Case study: Neonicotinoid insecticides
Insects are vital for our ecosystems, but sometimes there are places where we don’t want them – destroying our gardens, eating our food crops and trees, annoyingly buzzing around inside our homes, pooing on our stuff and ruining our food.
Insecticides are one way to control insect pests. There are many types of insecticides that use different chemicals to target different insect species
Insecticide spraying
Insecticides are chemicals that are toxic to insects. They are commonly used in agriculture to reduce the number of pest insects that might damage the crop or pasture. Today, insecticides are usually specific to insects and should not harm other animals. But scientists are finding that they may, in fact, have long-term effects on other non-target animals (species that are not the intended victims) through toxicity or reduced food sources.
Systemic insecticides are mostly designed to control insects that feed on plants. The chemicals are absorbed into the plant and an insect dies when it consumes the chemicals in the plant’s cells. Non-systemic insecticides are designed to kill insects that come into contact with the product – on surfaces or on plants. Many fly sprays we use at home are non-systemic.
An example of systemic insecticides are the neonicotinoids – a clas s of insecticides chemically similar to nicotine. Nicotine is the chemical that makes cigarettes addictive. Neonicotinoids were developed in the 1980s as safer alternatives to existing products. The name literally means ‘new nicotine-like insecticides’.
How do neonicotinoids work and where are they used?
Neonicotinoid insecticides are neurotoxic, meaning they affect the nervous system of organisms. Neonicotinoids were developed to target insects and reduce harm to non-target vertebrates. They are synthetic chemical compounds designed to affect insect neuroreceptors, rather than those found in mammals and other vertebrates. These chemicals target an insect’s nerve system, causing hyperstimulation, leading to paralysis and death.
Seeds treated with neonicotinoids
Soybean seeds treated with neonicotinoids (dyed blue to alert users to the presence of pesticide) and treated corn seeds (dyed red) versus untreated seeds.
Image and text from Farmers are overusing insecticide-coated seeds, with mounting harmful effects on nature, THE CONVERSATION (USA).
Neonicotinoids have become the most widely used insecticides in the world, mainly due to their ease of application. They are very effective against sucking and chewing insect pests that feed on plants. They are also commonly used as seed treatments – seeds are coated with the insecticide prior to sowing in soil. The insecticide is then taken up by the germinating plant and is distributed throughout the developing plant. This is known as systemic action. The chemicals then remain in the plant – including the leaves, pollen and nectar.
Neonicotinoids are also used in household insecticides, wood preservative products for controlling termites and several flea treatment products used on farm animals and domestic pets.
What do we know about the use and impacts of these insecticides in New Zealand?
In the report Knowing what’s out there: Regulating the environmental fate of chemicals, the Parliamentary Commissioner for the Environment (PCE) sets out to understand how chemicals get into the New Zealand environment and the impacts of these chemicals. One of four case studies within the report is a look at the environmental impacts, regulation and monitoring of neonicotinoids in Aotearoa New Zealand.
Knowing what’s out there report cover
Details from the cover of the Parliamentary Commissioner for the Environment report Knowing what’s out there: Regulating the environmental fate of chemicals.
A PDF of the report can be downloaded here.
Photos on cover: Autosampler vials, Matthew Bates, Flickr; culvert drain, Megan Martin; maize field, pxhere.com.
Regulation and monitoring
Neonicotinoid chemicals are approved for use in New Zealand by the Environmental Protection Authority (EPA) under the Hazardou s Substances and New Organisms Act 1996. The PCE report points out that imported seeds with neonicotinoid coatings are not regulatedmost likely because they are termed a ‘manufactured product’ and therefore slip between legal definitions the EPA works with. However, the EPA does regulate the use of neonicotinoid-containing products, with specific rules in place to protect non-target species like honey bees.
The report states that there is no systematic reporting for neonicotinoids imported, manufactured, sold or used in New Zealand. What data the PCE was able to access was from one-off monitoring studies and by contacting distributors and users directly for volumes of sales. The only regular monitoring of pesticides in the New Zealand environment is a 4-yearly survey of groundwater, but this survey does not currently include neonicotinoids.
What happens to neonicotinoids in the environment?
Research shows that neonicotinoids can remain in soils for long enough to accumulate over successive yearly uses. Several field studies (research conducted on location) have found neonicotinoid residues in agricultural soils more than a year after treated seeds were sown. Sowing treated seeds year after year causes chronic contamination of soils but with low concentrations of neonicotinoids (in the parts per billion range). Although the amounts of neonicotinoids are very, very small, they still act as a constant source of exposure for soil-dwelling organisms and can also be transported via water.
Neonicotinoids are water soluble – a property that is both useful and of concern. Solubility enables the germinating plant to take up the active ingredient and distribute it throughout its tissues. Studies have estimated that 2–20% is taken up by the plant and the remainder is left in the soil where it can persist (remain), break down or leach into groundwater and runoff into surface waters.
Neonicotinoids in the environment
Environmental fate and exposure of neonicotinoids to target and non-target organisms when applied as a seed coating.
Source: Sánchez-Bayo, Francisco. (2014). The trouble with neonicotinoids. Science. 346. 806-807. 10.1126/science.1259159.
Non-target species
Evidence shows that all arthropods are impacted by neonicotinoids, not just a select few targeted insects. This includes:
all insects (including bees), which are by far, the most sensitive group
myriapods (such as centipedes and millipedes)
arachnids (such asspiders, mites and scorpions)
crustaceans (such as slaters, prawns and crabs).
Arthropods make up 75% of biodiversity on Earth. They are important in ecosystems as pollinators, scavengers, nutrient recyclers and food for other animals.
Some terrestrial invertebrates such as worms and slugs are more tolerant of neonicotinoids than insects.
Bees for avocados
Beehives in an avocado orchard providing honey bees for pollination. Avocado trees need lots of bees to pollinate all the flowers. The bees don’t always do a good job of pollination, so fruit crops can be poor.
Honey bees and neonicotinoids
Bees are important pollinators of many cultivated food crops. Bee populations are in serious decline around the world, and this is a concern for food production.
Estimates of a chemical’s toxicity to bees depend on many factors, for example how the bee was exposed to the chemical – did it land on spray residue, or did it ingest the nectar using its mouth parts? Even if the dose is too low to kill the bee, it can impact bee health by impairing foraging activity, mobility, metabolism, early life-stage development, behaviour, learning and memory.
New Zealand regulations prohibit the spraying of neonicotinoids when crops are in flower to limit the damage to non-target and beneficial insects like honey bees and butterflies. Other regulations include requirements for products with these chemicals to be labelled so users are aware of and able to lessen the potential harm to bees.
In Europe, neonicotinoids are heavily restricted due to the negative impacts on bees and non-target species. There are campaigns around the world where groups and activists are seeking to have all neonicotinoids banned.
Ecotoxicity to New Zealand native species
There is some data available on neonicotinoid ecotoxicity for New Zealand native freshwater invertebrate species.
Native mayflies
Neonicotinoids are toxic to two native mayflies – Deleatidium spp. and Coloburiscus humeralis. They are also toxic to Deleatidium nymphs.
Deleatidium magnum adult (left) and nymph, Emily Roberts, CC BY-4.0. Coloburiscus humeralis adult, David Paulin, CC BY-NC 4.0. All images sourced from iNaturalistNZ.
Neonicotinoids are toxic to two stream-dwelling mayfly species – Deleatidium spp. and Coloburiscus humeralis. Deleatidium mayfly nymphs could also have impaired swimming ability from exposure to the chemicals. Another New Zealand study investigated the effect of neonicotinoids on stream macroinvertebrate communities. At certain concentrations the total number of invertebrates was reduced, with even stronger effects on mayflies and caddisflies.
Pesticide use – a socio-scientific issue
Socio-scientific issues often involve a combination of environmental, economic, social and political issues. Aotearoa New Zealand is a nation of primary producers – our agricultural and horticultural exports help to feed the world. Neonicotinoid insecticides are very effective at controlling insect pests on food crops. They have relatively low toxicity to mammals, birds and other beneficial insects.
On the other hand, some data and evidence is coming through that shows the toxic effects on important pollinators like honey bees. There is also emerging evidence that these insecticides are toxic to some freshwater invertebrate species that are important to stream and river ecosystems.
Concerns are also raised about the impacts of neonicotinoids on taonga species. Ecotoxicity information provided by some insecticide products is not specific to species in Aotearoa or has been tested on too few of our unique organisms.
Learning about neonicotinoids in the classroom
The PCE report Knowing what’s out there: Regulating the environmental fate of chemicals and its case studies on the use of neonicotinoids, tetracycline antibiotics and zinc provide rich opportunities for students to use relevant information to draw evidence-based conclusions about issues facing our society. The article The environmental fate of chemicals – a context for learning provides science and mātauranga Māori concepts, curriculum links and additional pedagogical help.
What would you do?
Some data and evidence is coming through that shows toxic effects on important pollinators like honey bees. There is also emerging evidence that these insecticides are toxic to some freshwater invertebrate species that are important to stream and river ecosystems.
Based on the available evidence, what would you do if you were a government official in charge of chemical regulation in Aotearoa New Zealand?
What would you do if you were a crop grower?
What would you recommend if you were a scientist?
Related content
The environmental fate of chemicals – a context for learning uses this case study and two others to explore the socio-scientific issue of chemical use and environmental risks. The PLD article provides pedagogical information, curriculum links and inquiry questions.
Toxins can be classified according to the location of the body where their effects are most notable. Learn about some of these classifications in Poisons and toxins.
Scientists measure the effects of toxins on animals in a variety of different ways. For example, some of the research looking at the effect of neonicotinoids on bees used LD50. Read more on Measuring toxicity.
The horticulture industry produces food – it is an important part of the New Zealand economy. Horticulture solutions outline some of the environmental impacts of the industry and solutions the industry is putting in place to lessen these impacts.
The scale insect is part of the large order called Hemiptera, which are all sucking bugs. Insects that feed by chewing and sucking are the key target of neonicotinoid insecticides used by the horticulture industry. Scale insects are a vital player within native beech forest ecosystems in New Zealand. Learn more in Honeydew ecosystem.
Non-target species affected by neonicotinoids include aquatic insects and freshwater macroinvertebrates.
There are many ways to control insect pests. Take a closer look at biocontrol and Bioforce, a New Zealand company that breeds bugs for biocontrol.
Use Biocontrol in action – unit plan to investigate the efficacy of a real biocontrol agent in New Zealand.
Finding out about chemicals is a useful activity for upper primary. It is designed to help students become aware that all substances are made of chemicals and that chemicals are made up of a combination of elements.
Useful links
In 2020, the New Zealand Environmental Protection Authority began to reassess the five neonicotinoid insecticides currently used in New Zealand. Read about the process here and the 2021 summary here.
Read the Foundation for Research’s good management practices for neonicotinoids.
Acknowledgement
This resource has been created from Knowing what’s out there: Regulating the environmental fate of chemicals and associated resources with support from the office of the Parliamentary Commissioner for the Environment.
Parliamentary Commissioner for the Environment logo
The Parliamentary Commissioner for the Environment is one of three Officers of Parliament that work in an independent watchdog capacity, helping Parliament hold to account the government of the day.
