Tag Archives: Pests

Wasps are effective pest controls, a new study shows

Although you may be terrified of them, common, social wasp species could help keep our crops pest-free, reports a new study.

A hornet queen.
Image credits David Hablützel.

The blue and black predators can act as solid pest control for at least two high-value crops: maize and sugarcane. While the experiment was carried out in Brazil, the team explains that wasps are found virtually all over the world and can easily be ‘recruited’ on small or large-scale farms to control a range of common pest insects.

The Buzz of victory

“There’s a global need for more sustainable methods to control agricultural pests, to reduce over-reliance on pesticides or imported pest controllers. Wasps are very common, but understudied, so here we’re providing important evidence of their economic value as pest controllers,” said the study’s lead author, Dr. Robin Southon from University College London’s (UCL) Centre for Biodiversity & Environmental Research.

The study was carried out in Brazil with the help of researchers at São Paulo State University and Universidade de São Paulo; the team explains that it is the first controlled experiment in semi-natural conditions on the subject, as it was performed on an outdoor research site. The maize crops used in the study were infested with fall armyworms, while the sugarcane crops were infested with sugarcane borers. As a pest control, the team used the social paper wasp, a hunting wasp common to the area.

All in all, the wasps seem to have been effective. Their presence reduced the pest populations and led to the crops suffering less damage. The team further found that even pests which already bored inside the plants (and weren’t present on their surfaces) were removed by the wasps.

The findings definitely suggest that the wasps have potential as pest control agents and could be used as part of a larger, integrated pest management mechanism. The team is especially excited for their use as wasps are native species and naturally part of many ecosystems today, which would make them a much more sustainable and environmentally-friendly alternative to today’s pesticides. Not only that, but the insects can also be a “cheap, accessible form of pest control, particularly helpful to small-scale or subsistence farmers in countries like Brazil, who could attract and encourage wasps to establish themselves,” according to co-author Professor Fabio Nascimento, who hosted the study at his labs in São Paulo State University.

The team plans to continue their research using larger, active agricultural fields. Wasps today are in decline across the world, similarly bees. The team notes that wasp loss can lead to a sharp increase in aphids, flies, and other species they prey on.

“This isn’t just about agriculture—this is about wasps in general and their role in regulating insect populations,” says Dr. Seirian Sumner (UCL Centre for Biodiversity & Environment Research), the study’s senior author. “Even your backyard garden could benefit from a more wasp-friendly attitude—instead of killing wasps and using pesticides on your plants, treat your local wasps as the helpful pest controllers they are.”

The paper “Social wasps are effective biocontrol agents of key lepidopteran crop pests” has been published in the journal Proceedings of the Royal Society B: Biological Sciences.

Essential oils, a novel way to deal with a major pest

When finding their plant hosts, agricultural insect pest always seeks familiar scents. But they can also be repelled by odors from other plant species, according to new research, which offers a new framework for exploiting plant odors to repel insect pests.

Broccoli, one of the affected crops. Credit: Living in Monrovia (Flickr)


A team at the University of Vermont worked on the swede midge, a small fly which has become a problem for farmers from the Northeast that work with cabbage-family crops like broccoli and kale. They discovered that a set of essential oils were effective at repelling the midge, such as garlic and spearmint.

“People often think more aromatic plant oils, like mint, basil and lavender will repel insects, but usually there is no rhyme or reason for choosing,” says senior author Yolanda Chen. “It turns out that as we go along the family tree, plants that are more distantly related from the host plant are generally more repellent.”

In order to survive, the small fly feeds on the brassica plant family, which includes a set of popular vegetables such as cabbage and brussels sprouts. If the midge laid its eggs on the wrong plant, it would mean the death of its offspring, according to observations by the researchers.

The midge’s larvae affect the plant’s control system, causing distorted growth – such as brown scarring. But, unfortunately for farmers, they can’t observe the problem until it’s too late and the midge has dropped off the plant. The tiny fly is known to cause crop losses of up to 100% in some areas of the US and Canada.

Trying to deal with the midge, farmers have turned to insecticides, which has been associated with a decline in bees. Organic farmers found no methods and just stopped growing the vulnerable crops. This led to the team at Vermont University to find new methods to control the small fly.

“It’s hard to get away from using insecticides because they’re good at killing insects,” said lead author Chase Stratton, who is now a postdoctoral researcher at The Land Institute in Kansas. “But plants have been naturally defending against insect herbivores for millions of years. Why are we so arrogant to think we can do it better than plants?”

Stratton and her colleagues were able to identify essential oils from 18 different plants that vary in their degree of relatedness to brassica host crops. They hypothesized that oils from plants that are more distantly related to brassicas would have more diverse odors and be more repellent.

They spent time observing how midges acted when facing broccoli plants that had been sprayed with each of the essential oils. The small fly, they discovered, was less likely to lay eggs on broccoli plants that had been treated with essential oils, compared to the untreated plants.

“Biologically, it makes sense that midges would be able to detect and avoid these plants because the similar odors would make it easier for them to misinterpret these plants as hosts, which would be deadly for their offspring,” said Stratton. “For swede midge, garlic appears to be one of the most promising repellents, particularly because certified organic products using garlic are already available for growers.”

Pests destroy around one quarter of our crops — even more in developing areas

If we want to be able to feed the world, we’d best pay closer attention to pests.

According to current estimates, the world population is 7.7 billion. It took over 200,000 years to reach the first billion, and only 200 more years to reach 7.7 billion. By 2100, even conservative estimates put the world population at 11 billion — all of which will have to be fed. Considering that today, over 800 million suffer from chronic undernourishment, feeding the population of tomorrow will be quite a challenge.

Our agricultural productivity has increased dramatically in the 20th century, in a period often called “the Green Revolution.” Norman Borlaug, the “father” of the Green Revolution and the most prominent scientist associated with the movement, is credited with personally saving over 1 billion lives through his work.

However, with no other such revolution in sight, we will need to optimize production and reduce losses as much as possible — and one of the most important problems to consider are pests.

Pests and pathogens are an integral part of agriculture. They’ve been around since mankind has been growing crops, coevolving with agricultural plants. However, that’s not to say that we can’t do anything to fight them. Different methods have been employed, with varying degrees of success. But before we can talk about large-scale campaigns against pests, we first need to understand the big picture.

This is exactly where the new study comes in. Serge Savary, a researcher working at the French National Centre for Scientific Research, and colleagues, took on the gargantuan task of measuring global crop losses caused by pests and pathogens. They focused on the five most popular crops: wheat, rice, maize, potato, and soybean. Together, these crops make up almost half of mankind’s calorie consumption.

They found that at a global level, pets destroy:

  • 21.5% of wheat crops;
  • 30% of rice crops;
  • 22.5% of maize crops;
  • 17.2% of potato crops; and
  • 21.4% of soybean crops.

This type of data is extremely valuable, especially as standardized information is difficult to compile across different regions and crops — and there is little in the way of good news.

All in all, almost one-quarter of this food is completely lost — and to make matters even worse, the highest losses are associated with regions with fast-growing populations and which are already struggling with malnutrition. These are also areas frequently hit by emerging or re-emerging pests and diseases.

Researchers hope that their work will serve as a guideline for policymakers and farmers alike. At a global scale, if we want to be able to feed the world, we need quick and efficient interventions in these areas.

There’s also another problem, a common culprit: climate change. It’s clear that climate change will affect plant-pathogen interactions, but it’s much less clear in what way. While they did not study this directly, Savary and colleagues quote another study, which ultimately concludes that “climate change will bring, above all, surprises.” Quite likely, they won’t be pleasant surprises.

