Pollination and pesticides

Bryn Jones, Crop Pollination Association

Hives of bees pollinating a cotton crop. Bryn Jones, Crop Pollination Association

In many northern hemisphere countries there are reports of large numbers of bee colonies dying. One of the popular theories blames the pesticides that are used in and around crops. Although it is still unclear to what degree pesticides cause bee losses, honey bee poisonings due to pest control chemicals do occur in most countries, including New Zealand and Australia.

Bee poisonings initially affect the beekeepers who are trying to derive their income from the bees. This may either reduce their willingness to supply hives for pollination or increase the fees that they charge to the grower. If poisoning occurs when the crop is flowering, it may also reduce the effectiveness of pollination, as foraging bees will be killed.

Bee poisonings have several common symptoms, such as large numbers of dead bees at the entrance of the hive. It is common to see a few dead bees at the hive entrance throughout the year, and particularly before winter, but thousands of dead bees suggests that they have been poisoned. Another symptom is live bees outside the entrance that have a very jerky motion.

Pest control has changed over time. Historically most pest control chemicals were ‘broad spectrum’ so that they would kill a wide range of invertebrates. However, with advances in chemistry, there has been a move to pesticides that are increasingly species specific. Although this has resulted in many chemicals being safer for honey bees, it has made the issue more complicated, as some pest control chemicals can safely be applied to flowers without killing bees while others cannot. Even with these safer chemicals being available, many of the older broad-spectrum chemicals are still being used.

Bryn Jones, Crop Pollination Association

Hives of bees pollinating a canola crop. Bryn Jones, Crop Pollination Association

Poisoning of hives introduced to a crop can occur because the grower has inappropriately applied a bee-toxic chemical to flowers in the crop. However, even if growers are very careful about the pest control chemicals they use, poisoning can still occur. Honey bee colonies have large flight ranges, so the bees from the colonies introduced to an orchard may be foraging on flowers up to 5 km away and be poisoned there. It can therefore be useful to remind neighbours that hives are being brought in for pollination and ask them not to put toxic sprays on flowers.

In some crops where sprays can cause significant bee deaths, growers, beekeeper organisations and chemical companies work together to put in place education programs designed to prevent bee poisonings. These programs may include seminars, mail drops, published articles and even erection of roadside signs.

There is a large variety of chemicals used to control insect pests that are also toxic to honey bees. The list (which is contained in the Pesticides toxic to honey bees section) does not include everything that is toxic to honey bees and new chemicals continue to become available to pose a threat to honey bees. The chemicals vary in their toxicity and under what conditions they are toxic. Some are very toxic and will kill bees on contact, some lose their toxicity very quickly, while others are not toxic when they are dry, and some are only mildly toxic.

Faced with this bewildering array of chemicals, the simplest way to prevent poisoning of bees is to remember that if a chemical is toxic to bees it should not be applied to flowers that are being (or are likely to be) visited by bees. In Australia, pest control chemicals come with instructions that describe whether they can be safely applied to flowers. Some of the instructions which may appear on pesticide labels are listed below:

  • Don’t apply to flowers that are, or are likely to be, visited by bees.
  • Don’t apply to flowers that are, or are likely to be, visited by bees, except in the evening.
  • The spray must be dry before it makes contact with bees.
  • Do not spray on flowers that are being visited by bees.
  • Can be applied while bees are foraging.
  • Dangerous to bees. Avoid direct application or drift of the spray mix onto beehives.
  • Dangerous to bees. Do not apply to any areas where the crop, weeds, or cover crops are in flower at the time of spraying, or are expected to flower within 28 days of spraying (7 days for pastures or sorghum).
  • Dangerous to bees. Do not spray any plants while bees are foraging. Ensure bee hives are removed from the area to be treated and from adjacent paddocks.

Always remember to tell your neighbour that you are introducing hives into an area, so that they do not inadvertently poison them. If applying bee-safe chemicals to flowers, ensure the spray tank is washed thoroughly beforehand.


The pollination and pesticides information is an excerpt from Mark Goodwin (2012) Pollination of Crops in Australia and New Zealand. Rural Industries Research and Development Corporation Publication No. 12/059