We know what happens to target pests after you spray a crop with a pesticide, but what happens to all the beneficial insects that get sprayed too?
Beneficial insects give growers a helping hand by snacking on or parasitising pests in their crop, alleviating some of the pressure on growers to keep pest populations in check.
As biological control through beneficial insects is an important part of Integrated Pest Management (IPM), we want to be able to conserve as many of them as possible.
However, when crops are sprayed with pesticides this can have unintended impacts on beneficial insects. Spraying a pesticide can have the same impact on beneficials as the pests they are designed to kill, which means that you could be getting rid of the ‘good’ bugs while trying to control the ‘bad’ bugs.
But what do we know about these impacts? Is a pesticide as toxic towards a ladybird beetle as it is to an aphid parasitoid? And importantly, how much information out there is relevant to the Australian grains industry?
Reviewing existing toxicity data
Teaming up with Prof. Ary Hoffmann from the University of Melbourne, we conducted a literature review to try and find existing toxicity data that quantifies the toxicity of a range of pesticides on beneficial insects relevant to Australian grain growing regions.
We found hundreds of relevant scientific journal articles, industry reports, and databases that have explored the toxicity effects (measured as survival or mortality) that can occur after a beneficial insect species is exposed to particular pesticide.
But how much of this data can be applied within an Australian grains context?
With this in mind, we tried to find some answers to several key questions.
1. What chemical groups have been researched the most?
Pesticides can be classified by their Mode of Action (MoA), which relates to how the chemical affects the pest.
We therefore classified all relevant active ingredients by their MoA, and found that ‘hard’ or broad-spectrum pesticides, specifically synthetic pyrethroids (Group 3A; 25.97% of all data), organophosphates (Group 1B; 19.73% of all data) and carbamates (Group 1A; 13.61% of all data), were the most researched MoA groups.
Avermectins (Group 6), neonicotinoids (Group 4A), Bacillus thuringiensis (Group 11A), oxadiazines (Group 22A), diamides (Group 28), and phenylpyrazoles (Group 2B) have received some research into their toxicities. However, very little research has been performed on paraffinic oil, sulfoximines (Group 4C), spinosyns (Group 5), diafenthiuron (Group 12A), and Nuclear Polyhedrosis Virus (Group 31).
We identified that many research gaps exist for pesticides that are marketed as ‘soft’ or ‘selective’ on some groups of beneficials, and in our review we highlight them as priority MoA groups that require future testing.
Further, we found that very few studies have tested the effects of seed treatments on natural enemies, which is a significant finding given the widespread global use of neonicotinoid seed treatments.
2. On what groups of beneficial insects do we need more data?
We found a number of research gaps for some of the most important generalist predators in Australian grains: hoverflies, carabid beetles, rove beetles, and spiders.
Further, we also found only one relevant study that tested the effect of pesticides on a species of predatory mite in the order Trombidiformes, which is an order that includes some of the most prolific redlegged earth mite (RLEM) predators.
Diaeretiella rapae (a species of parasitoid wasp) is one of the most important aphid parasitoids in grains, yet there has been very little toxicity testing performed on this species compared to other aphid parasitoids, such as those in the genus Aphidius.
3. Where has all of this research been done?
We found that the bulk of the research investigating pesticide toxicity on beneficials has been conducted internationally (83.88%), with significantly less conducted in Australia (16.12%).
This means that, at least at the moment, we have to rely quite heavily on toxicity data that has been generated using populations (and sometimes even species) of natural enemies that are not reflective of Australian environments and conditions.
Because of variables such as the scale at which we grow our grain crops, climate, humidity, rainfall, and temperature to name a few, this means that what has been reported internationally might not align with how our local beneficials might respond to pesticides.
4. At what experimental scales are these assays being conducted?
Most studies that have tested the toxicity of pesticides on beneficials are conducted in the lab (60.78%), with fewer studies conducted at field (27.19%) scales.
Validating laboratory findings in the field is key, as the toxicity of a particular active ingredient may vary depending on a suite of factors associated with varying climatic and geographic conditions, and also bear greater industry relevance.
What do our findings mean for the Australian grains industry?
While a wealth of research has already been conducted to try and understand some of the non-target effects that pesticide use can have on beneficial insects, there is still a lot more research required.
Until research is undertaken using Australian populations of beneficials, we are left with little option but to infer potential toxicities from international work.
We recommend that toxicity testing be generated in the laboratory first, before being further validated in replicated semi-field and/or field trials over multiple study sites and hence with different populations of beneficials.
Understanding the full impacts that pesticide use can have on the communities of insects consisting of both pests and beneficials will allow growers to make informed decisions when deciding how to manage pests, and will also allow us to take a step forward towards integrating more sustainable and long-term pest management strategies.
Through the Australian Grains Pest Innovation Program (AGPIP), laboratory-based assays have been underway since early 2020 in order to fill some of these identified research gaps. Keep a lookout in 2021 for further updates on our beneficial toxicity testing work.
This research was conducted as a part of AGPIP, which is a collaboration between the Pest & Environmental Adaptation Research Group at the University of Melbourne and Cesar Australia. The program is a co-investment by the Grains Research and Development Corporation (GRDC) and the University of Melbourne, together with in-kind contributions from all program partners.
This research was recently published in Overton K, Hoffmann AA, Reynolds OL, Umina PA (2021) Toxicity of Insecticides and Miticides to Natural Enemies in Australian Grains: A Review. Insects 2021, 12, 187.