbers using CRISPR technology,” said Michael J. Wade, Distinguished Professor of Biology at IU Bloomington. “Although rare, these naturally occurring genetic variants resistant to CRISPR are enough to halt attempts at population control using genetic technology, quickly returning wild populations to their earlier, ‘pre-CRISPR’ numbers.”

This means costly and time-consuming efforts to introduce genes that could control insect populations — such as a trait that causes female mosquitoes to lay fewer eggs — would disappear in a few months. This is because male mosquitoes — used to transmit new genes since they don’t bite — only live about 10 days.

The protective effect of naturally occurring genetic variation is strong enough to overcome the use of “gene drives” based on CRISPR-based technology — unless a gene drive is matched to the genetic background of a specific target population, Wade added. Gene drives refer to genes that spread at a rate of nearly 90 percent — significantly higher than the normal 50 percent chance of inherence that occurs in sexually reproducing organisms.

Wade, an expert in “selfish genes” that function similarly to gene drives due to their “super-Darwinian” ability to rapidly spread throughout a population, teamed up with colleagues at IU — including Gabriel E. Zentner, an expert in CRISPR-based genetic tools and assistant professor in the Department of Biology — to explore the effectiveness of CRISPR-based population control in flour beetles, a species estimated to destroy 20 percent of the world’s grain after harvest.

The team designed CRISPR-based interventions that targeted three segments in the genome of the flour beetle from four parts of the world: India, Spain, Peru and Indiana. They then analyzed the DNA of all four varieties of beetle and found naturally occurring variants in the targeted gene sequence, the presence of which would impact the effectiveness of the CRISPR-based technology.

The analysis revealed genetic variation in all four species at nearly every analyzed DNA segment, including a variance rate as high as 28 percent in the Peruvian beetles. Significantly, Wade’s statistical analysis found that a genetic variation rate as low as 1 percent — combined with a rate of inbreeding typical to mosquitos in the wild — was enough to eliminate any CRISPR-based population-control methods in six generations.

The results suggest that a careful analysis of genetic variation in the target population must precede efforts to control disease-carrying insects using CRISPR technology. They also suggest that the unintended spread of modified genes across the globe is highly unlikely since typical levels of genetic variation place a natural roadblock on spread between regions or species.

“Based on this study, anyone trying to reduce insect populations through this method should conduct a thorough genetic analysis of the target gene region to assess variation rates,” Wade said. “This will help predict the effectiveness of the method, as well as provide insight into ways to circumvent natural genetic variation through the use of Cas9 variants with an altered sequence specificity.”

Source: ScienceDaily

Indian scientists have discovered an ant species that kidnaps others, behavior seen for the first time in the tropics

A marauding gang of thieves is on the prowl. They find a house whose residents are in the middle of moving to another house. While the residents busy themselves attending to the chores necessary for the shift, one of the thieves moves in slyly and kidnaps the baby inside.

We are not talking about humans—these are ants.

Moving buddies
An Indian scientist has discovered this trait of kidnapping for the first time in a tropical ant species—one found in India, Sri Lanka and Japan.
Eight years ago, when Sumana Annagiri, an ecologist, relocated from the US to Kolkata, she found that she had company. A colony of ants was also moving in.
She began to observe their behaviour and what she found was fascinating. She says, “A single ant invited its nest mate and brought it along, travelling together as a tandem pair in physical contact with each other.”
It goes back and forth bringing its nest mates with it. A few other ants (about 15% of nest members) act similarly, taking up the job of leading the nest mates and in this manner, the entire colony of ants relocate to their new residence.

This mannerism, known as “tandem running”, was different from the usual manner in which ants normally relocate, which is following a chemical trail left by a member.
Captivated by this behaviour, Annagiri took up the study of this ant species Diacamma indicum, belonging to a primitive family of ants, Ponerinae, and set up the ant lab to study ant behaviour at the Indian Institute for Science Education and Research in Kolkata.
Like all ant species, these ants are eusocial, defined by three main features. One, there is an overlap of generations—a minimum of two generations is required. Two, cooperative care: The brood of the nest are pooled together and taken care of. Three, division of reproductive labour: Only one or a few members get to reproduce and lay eggs, while the rest are sterile and take care of the queen’s offspring.

In most eusocial ants, the queen is distinct from the rest of the workers due to the presence of wings and/or greater size. However, in this particular species, all the members look alike—there is no distinct queen.
All female ants are born with a thoracic gland in place of the wings. A single female worker mates and reproduces, who is known as the gamergate or the queen.
Annagiri explains, “The current ruling gamergate retains its position as the only reproductive member, by mutilating the thoracic gland of all newly born female members.” This forces them to become workers—the gamergate usually mates with a male of another colony.
These are monodomous ants—living in a single nest, as compared to some species where a single colony occupies multiple nests. The nest size is not large, members range from 12 to 261 adults.

