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Tag Archive for: agricultural systems

Insects resist genetic methods to control disease spread, study finds

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

Insects that help feed the world

Insects that help feed the world

The Cream Striped Owl moth is usually a sub-tropical and bushveld baby, with a range that extends up to equatorial Africa, according to my insect book, Field Guide to Insects of South Africa (Picker, Griffiths, Weaving, Struik 2002). They do seem to have been creeping slowly into Highveld areas for some time – I took the picture below of a slightly tattered individual in Cullinan in 2010.

There was one fluttering in my bathroom last night, a large member of a vast dancing throng of wings, ranging from almost translucent cream to rich sepia. I’ve never understood why people find moths scary; I know some superstitions hold that moths are signs of death (if that were the case, few families would survive an ordinary summer evening!) but to me, they’re signs of life. When not distracted by our lights, they do important nightshift work.

Many moth species are crucial pollinators, drawn by the night’s rich, sweet fragrances and nectars to flowering plants like Struthiola ciliate, a fynbos shrub, picking up pollen to transfer to the next plant they visit.

Despite the rightful focus on honeybees-as-pollinators, all sorts of wild animals are vital to both agriculture and wild plants. Flies are perhaps second to bees in the pollination stakes, visiting apple trees, cashews, onions and coriander, to give a tiny sample.

Wasps are important pollinators too (avos are among their beneficiaries), as are beetles and bumblebees (apparently they love canola).

Other nightshift pollinators are also often maligned. Bats trigger grils down the spine for many, but the fruit bat, with its appealing dog-like face, is the major pollinator of the baobab, for example. Mice also attract the ‘eeurrgh’ reaction, yet in recent years, scientists have discovered that some Protea species are pollinated by scurrying little rodents out at night.

If you like chocolate, you can thank those most-cursed creatures, the midges (what we call muggies), daytime workers spreading pollen from one cacao flower to another in cocoa plantations, according to Adrienne Mason in Planet Ark: Preserving Earth’s Biodiversity.

One in every three bites of food made possible by pollinators.

The staple crops of the world (wheat, maize, rice and other grasses) are wind-pollinated, but many of our other food crops are dependent on living creatures, from ants to birds, to reproduce. “87 out of 115 leading global food crops are dependent on animal pollination. One in three bites of food you take was made possible by the work of pollinators,” Mason writes.

While South Africa does not use ‘managed pollinators’ (beehives trucked between agricultural regions) nearly as intensively as the USA and Europe, 87% of the beehives in the Western Cape, where half the deciduous fruit in the country is grown, are ‘managed pollinators’ of fruit trees (the fruit industry was valued at R9 800m in 2014).

In 2008, Mike Allsopp and colleagues did a valuation of pollination services and arrived at these figures: “The contribution of managed honeybee pollination is found to be between US$28.0–122.8 million […]; the contribution of wild pollinators is found to be between US$49.1–310.9 million…” That’s a lot of money. And if insects and other animal pollinators died out, of course, the replacement cost would be much higher – we’d probably have to invest in those little robot pollinators!

No fear of that quite yet: Wits zoology and entomology Professor Marcus Byrne (famous for discovering that dung beetles use the Milky Way to navigate) is in the bush as I write. Following late but good rains, he notes that all is lush and green and singing with insect life, evidence of “the resilience of our fauna to not only what we do, in continually removing or degrading their habitat, but also their ability to bounce back from a serious drought”.

However, I would suggest that we do not test that ability to destruction. Even if you don’t give a damn about the aesthetics of nature, or the intrinsic worth of the lives around us, these ecosystems clearly have a raw commercial value and are crucial to our food security.

Hence “the importance of maintaining natural and other forage areas for the conservation of insect pollinators,” as Allsopp et al write, instead of creating bleak and rebarbative deserts, and using pesticides to kill all known insects dead.

For example, in our pesticide-free garden, leaves are piled onto beds as mulch, and dead branches are left to quietly decompose, providing micro-habitat that supports insects, bats and birds – evidenced by the quiet humming of life here compared to more manicured and pesticided environment like the townhouse complex down the road. The same difference can be seen on a walk from ploughed and disked farmland to adjacent veld.

The need for havens that support and protect biodiversity, specifically pollinators and pest controllers, should be as much part of land use management policies as water use is.

Rejoice in the fluttering moth-wings at night; manage birds, bats and rodents in your office parks, housing developments and municipal buildings without sprays and poisons; campaign against development of every last wild haven in your vicinity. We need them more than they need us.

Author: Mandi Smallhorne
Source: News24

Common insecticides are riskier than thought to predatory insects

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



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