The study has been published in Nature. DOI: 10.1038/s41559-018-0793-y


Surge in pest resistance is making biotech crops worldwide less effective

Since they were first introduced in 1996, about two billion acres of so-called ‘Bt crops’ have been planted around the world. These biotech crops — most frequently corn, soybean, or cotton — are engineered to contain genes from the bacterium Bacillus thuringiensis that produce proteins toxic to insects. These proteins kill common pests like caterpillars or beetles but are harmless to humans. While this approach has proven successful in improving yield and reducing pesticide use, widespread fears that the Bt proteins might trigger an evolutionary dash for resistance in pests have proven well founded, according to a comprehensive review. Pests around some crops haven’t developed resistance, however, which means there’s reason to believe Bt crops could prove effective for a long time.


Credit: Pixabay.

The international team of researchers analyzed 36 cases of biotech crops encompassing 15 pest species in 10 countries on every continent except Antarctica. The global data on Bt crop use and pest response suggests that as of 2016, the efficacy of Bt crops was substantially reduced in 16 out of 36 cases, compared to only three such cases in 2005. The pests evolved resistance in only five years, on average.

However, in 17 other cases, the pests did not evolve resistance to the Bt crops, even though some had stayed in place for two decades. The remaining three cases experienced some statistically significant resistance but not nearly as severe as elsewhere and, thus, were classified as ‘early warning of resistance’.

The biotech arms race

Since Bt crops were introduced, scientists have advocated incorporating so-called ‘refuges’ into farmers’ strategy. Refuges are just standard, non-Bt crops that are planted alongside the engineered variety. Pests that attack the refuges are not exposed to the Bt toxins but at some point, they will breed with insects that attack the engineered crops. Due to recessive inheritance, mating between a resistant parent and a susceptible parent will likely yield offspring that can still be killed by the Bt crop.

Computer models have shown that refuges ought to be effective at delaying pest resistance in biotech crops, but their value has proven controversial among academics. In the U.S., for instance, the Environmental Protection Agency (EPA) has relaxed its requirements for plating refuges.

The new review, however, plainly shows that refuges work. Most of the crops that didn’t show signs of pest resistance employed sound refuge strategies.

“Perhaps the most compelling evidence that refuges work comes from the pink bollworm, which evolved resistance rapidly to Bt cotton in India, but not in the U.S.,” said Bruce Tabashnik, a researcher at University of Arizona’s College of Agriculture and Life Sciences and lead author of the new stuy published in Nature Biotechnology. 

“Same pest, same crop, same Bt proteins, but very different outcomes,” he added in a public statement.

Southwestern US farmers had an effective refuge strategy while India didn’t — the country has some refuge plating rules, but farmer compliance is low. The latter saw significant increases in pest resistance.

While the study shows pest resistance to Bt crops is evolving rapidly, there are also some encouraging news. The most recent biotech crops produced a novel type of Bt protein called vegetative insecticidal protein (VIP). Previously, all other Bt proteins belonged to a totally different group called crystalline proteins. Since the two groups are worlds apart, cross-resistance between pest is virtually nil, the scientists reported.

Tabashnik says that we’re only beginning to use systematic data analyses to manage pest resilience but, even so, results are encouraging. After all, scientists always expect pests to adapt to whatever we throw at them, be it GM crops or otherwise. “However, if we can delay resistance from a few years to a few decades, that’s a big win,” he underscored.

“These plants have been remarkably useful, and resistance has generally evolved slower than most people expected,” Tabashnik said. “I see these crops as an increasingly important part of the future of agriculture. The progress made provides motivation to collect more data and to incorporate it in planning future crop deployments.”

“We’ve also started exchanging ideas and information with scientists facing related challenges, such as resistance to herbicides in weeds and resistance to drugs in cancer cells,” Tabashnik said.

Scientific reference: “Insect Resistance to Transgenic Crops: Second Decade Surge and Future Prospects,” Nature Biotechnology. DOI: 10.1038/nbt.3974.

Mixed cat-and-dog teams are the best defense against rodent pests

Cats and dogs working side by side may be the best rodent control method at our disposal according to an international team of researchers. The question now is, how do we reconcile these age-old rivals for the task at hand?

Image credits Rihaij / Pixabay.