A second surprise
It was during the course of the study, published in Nature last October, that Annagiri and her team, Bishwarup Paul and Manabi Paul, discovered another fascinating trait of these—stealing the young ones of neighbouring colonies and using these young ones as slaves for their own colony.
Usually, one ant first identifies a neighbouring colony that’s in the process of relocating. Then, one or several ants enter and raid the colony and kidnap their pupa. The ants prefer stealing pupae as opposed to the immature eggs or larvae, possibly because pupae are the last development stage, ready to grow into an adult.
The purpose of the kidnapping being that the pupae, when they become adults, can be incorporated as workers into their colony. The females are expected to be mutilated as the stolen pupae are treated in the same way as the host pupae, but this has not been tested.

Raiding other nests for young ones, food or other resources is common in the animal kingdom. The young ones, or brood of a species, are particularly vulnerable. They are often targeted to be used as food reserves of a colony.
Aggressive ant species such as army ants are especially noted for their raiding behaviour, where they form specialized columns or swarm and hunt for food, which includes the brood of other ants.
But thieving for the sake of enslaving is found only in ants. Although rare, thievery of brood for the purpose of slave-making has been known in certain ant families found in temperate regions of the world.
Of the 12,000 known ant species, about 50 species are known to be slave makers. Slave makers and their victims are usually genetically related. They could be of the same species or a related species.
In many of these species, slavery, or “dulosis”, as it is scientifically known, is obligatory. That is, these ants rely solely on workers captured in raids for colony building. All work of maintaining the nest is performed by slaves; if there are none left, the colony dies.

However, there are a few species where adults are capable of conducting all the tasks of the colony and occasionally conduct raids to increase the workforce of the colony.
Diacamma indicum seem to fall in the latter category. But their raiding pattern is different from any other species discovered so far, based on knowledge from published scientific literature. Slave-making ants typically conduct systematic raids in large groups. Diacamma indicum conducts the thefts individually, with only 1% of the colony taking up thievery.
Annagiri says, “The theft is more opportunistic in nature. When an ant goes out foraging for food such as termites and dead insects, and comes across a colony of its own species relocating, it takes the opportunity to steal the brood.”

Usually, when a colony relocates, the ants take temporary shelter in anywhere from one to eight temporary nest sites, before moving into the final nest site. They move their young, eggs and pupae along with other stored resources. Although the colony is not unguarded, they are vulnerable to predation.
Annagiri and her team observed the stealing behaviour of the ants both in their natural habitat, where they nest in cavities of stones, rocks, tree branches, trunks, fallen logs and cracks of walls, as well as in the lab.
They introduced a foreign colony inside a lab area where a colony of Diacamma indicum was already residing, to simulate relocation. Annagiri’s team recorded the brood thefts that took place. They observed that both the resident and foreign colonies attempted to steal brood from each other. The resident colonies, however, made significantly more attempts and were more successful at stealing.

But the victim colonies fought back frequently. If the thief was recognized, the colony would attack by biting, dragging, pushing down or antennal boxing. In this way, they were able to block more than half the attempts.
The team also studied the fate of the stolen pupae—if they are consumed as food like some ant species do. Using different paints to mark the foreign and resident pupae, they found that almost all stolen pupae were integrated into the colony, just like their own pupa. The stolen pupae were allowed to eclose (emerge as an adult from the pupa) and assimilated into the workforce of the colony.
Slave-making ants first find mention in Charles Darwin’s Origin of Species, in which he speculated that slavery in ants probably evolved as a by-product of brood predation. In temperate regions, history of slave-making ants has been known to exist for tens of thousands of years.

Until now though, there has been no record of slave-making in the tropics, so it’s hard to guess how long slavery here has existed. Annagiri hopes that more slave-making ants among tropical species will be discovered, which will help to understand the history and evolution of slavery in ants.
For now, she and her team plan to further study this thieving behaviour. “We are exploring the mechanism of stealing, how the behaviour is modulated. Do the ants even know if they are stealing?”
Deepa Padmanaban is a freelance science journalist, whose work has appeared in National Geographic, NYmag, BBC Earth and The Atlantic, among others.

Source: Live Mint

Scientists create mosquitoes resistant to dengue virus

Mosquitoes get infected when they feed on someone who has the disease. Then they pass dengue to healthy people by biting them.

Each year, dengue sickens about 96 million people worldwide. The virus kills more than 20,000 people, mostly children, the researchers said.

