Using ‘softer’ insecticides in farming is a pillar of integrated pest management (IPM). By choosing more selective insecticides over those with broad spectrum activity, the goal is to preserve predators and parasitoids of pests – also known as beneficial insects or natural enemies – thereby controlling pests through a combination of chemical and biological means.
But making informed choices about what chemicals to use can be a challenge in the grains industry, with many knowledge gaps existing around the extent to which insecticides impact beneficials.
That’s why our research scientists at Cesar Australia, in partnership with the Grains Research and Development Corporation and University of Melbourne, have been working to review the existing research and to fill the gaps.
From this research we’ve developed a table outlining the non-target impacts of insecticides commonly used in grains on beneficials. Consulting this table will allow growers to make more informed choices about which active ingredients to use when controlling pests within their crops while preserving natural enemies.
While insecticides are an important tool in preventing yield losses from insect pests, a downside of their widespread use is the non-target effects.
For example, insecticide use can lead to secondary pest outbreaks due to killing the beneficials that were providing biological pest control services. The presence of beneficials and the services they provide are often not noticed until they are lost.
While there is a growing awareness of the benefits that these biological control agents can play, uncertainty surrounding the impact of pesticides on these agents can make IPM programs difficult to implement.
To help tackle this issue, guides have been produced for both the cotton and horticultural industries in Australia which outline how commonly used insecticides can affect beneficials. This has allowed growers and advisors in those industries to make more informed decisions about what chemicals to use in pest control, in particular promoting the use of chemistries that can provide sufficient pest control without compromising locally abundant predators and parasitoids.
While these two guides represent a valuable data source, industry differences in the chemicals used, maximum registered field rates, growing environments and key pests mean that a guide specific to the grains industry is required to provide the best possible guidance to growers and advisors.
Grains focused research
To determine the non-target impact of insecticides, we exposed beneficial species representing key groups to insecticides in a series of standardised laboratory trials, based on protocols developed by the International Organisation for Biological Control. This involved exposing beneficials to insecticides in petri dishes at a rate per cm2 proportional to the labelled application rate per hectare and monitoring their survival over the next 2-3 days.
The insecticides tested were selected based on consultation with growers and chemical industry representatives regarding what active ingredients are most commonly used to control invertebrate pests in Australian grain crops.
The beneficials included in the research were a wide diversity of arthropods, from predatory bugs, beetles, flies and spiders to parasitic wasps that lay their eggs in or on pest organisms, ultimately killing them as their larvae hatch out and feed on the unsuspecting pest.
Selective options are available
Our research supports the claims around several active ingredients marketed as being ‘soft’ or ‘selective’ as having less acute toxic effects on beneficial organisms.
These include afidopyropen and flonicamid, which are selective against aphids, and chlorantraniliprole, which is selective against caterpillars. All resulted in relatively low mortality rates in the majority of the beneficial species tested.
Also showing very low levels of harm to beneficials were the two biological pesticides tested, Bt (Bacillus thuringiensis) and NPV (nucleopolyhedrovirus), both of which are diseases of caterpillars.
A few species stood out as being particularly hardy and good candidates for IPM programs. These include rove beetles, hoverflies and spiders, which were shown to be tolerant of a number of insecticides that produce high mortality rates in other species.
While rove beetles can be obtained from commercial suppliers, Australian hoverflies and spiders are not commercially bred, so growers wanting to use these species in biological control will need to use strategies to attract and maintain naturally occurring populations, such as providing nesting habitats or flowering plants as alternative food sources.
Using and accessing the table
Our findings give growers options for selecting insecticides for key pests with fewer negative effects on beneficial predators and parasitoids.
In situations where monitoring for beneficials is not feasible, and knowledge of the beneficials present in the local environment is limited, growers can select the insecticide from the list with the smallest overall impact that is effective against the target pest.
Where growers are able to monitor for important local beneficials, more nuanced selections can be made based on the insecticides most compatible with those local species.
We encourage all growers and advisors to check out the table when planning to spray, and to please circulate widely!
This research is being undertaken as part of the Australian Grains Pest Innovation Program (AGPIP). AGPIP 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.
Thanks to Julia Severi (Cesar Australia) for article contributions and edits.