09
May
Researchers Delve into Role of Gut Bacteria in Insect Resistance to Pesticides
(Beyond Pesticides, May 9, 2018) An insect’s gut microbiome plays an important role in conferring pesticide resistance, according to a new review published in the Annals of the Entomological Society of America. “Whether you’re looking at agricultural pests, household pests like cockroaches, or medical pests like disease-carrying mosquitoes, insects are great at adapting to whatever we throw at them, especially when it comes to different chemicals,” said lead author Jose Pietri, Ph.D to Entomology Today. The review adds to the numerous ways pests can evade the effects of chemical agriculture, reinforcing calls from recent studies showing that the best method of addressing this issue is to simply stop using synthetic pesticides and employ alternative pest management practices.
The authors identify two overarching methods through which microbes help confer resistance to toxic pesticides. The first involves the pest accepting a physiological trade-off, where a pest is able to better withstand an insecticide at the cost of losing its ability to regulate certain gut bacterium. For instance, diamondback moths resistant to fipronil and chlorpyrifos are found to contain higher levels of Lactobacillales, Pseudomonadales, and Xanthomonadales bacteria than non-resistant moths. While this trade-off affects the fitness of the organism, alterations of the bacterial community the pest is exposed to can reinforce and strengthen the pest. For example, culex mosquitoes that contain resistant genes can increase the likelihood that they will survive to adulthood through infection of a certain fungal parasite called Vavraia culicis.
The second method through which microbes could assist in conferring resistance to pests is directly through the bacterium. “There are several possible ways they can directly help insects deal with the toxins in insecticides, and one is a very direct mechanism whereby a toxin comes into the gut of an insect and, through enzymatic means, the microbes break it down and render it ineffective,” said Dr. Pietri. A specific example cited by authors was the development of fenitrothion (an organophosphate insecticide) resistance in bean bugs. During the nymph stage of the pest, the bugs pick up a soil bacterium called Burkholderia. Although generally uncommon, certain strains of Burkholderia have the ability to break down fenitrothion. However, when the chemical is continuously sprayed onto soil, fenitrothion-resistant Burkholderia become more common, leading to a greater number of bean bugs picking up the resistant strain of the bacterium.
This review underscores the variety of means insects can take advantage of in their environment to rapidly adapt to changing environmental factors. A 2013 study underscores this ability, finding that the common practice of “stacking” two or more Bacillus thuringiensis (Bt) toxins in genetically engineered plants did not work. Researchers assumed that pests resistant to the first Bt toxin would survive on the one-toxin plants, but die when consuming two-toxin plants because they had not yet developed resistance to the new formulation. However, pests selected for resistance to one toxin survived significantly better than caterpillars from a susceptible strain.
In the field, whether insect or weed, pests develop resistance because those that don’t die from toxic pesticide use develop some method to stop the chemical from causing it harm. A study published earlier this year in the journal Nature Ecology and Evolution found that the only tried and true method to reduce weed resistance was to eliminate the use of pesticides sprayed on target weeds.
While this study may lead to attempts to halt resistance to chemical pesticides, investigations of how microbes interact with insect detoxification could provide insight into new methods of bioremediation, or ways to model how humans may respond to changes in gut bacterial composition. There is already amble evidence that pesticide use alters the diversity of microflora in the human mouth and gut.
For more information about how chemical pesticides affect the human microbiome, see Beyond Pesticides’ Pesticides and You article on Monsanto’s Roundup, and the transcription of David Montgomery’s Talk at the 35th National Pesticide Forum titled Sustaining Life: From Soil Microbiota to the Gut Microbiome. Beyond Pesticides and the Organic Consumers Association have been given the green light from a Washington, DC Superior Court judge to sue Monsanto based on the argument that glyphosate (Roundup) has adverse impact on the gut biome and resulting adverse health effects. And to read more about pest and weed resistance, see visit our Genetic Engineering webpage.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: Annals of the Entomological Society of America, Entomology Today