“If you can replace a natural population of dengue-transmitting mosquitoes with genetically modified ones that are resistant to virus, you can stop disease transmission. This is a first step toward that goal,” said study leader George Dimopoulos, a professor of molecular microbiology and immunology at Hopkins.

The genetic modifications significantly increased the mosquitoes’ resistance to dengue. But the changes didn’t boost the mosquitoes’ defenses against Zika or chikungunya viruses.

“This finding, although disappointing, teaches us something about the mosquito’s immune system and how it deals with different viruses. It will guide us on how to make mosquitoes resistant to multiple types of viruses,” Dimopoulos said in a Hopkins news release.

He and his team said more research and testing is needed before these dengue-resistant mosquitoes are introduced into the wild, a process they said could take a decade or more.

Forty percent of the world’s population live in areas where they are at risk for dengue infection, the study authors said. The virus is most common in Southeast Asia and the western Pacific islands. But dengue infections have been increasing in Latin America and the Caribbean.

The research was published Jan. 12 in the journal PLOS Neglected Tropical Diseases.

Source: UPI

Behavioral Resistance: Mosquitoes Learn to Avoid Bed Nets

Malaria is a notoriously tricky infectious disease. Because of a unique genetic flexibility, it is able to change surface proteins, avoiding the immune response and greatly complicating vaccine development. Furthermore, the parasite is transmitted by mosquitoes, which are difficult to control. Insecticides work, but mosquitoes can develop resistance to them.

One method widely used to control malaria is for governments or charities to provide families with insecticide-treated bed nets. Overall, this strategy is very successful, and it has been credited with preventing some 451 million cases of malaria in the past 15 years. But bed nets are not successful everywhere. In some parts of the world, mosquitoes develop “behavioral resistance”; i.e., they learn to avoid bed nets by biting people earlier in the day.

A team led by Lisa Reimer of the Liverpool School of Tropical Medicine monitored mosquito behavior in villages in Papua New Guinea before (2008) and after (2009-2011) the distribution of bed nets. Data from one of the villages, Mauno, depicts a very noticeable shift in mosquito feeding behavior.

Before bed nets were distributed in 2008, the median biting time for mosquitoes was around midnight. After the distribution, the median time shifted back to 10 pm. Also, a greater proportion of mosquitoes took their dinner even earlier, from 7 to 9 pm.

Worryingly, it’s unclear whether the bed nets were effective at preventing malaria transmission. The number of bites per person per night dropped after the introduction of bed nets, but started to climb in subsequent years as mosquitoes began to adapt. Additionally, the prevalence of malaria infection in humans — arguably, the only statistic that actually matters — dropped in one village, remained the same in a second, and ticked up slightly (albeit insignificantly) in a third.

Despite the mixed results in Papua New Guinea, Dr Reimer believes that bed nets should continue to be used worldwide as part of a mosquito control strategy. However, she notes that behavioral resistance may prove just as vexing as insecticide resistance and, in some locations, may limit the efficacy of bed nets.

Thus, mosquitoes must be monitored for both behavioral and insecticide resistance, as the little creeps stubbornly refuse to die and may be cleverer than we thought.

Source: Edward K. Thomsen et al. “Mosquito behaviour change after distribution of bednets results in decreased protection against malaria exposure.”

Source : Acsh.org

Ants communicate by mouth-to-mouth fluid exchange

The study from the University of Lausanne, Switzerland, suggests Florida carpenter ants can collectively influence their communities by shifting the cocktail of proteins, hormones and other small molecules that they pass mouth-to-mouth to one another and their young through a process called trophallaxis.

“Food is passed to every adult and developing ant by trophallaxis. This creates a network of interactions linking every member of the colony,” says senior author Laurent Keller, Professor in the Department of Ecology and Evolution.

“A lot of researchers consider trophallaxis only as a means of food-sharing,” adds Professor Richard Benton of the Center for Integrative Genomics, also a senior author of the study. “But trophallaxis occurs in other contexts, such as when an ant is reunited with a nest-mate after isolation. We therefore wanted to see if the fluid exchanged by trophallaxis contains molecules that allow ants to pass other chemical messages to each other, and not just food.”

To answer this question, the team, led by first author and postdoctoral researcher Dr Adria LeBoeuf, analysed fluid from pairs of ants engaged in trophallaxis. Surprisingly, they identified a large number of proteins that appear to be involved in regulating the growth of ants, along with high levels of juvenile hormone, an important regulator of insect development, reproduction, and behaviour.

To see what effect this hormone has on the growth of larvae fed by trophallaxis, the scientists added it to the food of larvae-rearing ants and discovered that the hormone made it twice as likely that the larvae would survive to reach adulthood.

