Photo: Kochia, southwest Montana. © 2020 Delena Norris-Tull
Pesticide Impacts on Insects
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, October 2020.
Goode, et al., 2020, conducted experiments to examine the impact of the herbicide penoxsulam on biocontrol insects that were also being used to reduce the spread of water hyacinth (Pontederia crassipes) in Florida. Previous studies have indicated that establishing insect refuges, by maintaining an area of untreated plants near the treated area, were key to enabling biocontrol insects to survive herbicide application. In this study, insect refuges were not established. Fortunately, they found that the herbicide, which was also used to control water hyacinth, did not have a negative impact on the survival of the biocontrol agents, water hyacinth weevils, Neochetina eichhorniae and N. bruchi. Goode, et al., 2020, concluded, “Although the systemic activity of penoxsulam in the water column prevented the establishment of refuges in this study, biological control agent populations persisted following herbicide applications without additional releases and were able to remain at field densities after the decay and loss of P. crassipes.”
Gutierrez, et al., 2020, conducted an experiment on the impact of a phenoxy herbicide used to control broadleaf weeds in grasslands, on native grass diversity and the physiology of a native polyphagous grasshopper. In female grasshoppers, increased “grass diversity increased herbivory” and increased grasshopper weight and nitrogen content. “Herbicide reduced herbivory but increased the number of offspring” of female grasshoppers. In male grasshoppers, increased grass diversity increased herbivory and fat body volume, but had negative effects on weight. However, with increased plant diversity, males had an “increased capacity to store energy and invest in muscle tissues,” which suggests that males use different energy allocation strategies than females. In both males and females, herbicide reduced herbivory.
Gutierrez, et al., 2020, report that phenoxy herbicides have been shown to have detrimental effects on various insects and other animals, including native lady beetles, bees, moths, earthworms, and some vertebrates. They commented that, “Widespread application of synthetic pesticides and loss of plant diversity are regarded as significant drivers of current global change. The effects of such phenomena on insect performance have been extensively studied separately, yet the interactions of these two drivers have been poorly explored.” They concluded that, “plant diversity and herbicides may shift resource allocation in generalist terrestrial insect herbivores, indicating complex and unexpected effects of human-induced environmental change.” Given the importance of insects as food sources for many types of wildlife, it is crucial to pay attention to the potential impacts of various types of pesticides on insects and other invertebrates.
Schulz, et al., 2021, examined 381 pesticides and “considered 1591 substance-specific acute toxicity threshold values for eight non-target species groups.” They assessed that there are greatly reduced amounts of applied insecticides in the US (reductions of more than 40% between 1992 and 2016), and lowered pesticide toxicities among fish, mammals, and birds, due to the reduction in use of organophosphates. But pesticides have increased toxicity for aquatic invertebrates and pollinators, including honeybees. For these species, applied toxicity has more than doubled between 2005 and 2015. Schulz, et al., 2021, found that “the toxicity of applied insecticides to aquatic invertebrates and pollinators has increased considerably - in sharp contrast to the applied amount – and that this increase has been driven by highly toxic pyrethroids and neonicotinoids, respectively.” They specifically recorded “increasing applied toxicity to aquatic invertebrates and pollinators in genetically modified (GM) corn and to terrestrial plants in herbicide-tolerant soybeans.” While this study used data from the USA, which is more readily available than for many other countries, they expect similar results in many other regions of the world where modern agriculture is dominant.
References:
Links to other impacts of pesticides on insects:
Next Sections on impacts of pesticides:
Pesticide Impacts on Insects
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, October 2020.
Goode, et al., 2020, conducted experiments to examine the impact of the herbicide penoxsulam on biocontrol insects that were also being used to reduce the spread of water hyacinth (Pontederia crassipes) in Florida. Previous studies have indicated that establishing insect refuges, by maintaining an area of untreated plants near the treated area, were key to enabling biocontrol insects to survive herbicide application. In this study, insect refuges were not established. Fortunately, they found that the herbicide, which was also used to control water hyacinth, did not have a negative impact on the survival of the biocontrol agents, water hyacinth weevils, Neochetina eichhorniae and N. bruchi. Goode, et al., 2020, concluded, “Although the systemic activity of penoxsulam in the water column prevented the establishment of refuges in this study, biological control agent populations persisted following herbicide applications without additional releases and were able to remain at field densities after the decay and loss of P. crassipes.”
Gutierrez, et al., 2020, conducted an experiment on the impact of a phenoxy herbicide used to control broadleaf weeds in grasslands, on native grass diversity and the physiology of a native polyphagous grasshopper. In female grasshoppers, increased “grass diversity increased herbivory” and increased grasshopper weight and nitrogen content. “Herbicide reduced herbivory but increased the number of offspring” of female grasshoppers. In male grasshoppers, increased grass diversity increased herbivory and fat body volume, but had negative effects on weight. However, with increased plant diversity, males had an “increased capacity to store energy and invest in muscle tissues,” which suggests that males use different energy allocation strategies than females. In both males and females, herbicide reduced herbivory.
Gutierrez, et al., 2020, report that phenoxy herbicides have been shown to have detrimental effects on various insects and other animals, including native lady beetles, bees, moths, earthworms, and some vertebrates. They commented that, “Widespread application of synthetic pesticides and loss of plant diversity are regarded as significant drivers of current global change. The effects of such phenomena on insect performance have been extensively studied separately, yet the interactions of these two drivers have been poorly explored.” They concluded that, “plant diversity and herbicides may shift resource allocation in generalist terrestrial insect herbivores, indicating complex and unexpected effects of human-induced environmental change.” Given the importance of insects as food sources for many types of wildlife, it is crucial to pay attention to the potential impacts of various types of pesticides on insects and other invertebrates.
Schulz, et al., 2021, examined 381 pesticides and “considered 1591 substance-specific acute toxicity threshold values for eight non-target species groups.” They assessed that there are greatly reduced amounts of applied insecticides in the US (reductions of more than 40% between 1992 and 2016), and lowered pesticide toxicities among fish, mammals, and birds, due to the reduction in use of organophosphates. But pesticides have increased toxicity for aquatic invertebrates and pollinators, including honeybees. For these species, applied toxicity has more than doubled between 2005 and 2015. Schulz, et al., 2021, found that “the toxicity of applied insecticides to aquatic invertebrates and pollinators has increased considerably - in sharp contrast to the applied amount – and that this increase has been driven by highly toxic pyrethroids and neonicotinoids, respectively.” They specifically recorded “increasing applied toxicity to aquatic invertebrates and pollinators in genetically modified (GM) corn and to terrestrial plants in herbicide-tolerant soybeans.” While this study used data from the USA, which is more readily available than for many other countries, they expect similar results in many other regions of the world where modern agriculture is dominant.
References:
- Goode, A.B.C., Tipping, P.W., Gettys, L.A., Knowles, B.K., Valmonte, R.J., & Pokorny, E. (March, 2020). Florida Entomologist, 103(1):132-135.
- Gutierrez, Y., Ott, D., & Scherber, C. (April 29, 2020). Direct and indirect effects of plant diversity and phenoxy herbicide application on the development and reproduction of a polyphagous herbivore. Scientific Reports, 10(1):1-11.
- Schulz, R., Bub, S., Petschick, L.L., Stehle, S., & Wolfram, J. (April 2, 2021). Applied pesticide toxicity shifts toward plants and invertebrates, even in GM crops. Science, 372, (6537), 81-84. DOI: 10.1126/science.abe1148
Links to other impacts of pesticides on insects:
Next Sections on impacts of pesticides: