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

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 class 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.

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.

Regulation and monitoring

Neonicotinoid chemicals are approved for use in New Zealand by the Environmental Protection Authority (EPA) under the Hazardous 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.

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.

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.

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?