Protecting honeybees from harmful insecticides

The unintended consequence of spraying for grain pests could be the loss of beehives and pollination services in oilseed and horticultural crops, particularly almonds.

Honey bees (Image credit: Shutterstock).

During cold winter months, bees have relatively low food reserves. When crops (particularly canola) commence flowering, honeybees are moved in to pollinate and to exploit an excellent source of nectar. From mid-August onwards, hundreds of thousands of hives are moved into almond orchards, and other horticultural tree crops, where they play a critical role in pollination.

The accidental poisoning of bees can cause the collapse of bee colonies, and with them, the loss of pollination services to both grains and horticultural industries and the loss of income for apiarists.

Foraging habits of honeybees

Bees are active over temperatures ranging from about 13° to 37°C, with an optimum range of 19° to 30°C.  When temperatures allow, they can be active from about 8 am to 4 pm.  In late winter and early spring, most foraging occurs between 10 am and 3 pm when temperatures are above about 15°C. 

Bees typically forage within 2-4 km of their hive, but can travel up to 7 km in search of pollen and nectar when nearby pollen and nectar sources are in short supply or are of poor quality. Because flowering canola is so attractive to honeybees, it is highly likely that bees from hives situated many kilometres away will be foraging in canola crops when temperatures exceed 15°C.

Pesticides hazardous to bees

Most insecticides registered in Australia for oilseed and pulse crops will kill honeybees. The registered carbamates (except pirimicarb) (Group 1A), organophosphates (Group 1B), synthetic pyrethroids (Group 3A), neonicotinoids (Group 4A), sulfloxaflor (Group 4C), spinetoram (Group 5), emamectin benzoate (Group 6), and indoxacarb (Group 22A) are either toxic or highly toxic to honeybees after direct contact with spray or dust.

For neonicotinoids the Australian Pesticides and Veterinary Medicines Authority (APVMA) reports that:

“Australian honey bee populations are not in decline and Australia has robust regulatory and surveillance measures to monitor… the link between the use of neonicotinoids and declining health of honey bees.” “All neonicotinoids registered for use in Australia are considered safe and effective—provided products are used as per the label instructions”.

Some surfactants are also toxic to bees and when mixed and sprayed with bee-safe chemicals can cause bee poisoning. In Australia, surfactants and other adjuvants are regarded as pesticides in their own right.

Some insecticides such as Bt (Bacillus thuringiensis), NPV (nuclear polyhedrosis virus) and pirimicarb have very low impact on bees. 

Insecticides known to be hazardous to bees generally contain a warning on the label under Protection of Livestock. This is a mandatory instruction – ‘DO NOT spray any plants in flower whilst bees are foraging’.

This applies to both the target crop and any flowering weeds throughout the target crop and/or within the surrounding headland buffer zone. This means that in most instances, spraying insecticides on canola whilst in flower during daylight where temperatures exceed 12-15°C could be both illegal and potentially hazardous to bee hives within 7 km.

The insecticide risk

Honeybee poisoning may occur when:

• An insecticide is applied directly to a flowering crop while bees are foraging or where bees subsequently forage on contaminated nectar, pollen or water, or land on a contaminated plant part;
• An insecticide is applied to a crop not in flower, but is also applied to non-target flowering plants such as weeds;
• Insecticide drifts onto bees, flowering plants, hives, the bees’ water source or within the bees’ flight path; 
• A worker bee carries contaminated nectar, pollen or water back to the hive, contaminating the colony; or
• Two or more insecticides are combined, which although “bee safe” in their own right, may be harmful to bees when mixed.

Being proactive to reduce the risk of honeybee poisoning

Choice and use of insecticides

• Growers should note product warnings when reading the label and when planning a spray application.
• Understand the residual risk to bees. Microencapsulated forms of insecticides have significantly longer residual toxicity than other forms.
• Select chemicals that pose the lowest risk to bees, that have the lowest residual toxic effect, whilst still achieving the required outcome for the crop.
• Different chemicals vary in the period of residual toxicity. Bees should not be moved into a crop that was treated pre-flowering until the residual toxicity has dissipated. Similarly, bees moved from an area to be treated should not be returned until it is safe to do so.

Conditions for spraying

• Prior to spraying, ensure that bees are not foraging in the target area.  This is a condition of many product labels and is therefore a legal requirement. Monitor the target crop and area to determine:
  • Presence of flowering plants in the target crop, including the target crop and/or weeds throughout the target crop and/or within the surrounding headland buffer zone;
  • Presence of honeybees on flowering plants at 4 locations including those close to native vegetation, areas of flowering weeds, the edge of the crop and some distance into the crop.
• Where possible, apply insecticides harmful to bees in the evening when bees are not foraging.
• Choose appropriate spraying conditions so as to reduce the chance of spray drift affecting non-target flowering crops, hives, and water sources. Use a kestrel anemometer to measure wind speed rather than estimating it.

Communication

• Contact the owners of any beehives in the area well before spraying, so that they have an opportunity to relocate or protect their hives. Also consider owners of hives on adjacent properties.
• Beekeepers require as much notice possible, preferably 48 hours, to move hives.
• If using spray contractors, inform them of the location of any hives that may be affected and ensure that they understand the importance of reducing the risk of honeybee poisoning. 

These communications can be facilitated through the BeeConnected web site. This initiative connects registered beekeepers with registered farmers and contractors, enabling two-way communication on the location of hives and proposed pesticide activities.