Working as part of an international research team, Robert McCleery, associate professor of wildlife ecology and conservation at the University of Florida’s Institute of Food and Agricultural Sciences, found that a combined team of cats and dogs reduced rodent foraging in and around households or storage buildings. They also detail that neither species working by itself will help deter the pests.

Paw and claw

Pest rodents have caught on pretty early that agriculture means ample food. Even better for them, there’s a species who will do the heavy lifting of growing, harvesting, and storing all that food in one place for them to nibble on — that’s us. So they’ve become a staple of human settlements since times immemorial.

Naturally, this didn’t sit well with us humans. We brought our pet animals to bear upon the pests, starting the most literal game of ‘cat-and-mouse’ in history. That this idiom today stands for a very contrived, lengthy process with little chances of success should tell you how well it’s been going for us.

Hint: he didn’t bake his own bread.
Image credits Alice Rosen / Flickr.

So what can we do to finally stack the deck in the cat’s favor? Bring in dogs, one team of scientists says. Working in tandem, these two species of pets can significantly reduce pest rodents’ activity in and around human households or farms, they say.

Led by Themb’alilahlwa Mahlaba at the University of Swaziland, the team conducted an experiment in four agricultural villages in Swaziland. Although the research is limited geographically, McCleery said the findings apply globally. The worked on 40 households in the villages, dividing them into groups of ten. One group had only dogs, another only cats, one group of homes was guarded by both species, and a control group with neither. They studied rodent pests living in these households.

McCleery said that the team considered a species a pest if it “lives in your house or eats your crops and is usually not native to the area where it is found.” Their data shows that individual species of working animals aren’t very effective at deterring pests, but using both dogs and cats provides good results.

“This might reduce food damage and potential for disease transmission,” McCleery said.

“Farmers might want to consider cats and dogs as a way to discourage rodent pests in areas where they store their crops.”

GUD news

The team first placed plastic lunchboxes filled with sand and peanuts in the houses for seven consecutive days so the rodents would get used to this source of food. Then, they installed ‘control tiles’ — basically white square tiles sooted black — alongside the lunchboxes for 5 consecutive days and nights in July (the cool dry season) and 5 in October (the hot dry season).

As rodents passed over the tiles, their little paws would leave a white track. Each tile’s surface was broken down into squares, and the percentage of squares with tracks gave an estimate of rodent activity in each house.

The bait was refreshed before the control tiles were installed, and then each day during the experiment.

“A total of 86 rodents of two species were captured within buildings and out-houses around homesteads in the study area. The majority (73) of specimens were Rattus rattus, with the remainder (13) being Mastomys natalensis,” the paper reads.

The team also observed the rat’s Giving Up Density (GUD), which showed how often the animals gave up forage in homesteads with both cats and dogs — basically, the intensity of the ‘fear factor’ the guardians instilled. In boxplot below, you can see how much ‘ratctivity’ the houses have seen in July (left) and October (right).

I’ve put the basic gist of the graph in the caption, but here’s a more in-depth guide to reading boxplots.

Boxplots show the upper limit (topmost line), median value (strong line) and lowermost limit (lower line) of rodent activity. 
Image credits Themb’alilahlwa A. M. Mahlaba (2017) PLOS One.

And here’s the GUD.

Image credits Themb’alilahlwa A. M. Mahlaba (2017) PLOS One.

The results show that rodents displayed significantly more fear and reduced foraging activity in homesteads guarded by both cats and dogs. Taken alone, either species had less success deterring rodents, with cats having a slight edge across the board.

“The results of this study are particularly interesting to me as they will make a big contribution to the efforts at managing rodents in and around homesteads,” Mahlaba said.

“Showing that dogs have a role in rodent management has overturned my long held ideas on this subject. Now all we need to do is to find out why and how the combination of cats and dogs drastically reduces rodent activity in and around homesteads.”

The full paper Domestic cats and dogs create a landscape of fear for pest rodents around rural homesteads” have been published in the journal PLOS One.