“This indicates that juvenile hormone and other molecules transferred mouth-to-mouth over this social network could be used by the ants to collectively decide how their colony develops,” says LeBoeuf. “So, when the ants feed their larvae, they aren’t just feeding them food, they are casting quantitative ballots for their colony, administering different amounts of growth-promoting components to influence the next generation.

“The effects of juvenile hormone that we see are consistent with previous studies in other ants and in bees where larvae treated with an analogue of this hormone tend to develop into larger workers and even queens.”

Along with growth proteins and juvenile hormone, the team also identified small molecules and chemical signals in the carpenter ants’ trophallactic liquid that help them recognize their nest-mates. They demonstrated for the first time the presence of chemical cues in the fluid that are known to be important in providing ants with a colony-specific odour that allows them to distinguish family from non-family members.

“Overall, we show that liquid transmitted among ants contains much more than food and digestive enzymes,” adds LeBoeuf. “Our findings suggest that trophallaxis underlies a private communication channel that ants use to direct the development of their young, similar to milk in mammals.”

“More generally, this opens the possibility that the oral exchange of fluids, such as saliva, in other animals might also serve previously unsuspected roles.”

Source : ScienceDaily

Common insecticides are riskier than thought to predatory insects

Neonicotinoids — the most widely used class of insecticides — significantly reduce populations of predatory insects when used as seed coatings, according to researchers at Penn State. The team’s research challenges the previously held belief that neonicotinoid seed coatings have little to no effect on predatory insect populations. In fact, the work suggests that neonicotinoids reduce populations of insect predators as much as broadcast applications of commonly used pyrethroid insecticides.

“Predatory insects contribute billions of dollars a year to agriculture through the elimination of crop pest insects,” said Margaret Douglas, postdoctoral researcher in entomology, Penn State. “We have found that neonicotinoid seed coatings reduce populations of these natural enemies 10 to 20 percent.”

According to John Tooker, associate professor of entomology, Penn State, the use of neonicotinoids has risen dramatically in recent years, especially for large-acreage crop species like corn, soybeans and cotton. The insecticide is most often applied to seeds as a prophylactic coating. When the seeds are planted, the insecticide enters the soil where some of it is taken up by plant roots. The chemical then runs systemically through the plant, protecting young seedlings from insect pests.

“Applying insecticides to seeds rather than broadcasting them across a field was thought to reduce unwanted effects on natural enemies,” said Douglas. “But we found that seeds treated with neonicotinoid insecticides reduced populations of natural enemies by 10 to 20 percent in North American and European farming systems. Surprisingly, this effect was about the same as that associated with broadcast applications of pyrethroids.”

The team’s research appeared in the online journal PeerJ.

The team used a statistical method, called meta-analysis, to combine the results of more than 1,000 observations from 20 field studies across North America and Europe that tested the effects of seed-applied neonicotinoids on predatory insects. “Unfortunately, the available literature is difficult to interpret,” said Tooker. “Some studies show little influence of neonicotinoids presented as seed treatments on arthropod predators that are common in crop fields, whereas others show a strong influence of these seed treatments. By using a meta-analysis approach, we were able to combine the results of many studies to quantitatively reveal the overall influence of neonicotinoids on predator populations.”

Not only did the researchers find that neonicotinoid seed coatings significantly reduced natural enemy populations, they also found that the insecticide acted more strongly on insect predators than on spiders. In other words, spiders appeared to be less susceptible to neonicotinoids than insects, which is consistent with previous research.

“This result suggests that neonicotinoids are reducing populations of natural enemies at least partly through their toxic effects rather than simply by reducing the availability of their crop pest foods,” said Douglas. “After all, insects are more susceptible to these toxins than spiders, whereas the two groups should be similarly affected by a lack of food.” The researchers note that their results may help farmers and pest management professionals better weigh the costs and benefits of neonicotinoid seed treatments versus alternatives.

“Several governments have restricted the use of neonicotinoids out of concern for their possible effects on pollinators,” said Douglas. “But this raises the questions, ‘What will farmers do without these products? If they switch to broadcast applications of pyrethroids, will those products be better or worse for predatory insects?’ While our results do not speak to the pollinator issue, they do suggest that predatory insects are affected similarly by seed-applied neonicotinoids and broadcast pyrethroids.”

The answer to the problem, noted Tooker, lies in the application of integrated pest management (IPM), a strategy that uses a combination of techniques — which may or may not include the targeted use of insecticides — to control pests, rather than universally deploying prophylactic tactics like insecticidal seed coatings.

“Substantial research exists supporting the value of IPM for pest control,” he said. “It is the best chance we have of conserving beneficial insect species while maintaining productivity in our agricultural systems.”

Source: Science Daily