VIII SIMPOSIO INTERNAZIONALE ICPBR

HAZARDS OF PESTICIDES TO BEES

Bologna, 4-6 Settembre 2002

Metodologie dei test e studi sugli effetti dei pesticidi sulle api

The effects of IGRs on honeybee populations

Helen Thompson and Selwyn Wilkins

National Bee Unit, CSL, Sand Hutton, York, YO41 1LZ, UK. E-mail: h.thompson@csl.gov.uk

The effects of IGRs on colonies is usually assessed over a relatively short period and investigates the toxicity to honey bee larvae or pupae. The aim this project was to assess the longer term effects of fenoxycarb, a juvenile hormone agonist, and diflubenzuron, a chitin synthesis inhibitor, fed to honey bee colonies on the fate of the treated colonies over the following year. Assessments were also made on the effects on the viability of immature queens, i.e. egg production.

IGRs were diluted with sucrose to a rate equivalent to their maximum application rate on flowering crops. The effects of exposure to the treatments was assessed in brood up to 8 weeks after treatment. In addition all colonies were generally assessed prior to the day of test item application and 2 weekly after the application until November and then monthly until a year after treatment. The mean replacement/removal for the eggs marked over the 5 week period was 19% in the controls, 47% (max 60%) in the fenoxycarb treated and 44% (max 95%) in the diflubenzuron treated. Significantly greater numbers of sealed pupae did not emerge in the fenoxycarb treated colonies and in many cases these cells were present for several weeks. Colonies treated with fenoxycarb declined during the season earlier than the control and started the season slower; one fenoxycarb treated colony failing to survive over the winter. The fenoxycarb treatment resulted in significantly lower numbers of bees and brood in the month after treatment and affected the development of the colonies in the following spring. Colonies treated with diflubenzuron resulted in a short term reduction in the numbers of adult bees and brood after treatment when compared with controls. There was no significant effect on development of brood the following spring but there did appear to be a slower expansion when compared with controls.

Queens reared from grafted larvae were allowed to pupate in the reared colonies and each pupa was then transferred to an Apidea supplied with fondant containing the IGR at a rate equivalent to the application rate. Two to three weeks after emergence the number of mated queens was determined by recording egg production. The number of queens which successfully mated and laid eggs was 6/11 in the control, 9/12 in the diflubenzuron treated and 0/11 in the fenoxycarb treated. In the fenoxycarb treated 9/11 queens were present but showed virgin queen characteristics, e.g. small abdomen, suggesting they had not been mated.

The results so far show effects of fenoxycarb on the colony both in the short term and the following spring. Fenoxycarb also appears to have severe effects on queen viability. Diflubenzuron has effects on colonies in the short term but effects the following spring are less severe than after fenoxycarb exposure and no effects were observed on queen viability. The next stage is to assess the impacts of the ecdysteroid agonist tebufenozide and the ecdysteroid antagonist azadirachtin. This will ensure comparable data on effects are collated for the major types of IGR pesticides which are or may be used in the UK.