Impact of pesticides on beneficial insects and mites

Many pesticides (insecticides, fungicides and herbicides) are toxic to beneficial insects and mites, including insect pollinators. This is because beneficial insects are generally more susceptible to chemicals that the target pest species.

Many factors influence to the toxicity of pesticides to beneficial insects, and much care is needed when integrating the use of chemicals and beneficial insects in IPM programmes. The effect of pesticides can also be modified by application practices and environmental conditions, so, even though a chemical may generally be regarded as ‘safe’, how and when it is applied and the conditions under which it is applied may make it less safe to beneficial insects.

Besides the contact action of a pesticide resulting from direct spray contact, the ongoing action of pesticide residues may also be harmful to beneficial insects. The residues of many insecticides can kill beneficial insects and mites after very short exposure to residues on the leaf or soil surface. Even when the killing power of a chemical declines as the residues disappears, sub-lethal effects, e.g., reduced reproduction, disrupted prey searching and capturing behaviour can also disrupt the action of beneficial insects.

Chemicals that are not normally applied to control insects, such as fungicides, can also have a negative effect on beneficial insects. Therefore, it is important to consider all pesticides that will likely be used on a crop before beneficial insects are introduced, and select only those that are known to be less disruptive.

‘The Good Bug Book’ Second Edition (2002), Editor Richard Llewellyn, provides a list of commonly-used chemicals and their likely toxic effects on beneficial insects and mites, and the period or waiting time which should be allowed to pass following a pesticide application before introducing beneficial insects and mites into a crop.

Refer to the label on pesticide containers for specific information about the safety of that product to beneficial insects and mites.

Guiding principles for integrating the use of pesticides and beneficial insects and mites

• If you are intending to use beneficial insects in your crop, select and use only those products, including fungicides, which are known to have few or no effects on beneficial insects.
• Apply pesticides only when monitoring or crop inspection show pest numbers are approaching damaging or recognised threshold levels.
• Observe strictly any waiting periods that are recommended when releasing beneficial insects after a pesticide application.
• Be sure your application equipment is correctly calibrated and that spray mixtures are made up accurately. Over dosing, even with some so-called ‘safe’ pesticides can be harmful to beneficial insects.
• Use the lowest effective rate recommended on the pesticide label.
• Apply pesticides at a time or in a manner that is least disruptive to beneficial insects. For example, apply a pesticide when beneficial insects are least active and direct the spray to treat only the most pest-infested parts of the plant.
• If in doubt about the safety of any pesticide to beneficial insects contact BioForce Ltd, office@bioforce.net.nz .